A brief analysis of Java implementation Dynamic Proxy method _java

In some Java projects, Mapperscannerconfigurer is used in MyBatis and spring consolidation, which automatically generates an interface based dynamic proxy class through a reverse proxy.

In view of this, this article analyzes the Java dynamic Proxy.

This article uses a dynamic proxy to simulate the interceptor that handles transactions.

Interface:

Public interface UserService {public
  void AddUser ();
  public void Removeuser ();
  public void Searchuser ();
}

Implementation class:

public class Userserviceimpl implements UserService {public
  void AddUser () {
    System.out.println ("Add User"); c10/>} public
  void Removeuser () {
    System.out.println ("Remove user");
  }
  public void Searchuser () {
    System.out.println ("Search user");
  }

There are 2 ways to implement Java dynamic proxies

1.JDK Self-band dynamic agent

Dynamic proxies with JDK are required to understand the Invocationhandler interface and proxy classes, all under the Java.lang.reflect package.

Invocationhandler Introduction:

Invocationhandler is an interface implemented by the invocation handler of the proxy instance.

Each proxy instance has an associated invocationhandler. When a method is invoked on a proxy instance, this method invokes the Invocationhandler invoke method.

Proxy Introduction:

Proxy provides static methods for creating dynamic proxy classes and instances.

Instance (analog AOP processing transaction):

public class Transactioninterceptor implements Invocationhandler {

  private Object target;

  public void Settarget (Object target) {
    this.target = target;
  }
  
  @Override Public
  Object Invoke (Object Proxy, Method method, object[] args) throws Throwable {
    System.out.println ("Start Transaction");
    Method.invoke (target, args);
    System.out.println ("End Transaction");
    return null;
  }

}

Test code:

public class Testdynamicproxy {

  @Test public
  void Testjdk () {
    transactioninterceptor Transactioninterceptor = new Transactioninterceptor ();
    UserService userservice = new Userserviceimpl ();
    Transactioninterceptor.settarget (userservice);
    UserService userserviceproxy =
        (userservice) proxy.newproxyinstance (
            userservice.getclass (). getClassLoader (), Userservice.getclass (), getinterfaces ()
            ,
            transactioninterceptor);
    Userserviceproxy.adduser ();
  }

Test results:

Start Transaction
Add user end
Transaction

Obviously, when we make a method call by Userserviceproxy this proxy class, the transaction is opened and closed before and after the method call.

2. Third-party library Cglib

Cglib is a powerful, high-performance, high-quality code generation library for extending Java classes and implementing Java interfaces during runtime.

The biggest difference between it and the dynamic proxy for JDK is that:

The JDK dynamic proxy is for the interface, and the cglib is to implement the proxy for the class, the principle of cglib is to generate a subclass of the specified target class and overwrite the method implementation enhancement, but because of inheritance, the final decorated class cannot be represented.

The instance code is as follows:

The public class Userservicecallback implements Methodinterceptor {

  @Override
  the public object intercept (object o, Method method, object[] args, Methodproxy methodproxy) throws Throwable {
    System.out.println ("Start Transaction by CG Lib ");
    Methodproxy.invokesuper (o, args);
    System.out.println ("End Transaction by Cglib");
    return null;
  }

}

Test code:

public class Testdynamicproxy {

  @Test public
  void Testcglib () {
    enhancer enhancer = new enhancer ();
    Enhancer.setsuperclass (userserviceimpl.class);
    Enhancer.setcallback (New Userservicecallback ());
    Userserviceimpl proxy = (Userserviceimpl) enhancer.create ();
    Proxy.adduser ();
  }

Test results:

Start Transaction by cglib
Add user end
Transaction by Cglib

Interested readers can actually test the example of this article, I believe there will be a great harvest.