87 lines
1.8 KiB
Markdown
87 lines
1.8 KiB
Markdown
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---
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layout: pattern
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title: Registry
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folder: registry
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permalink: /patterns/registry/
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categories: Creational
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tags:
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- Instantiation
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---
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## Intent
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Stores the objects of a single class and provide a global point of access to them.
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Similar to Multiton pattern, only difference is that in a registry there is no restriction on the number of objects.
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## Explanation
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In Plain Words
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> Registry is a well-known object that other objects can use to find common objects and services.
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**Programmatic Example**
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Below is a `Customer` Class
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```java
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public class Customer {
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private final String id;
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private final String name;
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public Customer(String id, String name) {
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this.id = id;
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this.name = name;
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}
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public String getId() {
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return id;
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}
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public String getName() {
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return name;
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}
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}
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```
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This registry of the `Customer` objects is `CustomerRegistry`
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```java
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public final class CustomerRegistry {
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private static final CustomerRegistry instance = new CustomerRegistry();
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public static CustomerRegistry getInstance() {
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return instance;
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}
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private final Map<String, Customer> customerMap;
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private CustomerRegistry() {
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customerMap = new ConcurrentHashMap<>();
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}
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public Customer addCustomer(Customer customer) {
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return customerMap.put(customer.getId(), customer);
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}
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public Customer getCustomer(String id) {
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return customerMap.get(id);
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}
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}
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```
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## Class diagram
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## Applicability
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Use Registry pattern when
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* client wants reference of some object, so client can lookup for that object in the object's registry.
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## Consequences
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Large number of bulky objects added to registry would result in a lot of memory consumption as objects in the registry are not garbage collected.
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## Credits
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* https://www.martinfowler.com/eaaCatalog/registry.html
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* https://wiki.c2.com/?RegistryPattern
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