代理:为其他对象提供一个代理以控制对某个对象的访问。
静态代理
- 接口
public interface IDoSomething {
public int doSometing(int num);
}
- 被代理类的实现
public class Sing implements IDoSomething {
@Override
public int doSometing(int num) {
System.out.println("Sing a song");
return num;
}
}
- 代理类的实现
public class SingProxy implements IDoSomething{
private IDoSomething sing = new Sing();
@Override
public int doSometing(int num) {
System.out.println("Befor singing ");
int result = sing.doSometing(num);
System.out.println("After singing");
return result;
}
}
- 测试类
public class ProxyDemo {
public static int sing(IDoSomething sing, int num) {
return sing.doSometing(num);
}
public static void main(String[] args) {
System.out.println(ProxyDemo.sing(new SingProxy(), 5));
}
}
- 输出结果
Befor singing
Sing a song
After singing
5
动态代理
Java的动态代理可以动态的创建代理并动态的处理对所代理方法的调用。动态代理有两种实现方法,一种是使用JDK自带的,一种是使用Cglib实现。
实现JDK自带的动态代理
实现JDK自带的动态代理,关键是实现InvocationHandler,同时它要求被代理对象必须有接口。
- 接口
public interface IProxyClass {
public int doSomething(int i);
}
- 被代理类的实现
public class ProxyClassImpl implements IProxyClass {
@Override
public int doSomething(int num) {
System.out.println("方法执行中.....");
return num;
}
}
- 实现InvocationHandler接口 实现InvocationHandler接口,并手动生成了代理类,保存到了电脑上
public class DynamicProxyHandler implements InvocationHandler {
private Object proxied;
/**
* @param proxied 被代理对象
*/
public DynamicProxyHandler(Object proxied) {
this.proxied = proxied;
}
/**
* 返回代理对象
* @return
*/
public Object newProxyInstance() {
return Proxy.newProxyInstance(proxied.getClass().getClassLoader(), proxied.getClass().getInterfaces(), this);
}
/**
*
* @param proxy 代理对象
* @param method 代理方法
* @param args 方法参数
* @return
* @throws Throwable
*/
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
//将代理对象生成字节码到F盘上,方便反编译出java文件查看,实际动态代理是不需要自己生成的
addClassToDisk(proxy.getClass().getName(), ProxyClassImpl.class,"F:/$Proxy0.class");
System.out.println("method:"+method.getName());
System.out.println("args:"+args[0].getClass().getName());
System.out.println("Before invoke method...");
Object object=method.invoke(proxied, args);
System.out.println("After invoke method...");
return object;
}
/**
* 用于生产代理对象的字节码,并将其保存到硬盘上
* @param className
* @param cl
* @param path
*/
private void addClassToDisk(String className, Class<?> cl, String path) {
//用于生产代理对象的字节码
byte[] classFile = ProxyGenerator.generateProxyClass(className, cl.getInterfaces());
FileOutputStream out = null;
try {
out = new FileOutputStream(path);
//将代理对象的class字节码写到硬盘上
out.write(classFile);
out.flush();
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
out.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
- 测试类
public class SimpleProxyDemo {
public static void main(String[] args) throws SecurityException, NoSuchMethodException {
ProxyClassImpl c = new ProxyClassImpl();
DynamicProxyHandler proxyHandler = new DynamicProxyHandler(c);
IProxyClass proxyClass = (IProxyClass)proxyHandler.newProxyInstance();
System.out.println(proxyClass.getClass().getName());
System.out.println(proxyClass.doSomething(5));
}
}
- 输出结果
com.sun.proxy.$Proxy0
method:doSomething
args:java.lang.Integer
Before invoke method...
方法执行中.....
After invoke method...
