生成增强字节码的测试工具
测试代码
1.类的完整生命周期
Java动态代理包括两个关键步骤：
- 在内存中生成字节码，并进行字节码增强
- 根据生成字节码Class对象，利用反射实例化对象
Girl mother = (Girl) family.getProxyInstance();
public Object getProxyInstance(){
return Proxy.newProxyInstance(girl.getClass().getClassLoader(), girl.getClass().getInterfaces(), this);
}
@CallerSensitive
public static Object newProxyInstance(ClassLoader loader,
Class[] interfaces,
InvocationHandler h) {
Objects.requireNonNull(h);
final Class caller = System.getSecurityManager() == null
? null
: Reflection.getCallerClass();
/*
* Look up or generate the designated proxy class and its constructor.
*/
Constructor cons = getProxyConstructor(caller, loader, interfaces);
return newProxyInstance(caller, cons, h);
}
2.内存生成增强字节码getProxyConstructor
Constructor cons = getProxyConstructor(caller, loader, interfaces);
private static Constructor getProxyConstructor(Class caller,
ClassLoader loader,
Class... interfaces)
{
// optimization for single interface
if (interfaces.length == 1) {
Class intf = interfaces[0];
if (caller != null) {
checkProxyAccess(caller, loader, intf);
}
return proxyCache.sub(intf).computeIfAbsent(
loader,
(ld, clv) -> new ProxyBuilder(ld, clv.key()).build()
);
} else {
// interfaces cloned
final Class[] intfsArray = interfaces.clone();
if (caller != null) {
checkProxyAccess(caller, loader, intfsArray);
}
final List> intfs = Arrays.asList(intfsArray);
return proxyCache.sub(intfs).computeIfAbsent(
loader,
(ld, clv) -> new ProxyBuilder(ld, clv.key()).build()
);
}
}
Constructor build() {
Class proxyClass = defineProxyClass(module, interfaces);
final Constructor cons;
try {
cons = proxyClass.getConstructor(constructorParams);
} catch (NoSuchMethodException e) {
throw new InternalError(e.toString(), e);
}
AccessController.doPrivileged(new PrivilegedAction() {
public Void run() {
cons.setAccessible(true);
return null;
}
});
return cons;
}
其中核心的defineProxyClass如下：
private static Class defineProxyClass(Module m, List> interfaces) {
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; // non-public, final
String pkg = intf.getPackageName();
if (proxyPkg == null) {
proxyPkg = pkg;
} else if (!pkg.equals(proxyPkg)) {
throw new IllegalArgumentException(
"non-public interfaces from different packages");
}
}
}
if (proxyPkg == null) {
// all proxy interfaces are public
proxyPkg = m.isNamed() ? PROXY_PACKAGE_PREFIX + "." + m.getName()
: PROXY_PACKAGE_PREFIX;
} else if (proxyPkg.isEmpty() && m.isNamed()) {
throw new IllegalArgumentException(
"Unnamed package cannot be added to " + m);
}
if (m.isNamed()) {
if (!m.getDescriptor().packages().contains(proxyPkg)) {
throw new InternalError(proxyPkg + " not exist in " + m.getName());
}
}
/*
* Choose a name for the proxy class to generate.
*/
long num = nextUniqueNumber.getAndIncrement();
String proxyName = proxyPkg.isEmpty()
? proxyClassNamePrefix + num
: proxyPkg + "." + proxyClassNamePrefix + num;
ClassLoader loader = getLoader(m);
trace(proxyName, m, loader, interfaces);
/*
* Generate the specified proxy class.
*/
byte[] proxyClassFile = ProxyGenerator.generateProxyClass(
proxyName, interfaces.toArray(EMPTY_CLASS_ARRAY), accessFlags);
try {
Class pc = UNSAFE.defineClass(proxyName, proxyClassFile,
0, proxyClassFile.length,
loader, null);
reverseProxyCache.sub(pc).putIfAbsent(loader, Boolean.TRUE);
return pc;
} 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());
}
}
生成class字节码的方法generateProxyClass，此时生成了一个代理的Class对象：
static byte[] generateProxyClass(final String name,
Class[] interfaces,
int accessFlags)
{
ProxyGenerator gen = new ProxyGenerator(name, interfaces, accessFlags);
final byte[] classFile = gen.generateClassFile();
if (saveGeneratedFiles) {
java.security.AccessController.doPrivileged(
new java.security.PrivilegedAction() {
public Void run() {
try {
int i = name.lastIndexOf('.');
Path path;
if (i > 0) {
Path dir = Paths.get(name.substring(0, i).replace('.', File.separatorChar));
Files.createDirectories(dir);
path = dir.resolve(name.substring(i+1, name.length()) + ".class");
} else {
path = Paths.get(name + ".class");
}
Files.write(path, classFile);
return null;
} catch (IOException e) {
throw new InternalError(
"I/O exception saving generated file: " + e);
}
}
});
}
return classFile;
}
加载class字节码的核心方法defineClass：
public Class defineClass(String name, byte[] b, int off, int len,
ClassLoader loader,
ProtectionDomain protectionDomain) {
if (b == null) {
throw new NullPointerException();
}
if (len < 0) {
throw new ArrayIndexOutOfBoundsException();
}
return defineClass0(name, b, off, len, loader, protectionDomain);
}
3.反射实例化对象newProxyInstance
return newProxyInstance(caller, cons, h);
反射生成示例
private static Object newProxyInstance(Class caller, // null if no SecurityManager
Constructor cons,
InvocationHandler h) {
/*
* Invoke its constructor with the designated invocation handler.
