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Implemented Registry pattern (#1543)
* #1310 Implemented registry pattern * fixed parent pom version * added empty line in registry.urm.puml Co-authored-by: Subhrodip Mohanta <subhrodipmohanta@gmail.com>
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--- | ||
layout: pattern | ||
title: Registry | ||
folder: registry | ||
permalink: /patterns/registry/ | ||
categories: Creational | ||
tags: | ||
- Instantiation | ||
--- | ||
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## Intent | ||
Stores the objects of a single class and provide a global point of access to them. | ||
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. | ||
**Programmatic Example** | ||
Below is a `Customer` Class | ||
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```java | ||
public class Customer { | ||
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private final String id; | ||
private final String name; | ||
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public Customer(String id, String name) { | ||
this.id = id; | ||
this.name = name; | ||
} | ||
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public String getId() { | ||
return id; | ||
} | ||
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public String getName() { | ||
return name; | ||
} | ||
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} | ||
``` | ||
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This registry of the `Customer` objects is `CustomerRegistry` | ||
```java | ||
public final class CustomerRegistry { | ||
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private static final CustomerRegistry instance = new CustomerRegistry(); | ||
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public static CustomerRegistry getInstance() { | ||
return instance; | ||
} | ||
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private final Map<String, Customer> customerMap; | ||
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private CustomerRegistry() { | ||
customerMap = new ConcurrentHashMap<>(); | ||
} | ||
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public Customer addCustomer(Customer customer) { | ||
return customerMap.put(customer.getId(), customer); | ||
} | ||
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public Customer getCustomer(String id) { | ||
return customerMap.get(id); | ||
} | ||
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} | ||
``` | ||
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## Class diagram | ||
![Registry](./etc/registry.png) | ||
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## Applicability | ||
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 | ||
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 | ||
* https://www.martinfowler.com/eaaCatalog/registry.html | ||
* https://wiki.c2.com/?RegistryPattern |
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@startuml | ||
package com.iluwatar.registry { | ||
class App { | ||
- LOGGER : Logger {static} | ||
+ App() | ||
+ main(args : String[]) {static} | ||
} | ||
class Customer { | ||
- id : String | ||
- name : String | ||
+ getId() : String | ||
+ getName() : String | ||
+ toString() : String | ||
} | ||
class CustomerRegistry { | ||
+ addCustomer(customer : Customer) | ||
+ getCustomer(id : String) | ||
} | ||
} | ||
Customer --> "-addCustomer" CustomerRegistry | ||
@enduml |
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<?xml version="1.0" encoding="UTF-8"?> | ||
<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"> | ||
<modelVersion>4.0.0</modelVersion> | ||
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<parent> | ||
<groupId>com.iluwatar</groupId> | ||
<artifactId>java-design-patterns</artifactId> | ||
<version>1.24.0-SNAPSHOT</version> | ||
</parent> | ||
<artifactId>registry</artifactId> | ||
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<dependencies> | ||
<dependency> | ||
<groupId>org.junit.jupiter</groupId> | ||
<artifactId>junit-jupiter-engine</artifactId> | ||
<scope>test</scope> | ||
</dependency> | ||
<dependency> | ||
<groupId>junit</groupId> | ||
<artifactId>junit</artifactId> | ||
</dependency> | ||
</dependencies> | ||
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<build> | ||
<plugins> | ||
<plugin> | ||
<groupId>org.apache.maven.plugins</groupId> | ||
<artifactId>maven-assembly-plugin</artifactId> | ||
<executions> | ||
<execution> | ||
<configuration> | ||
<archive> | ||
<manifest> | ||
<mainClass>com.iluwatar.registry.App</mainClass> | ||
</manifest> | ||
</archive> | ||
</configuration> | ||
</execution> | ||
</executions> | ||
</plugin> | ||
</plugins> | ||
</build> | ||
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</project> |
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package com.iluwatar.registry; | ||
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import org.slf4j.Logger; | ||
import org.slf4j.LoggerFactory; | ||
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public class App { | ||
