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:

Implementing the org.springframework.beans.factory.config.Scope interface.
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.

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

Custom Bean Scope in Spring

1. Implementing the Scope interface:

2. Registering the custom scope:

1. Implementing the `Scope` interface: