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4 Commits
updateThro
...
updateTram
Author | SHA1 | Date | |
---|---|---|---|
5681340ec7 | |||
c66ca67201 | |||
2679f7aa6f | |||
8403fdacdd |
@ -1776,6 +1776,15 @@
|
|||||||
"contributions": [
|
"contributions": [
|
||||||
"code"
|
"code"
|
||||||
]
|
]
|
||||||
|
},
|
||||||
|
{
|
||||||
|
"login": "castleKing1997",
|
||||||
|
"name": "DragonDreamer",
|
||||||
|
"avatar_url": "https://avatars.githubusercontent.com/u/35420129?v=4",
|
||||||
|
"profile": "http://rosaecrucis.cn",
|
||||||
|
"contributions": [
|
||||||
|
"code"
|
||||||
|
]
|
||||||
}
|
}
|
||||||
],
|
],
|
||||||
"contributorsPerLine": 7,
|
"contributorsPerLine": 7,
|
||||||
|
@ -10,7 +10,7 @@
|
|||||||
[](https://sonarcloud.io/dashboard?id=iluwatar_java-design-patterns)
|
[](https://sonarcloud.io/dashboard?id=iluwatar_java-design-patterns)
|
||||||
[](https://gitter.im/iluwatar/java-design-patterns?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
|
[](https://gitter.im/iluwatar/java-design-patterns?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
|
||||||
<!-- ALL-CONTRIBUTORS-BADGE:START - Do not remove or modify this section -->
|
<!-- ALL-CONTRIBUTORS-BADGE:START - Do not remove or modify this section -->
|
||||||
[](#contributors-)
|
[](#contributors-)
|
||||||
<!-- ALL-CONTRIBUTORS-BADGE:END -->
|
<!-- ALL-CONTRIBUTORS-BADGE:END -->
|
||||||
|
|
||||||
<br/>
|
<br/>
|
||||||
@ -325,6 +325,7 @@ This project is licensed under the terms of the MIT license.
|
|||||||
<td align="center"><a href="https://github.com/interactwithankush"><img src="https://avatars.githubusercontent.com/u/18613127?v=4?s=100" width="100px;" alt=""/><br /><sub><b>interactwithankush</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=interactwithankush" title="Code">💻</a></td>
|
<td align="center"><a href="https://github.com/interactwithankush"><img src="https://avatars.githubusercontent.com/u/18613127?v=4?s=100" width="100px;" alt=""/><br /><sub><b>interactwithankush</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=interactwithankush" title="Code">💻</a></td>
|
||||||
<td align="center"><a href="https://github.com/yuhangbin"><img src="https://avatars.githubusercontent.com/u/17566866?v=4?s=100" width="100px;" alt=""/><br /><sub><b>CharlieYu</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=yuhangbin" title="Code">💻</a></td>
|
<td align="center"><a href="https://github.com/yuhangbin"><img src="https://avatars.githubusercontent.com/u/17566866?v=4?s=100" width="100px;" alt=""/><br /><sub><b>CharlieYu</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=yuhangbin" title="Code">💻</a></td>
|
||||||
<td align="center"><a href="https://github.com/Leisterbecker"><img src="https://avatars.githubusercontent.com/u/20650323?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Leisterbecker</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Leisterbecker" title="Code">💻</a></td>
|
<td align="center"><a href="https://github.com/Leisterbecker"><img src="https://avatars.githubusercontent.com/u/20650323?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Leisterbecker</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Leisterbecker" title="Code">💻</a></td>
|
||||||
|
<td align="center"><a href="http://rosaecrucis.cn"><img src="https://avatars.githubusercontent.com/u/35420129?v=4?s=100" width="100px;" alt=""/><br /><sub><b>DragonDreamer</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=castleKing1997" title="Code">💻</a></td>
|
||||||
</tr>
|
</tr>
|
||||||
</table>
|
</table>
|
||||||
|
|
||||||
|
@ -9,6 +9,10 @@ tags:
|
|||||||
- Reactive
|
- Reactive
|
||||||
---
|
---
|
||||||
|
|
||||||
|
## Name
|
||||||
|
|
||||||
|
Event Aggregator
|
||||||
|
|
||||||
## Intent
|
## Intent
|
||||||
A system with lots of objects can lead to complexities when a
|
A system with lots of objects can lead to complexities when a
|
||||||
client wants to subscribe to events. The client has to find and register for
|
client wants to subscribe to events. The client has to find and register for
|
||||||
@ -17,6 +21,136 @@ requires a separate subscription. An Event Aggregator acts as a single source
|
|||||||
of events for many objects. It registers for all the events of the many objects
|
of events for many objects. It registers for all the events of the many objects
|
||||||
allowing clients to register with just the aggregator.
|
allowing clients to register with just the aggregator.
|
||||||
|
|
||||||
|
## Explanation
|
||||||
|
|
||||||
|
Real-world example
|
||||||
|
|
||||||
|
> King Joffrey sits on the iron throne and rules the seven kingdoms of Westeros. He receives most
|
||||||
|
> of his critical information from King's Hand, the second in command. King's hand has many
|
||||||
|
> close advisors himself, feeding him with relevant information about events occurring in the
|
||||||
|
> kingdom.
|
||||||
|
|
||||||
|
In Plain Words
|
||||||
|
|
||||||
|
> Event Aggregator is an event mediator that collects events from multiple sources and delivers
|
||||||
|
> them to registered observers.
|
||||||
|
|
||||||
|
**Programmatic Example**
|
||||||
|
|
||||||
|
In our programmatic example, we demonstrate the implementation of an event aggregator pattern. Some of
|
||||||
|
the objects are event listeners, some are event emitters, and the event aggregator does both.
|
||||||
|
|
||||||
|
```java
|
||||||
|
public interface EventObserver {
|
||||||
|
void onEvent(Event e);
|
||||||
|
}
|
||||||
|
|
||||||
|
public abstract class EventEmitter {
|
||||||
|
|
||||||
|
private final Map<Event, List<EventObserver>> observerLists;
|
||||||
|
|
||||||
|
public EventEmitter() {
|
||||||
|
observerLists = new HashMap<>();
|
||||||
|
}
|
||||||
|
|
||||||
|
public final void registerObserver(EventObserver obs, Event e) {
|
||||||
|
...
|
||||||
|
}
|
||||||
|
|
||||||
|
protected void notifyObservers(Event e) {
|
||||||
|
...
|
||||||
|
}
|
||||||
|
}
|
||||||
|
```
|
||||||
|
|
||||||
|
`KingJoffrey` is listening to events from `KingsHand`.
|
||||||
|
|
||||||
|
```java
|
||||||
|
@Slf4j
|
||||||
|
public class KingJoffrey implements EventObserver {
|
||||||
|
@Override
|
||||||
|
public void onEvent(Event e) {
|
||||||
|
LOGGER.info("Received event from the King's Hand: {}", e.toString());
|
||||||
|
}
|
||||||
|
}
|
||||||
|
```
|
||||||
|
|
||||||
|
`KingsHand` is listening to events from his subordinates `LordBaelish`, `LordVarys`, and `Scout`.
|
||||||
|
Whatever he hears from them, he delivers to `KingJoffrey`.
|
||||||
|
|
||||||
|
```java
|
||||||
|
public class KingsHand extends EventEmitter implements EventObserver {
|
||||||
|
|
||||||
|
public KingsHand() {
|
||||||
|
}
|
||||||
|
|
||||||
|
public KingsHand(EventObserver obs, Event e) {
|
||||||
|
super(obs, e);
|
||||||
|
}
|
||||||
|
|
||||||
|
@Override
|
||||||
|
public void onEvent(Event e) {
|
||||||
|
notifyObservers(e);
|
||||||
|
}
|
||||||
|
}
|
||||||
|
```
|
||||||
|
|
||||||
|
For example, `LordVarys` finds a traitor every Sunday and notifies the `KingsHand`.
|
||||||
|
|
||||||
|
```java
|
||||||
|
@Slf4j
|
||||||
|
public class LordVarys extends EventEmitter implements EventObserver {
|
||||||
|
@Override
|
||||||
|
public void timePasses(Weekday day) {
|
||||||
|
if (day == Weekday.SATURDAY) {
|
||||||
|
notifyObservers(Event.TRAITOR_DETECTED);
|
||||||
|
}
|
||||||
|
}
|
||||||
|
}
|
||||||
|
```
|
||||||
|
|
||||||
|
The following snippet demonstrates how the objects are constructed and wired together.
|
||||||
|
|
||||||
|
```java
|
||||||
|
var kingJoffrey = new KingJoffrey();
|
||||||
|
|
||||||
|
var kingsHand = new KingsHand();
|
||||||
|
kingsHand.registerObserver(kingJoffrey, Event.TRAITOR_DETECTED);
|
||||||
|
kingsHand.registerObserver(kingJoffrey, Event.STARK_SIGHTED);
|
||||||
|
kingsHand.registerObserver(kingJoffrey, Event.WARSHIPS_APPROACHING);
|
||||||
|
kingsHand.registerObserver(kingJoffrey, Event.WHITE_WALKERS_SIGHTED);
|
||||||
|
|
||||||
|
var varys = new LordVarys();
|
||||||
|
varys.registerObserver(kingsHand, Event.TRAITOR_DETECTED);
|
||||||
|
varys.registerObserver(kingsHand, Event.WHITE_WALKERS_SIGHTED);
|
||||||
|
|
||||||
|
var scout = new Scout();
|
||||||
|
scout.registerObserver(kingsHand, Event.WARSHIPS_APPROACHING);
|
||||||
|
scout.registerObserver(varys, Event.WHITE_WALKERS_SIGHTED);
|
||||||
|
|
||||||
|
var baelish = new LordBaelish(kingsHand, Event.STARK_SIGHTED);
|
||||||
|
|
||||||
|
var emitters = List.of(
|
||||||
|
kingsHand,
|
||||||
|
baelish,
|
||||||
|
varys,
|
||||||
|
scout
|
||||||
|
);
|
||||||
|
|
||||||
|
Arrays.stream(Weekday.values())
|
||||||
|
.<Consumer<? super EventEmitter>>map(day -> emitter -> emitter.timePasses(day))
|
||||||
|
.forEachOrdered(emitters::forEach);
|
||||||
|
```
|
||||||
|
|
||||||
|
The console output after running the example.
