Java动态代理的应用详解
作者：
动态代理其实就是java.lang.reflect.Proxy类动态的根据您指定的所有接口生成一个class byte，该class会继承Proxy类，并实现所有你指定的接口（您在参数中传入的接口数组）；然后再利用您指定的classloader将 class byte加载进系统，最后生成这样一个类的对象，并初始化该对象的一些值，如invocationHandler,以即所有的接口对应的Method成员。 初始化之后将对象返回给调用的客户端。这样客户端拿到的就是一个实现你所有的接口的Proxy对象。请看实例分析：
package com.fans.common.proxy;
public interface BusinessProcessor {
public void processBusiness();
}
package com.fans.common.proxy;
/**
* 业务处理类
* @author fanshadoop
*
*/
public class BusinessProcessorImpl implements BusinessProcessor {
@Override
public void processBusiness() {
System.out.println("processing business.....");
}
}
package com.fans.common.proxy;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
/**
* 业务代理类
* @author fanshadoop
*
*/
public class BusinessProcessorHandler implements InvocationHandler {
private Object target = null;
BusinessProcessorHandler(Object target) {
this.target = target;
}
public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable {
System.out
.println("You can do something here before process your business");
Object result = method.invoke(target, args);
System.out
.println("You can do something here after process your business");
return result;
}
}
package com.fans.common.proxy;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.lang.reflect.Proxy;
public class Test {
/**
* @param args
*/
public static void main(String[] args) {
BusinessProcessorImpl bpimpl = new BusinessProcessorImpl();
BusinessProcessorHandler handler = new BusinessProcessorHandler(bpimpl);
BusinessProcessor bp = (BusinessProcessor) Proxy.newProxyInstance(
bpimpl.getClass().getClassLoader(), bpimpl.getClass()
.getInterfaces(), handler);
bp.processBusiness();
System.out.println(bp.getClass().getName());
printClassDefinition(bp.getClass());
}
public static String getModifier(int modifier) {
String result = "";
switch (modifier) {
case Modifier.PRIVATE:
result = "private";
case Modifier.PUBLIC:
result = "public";
case Modifier.PROTECTED:
result = "protected";
case Modifier.ABSTRACT:
result = "abstract";
case Modifier.FINAL:
result = "final";
case Modifier.NATIVE:
result = "native";
case Modifier.STATIC:
result = "static";
case Modifier.SYNCHRONIZED:
result = "synchronized";
case Modifier.STRICT:
result = "strict";
case Modifier.TRANSIENT:
result = "transient";
case Modifier.VOLATILE:
result = "volatile";
case Modifier.INTERFACE:
result = "interface";
}
return result;
}
public static void printClassDefinition(Class clz) {
String clzModifier = getModifier(clz.getModifiers());
if (clzModifier != null && !clzModifier.equals("")) {
clzModifier = clzModifier + " ";
}
String superClz = clz.getSuperclass().getName();
if (superClz != null && !superClz.equals("")) {
superClz = "extends " + superClz;
}
Class[] interfaces = clz.getInterfaces();
String inters = "";
for (int i = 0; i < interfaces.length; i++) {
if (i == 0) {
inters += "implements ";
}
inters += interfaces[i].getName();
}
System.out.println(clzModifier + clz.getName() + " " + superClz + " "
+ inters);
System.out.println("{");
Field[] fields = clz.getDeclaredFields();
for (int i = 0; i < fields.length; i++) {
String modifier = getModifier(fields[i].getModifiers());
if (modifier != null && !modifier.equals("")) {
modifier = modifier + " ";
}
String fieldName = fields[i].getName();
String fieldType = fields[i].getType().getName();
System.out.println(" " + modifier + fieldType + " " + fieldName
+ ";");
}
System.out.println();
Method[] methods = clz.getDeclaredMethods();
for (int i = 0; i < methods.length; i++) {
Method method = methods[i];
String modifier = getModifier(method.getModifiers());
if (modifier != null && !modifier.equals("")) {
modifier = modifier + " ";
}
String methodName = method.getName();
Class returnClz = method.getReturnType();
String retrunType = returnClz.getName();
Class[] clzs = method.getParameterTypes();
String paraList = "(";
for (int j = 0; j < clzs.length; j++) {
paraList += clzs[j].getName();
if (j != clzs.length - 1) {
paraList += ", ";
}
}
paraList += ")";
clzs = method.getExceptionTypes();
String exceptions = "";
for (int j = 0; j < clzs.length; j++) {
if (j == 0) {
exceptions += "throws ";
}
exceptions += clzs[j].getName();
if (j != clzs.length - 1) {
exceptions += ", ";
}
}
exceptions += ";";
String methodPrototype = modifier + retrunType + " " + methodName
+ paraList + exceptions;
System.out.println(" " + methodPrototype);
}
System.out.println("}");
}
}
运行结果：
You can do something here before process your business
processing business.....
You can do something here after process your business
$Proxy0
$Proxy0 extends java.lang.reflect.Proxy implements com.fans.common.proxy.BusinessProcessor
{
java.lang.reflect.Method m1;
java.lang.reflect.Method m3;
java.lang.reflect.Method m0;
java.lang.reflect.Method m2;
boolean equals(java.lang.Object);
java.lang.String toString();
int hashCode();
void processBusiness();
}
类BusinessProcessorHandler实现了InvocationHandler接口的invoke方法，这个类就是Proxy最终调用固定接口方法。
很明显，Proxy.newProxyInstance方法会做如下几件事：
1，根据传入的第二个参数interfaces动态生成一个类，实现interfaces中的接口，该例中即BusinessProcessor接口的processBusiness方法。并且继承了Proxy类，重写了hashcode,toString,equals等三个方法。具体实现可参看 ProxyGenerator.generateProxyClass(...); 该例中生成了$Proxy0类
2，通过传入的第一个参数classloder将刚生成的类加载到jvm中。即将$Proxy0类load
3，利用第三个参数，调用$Proxy0的$Proxy0(InvocationHandler)构造函数 创建$Proxy0的对象，并且用interfaces参数遍历其所有接口的方法，并生成Method对象初始化对象的几个Method成员变量
4，将$Proxy0的实例返回给客户端。
现在好了。我们再看客户端怎么调就清楚了。
1，客户端拿到的是$Proxy0的实例对象，由于$Proxy0继承了BusinessProcessor，因此转化为BusinessProcessor没任何问题。
BusinessProcessor bp = (BusinessProcessor)Proxy.newProxyInstance(....);
2，bp.processBusiness()；
实际上调用的是$Proxy0.processBusiness();那么$Proxy0.processBusiness()的实现就是通过InvocationHandler去调用invoke方法啦!