Spring 框架：当您将 Java bean 注入另一个 Java bean 时会发生什么，但它们具有不同的范围

Question

I'm new to Java and Spring framework programming. Please consider the following two Java files:

//AccountService.java

package org.mycompany.accountManagement

@Path("/bankaccount")
@Component
@Scope("session")
public class AccountService
{
  private Depositer myDepositer;

  @Autowired
  pubilc AccountService( Depositer depositer )
  { 
    myDepositer = depositer; 
  }
}

---

//Depositer.java

package org.mycompany.accountManagement

@Component
@Scope("request")
public class Depositer
{
  public void deposit(){ System.out.println("Depositing..."); }
}

The class AccountService is instantiated only once for a given HTTP session. When it is instantiated, a Depositer object was also instantiated and was kept by AccountService as a private variable. Since the lifetime of this AccountService object persists throughout the HTTP session, I suppose the Depositor object that it keeps is used throughout the session. However, the scope of the Depositor class was supposed to be "request," ie, instantiation for every request... I'm confused here, is a new Depositer object instantiated for every request? Or is the same Depositor object used throughout the session?

Answer 1

Spring uses Proxy pattern internally to solve this and create new instance for request scope bean inside session scoped bean, you know spring has access to every HttpServletRequest and you can even inject it in your class if you want. so it wraps the session scope bean with a proxy and when you reference request scope bean from the containing session scope bean if it is a new HttpServletRequest it will create new instance but if it is the same HttpServletRequest it returns the existing request scope bean.