|
||||||
|
|
||||||
|
```
|
||||||
|
18:21:52.955 [main] INFO com.iluwatar.event.aggregator.KingJoffrey - Received event from the King's Hand: Warships approaching
|
||||||
|
18:21:52.960 [main] INFO com.iluwatar.event.aggregator.KingJoffrey - Received event from the King's Hand: White walkers sighted
|
||||||
|
18:21:52.960 [main] INFO com.iluwatar.event.aggregator.KingJoffrey - Received event from the King's Hand: Stark sighted
|
||||||
|
18:21:52.960 [main] INFO com.iluwatar.event.aggregator.KingJoffrey - Received event from the King's Hand: Traitor detected
|
||||||
|
```
|
||||||
|
|
||||||
## Class diagram
|
## Class diagram
|
||||||

|

|
||||||
|
|
||||||
@ -26,9 +160,13 @@ Use the Event Aggregator pattern when
|
|||||||
* Event Aggregator is a good choice when you have lots of objects that are
|
* Event Aggregator is a good choice when you have lots of objects that are
|
||||||
potential event sources. Rather than have the observer deal with registering
|
potential event sources. Rather than have the observer deal with registering
|
||||||
with them all, you can centralize the registration logic to the Event
|
with them all, you can centralize the registration logic to the Event
|
||||||
Aggregator. As well as simplifying registration, a Event Aggregator also
|
Aggregator. As well as simplifying registration, an Event Aggregator also
|
||||||
simplifies the memory management issues in using observers.
|
simplifies the memory management issues in using observers.
|
||||||
|
|
||||||
|
## Related patterns
|
||||||
|
|
||||||
|
* [Observer](https://java-design-patterns.com/patterns/observer/)
|
||||||
|
|
||||||
## Credits
|
## Credits
|
||||||
|
|
||||||
* [Martin Fowler - Event Aggregator](http://martinfowler.com/eaaDev/EventAggregator.html)
|
* [Martin Fowler - Event Aggregator](http://martinfowler.com/eaaDev/EventAggregator.html)
|
||||||
|
182
metadata-mapping/README.md
Normal file
182
metadata-mapping/README.md
Normal file
@ -0,0 +1,182 @@
|
|||||||
|
---
|
||||||
|
layout: pattern
|
||||||
|
title: Metadata Mapping
|
||||||
|
folder: metadata-mapping
|
||||||
|
permalink: /patterns/metadata-mapping/
|
||||||
|
categories: Architectural
|
||||||
|
language: en
|
||||||
|
tags:
|
||||||
|
- Data access
|
||||||
|
---
|
||||||
|
|
||||||
|
## Intent
|
||||||
|
|
||||||
|
Holds details of object-relational mapping in the metadata.
|
||||||
|
|
||||||
|
## Explanation
|
||||||
|
|
||||||
|
Real world example
|
||||||
|
|
||||||
|
> Hibernate ORM Tool uses Metadata Mapping Pattern to specify the mapping between classes and tables either using XML or annotations in code.
|
||||||
|
|
||||||
|
In plain words
|
||||||
|
|
||||||
|
> Metadata Mapping specifies the mapping between classes and tables so that we could treat a table of any database like a Java class.
|
||||||
|
|
||||||
|
Wikipedia says
|
||||||
|
|
||||||
|
> Create a "virtual [object database](https://en.wikipedia.org/wiki/Object_database)" that can be used from within the programming language.
|
||||||
|
|
||||||
|
**Programmatic Example**
|
||||||
|
|
||||||
|
We give an example about visiting the information of `USER` table in `h2` database. Firstly, we create `USER` table with `h2`:
|
||||||
|
|
||||||
|
```java
|
||||||
|
@Slf4j
|
||||||
|
public class DatabaseUtil {
|
||||||
|
private static final String DB_URL = "jdbc:h2:mem:metamapping";
|
||||||
|
private static final String CREATE_SCHEMA_SQL = "DROP TABLE IF EXISTS `user`;"
|
||||||
|
+ "CREATE TABLE `user` (\n"
|
||||||
|
+ " `id` int(11) NOT NULL AUTO_INCREMENT,\n"
|
||||||
|
+ " `username` varchar(255) NOT NULL,\n"
|
||||||
|
+ " `password` varchar(255) NOT NULL,\n"
|
||||||
|
+ " PRIMARY KEY (`id`)\n"
|
||||||
|
+ ");";
|
||||||
|
|
||||||
|
/**
|
||||||
|
* Create database.
|
||||||
|
*/
|
||||||
|
static {
|
||||||
|
LOGGER.info("create h2 database");
|
||||||
|
var source = new JdbcDataSource();
|
||||||
|
source.setURL(DB_URL);
|
||||||
|
try (var statement = source.getConnection().createStatement()) {
|
||||||
|
statement.execute(CREATE_SCHEMA_SQL);
|
||||||
|
} catch (SQLException e) {
|
||||||
|
LOGGER.error("unable to create h2 data source", e);
|
||||||
|
}
|
||||||
|
}
|
||||||
|
}
|
||||||
|
```
|
||||||
|
|
||||||
|
Correspondingly, here's the basic `User` entity.
|
||||||
|
|
||||||
|
```java
|
||||||
|
@Setter
|
||||||
|
@Getter
|
||||||
|
@ToString
|
||||||
|
public class User {
|
||||||
|
private Integer id;
|
||||||
|
private String username;
|
||||||
|
private String password;
|
||||||
|
|
||||||
|
/**
|
||||||
|
* Get a user.
|
||||||
|
* @param username user name
|
||||||
|
* @param password user password
|
||||||
|
*/
|
||||||
|
public User(String username, String password) {
|
||||||
|
this.username = username;
|
||||||
|
this.password = password;
|
||||||
|
}
|
||||||
|
}
|
||||||
|
```
|
||||||
|
|
||||||
|
Then we write a `xml` file to show the mapping between the table and the object:
|
||||||
|
|
||||||
|
```xml
|
||||||
|
<?xml version="1.0" encoding="utf-8"?>
|
||||||
|
<!DOCTYPE hibernate-mapping PUBLIC
|
||||||
|
"-//Hibernate/Hibernate Mapping DTD//EN"
|
||||||
|
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
|
||||||
|
|
||||||
|
<hibernate-mapping>
|
||||||
|
<class name="com.iluwatar.metamapping.model.User" table="user">
|
||||||
|
<id name="id" type="java.lang.Integer" column="id">
|
||||||
|
<generator class="native"/>
|
||||||
|
</id>
|
||||||
|
<property name="username" column="username" type="java.lang.String"/>
|
||||||
|
<property name="password" column="password" type="java.lang.String"/>
|
||||||
|
</class>
|
||||||
|
</hibernate-mapping>
|
||||||
|
```
|
||||||
|
|
||||||
|
We use `Hibernate` to resolve the mapping and connect to our database, here's its configuration:
|
||||||
|
|
||||||
|
```xml
|
||||||
|
<?xml version="1.0" encoding="utf-8"?>
|
||||||
|
<!DOCTYPE hibernate-configuration PUBLIC
|
||||||
|
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
|
||||||
|
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
|
||||||
|
<hibernate-configuration>
|
||||||
|
<session-factory>
|
||||||
|
<!-- JDBC Database connection settings -->
|
||||||
|
<property name="connection.url">jdbc:h2:mem:metamapping</property>
|
||||||
|
<property name="connection.driver_class">org.h2.Driver</property>
|
||||||
|
<!-- JDBC connection pool settings ... using built-in test pool -->
|
||||||
|
<property name="connection.pool_size">1</property>
|
||||||
|
<!-- Select our SQL dialect -->
|
||||||
|
<property name="dialect">org.hibernate.dialect.H2Dialect</property>
|
||||||
|
<!-- Echo the SQL to stdout -->
|
||||||
|
<property name="show_sql">false</property>
|
||||||
|
<!-- Drop and re-create the database schema on startup -->
|
||||||
|
<property name="hbm2ddl.auto">create-drop</property>
|
||||||
|
<mapping resource="com/iluwatar/metamapping/model/User.hbm.xml" />
|
||||||
|
</session-factory>
|
||||||
|
</hibernate-configuration>
|
||||||
|
```
|
||||||
|
|
||||||
|
Then we can get access to the table just like an object with `Hibernate`, here's some CRUDs:
|
||||||
|
|
||||||
|
```java
|
||||||
|
@Slf4j
|
||||||
|
public class UserService {
|
||||||
|
private static final SessionFactory factory = HibernateUtil.getSessionFactory();
|
||||||
|
|
||||||
|
/**
|
||||||
|
* List all users.
|
||||||
|
* @return list of users
|
||||||
|
*/
|
||||||
|
public List<User> listUser() {
|
||||||
|
LOGGER.info("list all users.");
|
||||||
|
List<User> users = new ArrayList<>();
|
||||||
|
try (var session = factory.openSession()) {
|
||||||
|
var tx = session.beginTransaction();
|
||||||
|
List<User> userIter = session.createQuery("FROM User").list();
|
||||||
|
for (var iterator = userIter.iterator(); iterator.hasNext();) {
|
||||||
|
users.add(iterator.next());
|
||||||
|
}
|
||||||
|
tx.commit();
|
||||||
|
} catch (HibernateException e) {
|
||||||
|
LOGGER.debug("fail to get users", e);
|
||||||
|
}
|
||||||
|
return users;
|
||||||
|
}
|
||||||
|
|
||||||
|
// other CRUDs ->
|
||||||
|
...
|
||||||
|
|
||||||
|
public void close() {
|
||||||
|
HibernateUtil.shutdown();
|
||||||
|
}
|
||||||
|
}
|
||||||
|
```
|
||||||
|
|
||||||
|
## Class diagram
|
||||||
|
|
||||||
|

|
||||||
|
|
||||||
|
## Applicability
|
||||||
|
|
||||||
|
Use the Metadata Mapping when:
|
||||||
|
|
||||||
|
- you want reduce the amount of work needed to handle database mapping.
|
||||||
|
|
||||||
|
## Known uses
|
||||||
|
|
||||||
|
[Hibernate](https://hibernate.org/), [EclipseLink](https://www.eclipse.org/eclipselink/), [MyBatis](https://blog.mybatis.org/)......
|
||||||
|
|
||||||
|
## Credits
|
||||||
|
|
||||||
|
- [J2EE Design Patterns](https://www.amazon.com/gp/product/0596004273/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0596004273&linkCode=as2&tag=javadesignpat-20&linkId=48d37c67fb3d845b802fa9b619ad8f31)
|
||||||
|
|
BIN
metadata-mapping/etc/metamapping.png
Normal file
BIN
metadata-mapping/etc/metamapping.png
Normal file
Binary file not shown.
