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cglib学习笔记

cglib学习笔记

作者: realqiyan | 来源:发表于2017-04-24 00:17 被阅读0次

    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/Tutorial

    cglib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:<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:<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;
  }
}

    Bean copier

    Bulk bean

    Bean map

    Key factory

    Mixin

    String switcher

    Interface maker

    Method delegate

    Multicast delegate

    Constructor delegate

    Parallel sorter

    Fast class and fast members

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