JDK动态代理(proxy)可以在运行时创建一个实现一组给定接口的新类。但是略有限制,即被代理的类必须实现某个接口,否则无法使用JDK自带的动态代理,因此,如果不满足条件,就只能使用另一种更加灵活,功能更加强大的动态代理技术—— CGLIB。Spring里会自动在JDK的代理和CGLIB之间切换,同时我们也可以强制Spring使用CGLIB。
闲话少说,下面先用实例介绍使用方式,接着从proxy类源码角度分析实现过程:
(1)动态代理首先提供一个调度处理器接口(Invocationhandler),该接口实例封装了我们要代理的对象实例的数据。
public class TranceHander implements InvocationHandler{
private Object tObject;
public TranceHander(Object t){
tObject=t;
}
@Override
public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable {
// TODO Auto-generated method stub
System.out.println("被代理对象:"+tObject);
System.out.println("方法:"+method.getName());
return method.invoke(tObject,args);//方法反射
}
}
测试mian方法中,写了一个代理类,从1-1000的整数数组中使用二分查找随机查找一个整数,实现对象比较和toString接口代理
public class ProxyTest {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
Object[] elements=new Object[1000];
for(int i=0;i=0){
System.out.println(elements[res].toString());
}
System.out.println("查找Key:"+key);
}
}
Object proxy=Proxy.newProxyInstance(null, new Class[]{Comparable.class}, handler);
public static Object newProxyInstance(ClassLoader loader,
Class[] interfaces,
InvocationHandler h)
throws IllegalArgumentException
{
if (h == null) {
throw new NullPointerException();
}
final SecurityManager sm = System.getSecurityManager();
if (sm != null) {
checkProxyAccess(Reflection.getCallerClass(), loader, interfaces);
}
/*
* Look up or generate the designated proxy class.
*/
Class cl = getProxyClass0(loader, interfaces);
/*
* Invoke its constructor with the designated invocation handler.
*/
try {
final Constructor cons = cl.getConstructor(constructorParams);
final InvocationHandler ih = h;
if (sm != null && ProxyAccessHelper.needsNewInstanceCheck(cl)) {
// create proxy instance with doPrivilege as the proxy class may
// implement non-public interfaces that requires a special permission
return AccessController.doPrivileged(new PrivilegedAction
/* collect interface names to use as key for proxy class cache */
String[] interfaceNames = new String[interfaces.length];
// for detecting duplicates
Set> interfaceSet = new HashSet<>();
for (int i = 0; i < interfaces.length; i++) {
/*
* Verify that the class loader resolves the name of this
* interface to the same Class object.
*/
String interfaceName = interfaces[i].getName();
Class interfaceClass = null;
try {
interfaceClass = Class.forName(interfaceName, false, loader);
} catch (ClassNotFoundException e) {
}
if (interfaceClass != interfaces[i]) {
throw new IllegalArgumentException(
interfaces[i] + " is not visible from class loader");
}
/*
* Verify that the Class object actually represents an
* interface.
*/
if (!interfaceClass.isInterface()) {
throw new IllegalArgumentException(
interfaceClass.getName() + " is not an interface");
}
/*
* Verify that this interface is not a duplicate.
*/
if (interfaceSet.contains(interfaceClass)) {
throw new IllegalArgumentException(
"repeated interface: " + interfaceClass.getName());
}
interfaceSet.add(interfaceClass);
interfaceNames[i] = interfaceName;
}
for (int i = 0; i < interfaces.length; i++) {
int flags = interfaces[i].getModifiers();
if (!Modifier.isPublic(flags)) {
String name = interfaces[i].getName();
int n = name.lastIndexOf('.');
String pkg = ((n == -1) ? "" : name.substring(0, n + 1));
if (proxyPkg == null) {
proxyPkg = pkg;
} else if (!pkg.equals(proxyPkg)) {
throw new IllegalArgumentException(
"non-public interfaces from different packages");
}
}
}
if (proxyPkg == null) {
// if no non-public proxy interfaces, use com.sun.proxy package
proxyPkg = ReflectUtil.PROXY_PACKAGE + ".";
}
byte[] proxyClassFile = ProxyGenerator.generateProxyClass( proxyName, interfaces);
proxyClass = defineClass0(loader, proxyName,proxyClassFile, 0, proxyClassFile.length);
return proxyClass;
public static void main(String[] args) {
// TODO Auto-generated method stub
Integer value=1;
InvocationHandler handler=new TranceHander(value);//构建调度处理器
Object proxy=Proxy.newProxyInstance(null, Integer.class.getInterfaces(), handler);
String path = "D://aaa.class";
byte[] classFile = ProxyGenerator.generateProxyClass("$Proxy0",Integer.class.getInterfaces());
FileOutputStream out = null;
try {
out = new FileOutputStream(path);
out.write(classFile);
out.flush();
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
out.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.lang.reflect.UndeclaredThrowableException;
public final class $Proxy0 extends Proxy
implements Comparable
{
private static Method m3;
private static Method m1;
private static Method m0;
private static Method m2;
public $Proxy0(InvocationHandler paramInvocationHandler)
throws
{
super(paramInvocationHandler);
}
public final int compareTo(Object paramObject)
throws
{
try
{
return ((Integer)this.h.invoke(this, m3, new Object[] { paramObject })).intValue();
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
public final boolean equals(Object paramObject)
throws
{
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 int hashCode()
throws
{
try
{
return ((Integer)this.h.invoke(this, m0, null)).intValue();
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
public final String toString()
throws
{
try
{
return (String)this.h.invoke(this, m2, null);
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
static
{
try
{
m3 = Class.forName("java.lang.Comparable").getMethod("compareTo", new Class[] { Class.forName("java.lang.Object") });
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]);
m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
return;
}
catch (NoSuchMethodException localNoSuchMethodException)
{
throw new NoSuchMethodError(localNoSuchMethodException.getMessage());
}
catch (ClassNotFoundException localClassNotFoundException)
{
throw new NoClassDefFoundError(localClassNotFoundException.getMessage());
}
}
}