After Width: | Height: | Size: 49 KiB |
32
metadata-mapping/etc/metamapping.puml
Normal file
32
metadata-mapping/etc/metamapping.puml
Normal file
@ -0,0 +1,32 @@
|
|||||||
|
@startuml
|
||||||
|
interface com.iluwatar.metamapping.service.UserService {
|
||||||
|
+ List<User> listUser()
|
||||||
|
+ int createUser(User)
|
||||||
|
+ void updateUser(Integer,User)
|
||||||
|
+ void deleteUser(Integer)
|
||||||
|
+ User getUser(Integer)
|
||||||
|
+ void close()
|
||||||
|
}
|
||||||
|
class com.iluwatar.metamapping.utils.DatabaseUtil {
|
||||||
|
+ {static} void createDataSource()
|
||||||
|
}
|
||||||
|
class com.iluwatar.metamapping.model.User {
|
||||||
|
- Integer id
|
||||||
|
- String username
|
||||||
|
- String password
|
||||||
|
+ User(String username, String password)
|
||||||
|
}
|
||||||
|
class com.iluwatar.metamapping.utils.HibernateUtil {
|
||||||
|
+ {static} SessionFactory getSessionFactory()
|
||||||
|
+ {static} void shutdown()
|
||||||
|
}
|
||||||
|
class com.iluwatar.metamapping.App {
|
||||||
|
+ {static} void main(String[])
|
||||||
|
+ {static} List<User> generateSampleUsers()
|
||||||
|
}
|
||||||
|
|
||||||
|
com.iluwatar.metamapping.service.UserService <.. com.iluwatar.metamapping.App
|
||||||
|
com.iluwatar.metamapping.model.User <.. com.iluwatar.metamapping.service.UserService
|
||||||
|
com.iluwatar.metamapping.utils.HibernateUtil <.. com.iluwatar.metamapping.service.UserService
|
||||||
|
com.iluwatar.metamapping.utils.DatabaseUtil <-- com.iluwatar.metamapping.utils.HibernateUtil
|
||||||
|
@enduml
|
87
metadata-mapping/pom.xml
Normal file
87
metadata-mapping/pom.xml
Normal file
@ -0,0 +1,87 @@
|
|||||||
|
<?xml version="1.0" encoding="UTF-8"?>
|
||||||
|
<!--
|
||||||
|
|
||||||
|
The MIT License
|
||||||
|
Copyright © 2014-2021 Ilkka Seppälä
|
||||||
|
|
||||||
|
Permission is hereby granted, free of charge, to any person obtaining a copy
|
||||||
|
of this software and associated documentation files (the "Software"), to deal
|
||||||
|
in the Software without restriction, including without limitation the rights
|
||||||
|
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
|
||||||
|
copies of the Software, and to permit persons to whom the Software is
|
||||||
|
furnished to do so, subject to the following conditions:
|
||||||
|
|
||||||
|
The above copyright notice and this permission notice shall be included in
|
||||||
|
all copies or substantial portions of the Software.
|
||||||
|
|
||||||
|
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
|
||||||
|
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
|
||||||
|
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
|
||||||
|
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
|
||||||
|
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
|
||||||
|
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
|
||||||
|
THE SOFTWARE.
|
||||||
|
|
||||||
|
-->
|
||||||
|
<project xmlns="http://maven.apache.org/POM/4.0.0"
|
||||||
|
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
|
||||||
|
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
|
||||||
|
<parent>
|
||||||
|
<artifactId>java-design-patterns</artifactId>
|
||||||
|
<groupId>com.iluwatar</groupId>
|
||||||
|
<version>1.26.0-SNAPSHOT</version>
|
||||||
|
</parent>
|
||||||
|
<modelVersion>4.0.0</modelVersion>
|
||||||
|
|
||||||
|
<artifactId>metadata-mapping</artifactId>
|
||||||
|
<dependencies>
|
||||||
|
<dependency>
|
||||||
|
<groupId>org.junit.jupiter</groupId>
|
||||||
|
<artifactId>junit-jupiter-engine</artifactId>
|
||||||
|
<scope>test</scope>
|
||||||
|
</dependency>
|
||||||
|
<dependency>
|
||||||
|
<groupId>com.h2database</groupId>
|
||||||
|
<artifactId>h2</artifactId>
|
||||||
|
</dependency>
|
||||||
|
<dependency>
|
||||||
|
<groupId>org.hibernate</groupId>
|
||||||
|
<artifactId>hibernate-core</artifactId>
|
||||||
|
</dependency>
|
||||||
|
<dependency>
|
||||||
|
<groupId>com.h2database</groupId>
|
||||||
|
<artifactId>h2</artifactId>
|
||||||
|
</dependency>
|
||||||
|
<dependency>
|
||||||
|
<groupId>javax.xml.bind</groupId>
|
||||||
|
<artifactId>jaxb-api</artifactId>
|
||||||
|
</dependency>
|
||||||
|
<dependency>
|
||||||
|
<groupId>com.sun.xml.bind</groupId>
|
||||||
|
<artifactId>jaxb-impl</artifactId>
|
||||||
|
</dependency>
|
||||||
|
<dependency>
|
||||||
|
<groupId>com.sun.istack</groupId>
|
||||||
|
<artifactId>istack-commons-runtime</artifactId>
|
||||||
|
</dependency>
|
||||||
|
</dependencies>
|
||||||
|
<build>
|
||||||
|
<plugins>
|
||||||
|
<plugin>
|
||||||
|
<groupId>org.apache.maven.plugins</groupId>
|
||||||
|
<artifactId>maven-assembly-plugin</artifactId>
|
||||||
|
<executions>
|
||||||
|
<execution>
|
||||||
|
<configuration>
|
||||||
|
<archive>
|
||||||
|
<manifest>
|
||||||
|
<mainClass>com.iluwatar.metamapping.App</mainClass>
|
||||||
|
</manifest>
|
||||||
|
</archive>
|
||||||
|
</configuration>
|
||||||
|
</execution>
|
||||||
|
</executions>
|
||||||
|
</plugin>
|
||||||
|
</plugins>
|
||||||
|
</build>
|
||||||
|
</project>
|
@ -0,0 +1,72 @@
|
|||||||
|
package com.iluwatar.metamapping;
|
||||||
|
|
||||||
|
import com.iluwatar.metamapping.model.User;
|
||||||
|
import com.iluwatar.metamapping.service.UserService;
|
||||||
|
import com.iluwatar.metamapping.utils.DatabaseUtil;
|
||||||
|
import java.util.List;
|
||||||
|
import lombok.extern.slf4j.Slf4j;
|
||||||
|
import org.hibernate.service.ServiceRegistry;
|
||||||
|
|
||||||
|
/**
|
||||||
|
* Metadata Mapping specifies the mapping
|
||||||
|
* between classes and tables so that
|
||||||
|
* we could treat a table of any database like a Java class.
|
||||||
|
*
|
||||||
|
* <p>With hibernate, we achieve list/create/update/delete/get operations:
|
||||||
|
* 1)Create the H2 Database in {@link DatabaseUtil}.
|
||||||
|
* 2)Hibernate resolve hibernate.cfg.xml and generate service like save/list/get/delete.
|
||||||
|
* For learning metadata mapping pattern, we go deeper into Hibernate here:
|
||||||
|
* a)read properties from hibernate.cfg.xml and mapping from *.hbm.xml
|
||||||
|
* b)create session factory to generate session interacting with database
|
||||||
|
* c)generate session with factory pattern
|
||||||
|
* d)create query object or use basic api with session,
|
||||||
|
* hibernate will convert all query to database query according to metadata
|
||||||
|
* 3)We encapsulate hibernate service in {@link UserService} for our use.
|
||||||
|
* @see org.hibernate.cfg.Configuration#configure(String)
|
||||||
|
* @see org.hibernate.cfg.Configuration#buildSessionFactory(ServiceRegistry)
|
||||||
|
* @see org.hibernate.internal.SessionFactoryImpl#openSession()
|
||||||
|
*/
|
||||||
|
@Slf4j
|
||||||
|
public class App {
|
||||||
|
/**
|
||||||
|
* Program entry point.
|
||||||
|
*
|
||||||
|
* @param args command line args.
|
||||||
|
* @throws Exception if any error occurs.
|
||||||
|
*/
|
||||||
|
public static void main(String[] args) throws Exception {
|
||||||
|
// get service
|
||||||
|
var userService = new UserService();
|
||||||
|
// use create service to add users
|
||||||
|
for (var user: generateSampleUsers()) {
|
||||||
|
var id = userService.createUser(user);
|
||||||
|
LOGGER.info("Add user" + user + "at" + id + ".");
|
||||||
|
}
|
||||||
|
// use list service to get users
|
||||||
|
var users = userService.listUser();
|
||||||
|
LOGGER.info(String.valueOf(users));
|
||||||
|
// use get service to get a user
|
||||||
|
var user = userService.getUser(1);
|
||||||
|
LOGGER.info(String.valueOf(user));
|
||||||
|
// change password of user 1
|
||||||
|
user.setPassword("new123");
|
||||||
|
// use update service to update user 1
|
||||||
|
userService.updateUser(1, user);
|
||||||
|
// use delete service to delete user 2
|
||||||
|
userService.deleteUser(2);
|
||||||
|
// close service
|
||||||
|
userService.close();
|
||||||
|
}
|
||||||
|
|
||||||
|
/**
|
||||||
|
* Generate users.
