cglib的使用與解析
上一篇講解了java原生的動態(tài)代理的使用和部分原理，除了原生的動態(tài)代理很多java框架中使用了cglib來做動態(tài)代理算谈，so今天準(zhǔn)備寫一些cglib的使用與解析。
基本使用規(guī)則
共需要3個類（比jdk原生少了一個翼岁，因?yàn)楸淮眍惒恍枰獙?shí)現(xiàn)接口）,還是分三步走：
- 一個代理類
public class Car {
public void run() {
System.out.println("car run");
}
}
- 一個自定義的MethodInterceptor
public class MyMethodInterceptor implements MethodInterceptor {
public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
System.out.println("before");
Object result = proxy.invokeSuper(obj,args);
System.out.println("after");
return result;
}
}
- 最后一個測試main函數(shù)
public class Demo {
public static void main(String[] args) {
MyMethodInterceptor interceptor = new MyMethodInterceptor();
Enhancer e = new Enhancer();
e.setSuperclass(Car.class);
e.setCallback(interceptor);
Car car = (Car) e.create();
car.run();
}
}
- 運(yùn)行結(jié)果
before
car run
after
Process finished with exit code 0
一些細(xì)節(jié)
和jdk原生的代理一樣我也想通過閱讀源碼來找到是否能把cglib生成的class文件存到本地按灶。但是明顯cglib的源碼邏輯更為復(fù)雜，我沒有在短時間內(nèi)找到罗晕，所以我查了網(wǎng)上其他人的資料的知道了需要設(shè)置cglib生成class文件的目錄，就像這樣：System.setProperty(DebuggingClassWriter.DEBUG_LOCATION_PROPERTY,"E:\\cglib");,實(shí)際上得到源class文件后的我也是一臉懵逼赠堵，因?yàn)樗恢挂粋€小渊。事實(shí)上一共生成了5個：
screenshot.png
因?yàn)槲业臏y試demo都放在sampes下而且通過類名可以知道 sampes下三個生成的class大概和我的Car被代理類關(guān)聯(lián)比較大。但這也只是猜想茫叭，要搞清楚這五個類分別起的什么左右酬屉，帶著這個問題去看源碼可能更好。
現(xiàn)在我分別把上面的五個class文件稱為class1,class2,...,class5,
首先我通過斷點(diǎn)看到e.create()得到的類是class4
image.png
而class4反編譯后是這樣的：
//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//
package net.sf.cglib.samples;
import java.lang.reflect.Method;
import net.sf.cglib.core.ReflectUtils;
import net.sf.cglib.core.Signature;
import net.sf.cglib.proxy.Callback;
import net.sf.cglib.proxy.Factory;
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;
public class Car$$EnhancerByCGLIB$$bbb4952c extends Car implements Factory {
private boolean CGLIB$BOUND;
public static Object CGLIB$FACTORY_DATA;
private static final ThreadLocal CGLIB$THREAD_CALLBACKS;
private static final Callback[] CGLIB$STATIC_CALLBACKS;
private MethodInterceptor CGLIB$CALLBACK_0;
private static Object CGLIB$CALLBACK_FILTER;
private static final Method CGLIB$run$0$Method;
private static final MethodProxy CGLIB$run$0$Proxy;
private static final Object[] CGLIB$emptyArgs;
private static final Method CGLIB$equals$1$Method;
private static final MethodProxy CGLIB$equals$1$Proxy;
private static final Method CGLIB$toString$2$Method;
private static final MethodProxy CGLIB$toString$2$Proxy;
private static final Method CGLIB$hashCode$3$Method;
private static final MethodProxy CGLIB$hashCode$3$Proxy;
private static final Method CGLIB$clone$4$Method;
private static final MethodProxy CGLIB$clone$4$Proxy;
static void CGLIB$STATICHOOK1() {
CGLIB$THREAD_CALLBACKS = new ThreadLocal();
CGLIB$emptyArgs = new Object[0];
Class var0 = Class.forName("net.sf.cglib.samples.Car$$EnhancerByCGLIB$$bbb4952c");
Class var1;
Method[] var10000 = ReflectUtils.findMethods(new String[]{"equals", "(Ljava/lang/Object;)Z", "toString", "()Ljava/lang/String;", "hashCode", "()I", "clone", "()Ljava/lang/Object;"}, (var1 = Class.forName("java.lang.Object")).getDeclaredMethods());
CGLIB$equals$1$Method = var10000[0];
CGLIB$equals$1$Proxy = MethodProxy.create(var1, var0, "(Ljava/lang/Object;)Z", "equals", "CGLIB$equals$1");
