Java设计模式——代理模式
代理模式主要分为接口，委托类，代理类
接口：规定具体方法
委托类：实现接口，完成具体的业务逻辑
代理类：实现接口，在方法里面调用委托类的方法，自己不实现核心业务，在调用委托类的方法前后可以执行其他操作，也就是增强。
代理重要的特征就是： 委托类和代理类实现了相同的接口，由此对于调用者来说委托类和代理类没有什么不同，而且代理类的定制性更强，这也是和适配器模式的重要区别。
静态代理
静态代理是在编译时期就将接口，实现类，代理类全部编码，也就是在运行之前所有的class文件已经存在。
接口：
public interface Service {
int increaseOne(int num);
String toUpperCase(String str);
}
接口实现类（委托类）：
public class ServiceImpl implements Service {
@Override
public int increaseOne(int num) {
return ++num;
}
@Override
public String toUpperCase(String str) {
return str.toUpperCase();
}
}
代理类：
public class ServiceProxy implements Service{
private Service service;
public ServiceProxy(Service service) {
this.service = service;
}
@Override
public int increaseOne(int num) {
System.out.println("将要执行increaseOne");
int i = service.increaseOne(num);
System.out.println("increaseOne执行完毕");
return i;
}
@Override
public String toUpperCase(String str) {
return service.toUpperCase(str);
}
}
测试类：
public class MainTest {
public static void main(String[] args) {
Service service = new ServiceImpl();
ServiceProxy serviceProxy = new ServiceProxy(service);
/**
* 在执行真正 increaseOne方法之前或者之后可以执行一系列操作
* 这里用sout模拟
*/
System.out.println(serviceProxy.increaseOne(5));
/**
* 调用真正的 toUpperCase方法
*/
System.out.println(serviceProxy.toUpperCase("hello world"));
}
}
输出：
将要执行increaseOne
increaseOne执行完毕
6
HELLO WORLD
JDK动态代理
JDK动态代理简化了静态代理的繁琐操作，不需要人工硬编码代理类实现接口。
实现InvocationHandler接口：
public class DynamicProxyHandler implements InvocationHandler {
private Object target;
public DynamicProxyHandler(Object target) {
this.target = target;
}
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
Object result;
if ("increaseOne".equals(method.getName())) {
System.out.println("将要执行increaseOne");
result = method.invoke(target, args);
System.out.println("increaseOne执行完毕");
} else {
result = method.invoke(target, args);
}
return result;
}
测试类：
public class MainTest {
public static void main(String[] args) {
Service service = new ServiceImpl();
DynamicProxyHandler dynamicProxyHandler = new DynamicProxyHandler(service);
Service serviceProxy = (Service) Proxy.newProxyInstance(
Thread.currentThread().getContextClassLoader(),
service.getClass().getInterfaces(), dynamicProxyHandler);
System.out.println(serviceProxy.increaseOne(5));
System.out.println(serviceProxy.toUpperCase("hello world"));
}
}
输出：
将要执行increaseOne
increaseOne执行完毕
6
HELLO WORLD
比较分析
静态代理的实现方式：
代理类实现接口，实例化代理类，代理类的成员变量引用委托类对象，代理类调用方法，方法内部委托类对象调用方法。
JDK动态代理的实现方式：
与静态代理的过程是一样的，但是代理类编码是由JVM完成，我们只需要关注方法的实现细节。
-
实现
InvocationHandler接口：
先看看InvocationHandler接口：public interface InvocationHandler { public Object invoke(Object proxy, Method method, Object[] args) throws Throwable; }只有
invoke方法，三个参数：类型 参数 说明 Object proxy 自动生成的代理对象，后面详细说 Method method 调用的方法 Object[] args 调用的方法的参数 实现：
method.invoke(target, args)使用反射让委托对象调用方法，target就是委托对 象public class DynamicProxyHandler implements InvocationHandler { private Object target; public DynamicProxyHandler(Object target) { this.target = target; } @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { Object result; result = method.invoke(target, args); return result; } } -
生成代理对象：通过
Proxy类的静态方法newProxyInstancepublic static Object newProxyInstance(ClassLoader loader, Class<?>[] interfaces, InvocationHandler h)newProxyInstance需要三个参数：类型 参数 说明 ClassLoader loadery 类加载器，使用类的或者当前线程的都可以 Class<?> interfaces 代理类代理的接口，相当于示例中的 Service接口InvocationHandler h 回调对象，代理方法的具体实现细节在这里完成
-
具体过程：
-
调用