5
从结果我们可以看到(IProxyClass)proxyHandler.newProxyInstance();实际返回的是com.sun.proxy.Proxy0.class文件,使用jad.exe进行反编译。
jad -p java $Proxy0.class
public final class $Proxy0 extends Proxy
implements IProxyClass
{
public $Proxy0(InvocationHandler invocationhandler)
{
super(invocationhandler);
}
public final boolean equals(Object obj)
{
try
{
return ((Boolean)super.h.invoke(this, m1, new Object[] {
obj
})).booleanValue();
}
catch(Error _ex) { }
catch(Throwable throwable)
{
throw new UndeclaredThrowableException(throwable);
}
}
public final void doSomething(int i)
{
try
{
super.h.invoke(this, m3, new Object[] {
Integer.valueOf(i)
});
return;
}
catch(Error _ex) { }
catch(Throwable throwable)
{
throw new UndeclaredThrowableException(throwable);
}
}
public final int hashCode()
{
try
{
return ((Integer)super.h.invoke(this, m0, null)).intValue();
}
catch(Error _ex) { }
catch(Throwable throwable)
{
throw new UndeclaredThrowableException(throwable);
}
}
public final String toString()
{
try
{
return (String)super.h.invoke(this, m2, null);
}
catch(Error _ex) { }
catch(Throwable throwable)
{
throw new UndeclaredThrowableException(throwable);
}
}
private static Method m1;
private static Method m3;
private static Method m0;
private static Method m2;
static
{
try
{
m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[] {
Class.forName("java.lang.Object")
});
m3 = Class.forName("io.github.brightloong.proxy.IProxyClass").getMethod("doSomething", new Class[] {
Integer.TYPE
});
m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);
m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
}
catch(NoSuchMethodException nosuchmethodexception)
{
throw new NoSuchMethodError(nosuchmethodexception.getMessage());
}
catch(ClassNotFoundException classnotfoundexception)
{
throw new NoClassDefFoundError(classnotfoundexception.getMessage());
}
}
}
InvocationHandler的invoke方法是由谁来调用的,生成的代理对象在调用doSomething方法时,会调用通过反射获取的doSomething方法,进而调用了InvocationHandler的invoke方法。
JDK是怎样生成代理对象的。生成代理对象是用的Proxy类的静态方newProxyInstance。
/**
* loader:类加载器
* interfaces:目标对象实现的接口
* h:InvocationHandler的实现类
*/
public static Object newProxyInstance(ClassLoader loader,
Class<?>[] interfaces,
InvocationHandler h)
throws IllegalArgumentException
{
if (h == null) {
throw new NullPointerException();
}
/*
* Look up or generate the designated proxy class.
*/
Class cl = getProxyClass(loader, interfaces);
/*
* Invoke its constructor with the designated invocation handler.
*/
try {
// 调用代理对象的构造方法(也就是$Proxy0(InvocationHandler h))
Constructor cons = cl.getConstructor(constructorParams);
// 生成代理类的实例并把DynamicProxyHandler的实例传给它的构造方法
return (Object) cons.newInstance(new Object[] { h });
} catch (NoSuchMethodException e) {
throw new InternalError(e.toString());
} catch (IllegalAccessException e) {
throw new InternalError(e.toString());
} catch (InstantiationException e) {
throw new InternalError(e.toString());
} catch (InvocationTargetException e) {
throw new InternalError(e.toString());
}
}
public static Class<?> getProxyClass(ClassLoader loader,
Class<?>... interfaces)
throws IllegalArgumentException
{
// 如果目标类实现的接口数大于65535个则抛出异常(我XX,谁会写这么NB的代码啊?)
if (interfaces.length > 65535) {
throw new IllegalArgumentException("interface limit exceeded");
}
// 声明代理对象所代表的Class对象(有点拗口)
Class proxyClass = null;
String[] interfaceNames = new String[interfaces.length];
Set interfaceSet = new HashSet(); // for detecting duplicates
// 遍历目标类所实现的接口
for (int i = 0; i < interfaces.length; i++) {
// 拿到目标类实现的接口的名称
String interfaceName = interfaces[i].getName();
Class interfaceClass = null;
try {
// 加载目标类实现的接口到内存中
interfaceClass = Class.forName(interfaceName, false, loader);
} catch (ClassNotFoundException e) {
}
if (interfaceClass != interfaces[i]) {
throw new IllegalArgumentException(
interfaces[i] + " is not visible from class loader");
}
// 中间省略了一些无关紧要的代码 .......