CGLIB$toString$2$Method = var10000[1];
CGLIB$toString$2$Proxy = MethodProxy.create(var1, var0, "()Ljava/lang/String;", "toString", "CGLIB$toString$2");
CGLIB$hashCode$3$Method = var10000[2];
CGLIB$hashCode$3$Proxy = MethodProxy.create(var1, var0, "()I", "hashCode", "CGLIB$hashCode$3");
CGLIB$clone$4$Method = var10000[3];
CGLIB$clone$4$Proxy = MethodProxy.create(var1, var0, "()Ljava/lang/Object;", "clone", "CGLIB$clone$4");
CGLIB$run$0$Method = ReflectUtils.findMethods(new String[]{"run", "()V"}, (var1 = Class.forName("net.sf.cglib.samples.Car")).getDeclaredMethods())[0];
CGLIB$run$0$Proxy = MethodProxy.create(var1, var0, "()V", "run", "CGLIB$run$0");
}
final void CGLIB$run$0() {
super.run();
}
public final void run() {
MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
if (this.CGLIB$CALLBACK_0 == null) {
CGLIB$BIND_CALLBACKS(this);
var10000 = this.CGLIB$CALLBACK_0;
}
if (var10000 != null) {
var10000.intercept(this, CGLIB$run$0$Method, CGLIB$emptyArgs, CGLIB$run$0$Proxy);
} else {
super.run();
}
}
final boolean CGLIB$equals$1(Object var1) {
return super.equals(var1);
}
public final boolean equals(Object var1) {
MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
if (this.CGLIB$CALLBACK_0 == null) {
CGLIB$BIND_CALLBACKS(this);
var10000 = this.CGLIB$CALLBACK_0;
}
if (var10000 != null) {
Object var2 = var10000.intercept(this, CGLIB$equals$1$Method, new Object[]{var1}, CGLIB$equals$1$Proxy);
return var2 == null ? false : (Boolean)var2;
} else {
return super.equals(var1);
}
}
final String CGLIB$toString$2() {
return super.toString();
}
public final String toString() {
MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
if (this.CGLIB$CALLBACK_0 == null) {
CGLIB$BIND_CALLBACKS(this);
var10000 = this.CGLIB$CALLBACK_0;
}
return var10000 != null ? (String)var10000.intercept(this, CGLIB$toString$2$Method, CGLIB$emptyArgs, CGLIB$toString$2$Proxy) : super.toString();
}
final int CGLIB$hashCode$3() {
return super.hashCode();
}
public final int hashCode() {
MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
if (this.CGLIB$CALLBACK_0 == null) {
CGLIB$BIND_CALLBACKS(this);
var10000 = this.CGLIB$CALLBACK_0;
}
if (var10000 != null) {
Object var1 = var10000.intercept(this, CGLIB$hashCode$3$Method, CGLIB$emptyArgs, CGLIB$hashCode$3$Proxy);
return var1 == null ? 0 : ((Number)var1).intValue();
} else {
return super.hashCode();
}
}
final Object CGLIB$clone$4() throws CloneNotSupportedException {
return super.clone();
}
protected final Object clone() throws CloneNotSupportedException {
MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
if (this.CGLIB$CALLBACK_0 == null) {
CGLIB$BIND_CALLBACKS(this);
var10000 = this.CGLIB$CALLBACK_0;
}
return var10000 != null ? var10000.intercept(this, CGLIB$clone$4$Method, CGLIB$emptyArgs, CGLIB$clone$4$Proxy) : super.clone();
}
public static MethodProxy CGLIB$findMethodProxy(Signature var0) {
String var10000 = var0.toString();
switch(var10000.hashCode()) {
case -919875318:
if (var10000.equals("run()V")) {
return CGLIB$run$0$Proxy;
}
break;
case -508378822:
if (var10000.equals("clone()Ljava/lang/Object;")) {
return CGLIB$clone$4$Proxy;
}
break;
case 1826985398:
if (var10000.equals("equals(Ljava/lang/Object;)Z")) {
