Spring bean配置使用单例还是原型？

Question

I am using Java7 and Spring3. I have below classes.

Request.java

public interface Request {
  public void doProcess();

}

RequestImpl.java

    @Transactional
    public class RequestImpl implements Request{

     private String name;
     private String age;

     //setters and getters

     public void doProcess(){

      //use name and age and call third party class which will save data into database

      }
}

SpringConfig.xml

<bean id="request" class="pkg.RequestImpl.java" />

Now clients will use RequestImpl as below.

RequestImplreq = (RequestImpl)applicationContext.getBean("request");
req.setName("someName");
req.setAge("20");
req.doProcess();

Now my question is do i need to declare above RequestImpl.java scope as prototype or singleton?

Thanks!

Answer 1

@ user3269829：默认情况下，作用域为singleton这完全取决于您的要求，如果每个请求都需要一个bean对象，则可以使用“ prototype ”，如果要在多个请求中共享单个bean对象，则你可以去“ singleton ”

Answer 2

It depends on how your third party class is implemented. If you want to ensure a single instance of your class you can use factory-method of spring beans and ensure single instance.

Check "3.3.2.2 Instantiation with a static factory method" part of Spring Documentation

It should look like this in bean definition:

<!-- the factory bean, which contains a method called createInstance() -->
<bean id="serviceLocator" class="examples.DefaultServiceLocator">
  <!-- inject any dependencies required by this locator bean -->
</bean>

<!-- the bean to be created via the factory bean -->
<bean id="clientService"
      factory-bean="serviceLocator"
      factory-method="createClientServiceInstance"/>

and singleton creator:

public class DefaultServiceLocator {
  private static ClientService clientService = new ClientServiceImpl();
  private DefaultServiceLocator() {}

  public ClientService createClientServiceInstance() {
    return clientService;
  }
}

Answer 3

IMHO you are not working well: processes and data to process should be separated ( Can DTOs be spring managed beans? ) so doProcess() should be defined as doProcess(name,age) or shaded behind a factory or something similar.
Probably the best option is to define

public interface Request {
  public void doProcess(String name,String age);
}

@Transactional
public class RequestImpl implements Request{
  public void doProcess(String name,String age){
    // do what you want
  }
}

your SpringConfig.xml stay the same and call code will change to:

Request req= applicationContext.getBean(Request.class);
req.doProcess("someName", "20");

Beside all, perform a ApplicationContext.getBean() and cast result to an implementation is (usually) bad pratice because Spring can proxy returned object and cast to implementation will fail with a ClassCastException