Proxy.newProxyInstance(ClassLoader, Class<?>[] , InvocationHandler)public static Object newProxyInstance(ClassLoader loader, Class<?>[] interfaces, InvocationHandler h) throws IllegalArgumentException { Objects.requireNonNull(h); final Class<?>[] intfs = interfaces.clone(); final SecurityManager sm = System.getSecurityManager(); if (sm != null) { checkProxyAccess(Reflection.getCallerClass(), loader, intfs); } /* * Look up or generate the designated proxy class. */ Class<?> cl = getProxyClass0(loader, intfs); /* * Invoke its constructor with the designated invocation handler. */ try { if (sm != null) { checkNewProxyPermission(Reflection.getCallerClass(), cl); } final Constructor<?> cons = cl.getConstructor(constructorParams); final InvocationHandler ih = h; if (!Modifier.isPublic(cl.getModifiers())) { AccessController.doPrivileged(new PrivilegedAction<Void>() { public Void run() { cons.setAccessible(true); return null; } }); } return cons.newInstance(new Object[]{h}); } catch (IllegalAccessException|InstantiationException e) { throw new InternalError(e.toString(), e); } catch (InvocationTargetException e) { Throwable t = e.getCause(); if (t instanceof RuntimeException) { throw (RuntimeException) t; } else { throw new InternalError(t.toString(), t); } } catch (NoSuchMethodException e) { throw new InternalError(e.toString(), e); } }重要的有俩步：
-
Class<?> cl = getProxyClass0(loader, intfs)根据类加载器和接口参数会生成代理类的字节码， -
return cons.newInstance(new Object[]{h})返回生成代理类的实例
来看看生成的代理类（在内存中生成.class文件，需要先输出保存，再反编译）：
public final class $ServiceProxy extends Proxy implements Service { private static Method m1; private static Method m2; private static Method m3; private static Method m4; private static Method m0; public $ServiceProxy(InvocationHandler var1) throws { super(var1); } public final boolean equals(Object var1) throws { try { return (Boolean)super.h.invoke(this, m1, 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); } } public final String toUpperCase(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 int increaseOne(int var1) throws { try { return (Integer)super.h.invoke(this, m4, new Object[]{var1}); } 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); } catch (RuntimeException | Error var2) { throw var2; } catch (Throwable var3) { throw new UndeclaredThrowableException(var3); } } static { try { m1 = Class.forName("java.lang.Object").getMethod("equals", Class.forName("java.lang.Object")); m2 = Class.forName("java.lang.Object").getMethod("toString"); m3 = Class.forName("com.Service").getMethod("toUpperCase", Class.forName("java.lang.String")); m4 = Class.forName("com.Service").getMethod("increaseOne", Integer.TYPE); m0 = Class.forName("java.lang.Object").getMethod("hashCode"); } catch (NoSuchMethodException var2) { throw new NoSuchMethodError(var2.getMessage()); } catch (ClassNotFoundException var3) { throw new NoClassDefFoundError(var3.getMessage()); } } }生成的代理类实现l了
Service接口，这和静态代理的代码类似，但是这里还继承了Proxy类，构造函数接受InvocationHandler实现类对象，然后调用Proxy的构造函数，把对象传给Proxy的InvocationHandler类型成员变量，示例中获取代理对象后有个强制转换类型，之前一直有疑问为什么不会报错，直到反编译代理类后看到实现了Service接口才明白。 -
-
代理类对象调用接口方法：
继续看代理类，例如调用increaseOne方法public final int increaseOne(int var1) throws { try { return (Integer)super.h.invoke(this, m4, new Object[]{var1}); } catch (RuntimeException | Error var3) { throw var3; } catch (Throwable var4) { throw new UndeclaredThrowableException(var4); } }其实最终调用的就是我们传入的
InvocationHandler对象的invoke方法，this和new Object[]{var1}，可以理解，但是m4什么时候生成的呢代理类有个
