cglib学习笔记
cglib简介
cglib：Code Generation Library
主页：https://github.com/cglib/cglib/
教程：https://github.com/cglib/cglib/wiki/Tutorialcglib是java字节码生成和转换类库。它用于AOP，测试，数据访问框架，生成动态代理对象和拦截字段访问。
cglib基于ASM，通过ASM生成新的字节码。
cglib网络图片
cglib学习
Enhancer
字节码增强功能，主要用于生成新的class，spring的aop就会使用cglib生成代理类。
通过设置Enhancer属性，然后通过Enhancer#create生成新的增强类。
通过设置cglib.debugLocation可以指定生成class dump存放路径，通过查看生成的class更方便学习。
System.setProperty("cglib.debugLocation", "/Users/qiyan/cglib/classes");
首先来一个简单的POJO做为例子：
public class SampleClass {
public String test(String input) {
return "Hello world!";
}
}
Enhancer使用说明：
Enhancer enhancer = new Enhancer();
//设置Enhancer属性
enhancer.create();//创建增强类
Enhancer属性说明：
//增强类集成的接口列表
Class[] interfaces;
//父类
Class superclass;
//Callback选择器 返回值为callbacks的下标
CallbackFilter filter;
//回调处理器MethodInterceptor|NoOp|LazyLoader|Dispatcher|InvocationHandler|FixedValue的实现类
Callback[] callbacks;
//回调处理器类型MethodInterceptor|NoOp|LazyLoader|Dispatcher|InvocationHandler|FixedValue的Class
Type[] callbackTypes;
//是否使用工厂类
boolean useFactory = true;
//是否允许调用代理类构造器
boolean interceptDuringConstruction = true;
//是否校验回调类型
boolean validateCallbackTypes;
//是否仅创建代理类
boolean classOnly;
//是否仅创建工厂类
boolean factoryOnly;
//参数类型
Class[] argumentTypes;
//参数
Object[] arguments;
FixedValue
使用Enhancer生成代理类，callback设置为FixedValue。
使用FixedValue以后，所有接口都会返回固定值，test,toString,hashCode都会返回固定值，但是hashCode会因为数据转换抛出异常。
public static void testFixedValue() throws Exception {
Enhancer enhancer = new Enhancer();
enhancer.setSuperclass(SampleClass.class);
enhancer.setCallback(new FixedValue() {
@Override
public Object loadObject() throws Exception {
return "Hello cglib!";
}
});
SampleClass proxy = (SampleClass) enhancer.create();
System.out.println(proxy.test("1"));//输出结果Hello cglib!
System.out.println(proxy.toString());//输出结果Hello cglib!
System.out.println(proxy.hashCode());//异常（类型转换异常）
}
cglib会生成两个class，一个工厂类，一个代理类：
import net.sf.cglib.proxy.Callback;
import net.sf.cglib.proxy.Factory;
import net.sf.cglib.proxy.FixedValue;
public class SampleClass$$EnhancerByCGLIB$$9bebc1cf
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 FixedValue CGLIB$CALLBACK_0;
public static void CGLIB$SET_THREAD_CALLBACKS(Callback[] paramArrayOfCallback)
{
CGLIB$THREAD_CALLBACKS.set(paramArrayOfCallback);
}
public static void CGLIB$SET_STATIC_CALLBACKS(Callback[] paramArrayOfCallback)
{
CGLIB$STATIC_CALLBACKS = paramArrayOfCallback;
}
private static final void CGLIB$BIND_CALLBACKS(Object paramObject)
{
9bebc1cf local9bebc1cf = (9bebc1cf)paramObject;
if (!local9bebc1cf.CGLIB$BOUND)
{
local9bebc1cf.CGLIB$BOUND = true;
Object tmp23_20 = CGLIB$THREAD_CALLBACKS.get();
if (tmp23_20 == null)
{
tmp23_20;
CGLIB$STATIC_CALLBACKS;
}
local9bebc1cf.CGLIB$CALLBACK_0 = (tmp31_28 == null ? tmp31_28 : (FixedValue)((Callback[])tmp23_20)[0]);
}
}
public Object newInstance(Callback[] paramArrayOfCallback)
{
SampleClass..EnhancerByCGLIB..354348a.CGLIB$SET_THREAD_CALLBACKS(paramArrayOfCallback);
SampleClass..EnhancerByCGLIB..354348a.CGLIB$SET_THREAD_CALLBACKS(null);
return new SampleClass..EnhancerByCGLIB..354348a();
}
public Object newInstance(Callback paramCallback)
{
