Custom Bean Scope in Spring

Custom Bean Scope in Spring

In Spring, apart from the predefined bean scopes (singleton, prototype, request, session, application), you can also define custom scopes.

Creating a custom scope requires two primary steps:

  1. Implementing the org.springframework.beans.factory.config.Scope interface.
  2. Registering the custom scope in the Spring context.

Let's walk through these steps.

1. Implementing the Scope interface:

Suppose you want to create a custom scope called threadScope, where each thread gets its instance of a bean.

import org.springframework.beans.factory.ObjectFactory; import org.springframework.beans.factory.config.Scope; import java.util.HashMap; import java.util.Map; public class ThreadScope implements Scope { private final ThreadLocal<Map<String, Object>> threadScope = ThreadLocal.withInitial(HashMap::new); @Override public Object get(String name, ObjectFactory<?> objectFactory) { Map<String, Object> scope = threadScope.get(); Object obj = scope.get(name); if (obj == null) { obj = objectFactory.getObject(); scope.put(name, obj); } return obj; } @Override public Object remove(String name) { Map<String, Object> scope = threadScope.get(); return scope.remove(name); } @Override public void registerDestructionCallback(String name, Runnable callback) { // For this example, we are not registering any destruction callbacks } @Override public Object resolveContextualObject(String key) { return null; // Not needed for this simple example } @Override public String getConversationId() { return String.valueOf(Thread.currentThread().getId()); } }

2. Registering the custom scope:

This can be done in Java configuration or XML configuration.

  • Java Configuration:

    @Configuration public class AppConfig { @Bean public static CustomScopeConfigurer customScopeConfigurer() { CustomScopeConfigurer configurer = new CustomScopeConfigurer(); configurer.addScope("threadScope", new ThreadScope()); return configurer; } @Bean @Scope("threadScope") public MyBean myBean() { return new MyBean(); } }

  • XML Configuration:

    <beans ...> <bean class="org.springframework.beans.factory.config.CustomScopeConfigurer"> <property name="scopes"> <map> <entry key="threadScope"> <bean class="com.example.ThreadScope"/> </entry> </map> </property> </bean> <bean id="myBean" class="com.example.MyBean" scope="threadScope"/> </beans>

With the custom threadScope registered, you can now annotate beans with @Scope("threadScope"), and they'll be scoped to the lifecycle of a thread.

Remember that creating custom scopes can add complexity to your application. Always ensure you have a valid reason to deviate from the built-in scopes provided by Spring.

Examples

  1. Creating custom bean scopes in Spring:

    • Description: Spring provides several standard bean scopes (singleton, prototype, etc.), but you can create custom scopes tailored to your application's needs.
    • Code:
      public interface CustomScope extends Scope { // Custom scope methods }

  2. Defining a custom scope for Spring beans:

    • Description: Define a custom scope by implementing the Scope interface.
    • Code:
      public class MyCustomScope implements Scope { // Implement custom scope methods }

  3. Configuring custom bean scopes in Spring XML:

    • Description: Configure custom bean scopes in XML-based Spring configuration.
    • Code:
      <bean class="com.example.MyCustomScope"/>

  4. Custom bean scoping in annotation-based configuration in Spring:

    • Description: Achieve custom bean scoping using annotations and Java-based configuration.
    • Code:
      @Scope("myCustomScope") @Component public class MyScopedBean { // Bean definition }

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