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private static final Logger LOGGER = LoggerFactory.getLogger(App.class); | ||
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/** | ||
* Program entry point. | ||
* | ||
* @param args command line args | ||
*/ | ||
public static void main(String[] args) { | ||
CustomerRegistry customerRegistry = CustomerRegistry.getInstance(); | ||
var john = new Customer("1", "John"); | ||
customerRegistry.addCustomer(john); | ||
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var julia = new Customer("2", "Julia"); | ||
customerRegistry.addCustomer(julia); | ||
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LOGGER.info("John {}", customerRegistry.getCustomer("1")); | ||
LOGGER.info("Julia {}", customerRegistry.getCustomer("2")); | ||
} | ||
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} |
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registry/src/main/java/com/iluwatar/registry/Customer.java
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package com.iluwatar.registry; | ||
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public class Customer { | ||
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private final String id; | ||
private final String name; | ||
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public Customer(String id, String name) { | ||
this.id = id; | ||
this.name = name; | ||
} | ||
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public String getId() { | ||
return id; | ||
} | ||
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public String getName() { | ||
return name; | ||
} | ||
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@Override | ||
public String toString() { | ||
return "Customer{" | ||
+ "id='" + id + '\'' | ||
+ ", name='" + name + '\'' | ||
+ '}'; | ||
} | ||
} |
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28
registry/src/main/java/com/iluwatar/registry/CustomerRegistry.java
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package com.iluwatar.registry; | ||
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import java.util.Map; | ||
import java.util.concurrent.ConcurrentHashMap; | ||
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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() { | ||
return instance; | ||
} | ||
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private final Map<String, Customer> customerMap; | ||
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private CustomerRegistry() { | ||
customerMap = new ConcurrentHashMap<>(); | ||
} | ||
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public Customer addCustomer(Customer customer) { | ||
return customerMap.put(customer.getId(), customer); | ||
} | ||
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public Customer getCustomer(String id) { | ||
return customerMap.get(id); | ||
} | ||
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} |
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44
registry/src/test/java/com/iluwatar/registry/CustomerRegistryTest.java
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package com.iluwatar.registry; | ||
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import org.junit.jupiter.api.BeforeAll; | ||
import org.junit.jupiter.api.Test; | ||
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import static org.junit.jupiter.api.Assertions.assertEquals; | ||
import static org.junit.jupiter.api.Assertions.assertNotNull; | ||
import static org.junit.jupiter.api.Assertions.assertNull; | ||
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public class CustomerRegistryTest { | ||
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private static CustomerRegistry customerRegistry; | ||
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@BeforeAll | ||
public static void setUp() { | ||
customerRegistry = CustomerRegistry.getInstance(); | ||
} | ||
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@Test | ||
public void shouldBeAbleToAddAndQueryCustomerObjectFromRegistry() { | ||
Customer john = new Customer("1", "john"); | ||
Customer julia = new Customer("2", "julia"); | ||
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customerRegistry.addCustomer(john); | ||
customerRegistry.addCustomer(julia); | ||
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Customer customerWithId1 = customerRegistry.getCustomer("1"); | ||
assertNotNull(customerWithId1); | ||
assertEquals("1", customerWithId1.getId()); | ||
assertEquals("john", customerWithId1.getName()); | ||
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Customer customerWithId2 = customerRegistry.getCustomer("2"); | ||
assertNotNull(customerWithId2); | ||
assertEquals("2", customerWithId2.getId()); | ||
assertEquals("julia", customerWithId2.getName()); | ||
} | ||
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@Test | ||
public void shouldReturnNullWhenQueriedCustomerIsNotInRegistry() { | ||
Customer customerWithId5 = customerRegistry.getCustomer("5"); | ||
assertNull(customerWithId5); | ||
} | ||
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} |