问题

cglib是如何实现动态代理的
cglib如何支持类的代理
cglib和jdk的动态代理有什么区别

使用方式

cglib不属于jdk的一部分,因此要使用需要先引入相应的包,maven依赖如下

<dependency>
    <groupId>cglib</groupId>
    <artifactId>cglib</artifactId>
    <version>3.0</version>
</dependency>

另外因为spring的aop有使用cglib的实现，因此如果项目引入了spring-core包，那么spring-core包下面已经包含了cglib

使用例子

Test.java

public class Test {

    public static void main(String args[]){
        Enhancer enhancer = new Enhancer();
        enhancer.setSuperclass(TestCglib.class);
        enhancer.setCallback(new CglibMethodInterceptor());
        TestCglib testCglib = (TestCglib)enhancer.create();
        testCglib.sayBye("asdsd");
    }
}

TestCglib.java

public class TestCglib {
    public String sayHi(String str){
        System.out.println("我是被代理的sayHi方法");
        return str;
    }

    public String sayBye(String str){
        System.out.println("我是被代理的sayBye方法");
        return str;
    }
}

CglibMethodInterceptor.java

public class CglibMethodInterceptor implements MethodInterceptor {
    public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
        System.out.println(method.getName()+"执行之前做一些准备工作");
        Object result = methodProxy.invokeSuper(o,objects);
        System.out.println(method.getName()+"执行之后做一些准备的工作");
        return result;
    }
}

实现

和jdk的代理一样，我们先来看看生成的代理类长什么样：

TestCglib$$EnhancerByCGLIB$$8b20fd94.class(代理类)

public class TestCglib$$EnhancerByCGLIB$$8b20fd94 extends TestCglib implements Factory {
    private static final Method CGLIB$sayHi$1$Method;
    private static final MethodProxy CGLIB$sayHi$1$Proxy;


static void CGLIB$STATICHOOK1() {
    Class var0 = Class.forName("TestCglib$$EnhancerByCGLIB$$8b20fd94");
    Class var1;
    Method[] var10000 = ReflectUtils.findMethods(new String[]{"sayBye", "(Ljava/lang/String;)Ljava/lang/String;", "sayHi", "(Ljava/lang/String;)Ljava/lang/String;"}, (var1 = Class.forName("TestCglib")).getDeclaredMethods());
    CGLIB$sayHi$1$Method = var10000[1];
    CGLIB$sayHi$1$Proxy = MethodProxy.create(var1, var0, "(Ljava/lang/String;)Ljava/lang/String;", "sayHi", "CGLIB$sayHi$1");
}

final String CGLIB$sayHi$1(String var1) {
    return super.sayHi(var1);
}

public final String sayHi(String var1) {
    MethodInterceptor var10000 = this.CGLIB$CALLBACK_0;
    if (var10000 == null) {
        CGLIB$BIND_CALLBACKS(this);
        var10000 = this.CGLIB$CALLBACK_0;
    }

    return var10000 != null ? (String)var10000.intercept(this, CGLIB$sayHi$1$Method, new Object[]{var1}, CGLIB$sayHi$1$Proxy) : super.sayHi(var1);
}

}

TestCglib$$EnhancerByCGLIB$$8b20fd94$$FastClassByCGLIB$$2ada1598(代理类的FastClass类)

public class TestCglib$$EnhancerByCGLIB$$8b20fd94$$FastClassByCGLIB$$2ada1598 extends FastClass {
public TestCglib$$EnhancerByCGLIB$$8b20fd94$$FastClassByCGLIB$$2ada1598(Class var1) {
    super(var1);
}

public int getIndex(Signature var1) {
    String var10000 = var1.toString();
    switch(var10000.hashCode()) {
    case 481426893:
        if (var10000.equals("sayHi(Ljava/lang/String;)Ljava/lang/String;")) {
            return 7;
        }
        break;
    case 2082116023:
        if (var10000.equals("CGLIB$sayHi$1(Ljava/lang/String;)Ljava/lang/String;")) {
            return 11;
        }
    }

    return -1;
}


public Object invoke(int var1, Object var2, Object[] var3) throws InvocationTargetException {
    8b20fd94 var10000 = (8b20fd94)var2;
    int var10001 = var1;

    try {
        switch(var10001) {
        case 7:
            return var10000.sayHi((String)var3[0]);
        case 11:
            return var10000.CGLIB$sayHi$1((String)var3[0]);
        }
    } catch (Throwable var4) {
        throw new InvocationTargetException(var4);
    }

    throw new IllegalArgumentException("Cannot find matching method/constructor");
}

}

TestCglib$$FastClassByCGLIB$$2f8a820f(原始类的FastClass类)

public class TestCglib$$FastClassByCGLIB$$2f8a820f extends FastClass {
public TestCglib$$FastClassByCGLIB$$2f8a820f(Class var1) {
    super(var1);
}

public int getIndex(Signature var1) {
    String var10000 = var1.toString();
    switch(var10000.hashCode()) {
    case 481426893:
        if (var10000.equals("sayHi(Ljava/lang/String;)Ljava/lang/String;")) {
            return 1;
        }
        break;

    return -1;
}

public Object invoke(int var1, Object var2, Object[] var3) throws InvocationTargetException {
    TestCglib var10000 = (TestCglib)var2;
    int var10001 = var1;

    try {
        switch(var10001) {
        case 1:
            return var10000.sayHi((String)var3[0]);
        }
    } catch (Throwable var4) {
        throw new InvocationTargetException(var4);
    }

    throw new IllegalArgumentException("Cannot find matching method/constructor");
}

}

可以看到上面一共生成了三个类，为了突出重点我只保留了和sayHi这个方法相关的部分，这三个类的作用如下：