Java java.lang.reflect.Proxy Class的详细介绍

清疚 2023-09-23 22:51 38阅读 0赞

# 1.Defination #

*  A proxy class is present in `java.lang package`.
 *  A proxy class has certain methods which are used for **creating dynamic proxy classes** and **instances**, and **all the classes created by those methods act as subclasses for this proxy class**.

**Class declaration:**

> public class Proxy extends Object implements Serializable

**Fields:**

> protected `InvocationHandler` h  
> (It handles the invocation for this proxy instance.)

**Constructor:**

> protected Proxy(InvocationHandler h)

*  **Constructs a Proxy instance** from a subclass which is typically a dynamic proxy class.
 *  The instance is automatically created with the required value of this invocation handler h.

# 2. Code #

// Invocation handler implementation
    public class Test implements InvocationHandler{
        
    
        @Override
        public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        
            return null;
        }
    
        public static void main(String[] args) {
        
            InvocationHandler invocationHandler = new Test();
            System.out.println(invocationHandler);
        }
        
    }

com.Amy.model.proxy.Test@1b6d3586

# 3.Methods #

<table> 
 <thead> 
  <tr> 
   <th>Method</th> 
   <th>Description</th> 
   <th>Translate</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>getInvocationHandler(Object proxy)</td> 
   <td>This method returns the invocation handler for the specified proxy instance.</td> 
   <td>此方法返回指定代理实例的调用处理程序。</td> 
  </tr> 
  <tr> 
   <td>getProxyClass(ClassLoader loader, Class&lt;?&gt;… interfaces)</td> 
   <td>This method returns the java.lang.Class object for a proxy class given a class loader and an array of interfaces.</td> 
   <td>给定类加载器和接口数组，此方法返回代理类的 java.lang.Class 对象。</td> 
  </tr> 
  <tr> 
   <td>isProxyClass(Class&lt;?&gt; cl)</td> 
   <td>This method returns true if and only if the specified class was dynamically generated to be a proxy class using the getProxyClass method or the newProxyInstance method.</td> 
   <td>当且仅当指定类是使用 getProxyClass 方法或 newProxyInstance 方法动态生成为代理类时，此方法才返回 true。</td> 
  </tr> 
  <tr> 
   <td>newProxyInstance(ClassLoader loader, Class&lt;?&gt;[] interfaces, InvocationHandler h)</td> 
   <td>This method returns an instance of a proxy class for the specified interfaces that dispatches method invocations to the specified invocation handler.</td> 
   <td>此方法返回指定接口的代理类实例，该接口将方法调用分派给指定的调用处理程序。</td> 
  </tr> 
 </tbody> 
</table>

> ## 1. static InvocationHandler getInvocationHandler(Object proxy): ##

> Returns the invocation handler for this proxy instance.

**code:**

interface DemoInterface {
        
    }

public class DemoInvocationHandler implements InvocationHandler{
        
    
        @Override
        public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        
            return null;
        }
    
    }

public class Client {
        
        public static void main(String[] args) {
        
            // Object created
            InvocationHandler handler = new DemoInvocationHandler();
            // ProxyClass objects stored in list 列表中存储的 ProxyClass 对象
            List proxyClass = (List) Proxy.newProxyInstance(Client.class.getClassLoader(),new Class[]{
        List.class},new DemoInvocationHandler());
            System.out.println(Proxy.getInvocationHandler(proxyClass));
        }
    }

**result:**

com.Amy.model.proxy.Test@7ea987ac

> ## 2.static Class<?> getProxyClass(ClassLoader loader, Class<?>… interfaces): ##

>  *  Returns the java.lang.Class object for a proxy class.
>  *  The proxy class are going to be defined by the required class loader and can implement all the supplied interfaces.

**code:**

interface DemoInterface {
        
    }

public class demo {
        
    }

public class Client {
        
        public static void main(String[] args) {
        
            // Object created
            InvocationHandler handler = new DemoInvocationHandler();
    
           Class<?> proxyClass = (Class<?> ) Proxy.getProxyClass(demo.class.getClassLoader(),new Class[]{
        DemoInterface.class});
           System.out.println("success");
        }
    }

**result:**

success

> ## 3. static boolean isProxyClass(Class<?> cl): ##

> Returns true if this class was dynamically generated to be a proxy class using the getProxyClass method or the newProxyInstance method else returns false.

**code:**

interface DemoInterface {
        
    }

public class demo {
        
    }

public class Client {
        
        public static void main(String[] args) {
        
            // Object created
            InvocationHandler handler = new DemoInvocationHandler();
            
           Class<?> proxyClass = (Class<?> ) Proxy.getProxyClass(demo.class.getClassLoader(),new Class[]{
        DemoInterface.class});
           System.out.println(Proxy.isProxyClass(proxyClass));
        }
    }

**result:**

true

> ## 4. static Object newProxyInstance(ClassLoader loader, Class<?>\[\] interfaces, InvocationHandler h): ##

> Returns a proxy object of a proxy class which is defined by the class loader. It implements all the required interfaces.

**code:**

interface DemoInterface {
        
    }

public class Client {
        
        public static void main(String[] args) {
        
            // Object created
            InvocationHandler handler = new DemoInvocationHandler();
            // ProxyClass objects stored in list 列表中存储的 ProxyClass 对象
            List proxyClass = (List) Proxy.newProxyInstance(Client.class.getClassLoader(),new Class[]{
        List.class},new DemoInvocationHandler());
            System.out.println( "Proxy object returned successfully");
        }
    }

**result:**

Proxy object returned successfully