return CGLIB$equals$1$Proxy;
}
break;
case 1913648695:
if (var10000.equals("toString()Ljava/lang/String;")) {
return CGLIB$toString$2$Proxy;
}
break;
case 1984935277:
if (var10000.equals("hashCode()I")) {
return CGLIB$hashCode$3$Proxy;
}
}
return null;
}
public Car$$EnhancerByCGLIB$$bbb4952c() {
CGLIB$BIND_CALLBACKS(this);
}
public static void CGLIB$SET_THREAD_CALLBACKS(Callback[] var0) {
CGLIB$THREAD_CALLBACKS.set(var0);
}
public static void CGLIB$SET_STATIC_CALLBACKS(Callback[] var0) {
CGLIB$STATIC_CALLBACKS = var0;
}
private static final void CGLIB$BIND_CALLBACKS(Object var0) {
Car$$EnhancerByCGLIB$$bbb4952c var1 = (Car$$EnhancerByCGLIB$$bbb4952c)var0;
if (!var1.CGLIB$BOUND) {
var1.CGLIB$BOUND = true;
Object var10000 = CGLIB$THREAD_CALLBACKS.get();
if (var10000 == null) {
var10000 = CGLIB$STATIC_CALLBACKS;
if (CGLIB$STATIC_CALLBACKS == null) {
return;
}
}
var1.CGLIB$CALLBACK_0 = (MethodInterceptor)((Callback[])var10000)[0];
}
}
public Object newInstance(Callback[] var1) {
CGLIB$SET_THREAD_CALLBACKS(var1);
Car$$EnhancerByCGLIB$$bbb4952c var10000 = new Car$$EnhancerByCGLIB$$bbb4952c();
CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
return var10000;
}
public Object newInstance(Callback var1) {
CGLIB$SET_THREAD_CALLBACKS(new Callback[]{var1});
Car$$EnhancerByCGLIB$$bbb4952c var10000 = new Car$$EnhancerByCGLIB$$bbb4952c();
CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
return var10000;
}
public Object newInstance(Class[] var1, Object[] var2, Callback[] var3) {
CGLIB$SET_THREAD_CALLBACKS(var3);
Car$$EnhancerByCGLIB$$bbb4952c var10000 = new Car$$EnhancerByCGLIB$$bbb4952c;
switch(var1.length) {
case 0:
var10000.<init>();
CGLIB$SET_THREAD_CALLBACKS((Callback[])null);
return var10000;
default:
throw new IllegalArgumentException("Constructor not found");
}
}
public Callback getCallback(int var1) {
CGLIB$BIND_CALLBACKS(this);
MethodInterceptor var10000;
switch(var1) {
case 0:
var10000 = this.CGLIB$CALLBACK_0;
break;
default:
var10000 = null;
}
return var10000;
}
public void setCallback(int var1, Callback var2) {
switch(var1) {
case 0:
this.CGLIB$CALLBACK_0 = (MethodInterceptor)var2;
default:
}
}
public Callback[] getCallbacks() {
CGLIB$BIND_CALLBACKS(this);
return new Callback[]{this.CGLIB$CALLBACK_0};
}
public void setCallbacks(Callback[] var1) {
this.CGLIB$CALLBACK_0 = (MethodInterceptor)var1[0];
}
static {
CGLIB$STATICHOOK1();
}
}
只看run()方法的話邏輯并不復(fù)雜呐萨，最終會走到var10000.intercept(this, CGLIB$run$0$Method, CGLIB$emptyArgs, CGLIB$run$0$Proxy);也就是我自己實(shí)現(xiàn)的MyMethodInterceptor的intercept方法中。
剩余的一些東西其實(shí)通過看了源碼也才理解了1/3了更沒法通過語言很好的表述吗垮，所以就這次先鴿了垛吗。希望之后能結(jié)合別人和自己的看法再寫一篇。
一個坑
最后再講一下我在寫demo調(diào)試的時候遇到的一個坑吧
我是這樣寫的demo：
public class MyMethodInterceptor implements MethodInterceptor {
public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
System.out.println("before");
Object result = proxy.invokeSuper(obj, args);
System.out.println("method:" + method);
System.out.println("obj:" + obj);
System.out.println("after");
return result;
}
}
這里主要是 System.out.println("obj:" + obj);這句話有問題 烁登，因?yàn)檫@樣會調(diào)用obj的hashcode方法怯屉，而這個obj就是代理類蔚舀，代理類的hashcode方法會繼續(xù)調(diào)用MyMethodInterceptor.intercept，這樣形成了死循環(huán)锨络，最終stackoverflow赌躺。
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