Spring底层原理(六)

news/2024/10/24 7:23:30/

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 {@Overridepublic int foo() {System.out.println("foo");return 100;}@Overridepublic void bar() {System.out.println("bar");}}public static void main(String[] args) {$Proxy0 proxy0 = new $Proxy0(new InvocationHandler() {@Overridepublic 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;}@Overridepublic 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RuntimeExceptionthrow new UndeclaredThrowableException(e);}}@Overridepublic 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RuntimeExceptionthrow new UndeclaredThrowableException(e);}}
}

JDK动态代理源码

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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 volatileif (ma == null) {ma = acquireMethodAccessor();}return ma.invoke(obj, args);}