Java动态代理
最近在看spring的aop源码时，用到了动态代理模式，仅记录用于方便理解动态代理。
先上代码
1.接口类
package com.cx.proxy;
/**
* Created by cumt_cx on 2017/1/3.
*/
public interface HelloWorld {
void SaySomeThing(String someThing);
}
2.实现类
package com.cx.proxy;
/**
* Created by cumt_cx on 2017/1/3.
*/
public class HelloWorldImpl implements HelloWorld {
@Override public void SaySomeThing(String someThing) {
System.out.println("Yes You Do ["+someThing+"]");
}
}
package com.cx.proxy;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
/**
* Created by cumt_cx on 2017/1/3.
*/
public class MyInvocationHandler implements InvocationHandler {
private Object target;
public MyInvocationHandler(Object obj) {
this.target = obj;
}
@Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
System.out.println("method :"+method.getName()+" is invoked");
return method.invoke(target,args);
}
}
package com.cx.proxy;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Proxy;
/**
* Created by cumt_cx on 2017/1/3.
*/
public class ProxyDemo {
public static void main(String args[]) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException, InstantiationException {
//one way
Class proxyClass = Proxy.getProxyClass(ProxyDemo.class.getClassLoader(), HelloWorld.class);
final Constructor cons = proxyClass.getConstructor(InvocationHandler.class);
final InvocationHandler ih = new MyInvocationHandler(new HelloWorldImpl());
HelloWorld helloWorld = (HelloWorld) cons.newInstance(ih);
helloWorld.SaySomeThing("This is invoke,I am Coding");
//other way
HelloWorld helloWorld1 = (HelloWorld) Proxy
.newProxyInstance(ProxyDemo.class.getClassLoader(), new Class[] { HelloWorld.class }, new MyInvocationHandler
(new HelloWorldImpl()));
helloWorld1.SaySomeThing("This is invoke,Another Way ，I am Coding Too ");
}
}
JDK中具体的动态代理类是怎么产生
代理生成过程主要分为2步
-
- 代理类字节码生成
- 把字节码通过传入的类加载器加载到虚拟机中
具体细分则如下
获取动态代理类通过
Proxy类的getProxyClass方法
@CallerSensitive
public static Class getProxyClass(ClassLoader loader,
Class... interfaces)
throws IllegalArgumentException
{
final Class[] intfs = interfaces.clone();
final SecurityManager sm = System.getSecurityManager();
if (sm != null) {
checkProxyAccess(Reflection.getCallerClass(), loader, intfs);
}
return getProxyClass0(loader, intfs);代码直观的看到通过调用getProxyClass0方法
/**
* Generate a proxy class. Must call the checkProxyAccess method
* to perform permission checks before calling this.
*/
private static Class getProxyClass0(ClassLoader loader,
Class... interfaces) {
if (interfaces.length > 65535) {
throw new IllegalArgumentException("interface limit exceeded");
}
// If the proxy class defined by the given loader implementing
// the given interfaces exists, this will simply return the cached copy;
// otherwise, it will create the proxy class via the ProxyClassFactory
return proxyClassCache.get(loader, interfaces);
}
/**
* a cache of proxy classes
*/
private static final WeakCache[], Class>
proxyClassCache = new WeakCache<>(new KeyFactory(), new ProxyClassFactory());
/**
* A factory function that generates, defines and returns the proxy class given
* the ClassLoader and array of interfaces.
*/
private static final class ProxyClassFactory
implements BiFunction[], Class>
{
// prefix for all proxy class names
private static final String proxyClassNamePrefix = "$Proxy";
// next number to use for generation of unique proxy class names
private static final AtomicLong nextUniqueNumber = new AtomicLong();
@Override
public Class apply(ClassLoader loader, Class[] interfaces) {
Map, Boolean> interfaceSet = new IdentityHashMap<>(interfaces.length);
for (Class intf : interfaces) {
/*
* Verify that the class loader resolves the name of this
* interface to the same Class object.
*/
Class interfaceClass = null;
try {
interfaceClass = Class.forName(intf.getName(), false, loader);
} catch (ClassNotFoundException e) {
}
if (interfaceClass != intf) {
throw new IllegalArgumentException(
intf + " 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.put(interfaceClass, Boolean.TRUE) != null) {
throw new IllegalArgumentException(
"repeated interface: " + interfaceClass.getName());
}
}
String proxyPkg = null; // package to define proxy class in
int accessFlags = Modifier.PUBLIC | Modifier.FINAL;
/*
* Record the package of a non-public proxy interface so that the
* proxy class will be defined in the same package. Verify that
* all non-public proxy interfaces are in the same package.
*/
for (Class intf : interfaces) {
int flags = intf.getModifiers();
if (!Modifier.isPublic(flags)) {
accessFlags = Modifier.FINAL;
String name = intf.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 + ".";
}
/*
* Choose a name for the proxy class to generate.
*/
long num = nextUniqueNumber.getAndIncrement();
String proxyName = proxyPkg + proxyClassNamePrefix + num;
/*
* Generate the specified proxy class.
*/
byte[] proxyClassFile = ProxyGenerator.generateProxyClass(
proxyName, interfaces, accessFlags);
try {
return defineClass0(loader, proxyName,
proxyClassFile, 0, proxyClassFile.length);
} catch (ClassFormatError e) {
/*
* A ClassFormatError here means that (barring bugs in the
* proxy class generation code) there was some other
* invalid aspect of the arguments supplied to the proxy
* class creation (such as virtual machine limitations
* exceeded).
*/
throw new IllegalArgumentException(e.toString());
}
}
}
最后把字节码通过传入的类加载器加载到JVM中: defineClass0(loader, proxyName,proxyClassFile, 0, proxyClassFile.length);
至此，已经生成了动态代理类，具体每个代理方法：逻辑都差不多就是 h.invoke，主要是调用我们定义好的invocatinoHandler逻辑,触发目标对象target上对应的方法;