|
||||||
|
*
|
||||||
|
* @return list of users.
|
||||||
|
*/
|
||||||
|
public static List<User> generateSampleUsers() {
|
||||||
|
final var user1 = new User("ZhangSan", "zhs123");
|
||||||
|
final var user2 = new User("LiSi", "ls123");
|
||||||
|
final var user3 = new User("WangWu", "ww123");
|
||||||
|
return List.of(user1, user2, user3);
|
||||||
|
}
|
||||||
|
}
|
@ -0,0 +1,29 @@
|
|||||||
|
package com.iluwatar.metamapping.model;
|
||||||
|
|
||||||
|
import lombok.Getter;
|
||||||
|
import lombok.Setter;
|
||||||
|
import lombok.ToString;
|
||||||
|
|
||||||
|
/**
|
||||||
|
* User Entity.
|
||||||
|
*/
|
||||||
|
@Setter
|
||||||
|
@Getter
|
||||||
|
@ToString
|
||||||
|
public class User {
|
||||||
|
private Integer id;
|
||||||
|
private String username;
|
||||||
|
private String password;
|
||||||
|
|
||||||
|
public User() {}
|
||||||
|
|
||||||
|
/**
|
||||||
|
* Get a user.
|
||||||
|
* @param username user name
|
||||||
|
* @param password user password
|
||||||
|
*/
|
||||||
|
public User(String username, String password) {
|
||||||
|
this.username = username;
|
||||||
|
this.password = password;
|
||||||
|
}
|
||||||
|
}
|
@ -0,0 +1,114 @@
|
|||||||
|
package com.iluwatar.metamapping.service;
|
||||||
|
|
||||||
|
import com.iluwatar.metamapping.model.User;
|
||||||
|
import com.iluwatar.metamapping.utils.HibernateUtil;
|
||||||
|
import java.util.ArrayList;
|
||||||
|
import java.util.List;
|
||||||
|
import lombok.extern.slf4j.Slf4j;
|
||||||
|
import org.hibernate.HibernateException;
|
||||||
|
import org.hibernate.SessionFactory;
|
||||||
|
|
||||||
|
/**
|
||||||
|
* Service layer for user.
|
||||||
|
*/
|
||||||
|
@Slf4j
|
||||||
|
public class UserService {
|
||||||
|
private static final SessionFactory factory = HibernateUtil.getSessionFactory();
|
||||||
|
|
||||||
|
/**
|
||||||
|
* List all users.
|
||||||
|
* @return list of users
|
||||||
|
*/
|
||||||
|
public List<User> listUser() {
|
||||||
|
LOGGER.info("list all users.");
|
||||||
|
List<User> users = new ArrayList<>();
|
||||||
|
try (var session = factory.openSession()) {
|
||||||
|
var tx = session.beginTransaction();
|
||||||
|
List<User> userIter = session.createQuery("FROM User").list();
|
||||||
|
for (var iterator = userIter.iterator(); iterator.hasNext();) {
|
||||||
|
users.add(iterator.next());
|
||||||
|
}
|
||||||
|
tx.commit();
|
||||||
|
} catch (HibernateException e) {
|
||||||
|
LOGGER.debug("fail to get users", e);
|
||||||
|
}
|
||||||
|
return users;
|
||||||
|
}
|
||||||
|
|
||||||
|
/**
|
||||||
|
* Add a user.
|
||||||
|
* @param user user entity
|
||||||
|
* @return user id
|
||||||
|
*/
|
||||||
|
public int createUser(User user) {
|
||||||
|
LOGGER.info("create user: " + user.getUsername());
|
||||||
|
var id = -1;
|
||||||
|
try (var session = factory.openSession()) {
|
||||||
|
var tx = session.beginTransaction();
|
||||||
|
id = (Integer) session.save(user);
|
||||||
|
tx.commit();
|
||||||
|
} catch (HibernateException e) {
|
||||||
|
LOGGER.debug("fail to create user", e);
|
||||||
|
}
|
||||||
|
LOGGER.info("create user " + user.getUsername() + " at " + id);
|
||||||
|
return id;
|
||||||
|
}
|
||||||
|
|
||||||
|
/**
|
||||||
|
* Update user.
|
||||||
|
* @param id user id
|
||||||
|
* @param user new user entity
|
||||||
|
*/
|
||||||
|
public void updateUser(Integer id, User user) {
|
||||||
|
LOGGER.info("update user at " + id);
|
||||||
|
try (var session = factory.openSession()) {
|
||||||
|
var tx = session.beginTransaction();
|
||||||
|
user.setId(id);
|
||||||
|
session.update(user);
|
||||||
|
tx.commit();
|
||||||
|
} catch (HibernateException e) {
|
||||||
|
LOGGER.debug("fail to update user", e);
|
||||||
|
}
|
||||||
|
}
|
||||||
|
|
||||||
|
/**
|
||||||
|
* Delete user.
|
||||||
|
* @param id user id
|
||||||
|
*/
|
||||||
|
public void deleteUser(Integer id) {
|
||||||
|
LOGGER.info("delete user at: " + id);
|
||||||
|
try (var session = factory.openSession()) {
|
||||||
|
var tx = session.beginTransaction();
|
||||||
|
var user = session.get(User.class, id);
|
||||||
|
session.delete(user);
|
||||||
|
tx.commit();
|
||||||
|
} catch (HibernateException e) {
|
||||||
|
LOGGER.debug("fail to delete user", e);
|
||||||
|
}
|
||||||
|
}
|
||||||
|
|
||||||
|
/**
|
||||||
|
* Get user.
|
||||||
|
* @param id user id
|
||||||
|
* @return deleted user
|
||||||
|
*/
|
||||||
|
public User getUser(Integer id) {
|
||||||
|
LOGGER.info("get user at: " + id);
|
||||||
|
User user = null;
|
||||||
|
try (var session = factory.openSession()) {
|
||||||
|
var tx = session.beginTransaction();
|
||||||
|
user = session.get(User.class, id);
|
||||||
|
tx.commit();
|
||||||
|
} catch (HibernateException e) {
|
||||||
|
LOGGER.debug("fail to get user", e);
|
||||||
|
}
|
||||||
|
return user;
|
||||||
|
}
|
||||||
|
|
||||||
|
/**
|
||||||
|
* Close hibernate.
|
||||||
|
*/
|
||||||
|
public void close() {
|
||||||
|
HibernateUtil.shutdown();
|
||||||
|
}
|
||||||
|
}
|
@ -0,0 +1,39 @@
|
|||||||
|
package com.iluwatar.metamapping.utils;
|
||||||
|
|
||||||
|
import java.sql.SQLException;
|
||||||
|
import lombok.extern.slf4j.Slf4j;
|
||||||
|
import org.h2.jdbcx.JdbcDataSource;
|
||||||
|
|
||||||
|
/**
|
||||||
|
* Create h2 database.
|
||||||
|
*/
|
||||||
|
@Slf4j
|
||||||
|
public class DatabaseUtil {
|
||||||
|
private static final String DB_URL = "jdbc:h2:mem:metamapping";
|
||||||
|
private static final String CREATE_SCHEMA_SQL = "DROP TABLE IF EXISTS `user`;"
|
||||||
|
+ "CREATE TABLE `user` (\n"
|
||||||
|
+ " `id` int(11) NOT NULL AUTO_INCREMENT,\n"
|
||||||
|
+ " `username` varchar(255) NOT NULL,\n"
|
||||||
|
+ " `password` varchar(255) NOT NULL,\n"
|
||||||
|
+ " PRIMARY KEY (`id`)\n"
|
||||||
|
+ ");";
|
||||||
|
|
||||||
|
/**
|
||||||
|
* Hide constructor.
|
||||||
|
*/
|
||||||
|
private DatabaseUtil() {}
|
||||||
|
|
||||||
|
/**
|
||||||
|
* Create database.
|
||||||
|
*/
|
||||||
|
static {
|
||||||
|
LOGGER.info("create h2 database");
|
||||||
|
var source = new JdbcDataSource();
|
||||||
|
source.setURL(DB_URL);
|
||||||
|
try (var statement = source.getConnection().createStatement()) {
|
||||||
|
statement.execute(CREATE_SCHEMA_SQL);
|
||||||
|
} catch (SQLException e) {
|
||||||
|
LOGGER.error("unable to create h2 data source", e);
|
||||||
|
}
|
||||||
|
}
|
||||||
|
}
|
@ -0,0 +1,45 @@
|
|||||||
|
package com.iluwatar.metamapping.utils;
|
||||||
|
|
||||||
|
import lombok.extern.slf4j.Slf4j;
|
||||||
|
import org.hibernate.SessionFactory;
|
||||||
|
import org.hibernate.cfg.Configuration;
|
||||||
|
|
||||||
|
/**
|
||||||
|
* Manage hibernate.
|
||||||
|
*/
|
||||||
|
@Slf4j
|
||||||
|
public class HibernateUtil {
|
||||||
|
|
||||||
|
private static final SessionFactory sessionFactory = buildSessionFactory();
|
||||||
|
|
||||||
|
/**
|
||||||
|
* Hide constructor.
|
||||||
|
*/
|
||||||
|
private HibernateUtil() {}
|
||||||
|
|
||||||
|
/**
|
||||||
|
* Build session factory.
|
||||||
|
* @return session factory
|
||||||
|
*/
|
||||||
|
private static SessionFactory buildSessionFactory() {
|
||||||
|
// Create the SessionFactory from hibernate.cfg.xml
|
||||||
|
return new Configuration().configure().buildSessionFactory();
|
||||||
|
}
|
||||||
|
|
||||||
|
/**
|
||||||
|
* Get session factory.
|
||||||
|
* @return session factory
|
||||||
|
*/
|
||||||
|
public static SessionFactory getSessionFactory() {
|
||||||
|
return sessionFactory;
|
||||||
|
}
|
||||||
|
|
||||||
|
/**
|
||||||
|
* Close session factory.
|
||||||
|
*/
|
||||||
|
public static void shutdown() {
|
||||||
|
// Close caches and connection pools
|
||||||
|
getSessionFactory().close();
|
||||||
|
}
|
||||||
|
|
||||||
|
}
|
@ -0,0 +1,14 @@
|
|||||||
|
<?xml version="1.0" encoding="utf-8"?>
|
||||||
|
<!DOCTYPE hibernate-mapping PUBLIC
|
||||||
|
"-//Hibernate/Hibernate Mapping DTD//EN"
|
||||||
|
"http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
|
||||||
|
|
||||||
|
<hibernate-mapping>
|
||||||
|
<class name="com.iluwatar.metamapping.model.User" table="user">
|
||||||
|
<id name="id" type="java.lang.Integer" column="id">
|
||||||
|
<generator class="native"/>
|
||||||
|
</id>
|
||||||
|
<property name="username" column="username" type="java.lang.String"/>
|
||||||
|
<property name="password" column="password" type="java.lang.String"/>
|
||||||
|
</class>
|
||||||
|
</hibernate-mapping>
|
20
metadata-mapping/src/main/resources/hibernate.cfg.xml
Normal file
20
metadata-mapping/src/main/resources/hibernate.cfg.xml
Normal file
@ -0,0 +1,20 @@
|
|||||||
|
<?xml version="1.0" encoding="utf-8"?>
|
||||||
|
<!DOCTYPE hibernate-configuration PUBLIC
|
||||||
|
"-//Hibernate/Hibernate Configuration DTD 3.0//EN"
|
||||||
|
"http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
|
||||||
|
<hibernate-configuration>
|
||||||
|
<session-factory>
|
||||||
|
<!-- JDBC Database connection settings -->
|
||||||
|
<property name="connection.url">jdbc:h2:mem:metamapping</property>
|
||||||
|
<property name="connection.driver_class">org.h2.Driver</property>
|
||||||
|
<!-- JDBC connection pool settings ... using built-in test pool -->
|
||||||
|
<property name="connection.pool_size">1</property>
|
||||||
|
<!-- Select our SQL dialect -->
|
||||||
|
<property name="dialect">org.hibernate.dialect.H2Dialect</property>
|
||||||
|
<!-- Echo the SQL to stdout -->
|
||||||
|
<property name="show_sql">false</property>
|
||||||
|
<!-- Drop and re-create the database schema on startup -->
|
||||||
|
<property name="hbm2ddl.auto">create-drop</property>
|
||||||
|
<mapping resource="com/iluwatar/metamapping/model/User.hbm.xml" />
|
||||||
|
</session-factory>
|
||||||
|
</hibernate-configuration>
|
@ -0,0 +1,20 @@
|
|||||||
|
package com.iluwatar.metamapping;
|
||||||
|
|
||||||
|
import org.junit.jupiter.api.Test;
|
||||||
|
import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
|
||||||
|
|
||||||
|
/**
|
||||||
|
* Tests that metadata mapping example runs without errors.
|
||||||
|
*/
|
||||||
|
class AppTest {
|
||||||
|
/**
|
||||||
|
* Issue: Add at least one assertion to this test case.
|
||||||
|
*
|
||||||
|
* Solution: Inserted assertion to check whether the execution of the main method in {@link App#main(String[])}
|
||||||
|
* throws an exception.
|
||||||
|
*/
|
||||||
|
@Test
|
||||||
|
void shouldExecuteMetaMappingWithoutException() {
|
||||||
|
assertDoesNotThrow(() -> App.main(new String[]{}));
|
||||||
|
}
|
||||||
|
}
|
7
pom.xml
7
pom.xml
@ -75,6 +75,7 @@
|
|||||||
<license-maven-plugin.version>3.0</license-maven-plugin.version>
|
<license-maven-plugin.version>3.0</license-maven-plugin.version>
|
||||||
<urm-maven-plugin.version>1.4.8</urm-maven-plugin.version>
|
<urm-maven-plugin.version>1.4.8</urm-maven-plugin.version>
|
||||||
<commons-io.version>2.7</commons-io.version>
|
<commons-io.version>2.7</commons-io.version>
|
||||||
|
<istack-commons-runtime.version>4.0.1</istack-commons-runtime.version>
|
||||||
<!-- SonarCloud -->
|
<!-- SonarCloud -->
|
||||||
<sonar.host.url>https://sonarcloud.io</sonar.host.url>
|
<sonar.host.url>https://sonarcloud.io</sonar.host.url>
|
||||||
<sonar.organization>iluwatar</sonar.organization>
|
<sonar.organization>iluwatar</sonar.organization>
|
||||||
@ -227,6 +228,7 @@
|
|||||||
<module>lockable-object</module>
|
<module>lockable-object</module>
|
||||||
<module>fanout-fanin</module>
|
<module>fanout-fanin</module>
|
||||||
<module>domain-model</module>
|
<module>domain-model</module>
|
||||||
|
<module>metadata-mapping</module>
|
||||||
</modules>
|
</modules>
|
||||||
<repositories>
|
<repositories>
|
||||||
<repository>
|
<repository>
|
||||||
@ -377,6 +379,11 @@
|
|||||||
<artifactId>commons-io</artifactId>
|
<artifactId>commons-io</artifactId>
|
||||||
<version>${commons-io.version}</version>
|
<version>${commons-io.version}</version>
|
||||||
</dependency>
|
</dependency>
|
||||||
|
<dependency>
|
||||||
|
<groupId>com.sun.istack</groupId>
|
||||||
|
<artifactId>istack-commons-runtime</artifactId>
|
||||||
|
<version>${istack-commons-runtime.version}</version>
|
||||||
|
</dependency>
|
||||||
</dependencies>
|
</dependencies>
|
||||||
</dependencyManagement>
|
</dependencyManagement>
|
||||||
<dependencies>
|
<dependencies>
|
||||||
|
@ -18,11 +18,11 @@ threads and eliminating the latency of creating new threads.
|
|||||||
|
|
||||||
## Explanation
|
## Explanation
|
||||||
|
|
||||||
Real-world example
|
Real world example
|
||||||
|
|
||||||
> We have a large number of relatively short tasks at hand. We need to peel huge amounts of potatoes
|
> We have a large number of relatively short tasks at hand. We need to peel huge amounts of potatoes
|
||||||
> and serve a mighty amount of coffee cups. Creating a new thread for each task would be a waste so
|
> and serve mighty amount of coffee cups. Creating a new thread for each task would be a waste so we
|
||||||
> we establish a thread pool.
|
> establish a thread pool.
|
||||||
|
|
||||||
In plain words
|
In plain words
|
||||||
|
|
||||||
@ -99,7 +99,7 @@ public class PotatoPeelingTask extends Task {
|
|||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
Next, we present a runnable `Worker` class that the thread pool will utilize to handle all the potato
|
Next we present a runnable `Worker` class that the thread pool will utilize to handle all the potato
|
||||||
peeling and coffee making.
|
peeling and coffee making.
|
||||||
|
|
||||||
```java
|
```java
|
||||||
|
@ -16,12 +16,10 @@ Ensure that a given client is not able to access service resources more than the
|
|||||||
|
|
||||||
## Explanation
|
## Explanation
|
||||||
|
|
||||||
Real-world example
|
Real world example
|
||||||
|
|
||||||
> A young human and an old dwarf walk into a bar. They start ordering beers from the bartender.
|
> A large multinational corporation offers API to its customers. The API is rate-limited and each
|
||||||
> The bartender immediately sees that the young human shouldn't consume too many drinks too fast
|
> customer can only make certain amount of calls per second.
|
||||||
> and refuses to serve if enough time has not passed. For the old dwarf, the serving rate can
|
|
||||||
> be higher.
|
|
||||||
|
|
||||||
In plain words
|
In plain words
|
||||||
|
|
||||||
@ -35,25 +33,30 @@ In plain words
|
|||||||
|
|
||||||
**Programmatic Example**
|
**Programmatic Example**
|
||||||
|
|
||||||
`BarCustomer` class presents the clients of the `Bartender` API. `CallsCount` tracks the number of
|
Tenant class presents the clients of the API. CallsCount tracks the number of API calls per tenant.
|
||||||
calls per `BarCustomer`.
|
|
||||||
|
|
||||||
```java
|
```java
|
||||||
public class BarCustomer {
|
public class Tenant {
|
||||||
|
|
||||||
@Getter
|
private final String name;
|
||||||
private final String name;
|
private final int allowedCallsPerSecond;
|
||||||
@Getter
|
|
||||||
private final int allowedCallsPerSecond;
|
|
||||||
|
|
||||||
public BarCustomer(String name, int allowedCallsPerSecond, CallsCount callsCount) {
|
public Tenant(String name, int allowedCallsPerSecond, CallsCount callsCount) {
|
||||||
if (allowedCallsPerSecond < 0) {
|
if (allowedCallsPerSecond < 0) {
|
||||||
throw new InvalidParameterException("Number of calls less than 0 not allowed");
|
throw new InvalidParameterException("Number of calls less than 0 not allowed");
|
||||||
}
|
|
||||||
this.name = name;
|
|
||||||
this.allowedCallsPerSecond = allowedCallsPerSecond;
|
|
||||||
callsCount.addTenant(name);
|
|
||||||
}
|
}
|
||||||
|
this.name = name;
|
||||||
|
this.allowedCallsPerSecond = allowedCallsPerSecond;
|
||||||
|
callsCount.addTenant(name);
|
||||||
|
}
|
||||||
|
|
||||||
|
public String getName() {
|
||||||
|
return name;
|
||||||
|
}
|
||||||
|
|
||||||
|
public int getAllowedCallsPerSecond() {
|
||||||
|
return allowedCallsPerSecond;
|
||||||
|
}
|
||||||
}
|
}
|
||||||
|
|
||||||
@Slf4j
|
@Slf4j
|
||||||
@ -73,14 +76,14 @@ public final class CallsCount {
|
|||||||
}
|
}
|
||||||
|
|
||||||
public void reset() {
|
public void reset() {
|
||||||
|
LOGGER.debug("Resetting the map.");
|
||||||
tenantCallsCount.replaceAll((k, v) -> new AtomicLong(0));
|
tenantCallsCount.replaceAll((k, v) -> new AtomicLong(0));
|
||||||
LOGGER.info("reset counters");
|
|
||||||
}
|
}
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
Next, the service that the tenants are calling is introduced. To track the call count, a throttler
|
Next we introduce the service that the tenants are calling. To track the call count we use the
|
||||||
timer is used.