SampleClass..EnhancerByCGLIB..354348a.CGLIB$SET_THREAD_CALLBACKS(new Callback[] { paramCallback });
SampleClass..EnhancerByCGLIB..354348a.CGLIB$SET_THREAD_CALLBACKS(null);
return new SampleClass..EnhancerByCGLIB..354348a();
}
/* Error */
public Object newInstance(Class[] arg1, Object[] arg2, Callback[] arg3)
{
// Byte code:
// 0: aload_3
// 1: invokestatic 52 cglib/SampleClass$$EnhancerByCGLIB$$354348a:CGLIB$SET_THREAD_CALLBACKS ([Lnet/sf/cglib/proxy/Callback;)V
// 4: new 50 cglib/SampleClass$$EnhancerByCGLIB$$354348a
// 7: dup
// 8: aload_1
// 9: dup
// 10: arraylength
// 11: tableswitch default:+24->35, 0:+17->28
// 28: pop
// 29: invokespecial 53 cglib/SampleClass$$EnhancerByCGLIB$$354348a: ()V
// 32: goto +17 -> 49
// 35: goto +3 -> 38
// 38: pop
// 39: new 59 java/lang/IllegalArgumentException
// 42: dup
// 43: ldc 61
// 45: invokespecial 64 java/lang/IllegalArgumentException: (Ljava/lang/String;)V
// 48: athrow
// 49: aconst_null
// 50: invokestatic 52 cglib/SampleClass$$EnhancerByCGLIB$$354348a:CGLIB$SET_THREAD_CALLBACKS ([Lnet/sf/cglib/proxy/Callback;)V
// 53: areturn
}
public Callback getCallback(int paramInt)
{
CGLIB$BIND_CALLBACKS(this);
switch (paramInt)
{
case 0:
break;
}
return null;
}
public void setCallback(int paramInt, Callback paramCallback)
{
switch (paramInt)
{
case 0:
this.CGLIB$CALLBACK_0 = ((FixedValue)paramCallback);
break;
}
}
public Callback[] getCallbacks()
{
CGLIB$BIND_CALLBACKS(this);
return new Callback[] { this.CGLIB$CALLBACK_0 };
}
public void setCallbacks(Callback[] paramArrayOfCallback)
{
this.CGLIB$CALLBACK_0 = ((FixedValue)paramArrayOfCallback[0]);
}
}
cglib生成的代理类：
import net.sf.cglib.proxy.Callback;
import net.sf.cglib.proxy.Factory;
import net.sf.cglib.proxy.FixedValue;
public class SampleClass$$EnhancerByCGLIB$$354348a
extends SampleClass
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 FixedValue CGLIB$CALLBACK_0;
/* Error */
static void CGLIB$STATICHOOK1()
{
// Byte code:
// 0: new 21 java/lang/ThreadLocal
// 3: dup
// 4: invokespecial 24 java/lang/ThreadLocal: ()V
// 7: putstatic 26 cglib/SampleClass$$EnhancerByCGLIB$$354348a:CGLIB$THREAD_CALLBACKS Ljava/lang/ThreadLocal;
// 10: return
// 11: athrow
}
public final String test(String paramString)
{
FixedValue tmp4_1 = this.CGLIB$CALLBACK_0;
if (tmp4_1 == null)
{
tmp4_1;
CGLIB$BIND_CALLBACKS(this);
}
return (String)this.CGLIB$CALLBACK_0.loadObject();
}
public final boolean equals(Object paramObject)
{
FixedValue tmp4_1 = this.CGLIB$CALLBACK_0;
if (tmp4_1 == null)
{
tmp4_1;
CGLIB$BIND_CALLBACKS(this);
}
Object tmp22_17 = this.CGLIB$CALLBACK_0.loadObject();
tmp22_17;
return tmp22_17 == null ? false : ((Boolean)tmp22_17).booleanValue();
}
public final String toString()
{
FixedValue tmp4_1 = this.CGLIB$CALLBACK_0;
if (tmp4_1 == null)
{
tmp4_1;
CGLIB$BIND_CALLBACKS(this);
}
return (String)this.CGLIB$CALLBACK_0.loadObject();
}
public final int hashCode()
{
FixedValue tmp4_1 = this.CGLIB$CALLBACK_0;
if (tmp4_1 == null)
{
tmp4_1;
CGLIB$BIND_CALLBACKS(this);
}
Object tmp22_17 = this.CGLIB$CALLBACK_0.loadObject();
tmp22_17;
return tmp22_17 == null ? 0 : ((Number)tmp22_17).intValue();
}
protected final Object clone()
throws CloneNotSupportedException
{
FixedValue tmp4_1 = this.CGLIB$CALLBACK_0;
