Custom scopes in CDI 1.0 and Spring 3.1

Niklas Schlimm

Jul. 05, 11 · Java Zone · Interview

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This blog post describes in short how to implement custom scopes in CDI using Weld 1.1 and Spring 3.1. To get basic information on scoping see the Spring reference or the Weld reference respectively.

Custom scopes in Spring

In Spring you have to implement your custom scope using the Scope interface. I have implemented a custom scope as a copy of request scope for illustration:

package com.mycompany.springapp.scope;
 
import org.springframework.beans.factory.config.Scope;
import org.springframework.web.context.request.AbstractRequestAttributesScope;
import org.springframework.web.context.request.RequestAttributes;
 
public class MyCustomScope extends AbstractRequestAttributesScope implements Scope {
 
 @Override
 protected int getScope() {
  return RequestAttributes.SCOPE_REQUEST;
 }
 
 /**
  * There is no conversation id concept for a request, so this method
  * returns <code>null</code>.
  */
 public String getConversationId() {
  return null;
 }
 
}

Then you register your new scope like this in your beans.xml:

<beans>
 <bean class="org.springframework.beans.factory.config.CustomScopeConfigurer">
  <property name="scopes">
   <map>
    <entry key="custom">
     <bean class="com.mycompany.springapp.scope.MyCustomScope">
    </bean></entry>
   </map>
  </property>
 </bean>
</beans>

You can then use it like all the other built-in scopes:

package com.mycompany.springapp.scope;
 
import org.springframework.context.annotation.Scope;
import org.springframework.stereotype.Component;
 
@Component
@Scope("custom")
public class MyCustomScopedService {
 
}

See here for additional information.

Custom scopes with CDI

In CDI - according to the CDI programming model - you first define your own scope annotation:

package com.mycompany.jeeapp.scope.extension;
 
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;
 
import javax.enterprise.context.NormalScope;
 
@Retention(java.lang.annotation.RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE, ElementType.METHOD})
@NormalScope
public @interface CustomScoped {
 
}

Then there is the Context interface that you need to implement. I have made it a copy of HttpRequestScope for illustration.

	
package com.mycompany.jeeapp.scope.extension;
 
import org.jboss.weld.context.http.HttpRequestContext;
import org.jboss.weld.context.http.HttpRequestContextImpl;
import java.lang.Class;
 
public class MyCustomScope extends HttpRequestContextImpl implements HttpRequestContext {
 
 public Class getScope() {
  return CustomScoped.class;
 }
  
}

You assign your new scope annotation to the beans that are instintiated in this scope:

@CustomScoped
public class MyCustomScopeService { ... }

To register the scope create this class and drop it together with your application into the CDI enabled container. The CDI runtime will register it automatically.

package com.mycompany.jeeapp.scope.extension;
 
import javax.enterprise.event.Observes;
import javax.enterprise.inject.spi.AfterBeanDiscovery;
import javax.enterprise.inject.spi.BeanManager;
import javax.enterprise.inject.spi.Extension;
 
public class MyCustomScopeExtension implements Extension{
 
    public void afterBeanDiscovery(@Observes AfterBeanDiscovery event, BeanManager manager) {
        event.addContext(new MyCustomScope());
    }
}

See this blog entry for a comprehensive example.

Nothing to complain about! Both technologies perfectly support extensions for scopes and context.

From http://niklasschlimm.blogspot.com/2011/07/custom-scopes-in-cdi-10-and-spring-31.html

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Custom scopes in CDI 1.0 and Spring 3.1

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