|
throttler timer.
|
||||||
|
|
||||||
```java
|
```java
|
||||||
public interface Throttler {
|
public interface Throttler {
|
||||||
@ -108,103 +111,71 @@ public class ThrottleTimerImpl implements Throttler {
|
|||||||
}, 0, throttlePeriod);
|
}, 0, throttlePeriod);
|
||||||
}
|
}
|
||||||
}
|
}
|
||||||
```
|
|
||||||
|
|
||||||
`Bartender` offers the `orderDrink` service to the `BarCustomer`s. The customers probably don't
|
class B2BService {
|
||||||
know that the beer serving rate is limited by their appearances.
|
|
||||||
|
|
||||||
```java
|
private static final Logger LOGGER = LoggerFactory.getLogger(B2BService.class);
|
||||||
class Bartender {
|
private final CallsCount callsCount;
|
||||||
|
|
||||||
private static final Logger LOGGER = LoggerFactory.getLogger(Bartender.class);
|
public B2BService(Throttler timer, CallsCount callsCount) {
|
||||||
private final CallsCount callsCount;
|
this.callsCount = callsCount;
|
||||||
|
timer.start();
|
||||||
|
}
|
||||||
|
|
||||||
public Bartender(Throttler timer, CallsCount callsCount) {
|
public int dummyCustomerApi(Tenant tenant) {
|
||||||
this.callsCount = callsCount;
|
var tenantName = tenant.getName();
|
||||||
timer.start();
|
var count = callsCount.getCount(tenantName);
|
||||||
|
LOGGER.debug("Counter for {} : {} ", tenant.getName(), count);
|
||||||
|
if (count >= tenant.getAllowedCallsPerSecond()) {
|
||||||
|
LOGGER.error("API access per second limit reached for: {}", tenantName);
|
||||||
|
return -1;
|
||||||
}
|
}
|
||||||
|
callsCount.incrementCount(tenantName);
|
||||||
|
return getRandomCustomerId();
|
||||||
|
}
|
||||||
|
|
||||||
public int orderDrink(BarCustomer barCustomer) {
|
private int getRandomCustomerId() {
|
||||||
var tenantName = barCustomer.getName();
|
return ThreadLocalRandom.current().nextInt(1, 10000);
|
||||||
var count = callsCount.getCount(tenantName);
|
}
|
||||||
if (count >= barCustomer.getAllowedCallsPerSecond()) {
|
|
||||||
LOGGER.error("I'm sorry {}, you've had enough for today!", tenantName);
|
|
||||||
return -1;
|
|
||||||
}
|
|
||||||
callsCount.incrementCount(tenantName);
|
|
||||||
LOGGER.debug("Serving beer to {} : [{} consumed] ", barCustomer.getName(), count+1);
|
|
||||||
return getRandomCustomerId();
|
|
||||||
}
|
|
||||||
|
|
||||||
private int getRandomCustomerId() {
|
|
||||||
return ThreadLocalRandom.current().nextInt(1, 10000);
|
|
||||||
}
|
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
Now it is possible to see the full example in action. `BarCustomer` young human is rate-limited to 2
|
Now we are ready to see the full example in action. Tenant Adidas is rate-limited to 5 calls per
|
||||||
calls per second and the old dwarf to 4.
|
second and Nike to 6.
|
||||||
|
|
||||||
```java
|
```java
|
||||||
public static void main(String[] args) {
|
public static void main(String[] args) {
|
||||||
var callsCount = new CallsCount();
|
var callsCount = new CallsCount();
|
||||||
var human = new BarCustomer("young human", 2, callsCount);
|
var adidas = new Tenant("Adidas", 5, callsCount);
|
||||||
var dwarf = new BarCustomer("dwarf soldier", 4, callsCount);
|
var nike = new Tenant("Nike", 6, callsCount);
|
||||||
|
|
||||||
var executorService = Executors.newFixedThreadPool(2);
|
var executorService = Executors.newFixedThreadPool(2);
|
||||||
|
executorService.execute(() -> makeServiceCalls(adidas, callsCount));
|
||||||
executorService.execute(() -> makeServiceCalls(human, callsCount));
|
executorService.execute(() -> makeServiceCalls(nike, callsCount));
|
||||||
executorService.execute(() -> makeServiceCalls(dwarf, callsCount));
|
|
||||||
|
|
||||||
executorService.shutdown();
|
executorService.shutdown();
|
||||||
|
|
||||||
try {
|
try {
|
||||||
executorService.awaitTermination(10, TimeUnit.SECONDS);
|
executorService.awaitTermination(10, TimeUnit.SECONDS);
|
||||||
} catch (InterruptedException e) {
|
} catch (InterruptedException e) {
|
||||||
LOGGER.error("Executor service terminated: {}", e.getMessage());
|
LOGGER.error("Executor Service terminated: {}", e.getMessage());
|
||||||
}
|
}
|
||||||
}
|
}
|
||||||
|
|
||||||
private static void makeServiceCalls(BarCustomer barCustomer, CallsCount callsCount) {
|
private static void makeServiceCalls(Tenant tenant, CallsCount callsCount) {
|
||||||
var timer = new ThrottleTimerImpl(1000, callsCount);
|
var timer = new ThrottleTimerImpl(10, callsCount);
|
||||||
var service = new Bartender(timer, callsCount);
|
var service = new B2BService(timer, callsCount);
|
||||||
// Sleep is introduced to keep the output in check and easy to view and analyze the results.
|
// Sleep is introduced to keep the output in check and easy to view and analyze the results.
|
||||||
IntStream.range(0, 50).forEach(i -> {
|
IntStream.range(0, 20).forEach(i -> {
|
||||||
service.orderDrink(barCustomer);
|
service.dummyCustomerApi(tenant);
|
||||||
try {
|
try {
|
||||||
Thread.sleep(100);
|
Thread.sleep(1);
|
||||||
} catch (InterruptedException e) {
|
} catch (InterruptedException e) {
|
||||||
LOGGER.error("Thread interrupted: {}", e.getMessage());
|
LOGGER.error("Thread interrupted: {}", e.getMessage());
|
||||||
}
|
}
|
||||||
});
|
});
|
||||||
}
|
}
|
||||||
```
|
```
|
||||||
|
|
||||||
An excerpt from the example's console output:
|
|
||||||
|
|
||||||
```
|
|
||||||
18:46:36.218 [Timer-0] INFO com.iluwatar.throttling.CallsCount - reset counters
|
|
||||||
18:46:36.218 [Timer-1] INFO com.iluwatar.throttling.CallsCount - reset counters
|
|
||||||
18:46:36.242 [pool-1-thread-2] DEBUG com.iluwatar.throttling.Bartender - Serving beer to dwarf soldier : [1 consumed]
|
|
||||||
18:46:36.242 [pool-1-thread-1] DEBUG com.iluwatar.throttling.Bartender - Serving beer to young human : [1 consumed]
|
|
||||||
18:46:36.342 [pool-1-thread-2] DEBUG com.iluwatar.throttling.Bartender - Serving beer to dwarf soldier : [2 consumed]
|
|
||||||
18:46:36.342 [pool-1-thread-1] DEBUG com.iluwatar.throttling.Bartender - Serving beer to young human : [2 consumed]
|
|
||||||
18:46:36.443 [pool-1-thread-1] ERROR com.iluwatar.throttling.Bartender - I'm sorry young human, you've had enough for today!
|
|
||||||
18:46:36.443 [pool-1-thread-2] DEBUG com.iluwatar.throttling.Bartender - Serving beer to dwarf soldier : [3 consumed]
|
|
||||||
18:46:36.544 [pool-1-thread-1] ERROR com.iluwatar.throttling.Bartender - I'm sorry young human, you've had enough for today!
|
|
||||||
18:46:36.544 [pool-1-thread-2] DEBUG com.iluwatar.throttling.Bartender - Serving beer to dwarf soldier : [4 consumed]
|
|
||||||
18:46:36.645 [pool-1-thread-2] ERROR com.iluwatar.throttling.Bartender - I'm sorry dwarf soldier, you've had enough for today!
|
|
||||||
18:46:36.645 [pool-1-thread-1] ERROR com.iluwatar.throttling.Bartender - I'm sorry young human, you've had enough for today!
|
|
||||||
18:46:36.745 [pool-1-thread-1] ERROR com.iluwatar.throttling.Bartender - I'm sorry young human, you've had enough for today!
|
|
||||||
18:46:36.745 [pool-1-thread-2] ERROR com.iluwatar.throttling.Bartender - I'm sorry dwarf soldier, you've had enough for today!
|
|
||||||
18:46:36.846 [pool-1-thread-1] ERROR com.iluwatar.throttling.Bartender - I'm sorry young human, you've had enough for today!
|
|
||||||
18:46:36.846 [pool-1-thread-2] ERROR com.iluwatar.throttling.Bartender - I'm sorry dwarf soldier, you've had enough for today!
|
|
||||||
18:46:36.947 [pool-1-thread-2] ERROR com.iluwatar.throttling.Bartender - I'm sorry dwarf soldier, you've had enough for today!
|
|
||||||
18:46:36.947 [pool-1-thread-1] ERROR com.iluwatar.throttling.Bartender - I'm sorry young human, you've had enough for today!
|
|
||||||
18:46:37.048 [pool-1-thread-2] ERROR com.iluwatar.throttling.Bartender - I'm sorry dwarf soldier, you've had enough for today!
