Spring底层原理(六)

本章内容

介绍AOP的实现方式、JDK代理的模拟实现与源码

AOP的实现方式

使用代理模式
- jdk动态代理
- cglib动态代理
使用aspectj的编译器，该编译器会直接对字节码进行修改，可以实现静态方法增强
使用javaagent,在jvm option中指定-javaagent:aspectjweaver.jar,它会在字节码加载阶段对方法进行织入

JDK动态代理的模拟实现

public interface InvocationHandler {
    /**
     * @param proxy  代理对象
     * @param method 调用的方法
     * @param args   方法参数
     * @return       返回结果
     * @throws Throwable 运行异常
     */
    Object invoke(Object proxy, Method method,Object[] args) throws Throwable;
}

public interface Foo {
    int foo();
    void bar();
}

public class Obj {
    static class Target implements Foo {
        @Override
        public int foo() {
            System.out.println("foo");
            return 100;
        }

        @Override
        public void bar() {
            System.out.println("bar");
        }
    }

    public static void main(String[] args) {
        $Proxy0 proxy0 = new $Proxy0(new InvocationHandler() {
            @Override
            public Object invoke(Object proxy, Method method, Object[] args) throws Exception {
                System.out.println("before...");
                return method.invoke(new Target(),args);
            }
        });
        proxy0.bar();
        int foo = proxy0.foo();
        System.out.println(foo);
    }
}

public class $Proxy0 implements Foo {
    private InvocationHandler h;

    static Method foo;
    static Method bar;

    static {
        try {
            bar = Foo.class.getDeclaredMethod("bar");
            foo = Foo.class.getDeclaredMethod("foo");
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        }
    }

    public $Proxy0(InvocationHandler h) {
        this.h = h;
    }

    @Override
    public int foo() {
        try {
            return (int) h.invoke(this, foo, new Object[0]) + 1;
        } catch (RuntimeException | Error e) {
            throw e;
        } catch (Throwable e) {
            //对于检查异常需要包装成RuntimeException
            throw new UndeclaredThrowableException(e);
        }
    }

    @Override
    public void bar() {
        try {
            h.invoke(this, bar, new Object[0]);
        } catch (RuntimeException | Error e) {
            throw e;
        } catch (Throwable e) {
            //对于检查异常需要包装成RuntimeException
            throw new UndeclaredThrowableException(e);
        }
    }
}

JDK动态代理源码

在这里插入图片描述

JDK动态代理的优化

 public Object invoke(Object obj, Object... args)
        throws IllegalAccessException, IllegalArgumentException,
           InvocationTargetException
    {
        if (!override) {
            Class<?> caller = Reflection.getCallerClass();
            checkAccess(caller, clazz,
                        Modifier.isStatic(modifiers) ? null : obj.getClass(),
                        modifiers);
        }
        MethodAccessor ma = methodAccessor;             // read volatile
        if (ma == null) {
            ma = acquireMethodAccessor();
        }
        return ma.invoke(obj, args);
    }