// 把目标类实现的接口代表的Class对象放到Set中
interfaceSet.add(interfaceClass);
interfaceNames[i] = interfaceName;
}
// 把目标类实现的接口名称作为缓存(Map)中的key
Object key = Arrays.asList(interfaceNames);
Map cache;
synchronized (loaderToCache) {
// 从缓存中获取cache
cache = (Map) loaderToCache.get(loader);
if (cache == null) {
// 如果获取不到,则新建地个HashMap实例
cache = new HashMap();
// 把HashMap实例和当前加载器放到缓存中
loaderToCache.put(loader, cache);
}
}
synchronized (cache) {
do {
// 根据接口的名称从缓存中获取对象
Object value = cache.get(key);
if (value instanceof Reference) {
proxyClass = (Class) ((Reference) value).get();
}
if (proxyClass != null) {
// 如果代理对象的Class实例已经存在,则直接返回
return proxyClass;
} else if (value == pendingGenerationMarker) {
try {
cache.wait();
} catch (InterruptedException e) {
}
continue;
} else {
cache.put(key, pendingGenerationMarker);
break;
}
} while (true);
}
try {
// 中间省略了一些代码 .......
// 这里就是动态生成代理对象的最关键的地方
byte[] proxyClassFile = ProxyGenerator.generateProxyClass(
proxyName, interfaces);
try {
// 根据代理类的字节码生成代理类的实例
proxyClass = defineClass0(loader, proxyName,
proxyClassFile, 0, proxyClassFile.length);
} catch (ClassFormatError e) {
throw new IllegalArgumentException(e.toString());
}
}
// add to set of all generated proxy classes, for isProxyClass
proxyClasses.put(proxyClass, null);
}
// 中间省略了一些代码 .......
return proxyClass;
}
public static byte[] generateProxyClass(final String name,
Class[] interfaces)
{
ProxyGenerator gen = new ProxyGenerator(name, interfaces);
// 这里动态生成代理类的字节码,由于比较复杂就不进去看了
final byte[] classFile = gen.generateClassFile();
// 如果saveGeneratedFiles的值为true,则会把所生成的代理类的字节码保存到硬盘上
if (saveGeneratedFiles) {
java.security.AccessController.doPrivileged(
new java.security.PrivilegedAction<Void>() {
public Void run() {
try {
FileOutputStream file =
new FileOutputStream(dotToSlash(name) + ".class");
file.write(classFile);
file.close();
return null;
} catch (IOException e) {
throw new InternalError(
"I/O exception saving generated file: " + e);
}
}
});
}
// 返回代理类的字节码
return classFile;
}
使用Cglib实现动态代理
- 实现MethodInterceptor接口
public class CglibProxy implements MethodInterceptor{
private Enhancer enhancer = new Enhancer();
@Override
/**
*
* @param o 是被代理对象
* @param method 调用方法的Method对象
* @param args 方法参数
* @param methodProxy
* @return cglib生成用来代替Method对象的一个对象,使用MethodProxy比调用JDK自身的Method直接执行方法效率会有提升
* @throws Throwable
*/
public Object intercept(Object o, Method method, Object[] args,
MethodProxy methodProxy) throws Throwable {
System.out.println("before " + methodProxy.getSuperName());
System.out.println(method.getName());
Object o1 = methodProxy.invokeSuper(o, args);
//Object o2 = method.invoke(o, args); 使用这种方式会发生死循环,因为方法会被拦截
System.out.println("after " + methodProxy.getSuperName());
return o1;
}
public Object newProxyInstance(Class<?> c) {
//设置产生的代理对象的父类。
enhancer.setSuperclass(c);
//设置CallBack接口的实例
enhancer.setCallback(this);
//使用默认无参数的构造函数创建目标对象
return enhancer.create();
}
}
- 被代理对象和测试类
public class CglibDemo {
public static void main(String[] args) {
CglibProxy cglibProxy = new CglibProxy();
Do o = (Do)cglibProxy.newProxyInstance(Do.class);
System.out.println(o.doSomething(5));
}
}
class Do{
public int doSomething(int num){
System.out.println("方法执行中。。。。。。");
return num;
}
}
- 输出结果
before CGLIB$doSomething$0
doSomething
方法执行中。。。。。。
after CGLIB$doSomething$0
5