if (tmp4_1 == null)
{
tmp4_1;
CGLIB$BIND_CALLBACKS(this);
}
return this.CGLIB$CALLBACK_0.loadObject();
}
public SampleClass$$EnhancerByCGLIB$$354348a()
{
CGLIB$BIND_CALLBACKS(this);
}
public static void CGLIB$SET_THREAD_CALLBACKS(Callback[] paramArrayOfCallback)
{
CGLIB$THREAD_CALLBACKS.set(paramArrayOfCallback);
}
public static void CGLIB$SET_STATIC_CALLBACKS(Callback[] paramArrayOfCallback)
{
CGLIB$STATIC_CALLBACKS = paramArrayOfCallback;
}
private static final void CGLIB$BIND_CALLBACKS(Object paramObject)
{
354348a local354348a = (354348a)paramObject;
if (!local354348a.CGLIB$BOUND)
{
local354348a.CGLIB$BOUND = true;
Object tmp23_20 = CGLIB$THREAD_CALLBACKS.get();
if (tmp23_20 == null)
{
tmp23_20;
CGLIB$STATIC_CALLBACKS;
}
local354348a.CGLIB$CALLBACK_0 = (tmp31_28 == null ? tmp31_28 : (FixedValue)((Callback[])tmp23_20)[0]);
}
}
public Object newInstance(Callback[] paramArrayOfCallback)
{
CGLIB$SET_THREAD_CALLBACKS(paramArrayOfCallback);
CGLIB$SET_THREAD_CALLBACKS(null);
return new 354348a();
}
public Object newInstance(Callback paramCallback)
{
CGLIB$SET_THREAD_CALLBACKS(new Callback[] { paramCallback });
CGLIB$SET_THREAD_CALLBACKS(null);
return new 354348a();
}
/* Error */
public Object newInstance(Class[] arg1, Object[] arg2, Callback[] arg3)
{
// Byte code:
// 0: aload_3
// 1: invokestatic 83 cglib/SampleClass$$EnhancerByCGLIB$$354348a:CGLIB$SET_THREAD_CALLBACKS ([Lnet/sf/cglib/proxy/Callback;)V
// 4: new 2 cglib/SampleClass$$EnhancerByCGLIB$$354348a
// 7: dup
// 8: aload_1
// 9: dup
// 10: arraylength
// 11: tableswitch default:+24->35, 0:+17->28
// 28: pop
// 29: invokespecial 84 cglib/SampleClass$$EnhancerByCGLIB$$354348a: ()V
// 32: goto +17 -> 49
// 35: goto +3 -> 38
// 38: pop
// 39: new 90 java/lang/IllegalArgumentException
// 42: dup
// 43: ldc 92
// 45: invokespecial 95 java/lang/IllegalArgumentException: (Ljava/lang/String;)V
// 48: athrow
// 49: aconst_null
// 50: invokestatic 83 cglib/SampleClass$$EnhancerByCGLIB$$354348a:CGLIB$SET_THREAD_CALLBACKS ([Lnet/sf/cglib/proxy/Callback;)V
// 53: areturn
}
public Callback getCallback(int paramInt)
{
CGLIB$BIND_CALLBACKS(this);
switch (paramInt)
{
case 0:
break;
}
return null;
}
public void setCallback(int paramInt, Callback paramCallback)
{
switch (paramInt)
{
case 0:
this.CGLIB$CALLBACK_0 = ((FixedValue)paramCallback);
break;
}
}
public Callback[] getCallbacks()
{
CGLIB$BIND_CALLBACKS(this);
return new Callback[] { this.CGLIB$CALLBACK_0 };
}
public void setCallbacks(Callback[] paramArrayOfCallback)
{
this.CGLIB$CALLBACK_0 = ((FixedValue)paramArrayOfCallback[0]);
}
static {}
}
MethodInterceptor
高级一点的回调方法：
public static void testMethodInterceptor() throws Exception {
Enhancer enhancer = new Enhancer();
enhancer.setSuperclass(SampleClass.class);
enhancer.setCallback(new MethodInterceptor() {
@Override
public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy)
throws Throwable {
if (method.getDeclaringClass() != Object.class && method.getReturnType() == String.class) {
return "Hello cglib!";
} else {
return proxy.invokeSuper(obj, args);
}
}
});
SampleClass proxy = (SampleClass) enhancer.create();
System.out.println(proxy.test("1"));//输出结果Hello cglib!