static代码块：static { try { m1 = Class.forName("java.lang.Object").getMethod("equals", Class.forName("java.lang.Object")); m2 = Class.forName("java.lang.Object").getMethod("toString"); m3 = Class.forName("com.Service").getMethod("toUpperCase", Class.forName("java.lang.String")); m4 = Class.forName("com.Service").getMethod("increaseOne", Integer.TYPE); m0 = Class.forName("java.lang.Object").getMethod("hashCode"); } catch (NoSuchMethodException var2) { throw new NoSuchMethodError(var2.getMessage()); } catch (ClassNotFoundException var3) { throw new NoClassDefFoundError(var3.getMessage()); } }可以看到
m3和m4是Service接口方法的引用，其他的三个方法引用是Object类的equals，toString以及hashCode方法，而且这三个方法里面也调用了invoke方法，所以不能在invoke方法里面输出proxy对象，相当于循环调用方法。
-
CGLIB动态代理
CGLIB代理的是类，不同于JDK只能代理接口
委托类：
public class DelegateClass {
public int increaseOne(int num) {
return ++num;
}
public String toUpperCase(String str) {
return str.toUpperCase();
}
}
代理类：
public class CGLIBProxy implements MethodInterceptor {
private Object target;
public CGLIBProxy(Object target) {
this.target = target;
}
@Override
public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
Object result;
if ("increaseOne".equals(method.getName())) {
System.out.println("将要执行increaseOne");
result = method.invoke(target, args);
System.out.println("increaseOne执行完毕");
} else {
result = method.invoke(target, args);
}
return result;
}
}
测试类：
public class MainTest {
public static void main(String[] args) {
DelegateClass delegateClass = new DelegateClass();
MethodInterceptor methodInterceptor = new CGLIBProxy(delegateClass);
Enhancer enhancer = new Enhancer();
enhancer.setSuperclass(DelegateClass.class);
enhancer.setCallback(methodInterceptor);
DelegateClass cglibProxy = (DelegateClass) enhancer.create();
System.out.println(cglibProxy.increaseOne(5));
System.out.println(cglibProxy.toUpperCase("hello world"));
}
}
分析：
-
自动生成的代理类：
public class DelegateClass$$EnhancerByCGLIB$$50d8bc59 extends DelegateClass implements Factory { private boolean CGLIB$BOUND; public static Object CGLIB$FACTORY_DATA; private static final ThreadLocal CGLIB$THREAD_CALLBACKS; private static final Callback[] CGLIB$STATIC_CALLBACKS; private MethodInterceptor CGLIB$CALLBACK_0; private static Object CGLIB$CALLBACK_FILTER; private static final Method CGLIB$toUpperCase$0$Method; private static final MethodProxy CGLIB$toUpperCase$0$Proxy; private static final Object[] CGLIB$emptyArgs; private static final Method CGLIB$increaseOne$1$Method; private static final MethodProxy CGLIB$increaseOne$1$Proxy; private static final Method CGLIB$equals$2$Method; private static final MethodProxy CGLIB$equals$2$Proxy; private static final Method CGLIB$toString$3$Method; private static final MethodProxy CGLIB$toString$3$Proxy; private static final Method CGLIB$hashCode$4$Method; private static final MethodProxy CGLIB$hashCode$4$Proxy; private static final Method CGLIB$clone$5$Method; private static final MethodProxy CGLIB$clone$5$Proxy; static void CGLIB$STATICHOOK1() { CGLIB$THREAD_CALLBACKS = new ThreadLocal(); CGLIB$emptyArgs = new Object[0]; Class var0 = Class.forName("com.cglibproxy.DelegateClass$$EnhancerByCGLIB$$50d8bc59"); Class var1; Method[] var10000 = ReflectUtils.findMethods(new String[]{"equals", "(Ljava/lang/Object;)Z", "toString", "()Ljava/lang/String;", "hashCode", "()I", "clone", "()Ljava/lang/Object;"}, (var1 = Class.forName("java.lang.Object")).getDeclaredMethods()); CGLIB$equals$2$Method = var10000[0]; CGLIB$equals$2$Proxy = MethodProxy.create(var1, var0, "(Ljava/lang/Object;)Z", "equals", "CGLIB$equals$2"); CGLIB$toString$3$Method = var10000[1]; CGLIB$toString$3$Proxy = MethodProxy.create(var1, var0, "()Ljava/lang/String;", "toString", "CGLIB$toString$3"); CGLIB$hashCode$4$Method = var10000[2]; CGLIB$hashCode$4$Proxy = MethodProxy.create(var1, var0, "()I", "hashCode", "CGLIB$hashCode$4"); CGLIB$clone$5$Method = var10000[3]; CGLIB$clone$5$Proxy = MethodProxy.create(var1, var0, "()Ljava/lang/Object;", "clone", "CGLIB$clone$5"); var10000 = ReflectUtils.findMethods(new String[]{"toUpperCase", "(Ljava/lang/String;)Ljava/lang/String;", "increaseOne", "(I)I"}, (var1 = Class.forName("com.cglibproxy.DelegateClass")).getDeclaredMethods()); CGLIB$toUpperCase$0$Method = var10000[0]; CGLIB$toUpperCase$0$Proxy = MethodProxy.create(var1, var0, "(Ljava/lang/String;)Ljava/lang/String;", "toUpperCase", "CGLIB$toUpperCase$0"); CGLIB$increaseOne$1$Method = var10000[1]; CGLIB$increaseOne$1$Proxy = MethodProxy.create(var1, var0, "(I)I", "increaseOne", "CGLIB$increaseOne$1"); } final String CGLIB$toUpperCase$0(String var1) { return super.toUpperCase(var1); } public final String toUpperCase(String var1) { MethodInterceptor var10000 = this.CGLIB$CALLBACK_0; if (this.CGLIB$CALLBACK_0 == null) { CGLIB$BIND_CALLBACKS(this); var10000 = this.CGLIB$CALLBACK_0; } return var10000 != null ? (String)var10000.intercept(this, CGLIB$toUpperCase$0$Method, new Object[]{var1}, CGLIB$toUpperCase$0$Proxy) : super.toUpperCase(var1); } final int CGLIB$increaseOne$1(int var1) { return super.increaseOne(var1); } public final int increaseOne(int var1) { MethodInterceptor var10000 = this.CGLIB$CALLBACK_0; if (this.CGLIB$CALLBACK_0 == null) { CGLIB$BIND_CALLBACKS(this); var10000 = this.CGLIB$CALLBACK_0; } if (var10000 != null) { Object var2 = var10000.intercept(this, CGLIB$increaseOne$1$Method, new Object[]{new Integer(var1)}, CGLIB$increaseOne$1$Proxy); return var2 == null ? 0 : ((Number)var2).intValue(); } else { return super.increaseOne(var1); } } final boolean CGLIB$equals$2(Object var1) { return super.equals(var1); } public final boolean equals(Object var1) { MethodInterceptor var10000 = this.CGLIB$CALLBACK_0; if (this.CGLIB$CALLBACK_0 == null) { CGLIB$BIND_CALLBACKS(this); var10000 = this.CGLIB$CALLBACK_0; } if (var10000 != null) { Object var2 = var10000.intercept(this, CGLIB$equals$2$Method, new Object[]{var1}, CGLIB$equals$2$Proxy); return var2 == null ? false : (Boolean)var2; } else { return super.equals(var1); } } final String CGLIB$toString$3() { return super.toString(); } public final String toString() { MethodInterceptor var10000 = this.CGLIB$CALLBACK_0; if (this.CGLIB$CALLBACK_0 == null) { CGLIB$BIND_CALLBACKS(this); var10000 = this.CGLIB$CALLBACK_0; } return var10000 != null ? (String)var10000.intercept(this, CGLIB$toString$3$Method, CGLIB$emptyArgs, CGLIB$toString$3$Proxy) : super.toString(); } final int CGLIB$hashCode$4() { return super.hashCode(); } public final int hashCode() { MethodInterceptor var10000 = this.CGLIB$CALLBACK_0; if (this.CGLIB$CALLBACK_0 == null) { CGLIB$BIND_CALLBACKS(this); var10000 = this.CGLIB$CALLBACK_0; } if (var10000 != null) { Object var1 = var10000.intercept(this, CGLIB$hashCode$4$Method, CGLIB$emptyArgs, CGLIB$hashCode$4$Proxy); return var1 == null ? 