|
|
||||||
18:46:37.048 [pool-1-thread-1] ERROR com.iluwatar.throttling.Bartender - I'm sorry young human, you've had enough for today!
|
|
||||||
18:46:37.148 [pool-1-thread-1] ERROR com.iluwatar.throttling.Bartender - I'm sorry young human, you've had enough for today!
|
|
||||||
18:46:37.148 [pool-1-thread-2] ERROR com.iluwatar.throttling.Bartender - I'm sorry dwarf soldier, you've had enough for today!
|
|
||||||
```
|
|
||||||
|
|
||||||
## Class diagram
|
## Class diagram
|
||||||
|
|
||||||
@ -214,7 +185,7 @@ An excerpt from the example's console output:
|
|||||||
|
|
||||||
The Throttling pattern should be used:
|
The Throttling pattern should be used:
|
||||||
|
|
||||||
* When service access needs to be restricted not to have high impact on the performance of the service.
|
* When a service access needs to be restricted to not have high impacts on the performance of the service.
|
||||||
* When multiple clients are consuming the same service resources and restriction has to be made according to the usage per client.
|
* When multiple clients are consuming the same service resources and restriction has to be made according to the usage per client.
|
||||||
|
|
||||||
## Credits
|
## Credits
|
||||||
|
@ -34,11 +34,11 @@ import lombok.extern.slf4j.Slf4j;
|
|||||||
* complete service by users or a particular tenant. This can allow systems to continue to function
|
* complete service by users or a particular tenant. This can allow systems to continue to function
|
||||||
* and meet service level agreements, even when an increase in demand places load on resources.
|
* and meet service level agreements, even when an increase in demand places load on resources.
|
||||||
* <p>
|
* <p>
|
||||||
* In this example there is a {@link Bartender} serving beer to {@link BarCustomer}s. This is a time
|
* In this example we have ({@link App}) as the initiating point of the service. This is a time
|
||||||
* based throttling, i.e. only a certain number of calls are allowed per second.
|
* based throttling, i.e. only a certain number of calls are allowed per second.
|
||||||
* </p>
|
* </p>
|
||||||
* ({@link BarCustomer}) is the service tenant class having a name and the number of calls allowed.
|
* ({@link Tenant}) is the Tenant POJO class with which many tenants can be created ({@link
|
||||||
* ({@link Bartender}) is the service which is consumed by the tenants and is throttled.
|
* B2BService}) is the service which is consumed by the tenants and is throttled.
|
||||||
*/
|
*/
|
||||||
@Slf4j
|
@Slf4j
|
||||||
public class App {
|
public class App {
|
||||||
@ -50,35 +50,33 @@ public class App {
|
|||||||
*/
|
*/
|
||||||
public static void main(String[] args) {
|
public static void main(String[] args) {
|
||||||
var callsCount = new CallsCount();
|
var callsCount = new CallsCount();
|
||||||
var human = new BarCustomer("young human", 2, callsCount);
|
var adidas = new Tenant("Adidas", 5, callsCount);
|
||||||
var dwarf = new BarCustomer("dwarf soldier", 4, callsCount);
|
var nike = new Tenant("Nike", 6, callsCount);
|
||||||
|
|
||||||
var executorService = Executors.newFixedThreadPool(2);
|
var executorService = Executors.newFixedThreadPool(2);
|
||||||
|
|
||||||
executorService.execute(() -> makeServiceCalls(human, callsCount));
|
executorService.execute(() -> makeServiceCalls(adidas, callsCount));
|
||||||
executorService.execute(() -> makeServiceCalls(dwarf, callsCount));
|
executorService.execute(() -> makeServiceCalls(nike, callsCount));
|
||||||
|
|
||||||
executorService.shutdown();
|
executorService.shutdown();
|
||||||
try {
|
try {
|
||||||
if (!executorService.awaitTermination(10, TimeUnit.SECONDS)) {
|
executorService.awaitTermination(10, TimeUnit.SECONDS);
|
||||||
executorService.shutdownNow();
|
|
||||||
}
|
|
||||||
} catch (InterruptedException e) {
|
} catch (InterruptedException e) {
|
||||||
executorService.shutdownNow();
|
LOGGER.error("Executor Service terminated: {}", e.getMessage());
|
||||||
}
|
}
|
||||||
}
|
}
|
||||||
|
|
||||||
/**
|
/**
|
||||||
* Make calls to the bartender.
|
* Make calls to the B2BService dummy API.
|
||||||
*/
|
*/
|
||||||
private static void makeServiceCalls(BarCustomer barCustomer, CallsCount callsCount) {
|
private static void makeServiceCalls(Tenant tenant, CallsCount callsCount) {
|
||||||
var timer = new ThrottleTimerImpl(1000, callsCount);
|
var timer = new ThrottleTimerImpl(10, callsCount);
|
||||||
var service = new Bartender(timer, callsCount);
|
var service = new B2BService(timer, callsCount);
|
||||||
// Sleep is introduced to keep the output in check and easy to view and analyze the results.
|
// Sleep is introduced to keep the output in check and easy to view and analyze the results.
|
||||||
IntStream.range(0, 50).forEach(i -> {
|
IntStream.range(0, 20).forEach(i -> {
|
||||||
service.orderDrink(barCustomer);
|
service.dummyCustomerApi(tenant);
|
||||||
try {
|
try {
|
||||||
Thread.sleep(100);
|
Thread.sleep(1);
|
||||||
} catch (InterruptedException e) {
|
} catch (InterruptedException e) {
|
||||||
LOGGER.error("Thread interrupted: {}", e.getMessage());
|
LOGGER.error("Thread interrupted: {}", e.getMessage());
|
||||||
}
|
}
|
||||||
|
@ -29,32 +29,33 @@ import org.slf4j.Logger;
|
|||||||
import org.slf4j.LoggerFactory;
|
import org.slf4j.LoggerFactory;
|
||||||
|
|
||||||
/**
|
/**
|
||||||
* Bartender is a service which accepts a BarCustomer (tenant) and throttles
|
* A service which accepts a tenant and throttles the resource based on the time given to the
|
||||||
* the resource based on the time given to the tenant.
|
* tenant.
|
||||||
*/
|
*/
|
||||||
class Bartender {
|
class B2BService {
|
||||||
|
|
||||||
private static final Logger LOGGER = LoggerFactory.getLogger(Bartender.class);
|
private static final Logger LOGGER = LoggerFactory.getLogger(B2BService.class);
|
||||||
private final CallsCount callsCount;
|
private final CallsCount callsCount;
|
||||||
|
|
||||||
public Bartender(Throttler timer, CallsCount callsCount) {
|
public B2BService(Throttler timer, CallsCount callsCount) {
|
||||||
this.callsCount = callsCount;
|
this.callsCount = callsCount;
|
||||||
timer.start();
|
timer.start();
|
||||||
}
|
}
|
||||||
|
|
||||||
/**
|
/**
|
||||||
* Orders a drink from the bartender.
|
* Calls dummy customer api.
|
||||||
|
*
|
||||||
* @return customer id which is randomly generated
|
* @return customer id which is randomly generated
|
||||||
*/
|
*/
|
||||||
public int orderDrink(BarCustomer barCustomer) {
|
public int dummyCustomerApi(Tenant tenant) {
|
||||||
var tenantName = barCustomer.getName();
|
var tenantName = tenant.getName();
|
||||||
var count = callsCount.getCount(tenantName);
|
var count = callsCount.getCount(tenantName);
|
||||||
if (count >= barCustomer.getAllowedCallsPerSecond()) {
|
LOGGER.debug("Counter for {} : {} ", tenant.getName(), count);
|
||||||
LOGGER.error("I'm sorry {}, you've had enough for today!", tenantName);
|
if (count >= tenant.getAllowedCallsPerSecond()) {
|
||||||
|
LOGGER.error("API access per second limit reached for: {}", tenantName);
|
||||||
return -1;
|
return -1;
|
||||||
}
|
}
|
||||||
callsCount.incrementCount(tenantName);
|
callsCount.incrementCount(tenantName);
|
||||||
LOGGER.debug("Serving beer to {} : [{} consumed] ", barCustomer.getName(), count + 1);
|
|
||||||
return getRandomCustomerId();
|
return getRandomCustomerId();
|
||||||
}
|
}
|
||||||
|
|
@ -69,7 +69,7 @@ public final class CallsCount {
|
|||||||
* Resets the count of all the tenants in the map.
|
* Resets the count of all the tenants in the map.
|
||||||
*/
|
*/
|
||||||
public void reset() {
|
public void reset() {
|
||||||
|
LOGGER.debug("Resetting the map.");
|
||||||
tenantCallsCount.replaceAll((k, v) -> new AtomicLong(0));
|
tenantCallsCount.replaceAll((k, v) -> new AtomicLong(0));
|
||||||
LOGGER.info("reset counters");
|
|
||||||
}
|
}
|
||||||
}
|
}
|
||||||
|
@ -25,26 +25,22 @@ package com.iluwatar.throttling;
|
|||||||
|
|
||||||
import java.security.InvalidParameterException;
|
import java.security.InvalidParameterException;
|
||||||
|
|
||||||
import lombok.Getter;
|
|
||||||
|
|
||||||
/**
|
/**
|
||||||
* BarCustomer is a tenant with a name and a number of allowed calls per second.
|
* A Pojo class to create a basic Tenant with the allowed calls per second.
|
||||||
*/
|
*/
|
||||||
public class BarCustomer {
|
public class Tenant {
|
||||||
|
|
||||||
@Getter
|
|
||||||
private final String name;
|
private final String name;
|
||||||
@Getter
|
|
||||||
private final int allowedCallsPerSecond;
|
private final int allowedCallsPerSecond;
|
||||||
|
|
||||||
/**
|
/**
|
||||||
* Constructor.
|
* Constructor.
|
||||||
*
|
*
|
||||||
* @param name Name of the BarCustomer
|
* @param name Name of the tenant
|
||||||
* @param allowedCallsPerSecond The number of calls allowed for this particular tenant.
|
* @param allowedCallsPerSecond The number of calls allowed for a particular tenant.
|
||||||
* @throws InvalidParameterException If number of calls is less than 0, throws exception.