*/
try {
if (caller != null) {
checkNewProxyPermission(caller, cons.getDeclaringClass());
}
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);
}
}
}
4.测试内存生成增强字节码
注意：
java.lang.reflect.ProxyGenerator is not public in java.lang.reflect package, Cannot be accessed from outside.
jdk1.10将ProxyGenerator从1.8的sum.misc放到了java.lang.reflect，并且不对外开放。
解决方法：使用openjdk，这里所有包都可以用！
将生成的字节码写到硬盘上：
public class ProxyUtil {
/*
* 将根据类信息 动态生成的二进制字节码保存到硬盘中， 默认的是clazz目录下 params :clazz 需要生成动态代理类的类
* proxyName : 为动态生成的代理类的名称
*/
public static void generateClassFile(Class clazz, String proxyName) {
// 根据类信息和提供的代理类名称，生成字节码
byte[] classFile = ProxyGenerator.generateProxyClass(proxyName,
new Class[]{clazz});
String paths = clazz.getResource(".").getPath();
System.out.println(paths);
FileOutputStream out = null;
try {
// 保留到硬盘中
out = new FileOutputStream(paths + proxyName + ".class");
out.write(classFile);
out.flush();
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
out.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
测试程序：
public class Lison {
public static void main(String[] args) {
//隔壁有个女孩，叫王美丽
Girl girl = new WangMeiLi();
//他有个庞大的家庭，想要跟她约会必须征得她家里人的同意
WangMeiLiProxy family = new WangMeiLiProxy(girl);
//有一次我去约王美丽，碰到了她的妈妈，我征得了她妈妈的同意
Girl mother = (Girl) family.getProxyInstance();
//通过她的妈妈这个代理才能与王美丽约会
mother.date();
//华丽分割线
System.out.println("-----------------------------------");
//通过她的妈妈这个代理才能与王美丽看电影
mother.watchMovie();
ProxyUtil.generateClassFile(Girl.class, mother.getClass().getName());
}
}
测试结果：
/E:/IdeaProjects/mybatisconfig/target/classes/com/enjoylearning/mybatis/proxy/
使用jd打开：
package com.sun.proxy;
import com.enjoylearning.mybatis.proxy.Girl;
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 Girl
{
private static Method m1;
private static Method m2;
private static Method m3;
private static Method m0;
private static Method m4;
public $Proxy0(InvocationHandler paramInvocationHandler)
{
super(paramInvocationHandler);
}
public final boolean equals(Object paramObject)
{
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 String toString()
{
try
{
return (String)this.h.invoke(this, m2, null);
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
public final void date()
{
try
{
this.h.invoke(this, m3, null);
return;
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
public final int hashCode()
{
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 void watchMovie()
{
try
{
this.h.invoke(this, m4, null);
return;
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
static
{
try
{
m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[] { Class.forName("java.lang.Object") });
m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
m3 = Class.forName("com.enjoylearning.mybatis.proxy.Girl").getMethod("date", new Class[0]);
m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);
m4 = Class.forName("com.enjoylearning.mybatis.proxy.Girl").getMethod("watchMovie", new Class[0]);
return;
}
catch (NoSuchMethodException localNoSuchMethodException)
{
throw new NoSuchMethodError(localNoSuchMethodException.getMessage());
}
catch (ClassNotFoundException localClassNotFoundException)
{
throw new NoClassDefFoundError(localClassNotFoundException.getMessage());
}
}
}
4.1 核心要点
1）继承父类Proxy，实现Girl
Proxy是所有动态代理的父类！
public final class $Proxy0
extends Proxy
implements Girl2）怎样进行增强（拦截）
public final void date()
{
try
{
this.h.invoke(this, m3, null);
return;
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
public final void watchMovie()
{
try
{
this.h.invoke(this, m4, null);
return;
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}
哪里来的h？查看Proxy源码：
public class Proxy implements java.io.Serializable {
/**
* the invocation handler for this proxy instance.
* @serial
*/
protected InvocationHandler h;
溯源：
WangMeiLiProxy family = new WangMeiLiProxy(girl);
//有一次我去约王美丽，碰到了她的妈妈，我征得了她妈妈的同意
Girl mother = (Girl) family.getProxyInstance();
public class WangMeiLiProxy implements InvocationHandler {
public Object getProxyInstance(){
return Proxy.newProxyInstance(girl.getClass().getClassLoader(), girl.getClass().getInterfaces(), this);
}
}
可知，这个h就是指代理对象WangMeiLiProxy，调用这个对象的方法进行增强：
public class WangMeiLiProxy implements InvocationHandler {
@Override
public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable {
doSomeThingBefore();
Object ret = method.invoke(girl, args);
doSomeThingEnd();
return ret;
}
参考
- 1）享学课堂Lison老师笔记