0 : ((Number)var1).intValue(); } else { return super.hashCode(); } } final Object CGLIB$clone$5() throws CloneNotSupportedException { return super.clone(); } protected final Object clone() throws CloneNotSupportedException { MethodInterceptor var10000 = this.CGLIB$CALLBACK_0; if (this.CGLIB$CALLBACK_0 == null) { CGLIB$BIND_CALLBACKS(this); var10000 = this.CGLIB$CALLBACK_0; } return var10000 != null ? var10000.intercept(this, CGLIB$clone$5$Method, CGLIB$emptyArgs, CGLIB$clone$5$Proxy) : super.clone(); } public static MethodProxy CGLIB$findMethodProxy(Signature var0) { String var10000 = var0.toString(); switch(var10000.hashCode()) { case -1961280283: if (var10000.equals("increaseOne(I)I")) { return CGLIB$increaseOne$1$Proxy; } break; case -508378822: if (var10000.equals("clone()Ljava/lang/Object;")) { return CGLIB$clone$5$Proxy; } break; case 893465080: if (var10000.equals("toUpperCase(Ljava/lang/String;)Ljava/lang/String;")) { return CGLIB$toUpperCase$0$Proxy; } break; case 1826985398: if (var10000.equals("equals(Ljava/lang/Object;)Z")) { return CGLIB$equals$2$Proxy; } break; case 1913648695: if (var10000.equals("toString()Ljava/lang/String;")) { return CGLIB$toString$3$Proxy; } break; case 1984935277: if (var10000.equals("hashCode()I")) { return CGLIB$hashCode$4$Proxy; } } return null; } public DelegateClass$$EnhancerByCGLIB$$50d8bc59() { CGLIB$BIND_CALLBACKS(this); } public static void CGLIB$SET_THREAD_CALLBACKS(Callback[] var0) { CGLIB$THREAD_CALLBACKS.set(var0); } public static void CGLIB$SET_STATIC_CALLBACKS(Callback[] var0) { CGLIB$STATIC_CALLBACKS = var0; } private static final void CGLIB$BIND_CALLBACKS(Object var0) { DelegateClass$$EnhancerByCGLIB$$50d8bc59 var1 = (DelegateClass$$EnhancerByCGLIB$$50d8bc59)var0; if (!var1.CGLIB$BOUND) { var1.CGLIB$BOUND = true; Object var10000 = CGLIB$THREAD_CALLBACKS.get(); if (var10000 == null) { var10000 = CGLIB$STATIC_CALLBACKS; if (CGLIB$STATIC_CALLBACKS == null) { return; } } var1.CGLIB$CALLBACK_0 = (MethodInterceptor)((Callback[])var10000)[0]; } } public Object newInstance(Callback[] var1) { CGLIB$SET_THREAD_CALLBACKS(var1); DelegateClass$$EnhancerByCGLIB$$50d8bc59 var10000 = new DelegateClass$$EnhancerByCGLIB$$50d8bc59(); CGLIB$SET_THREAD_CALLBACKS((Callback[])null); return var10000; } public Object newInstance(Callback var1) { CGLIB$SET_THREAD_CALLBACKS(new Callback[]{var1}); DelegateClass$$EnhancerByCGLIB$$50d8bc59 var10000 = new DelegateClass$$EnhancerByCGLIB$$50d8bc59(); CGLIB$SET_THREAD_CALLBACKS((Callback[])null); return var10000; } public Object newInstance(Class[] var1, Object[] var2, Callback[] var3) { CGLIB$SET_THREAD_CALLBACKS(var3); DelegateClass$$EnhancerByCGLIB$$50d8bc59 var10000 = new DelegateClass$$EnhancerByCGLIB$$50d8bc59; switch(var1.length) { case 0: var10000.<init>(); CGLIB$SET_THREAD_CALLBACKS((Callback[])null); return var10000; default: throw new IllegalArgumentException("Constructor not found"); } } public Callback getCallback(int var1) { CGLIB$BIND_CALLBACKS(this); MethodInterceptor var10000; switch(var1) { case 0: var10000 = this.CGLIB$CALLBACK_0; break; default: var10000 = null; } return var10000; } public void setCallback(int var1, Callback var2) { switch(var1) { case 0: this.CGLIB$CALLBACK_0 = (MethodInterceptor)var2; default: } } public Callback[] getCallbacks() { CGLIB$BIND_CALLBACKS(this); return new Callback[]{this.CGLIB$CALLBACK_0}; } public void setCallbacks(Callback[] var1) { this.CGLIB$CALLBACK_0 = (MethodInterceptor)var1[0]; } static { CGLIB$STATICHOOK1(); } }类继承了委托类
DelegateClass，测试类代码中一行代码DelegateClass cglibProxy = (DelegateClass) enhancer.create();cglibProxy引用的就是DelegateClass$$EnhancerByCGLIB$$50d8bc59的实例，属于子类强制转父类，除了代理increaseOne和toUpperCase方法外，还有toString，equal，hashCode，clone方法也被代理，代理类的方法会判断是否有回调对象，也就是MethodInterceptor的实例，有的话调用回调对象的intercept方法，否则使用super.increaseOne(var1)调用委托类的方法，没有增强处理。
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