最近做个动态代理测试,鬼畜地写了如下代码:
public interface SayHello {
String say(String message);
}
public class SayHelloInvocationHandler implements InvocationHandler {
private SayHello target;
public SayHelloInvocationHandler(SayHello target) {
this.target = target;
}
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
if(StringUtils.equals(method.getName(), "say")) {
System.out.println(proxy.getClass()); //打印第一行
System.out.println(proxy.toString()); //打印第二行
return method.invoke(target, args);
} else {
return method.invoke(proxy, args); //鬼畜行
}
}
都知道了,对,没错,控制台输出打印第一行
的执行结果后就在鬼畜行
的进行死循环了!
class com.sun.proxy.$Proxy21
经过查找原因,死循环触发行是打印第二行
执行,之后进入鬼畜行
;
于是就是想看看这个class com.sun.proxy.$Proxy21
的内容到底是个什么!
经搜索,原来 JDK 生成的动态代理类也是可以写入磁盘的,需要修改系统属性sun.misc.ProxyGenerator.saveGeneratedFiles
为true
;
JDK 动态代理类生成是由sun.misc.ProxyGenerator
类来完成;查看内此类中的关键两行,就知道了:
……
private static final boolean saveGeneratedFiles = ((Boolean)AccessController.doPrivileged(new GetBooleanAction("sun.misc.ProxyGenerator.saveGeneratedFiles"))).booleanValue();
……
/**
* Generate a proxy class given a name and a list of proxy interfaces.
*/
public static byte[] generateProxyClass(final String name,
Class[] interfaces)
{
ProxyGenerator gen = new ProxyGenerator(name, interfaces);
final byte[] classFile = gen.generateClassFile();
if (saveGeneratedFiles) {
……
了解这些,我将$Proxy21.class
内容拿到并进行反编译,得到如下结果:
public final class $Proxy21 extends Proxy implements SayHello {
private static Method m1;
private static Method m0;
private static Method m3;
private static Method m2;
public $Proxy21(InvocationHandler var1) throws {
super(var1);
}
public final boolean equals(Object var1) throws {
try {
return ((Boolean)super.h.invoke(this, m1, new Object[]{var1})).booleanValue();
} catch (RuntimeException | Error var3) {
throw var3;
} catch (Throwable var4) {
throw new UndeclaredThrowableException(var4);
}
}
public final int hashCode() throws {
try {
return ((Integer)super.h.invoke(this, m0, (Object[])null)).intValue();
} catch (RuntimeException | Error var2) {
throw var2;
} catch (Throwable var3) {
throw new UndeclaredThrowableException(var3);
}
}
public final String say(String var1) throws {
try {
return (String)super.h.invoke(this, m3, new Object[]{var1});
} catch (RuntimeException | Error var3) {
throw var3;
} catch (Throwable var4) {
throw new UndeclaredThrowableException(var4);
}
}
public final String toString() throws {
try {
return (String)super.h.invoke(this, m2, (Object[])null);
} catch (RuntimeException | Error var2) {
throw var2;
} catch (Throwable var3) {
throw new UndeclaredThrowableException(var3);
}
}
static {
try {
m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[]{Class.forName("java.lang.Object")});
m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);
m3 = Class.forName("manbu.demo.proxy.SayHello").getMethod("say", new Class[]{Class.forName("java.lang.String")});
m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
} catch (NoSuchMethodException var2) {
throw new NoSuchMethodError(var2.getMessage());
} catch (ClassNotFoundException var3) {
throw new NoClassDefFoundError(var3.getMessage());
}
}
}
原来生成的动态中除了对接口中定义的方法进行代理处理外,还对equals
、hashCode
和 toString
方法进行也都进行了代理处理;这就解释了鬼畜行
的问题了;