System.out.println(proxy.toString());//输出结果cglib.SampleClass$$EnhancerByCGLIB$$e7ad6a0f@53e25b76
System.out.println(proxy.hashCode());//输出结果1407343478
}
生成的代理方法：
public final String test(String paramString)
{
MethodInterceptor tmp4_1 = this.CGLIB$CALLBACK_0;
if (tmp4_1 == null)
{
tmp4_1;
CGLIB$BIND_CALLBACKS(this);
}
MethodInterceptor tmp17_14 = this.CGLIB$CALLBACK_0;
if (tmp17_14 != null) {
return (String)tmp17_14.intercept(this, CGLIB$test$0$Method, new Object[] { paramString }, CGLIB$test$0$Proxy);
}
return super.test(paramString);
}
InvocationHandler
public static void testInvocationHandler() throws Exception {
Enhancer enhancer = new Enhancer();
enhancer.setSuperclass(SampleClass.class);
enhancer.setCallback(new InvocationHandler() {
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
if(method.getReturnType() == String.class) {
System.out.print("cglib -> "+method.toGenericString());
return "Hello cglib!";
} else {
throw new RuntimeException("Do not know what to do.");
}
}
});
SampleClass proxy = (SampleClass) enhancer.create();
System.out.println(proxy.test("1"));//输出结果cglib -> public java.lang.String cglib.SampleClass.test(java.lang.String)Hello cglib!
System.out.println(proxy.toString());//cglib -> public java.lang.String java.lang.Object.toString()Hello cglib!
System.out.println(proxy.hashCode());//异常（java.lang.RuntimeException: Do not know what to do.）
}
NoOp|LazyLoader|Dispatcher
NoOp|LazyLoader|Dispatcher就不重复了，生成的类细节可以自行去class dump的目录查看。
Immutable bean
生成不可变对象，可以用于参数传递时防止对象参数修改的场景。
原始对象是可以继续修改的，并且修改的值会影响不可变的对象。
例子：
public class SampleBean {
private String value;
public String getValue() {
return value;
}
public void setValue(String value) {
this.value = value;
}
}
测试方法：
public static void testImmutableBean() throws Exception {
SampleBean bean = new SampleBean();
bean.setValue("Hello world!");
SampleBean immutableBean = (SampleBean) ImmutableBean.create(bean);
System.out.println(immutableBean.getValue());//Hello world!
bean.setValue("Hello world, again!");
System.out.println(immutableBean.getValue());//Hello world, again!
immutableBean.setValue("Hello cglib!"); // 抛出异常
}
cglib生成的不可变对象：
public class SampleBean$$ImmutableBeanByCGLIB$$b26aa907
extends SampleBean
{
private final SampleBean CGLIB$RWBean;
public SampleBean$$ImmutableBeanByCGLIB$$b26aa907(Object paramObject)
{
this.CGLIB$RWBean = ((SampleBean)paramObject);
}
public String getValue()
{
return this.CGLIB$RWBean.getValue();
}
public void setValue(String paramString)
{
throw new IllegalStateException("Bean is immutable");
}
}
Bean generator
用于运行时动态生成class。
例子：
public static void testBeanGenerator() throws Exception {
BeanGenerator beanGenerator = new BeanGenerator();
beanGenerator.addProperty("value", String.class);
Object myBean = beanGenerator.create();
Method setter = myBean.getClass().getMethod("setValue", String.class);
setter.invoke(myBean, "Hello cglib!");
Method getter = myBean.getClass().getMethod("getValue");
System.out.println(getter.invoke(myBean));
}
cglib生成的class：
package net.sf.cglib.empty;
public class Object$$BeanGeneratorByCGLIB$$60b0c82c
{
private String $cglib_prop_value;
public String getValue()
{
return this.$cglib_prop_value;
}
public void setValue(String paramString)
{
this.$cglib_prop_value = paramString;
}
}