jdk 動態代理與 cglib 動態代理原理

阿新 • • 發佈：2020-07-24

1. JDK動態代理

jdk 動態代理是通過實現被代理的介面來實現的，通過 jdk 動態代理生成的類會繼承 java.lang.reflect.Proxy，同時實現被代理的介面

舉例：為 IHello 介面生成一個動態代理類，並將它的位元組碼檔案輸出到檔案中

public interface IHello {
    public String sayHello();
}

// 通過 java.lang.reflect.Proxy 來為 IHello 生成一個代理類
IHello realObj = new HelloImpl();
IHello proxyObj = (IHello) Proxy.newProxyInstance(invocationHandler.getClass().getClassLoader(),realObj.getClass().getInterfaces(), invocationHandler);

斷點打在 java.lang.reflect.Proxy.ProxyClassFactory#apply() Line 642 處
呼叫如下程式碼，將位元組碼檔案進行輸出，然後拿到檔案反編譯
new FileOutputStream("d:\\a.class").getChannel().write(ByteBuffer.wrap(proxyClassFile))

 1 public final class $Proxy0 extends Proxy implements IHello
 2 {
 3     private static Method m1;
 4     private 
 static Method m3;
 5     private static Method m2;
 6     private static Method m0;
 7     
 8     public $Proxy0(final InvocationHandler invocationHandler) {
 9         super(invocationHandler);
10     }
11     
12     public final boolean equals(final Object o) {
13         try {
14             return 
 (boolean)super.h.invoke(this, $Proxy0.m1, new Object[] { o });
15         }
16         catch (Error | RuntimeException error) {
17             throw;
18         }
19         catch (Throwable t) {
20             throw new UndeclaredThrowableException(t);
21         }
22     }
23     
24     public final String sayHello() {
25         try {
26             return (String)super.h.invoke(this, $Proxy0.m3, null);
27         }
28         catch (Error | RuntimeException error) {
29             throw;
30         }
31         catch (Throwable t) {
32             throw new UndeclaredThrowableException(t);
33         }
34     }
35     
36     public final String toString() {
37         try {
38             return (String)super.h.invoke(this, $Proxy0.m2, null);
39         }
40         catch (Error | RuntimeException error) {
41             throw;
42         }
43         catch (Throwable t) {
44             throw new UndeclaredThrowableException(t);
45         }
46     }
47     
48     public final int hashCode() {
49         try {
50             return (int)super.h.invoke(this, $Proxy0.m0, null);
51         }
52         catch (Error | RuntimeException error) {
53             throw;
54         }
55         catch (Throwable t) {
56             throw new UndeclaredThrowableException(t);
57         }
58     }
59     
60     static {
61         try {
62             $Proxy0.m1 = Class.forName("java.lang.Object").getMethod("equals", Class.forName("java.lang.Object"));
63             $Proxy0.m3 = Class.forName("com.cn.zsy.proxy.jdkProxy.IHello").getMethod("sayHello", (Class<?>[])new Class[0]);
64             $Proxy0.m2 = Class.forName("java.lang.Object").getMethod("toString", (Class<?>[])new Class[0]);
65             $Proxy0.m0 = Class.forName("java.lang.Object").getMethod("hashCode", (Class<?>[])new Class[0]);
66         }
67         catch (NoSuchMethodException ex) {
68             throw new NoSuchMethodError(ex.getMessage());
69         }
70         catch (ClassNotFoundException ex2) {
71             throw new NoClassDefFoundError(ex2.getMessage());
72         }
73     }
74 }

View Code

跟原始碼：

1. java.lang.reflect.Proxy#newProxyInstance()
    1.1 sun.misc.ProxyGenerator#generateClassFile()
        1.1.1 sun.misc.ProxyGenerator#generateProxyClass()
            1.1.1.1 sun.misc.ProxyGenerator#generateClassFile() // line 209，直接生成 java 位元組碼陣列。裡面會繼承 java.lang.reflect.Proxy