静态代理
编译阶段就生产了对应的代理类
public interface IBussiness {
void execute();
}
public class BussinessImpl implements IBussiness{
@Override
public void execute() {
System.out.println("执行业务逻辑...");
}
}
public class BussinessProxy implements IBussiness{
private IBussiness bussinessImpl;
public BussinessProxy(IBussiness bussinessImpl) {
this.bussinessImpl = bussinessImpl;
}
@Override
public void execute() {
System.out.println("前拦截...");
bussinessImpl.execute();
System.out.println("后拦截...");
}
}
public class Test {
public static void main(String[] args) {
IBussiness bussiness = new BussinessImpl();
BussinessProxy proxy = new BussinessProxy(bussiness);
proxy.execute();
}
}
JDK动态代理
动态生成字节码，加载到内存中，利用反射去执行真正的方法
关键代码：
Proxy.newProxyInstance(ClassLoader, Interfaces, InvocationHandler);
生成代理类时，要将类加载器，接口和InvocationHandler传递过去，
类加载器的作用是，生成的字节码要加载到JVM当中
接口的作用是，生成的代理类要知道代理的有哪些方法
InvocationHandler的作用是，在代理类中实际执行的是InvocationHandler的invoke方法
public interface Person {
/**
* 唱歌
*/
void sing();
/**
* 跳舞
* @param name 舞曲名
* @return
*/
String dance(String name);
}
public class PersonImpl implements Person{
@Override
public void sing() {
System.out.println("开始唱歌");
}
@Override
public String dance(String name) {
System.out.println("跳" + name);
return "不好玩";
}
}
public class PersonImplProxy {
private Person person = new PersonImpl();
/**
* 创建代理
* @return 返回值是接口类型
*/
public Person createProxy() {
/**
* 产生某个对象的代理对象
* ClassLoader loader 当前代理对象的类加载器
* Class<?>[] interfaces 代理对象的接口
* InvocationHandler h InvocationHandler对象
*/
return (Person) Proxy.newProxyInstance(PersonImplProxy.class.getClassLoader(), person.getClass().getInterfaces(), new InvocationHandler() {
/**
* @param proxy 把代理对象自身传进去
* @param method 代表当前调用的方法
* @param args 当前调用方法的参数
*/
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
// 获取方法名
String methodName = method.getName();
if ("sing".equals(methodName)) {
System.out.println();
System.out.println("前置通知... 唱歌开始");
method.invoke(person, args);
System.out.println("后置通知... 唱歌结束");
} else if ("dance".equals(methodName)) {
System.out.println();
System.out.println("前置通知 ... 跳舞开始");
Object res = method.invoke(person, args);
System.out.println("后置通知 ... 跳舞结束");
return res;
}
return null;
}
});
}
}
public class Test {
public static void main(String[] args) {
//设置为true后，可以保存生成的代理类的字节码，
//注意字节码文件用jd-gui.exe打开，用javap打开显示不全,javap是JDK自带的工具，他们之间的具体实现是不一样的
System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", "true");
PersonImplProxy proxy = new PersonImplProxy();
Person person = proxy.createProxy();
person.sing();
System.out.println(person.dance("华尔兹三章"));
System.out.println();
System.out.println("生成的代理类的名称: " + person.getClass().getName());
}
}
测试结果
生成字节码文件
将字节码文件反编译后
public final class $Proxy0 extends Proxy implements Person {
private static Method m1;
private static Method m2;
private static Method m3;
private static Method m4;
private static Method m0;
public $Proxy0(InvocationHandler paramInvocationHandler) {
super(paramInvocationHandler);
}
public final boolean equals(Object paramObject) {
try {
return ((Boolean) this.h.invoke(this, m1, new Object[] { paramObject })).booleanValue();
} catch (Error | RuntimeException localError) {
throw localError;
} catch (Throwable localThrowable) {
throw new UndeclaredThrowableException(localThrowable);
}
}
public final String toString() {
try {
return (String) this.h.invoke(this, m2, null);
} catch (Error | RuntimeException localError) {
throw localError;
} catch (Throwable localThrowable) {
throw new UndeclaredThrowableException(localThrowable);
}
}
public final void sing() {
try {
this.h.invoke(this, m3, null);
return;
} catch (Error | RuntimeException localError) {
throw localError;
} catch (Throwable localThrowable) {
throw new UndeclaredThrowableException(localThrowable);
}
}
public final String dance(String paramString) {
try {
return (String) this.h.invoke(this, m4, new Object[] { paramString });
} catch (Error | RuntimeException localError) {
throw localError;
} catch (Throwable localThrowable) {
throw new UndeclaredThrowableException(localThrowable);
}
}
public final int hashCode() {
try {
return ((Integer) this.h.invoke(this, m0, null)).intValue();
} catch (Error | RuntimeException localError) {
throw localError;
} catch (Throwable localThrowable) {
throw new UndeclaredThrowableException(localThrowable);
}
}
static {
try {
m1 = Class.forName("java.lang.Object").getMethod("equals",
new Class[] { Class.forName("java.lang.Object") });
m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[]);
m3 = Class.forName("com.irish.deligate.Person").getMethod("sing", new Class[]);
m4 = Class.forName("com.irish.deligate.Person").getMethod("dance",
new Class[] { Class.forName("java.lang.String") });
m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[]);
return;
} catch (NoSuchMethodException localNoSuchMethodException) {
throw new NoSuchMethodError(localNoSuchMethodException.getMessage());
} catch (ClassNotFoundException localClassNotFoundException) {
throw new NoClassDefFoundError(localClassNotFoundException.getMessage());
}
}
}
可以看到代理类继承了Proxy，实现了我们传递的接口，当调用dance方法时，会转调InvocationHandler的invoke方法，将方法和参数传递过去，由invoke来具体执行代理的逻辑，InvocationHandler持有真正的对象，一般是在调用真正的对象方法前后，执行我们要进行增强的操作。