|
* @throws InvalidParameterException If number of calls is less than 0, throws exception.
|
||||||
*/
|
*/
|
||||||
public BarCustomer(String name, int allowedCallsPerSecond, CallsCount callsCount) {
|
public Tenant(String name, int allowedCallsPerSecond, CallsCount callsCount) {
|
||||||
if (allowedCallsPerSecond < 0) {
|
if (allowedCallsPerSecond < 0) {
|
||||||
throw new InvalidParameterException("Number of calls less than 0 not allowed");
|
throw new InvalidParameterException("Number of calls less than 0 not allowed");
|
||||||
}
|
}
|
||||||
@ -52,4 +48,12 @@ public class BarCustomer {
|
|||||||
this.allowedCallsPerSecond = allowedCallsPerSecond;
|
this.allowedCallsPerSecond = allowedCallsPerSecond;
|
||||||
callsCount.addTenant(name);
|
callsCount.addTenant(name);
|
||||||
}
|
}
|
||||||
|
|
||||||
|
public String getName() {
|
||||||
|
return name;
|
||||||
|
}
|
||||||
|
|
||||||
|
public int getAllowedCallsPerSecond() {
|
||||||
|
return allowedCallsPerSecond;
|
||||||
|
}
|
||||||
}
|
}
|
@ -32,18 +32,19 @@ import org.junit.jupiter.api.Test;
|
|||||||
/**
|
/**
|
||||||
* B2BServiceTest class to test the B2BService
|
* B2BServiceTest class to test the B2BService
|
||||||
*/
|
*/
|
||||||
public class BartenderTest {
|
public class B2BServiceTest {
|
||||||
|
|
||||||
private final CallsCount callsCount = new CallsCount();
|
private final CallsCount callsCount = new CallsCount();
|
||||||
|
|
||||||
@Test
|
@Test
|
||||||
void dummyCustomerApiTest() {
|
void dummyCustomerApiTest() {
|
||||||
var tenant = new BarCustomer("pirate", 2, callsCount);
|
var tenant = new Tenant("testTenant", 2, callsCount);
|
||||||
// In order to assure that throttling limits will not be reset, we use an empty throttling implementation
|
// In order to assure that throttling limits will not be reset, we use an empty throttling implementation
|
||||||
var timer = (Throttler) () -> {};
|
var timer = (Throttler) () -> {
|
||||||
var service = new Bartender(timer, callsCount);
|
};
|
||||||
|
var service = new B2BService(timer, callsCount);
|
||||||
|
|
||||||
IntStream.range(0, 5).mapToObj(i -> tenant).forEach(service::orderDrink);
|
IntStream.range(0, 5).mapToObj(i -> tenant).forEach(service::dummyCustomerApi);
|
||||||
var counter = callsCount.getCount(tenant.getName());
|
var counter = callsCount.getCount(tenant.getName());
|
||||||
assertEquals(2, counter, "Counter limit must be reached");
|
assertEquals(2, counter, "Counter limit must be reached");
|
||||||
}
|
}
|
@ -23,21 +23,20 @@
|
|||||||
|
|
||||||
package com.iluwatar.throttling;
|
package com.iluwatar.throttling;
|
||||||
|
|
||||||
import org.junit.jupiter.api.Test;
|
import static org.junit.jupiter.api.Assertions.assertThrows;
|
||||||
|
|
||||||
import java.security.InvalidParameterException;
|
import java.security.InvalidParameterException;
|
||||||
|
import org.junit.jupiter.api.Test;
|
||||||
import static org.junit.jupiter.api.Assertions.assertThrows;
|
|
||||||
|
|
||||||
/**
|
/**
|
||||||
* TenantTest to test the creation of Tenant with valid parameters.
|
* TenantTest to test the creation of Tenant with valid parameters.
|
||||||
*/
|
*/
|
||||||
public class BarCustomerTest {
|
public class TenantTest {
|
||||||
|
|
||||||
@Test
|
@Test
|
||||||
void constructorTest() {
|
void constructorTest() {
|
||||||
assertThrows(InvalidParameterException.class, () -> {
|
assertThrows(InvalidParameterException.class, () -> {
|
||||||
new BarCustomer("sirBrave", -1, new CallsCount());
|
new Tenant("FailTenant", -1, new CallsCount());
|
||||||
});
|
});
|
||||||
}
|
}
|
||||||
}
|
}
|
@ -17,19 +17,19 @@ and to interleave the execution of functions without hard coding them together.
|
|||||||
## Explanation
|
## Explanation
|
||||||
|
|
||||||
Recursion is a frequently adopted technique for solving algorithmic problems in a divide and conquer
|
Recursion is a frequently adopted technique for solving algorithmic problems in a divide and conquer
|
||||||
style. For example calculating fibonacci accumulating sum and factorials. In these kinds of problems
|
style. For example, calculating Fibonacci accumulating sum and factorials. In these kinds of
|
||||||
recursion is more straightforward than their loop counterpart. Furthermore recursion may need less
|
problems, recursion is more straightforward than its loop counterpart. Furthermore, recursion may
|
||||||
code and looks more concise. There is a saying that every recursion problem can be solved using
|
need less code and looks more concise. There is a saying that every recursion problem can be solved
|
||||||
a loop with the cost of writing code that is more difficult to understand.
|
using a loop with the cost of writing code that is more difficult to understand.
|
||||||
|
|
||||||
However recursion type solutions have one big caveat. For each recursive call it typically needs
|
However, recursion-type solutions have one big caveat. For each recursive call, it typically needs
|
||||||
an intermediate value stored and there is a limited amount of stack memory available. Running out of
|
an intermediate value stored and there is a limited amount of stack memory available. Running out of
|
||||||
stack memory creates a stack overflow error and halts the program execution.
|
stack memory creates a stack overflow error and halts the program execution.
|
||||||
|
|
||||||
Trampoline pattern is a trick that allows us define recursive algorithms in Java without blowing the
|
Trampoline pattern is a trick that allows defining recursive algorithms in Java without blowing the
|
||||||
stack.
|
stack.
|
||||||
|
|
||||||
Real world example
|
Real-world example
|
||||||
|
|
||||||
> A recursive Fibonacci calculation without the stack overflow problem using the Trampoline pattern.
|
> A recursive Fibonacci calculation without the stack overflow problem using the Trampoline pattern.
|
||||||
|
|
||||||
@ -105,24 +105,26 @@ public interface Trampoline<T> {
|
|||||||
Using the `Trampoline` to get Fibonacci values.
|
Using the `Trampoline` to get Fibonacci values.
|
||||||
|
|
||||||
```java
|
```java
|
||||||
public static Trampoline<Integer> loop(int times, int prod) {
|
public static void main(String[] args) {
|
||||||
|
LOGGER.info("Start calculating war casualties");
|
||||||
|
var result = loop(10, 1).result();
|
||||||
|
LOGGER.info("The number of orcs perished in the war: {}", result);
|
||||||
|
}
|
||||||
|
|
||||||
|
public static Trampoline<Integer> loop(int times, int prod) {
|
||||||
if (times == 0) {
|
if (times == 0) {
|
||||||
return Trampoline.done(prod);
|
return Trampoline.done(prod);
|
||||||
} else {
|
} else {
|
||||||
return Trampoline.more(() -> loop(times - 1, prod * times));
|
return Trampoline.more(() -> loop(times - 1, prod * times));
|
||||||
}
|
}
|
||||||
}
|
}
|
||||||
|
|
||||||
log.info("start pattern");
|
|
||||||
var result = loop(10, 1).result();
|
|
||||||
log.info("result {}", result);
|
|
||||||
```
|
```
|
||||||
|
|
||||||
Program output:
|
Program output:
|
||||||
|
|
||||||
```
|
```
|
||||||
start pattern
|
19:22:24.462 [main] INFO com.iluwatar.trampoline.TrampolineApp - Start calculating war casualties
|
||||||
result 3628800
|
19:22:24.472 [main] INFO com.iluwatar.trampoline.TrampolineApp - The number of orcs perished in the war: 3628800
|
||||||
```
|
```
|
||||||
|
|
||||||
## Class diagram
|
## Class diagram
|
||||||
@ -133,8 +135,8 @@ result 3628800
|
|||||||
|
|
||||||
Use the Trampoline pattern when
|
Use the Trampoline pattern when
|
||||||
|
|
||||||
* For implementing tail recursive function. This pattern allows to switch on a stackless operation.
|
* For implementing tail-recursive functions. This pattern allows to switch on a stackless operation.
|
||||||
* For interleaving the execution of two or more functions on the same thread.
|
* For interleaving execution of two or more functions on the same thread.
|
||||||
|
|
||||||
## Known uses
|
## Known uses
|
||||||
|
|
||||||
|
@ -107,6 +107,4 @@ public interface Trampoline<T> {
|
|||||||
}
|
}
|
||||||
};
|
};
|
||||||
}
|
}
|
||||||
|
|
||||||
|
|
||||||
}
|
}
|
||||||
|
@ -39,9 +39,9 @@ public class TrampolineApp {
|
|||||||
* Main program for showing pattern. It does loop with factorial function.
|
* Main program for showing pattern. It does loop with factorial function.
|
||||||
*/
|
*/
|
||||||
public static void main(String[] args) {
|
public static void main(String[] args) {
|
||||||
LOGGER.info("start pattern");
|
LOGGER.info("Start calculating war casualties");
|
||||||
var result = loop(10, 1).result();
|
var result = loop(10, 1).result();
|
||||||
LOGGER.info("result {}", result);
|
LOGGER.info("The number of orcs perished in the war: {}", result);
|
||||||
|
|
||||||
}
|
}
|
||||||
|
|
||||||
@ -55,5 +55,4 @@ public class TrampolineApp {
|
|||||||
return Trampoline.more(() -> loop(times - 1, prod * times));
|
return Trampoline.more(() -> loop(times - 1, prod * times));
|
||||||
}
|
}
|
||||||
}
|
}
|
||||||
|
|
||||||
}
|
}
|
||||||
|
Reference in New Issue
Block a user