cglib學習筆記
cglib簡介
cglib:Code Generation Library
主頁:https://github.com/cglib/cglib/
教程:https://github.com/cglib/cglib/wiki/Tutorialcglib是java字節(jié)碼生成和轉換類庫。它用于AOP,測試手销,數(shù)據(jù)訪問框架,生成動態(tài)代理對象和攔截字段訪問贱鄙。
cglib基于ASM而晒,通過ASM生成新的字節(jié)碼搪桂。
cglib學習
Enhancer
字節(jié)碼增強功能略步,主要用于生成新的class描扯,spring的aop就會使用cglib生成代理類。
通過設置Enhancer屬性趟薄,然后通過Enhancer#create生成新的增強類绽诚。
通過設置cglib.debugLocation可以指定生成class dump存放路徑,通過查看生成的class更方便學習杭煎。
System.setProperty("cglib.debugLocation", "/Users/qiyan/cglib/classes");
首先來一個簡單的POJO做為例子:
public class SampleClass {
public String test(String input) {
return "Hello world!";
}
}
Enhancer使用說明:
Enhancer enhancer = new Enhancer();
//設置Enhancer屬性
enhancer.create();//創(chuàng)建增強類
Enhancer屬性說明:
//增強類集成的接口列表
Class[] interfaces;
//父類
Class superclass;
//Callback選擇器 返回值為callbacks的下標
CallbackFilter filter;
//回調處理器MethodInterceptor|NoOp|LazyLoader|Dispatcher|InvocationHandler|FixedValue的實現(xiàn)類
Callback[] callbacks;
//回調處理器類型MethodInterceptor|NoOp|LazyLoader|Dispatcher|InvocationHandler|FixedValue的Class
Type[] callbackTypes;
//是否使用工廠類
boolean useFactory = true;
//是否允許調用代理類構造器
boolean interceptDuringConstruction = true;
//是否校驗回調類型
boolean validateCallbackTypes;
//是否僅創(chuàng)建代理類
boolean classOnly;
//是否僅創(chuàng)建工廠類
boolean factoryOnly;
//參數(shù)類型
Class[] argumentTypes;
//參數(shù)
Object[] arguments;
FixedValue
使用Enhancer生成代理類恩够,callback設置為FixedValue。
使用FixedValue以后羡铲,所有接口都會返回固定值蜂桶,test,toString,hashCode都會返回固定值,但是hashCode會因為數(shù)據(jù)轉換拋出異常也切。
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"));//輸出結果Hello cglib!
System.out.println(proxy.toString());//輸出結果Hello cglib!
System.out.println(proxy.hashCode());//異常(類型轉換異常)
}
cglib會生成兩個class屎飘,一個工廠類妥曲,一個代理類:
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:<init> ()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:<init> (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生成的代理類:
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:<init> ()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:<init> ()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:<init> (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
高級一點的回調方法:
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"));//輸出結果Hello cglib!
System.out.println(proxy.toString());//輸出結果cglib.SampleClass$$EnhancerByCGLIB$$e7ad6a0f@53e25b76
System.out.println(proxy.hashCode());//輸出結果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"));//輸出結果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());//異常(java.lang.RuntimeException: Do not know what to do.)
}
NoOp|LazyLoader|Dispatcher
NoOp|LazyLoader|Dispatcher就不重復了,生成的類細節(jié)可以自行去class dump的目錄查看钦购。
Immutable bean
生成不可變對象,可以用于參數(shù)傳遞時防止對象參數(shù)修改的場景褂萧。
原始對象是可以繼續(xù)修改的押桃,并且修改的值會影響不可變的對象。
例子:
public class SampleBean {
private String value;
public String getValue() {
return value;
}
public void setValue(String value) {
this.value = value;
}
}
測試方法:
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!"); // 拋出異常
}
cglib生成的不可變對象:
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
用于運行時動態(tài)生成class导犹。
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;
}
}