f597fc1b07
* Fix languages * Missed change for version number * Add language field for presentation * Revert change in README for double buffer Co-authored-by: Jackie Nim <=>
83 lines
2.3 KiB
Markdown
83 lines
2.3 KiB
Markdown
---
|
|
layout: pattern
|
|
title: Execute Around
|
|
folder: execute-around
|
|
permalink: /patterns/execute-around/
|
|
categories: Idiom
|
|
language: en
|
|
tags:
|
|
- Extensibility
|
|
---
|
|
|
|
## Intent
|
|
|
|
Execute Around idiom frees the user from certain actions that should always be executed before and
|
|
after the business method. A good example of this is resource allocation and deallocation leaving
|
|
the user to specify only what to do with the resource.
|
|
|
|
## Explanation
|
|
|
|
Real world example
|
|
|
|
> We need to provide a class that can be used to write text strings to files. To make it easy for
|
|
> the user we let our service class open and close the file automatically, the user only has to
|
|
> specify what is written into which file.
|
|
|
|
In plain words
|
|
|
|
> Execute Around idiom handles boilerplate code before and after business method.
|
|
|
|
[Stack Overflow](https://stackoverflow.com/questions/341971/what-is-the-execute-around-idiom) says
|
|
|
|
> Basically it's the pattern where you write a method to do things which are always required, e.g.
|
|
> resource allocation and clean-up, and make the caller pass in "what we want to do with the
|
|
> resource".
|
|
|
|
**Programmatic Example**
|
|
|
|
Let's introduce our file writer class.
|
|
|
|
```java
|
|
@FunctionalInterface
|
|
public interface FileWriterAction {
|
|
|
|
void writeFile(FileWriter writer) throws IOException;
|
|
|
|
}
|
|
|
|
public class SimpleFileWriter {
|
|
|
|
public SimpleFileWriter(String filename, FileWriterAction action) throws IOException {
|
|
try (var writer = new FileWriter(filename)) {
|
|
action.writeFile(writer);
|
|
}
|
|
}
|
|
}
|
|
```
|
|
|
|
To utilize the file writer the following code is needed.
|
|
|
|
```java
|
|
FileWriterAction writeHello = writer -> {
|
|
writer.write("Hello");
|
|
writer.append(" ");
|
|
writer.append("there!");
|
|
};
|
|
new SimpleFileWriter("testfile.txt", writeHello);
|
|
```
|
|
|
|
## Class diagram
|
|
|
|
|
|
|
|
## Applicability
|
|
|
|
Use the Execute Around idiom when
|
|
|
|
* You use an API that requires methods to be called in pairs such as open/close or
|
|
allocate/deallocate.
|
|
|
|
## Credits
|
|
|
|
* [Functional Programming in Java: Harnessing the Power of Java 8 Lambda Expressions](https://www.amazon.com/gp/product/1937785467/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=1937785467&linkCode=as2&tag=javadesignpat-20&linkId=7e4e2fb7a141631491534255252fd08b)
|