手动写源码---模拟实现动态代理

AOP的实现有两种，一种是接口的实现，一种是产生自己实现，分别的代表为JDK的Proxy和CGLIB的Proxy

下面是模拟接口代理实现 ，通过模拟JDK的动态代理，更深刻的理解

通过动态代理可以面向切面编程

1 定义被代理的对象和接口

public interface BookInterface {
    void selling();
}

public interface PhoneInterface {
    void selling();
}

public class Book implements BookInterface {
    @Override
    public void selling() {
        System.out.println("books selling.....");
    }
}

public class VivoPhone implements PhoneInterface {
    @Override
    public void selling() {
        System.out.println("selling vivo x5");
    }
}

 2 定义切面类

public class TimeAspect {
    static long bgn;
    public static void before(){
        bgn = System.currentTimeMillis();
        System.out.println("begin time...  " + bgn);
    }
    public static void after(){
        long end = System.currentTimeMillis();
        System.out.println("end time...  " + (end-bgn));
    }
}

public class LogAspect{
    public static void before(){

        System.out.println("begin log...");
    }
    public static void after(){
        System.out.println("finish log...");
    }
}

 3 定义InvocationHander  代理接口

import java.lang.reflect.Method;
public interface InvocationHander {
    public void invoke(Object o,Method m);
}

   代理类（切面编程里面也可以做一些特殊的处理）

import java.lang.reflect.Method;
import jdkproxy.LogTranService;
import jdkproxy.TimeTranService;

public class ProxyHander implements InvocationHander {
    private Object target;
    public ProxyHander(Object target) {
        this.target = target;
    }
    @Override
    public void invoke(Object o, Method m) {
        try {
            TimeTranService.before();
            if(!(o instanceof BookInterface)){//只有非BookInterface接口调用日志
                LogTranService.before();
            }

            m.invoke(target);

            if(!(o instanceof BookInterface)){
                LogTranService.after();
            }
            TimeTranService.after();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

    动态代理类

import java.io.File;
import java.io.IOException;
import java.lang.reflect.Constructor;
import java.lang.reflect.Method;

import javax.tools.JavaCompiler;
import javax.tools.JavaCompiler.CompilationTask;
import javax.tools.StandardJavaFileManager;
import javax.tools.ToolProvider;


import org.apache.commons.io.FileUtils;

public class Proxy {
    /*
     * 空的构造函数
     */
    private Proxy(){
    }
    /*
     * 返回代理类
     */
    public static Object newProxyInstance(Class inter,InvocationHander h){
        String packageName  = inter.getPackage().getName();
        // String temp = new String(packageName);
        String proxyClassName = "$"+packageName.replace(".","_") + "_" + inter.getSimpleName() +"Proxy";

        String InHanderPackage = h.getClass().getPackage().getName();
        String rt = "
";// 换行
        String methodCode = "";
        for (Method method:inter.getMethods()) {
            methodCode+="   @Override"+rt+

            "   public void "+ method.getName()+"() {"+rt+
            "       try{"+rt+
            "           Method method  = "+inter.getName()+".class.getMethod(""
            +           method.getName()+   "");"+rt+
            "           h.invoke(this,method);      "+rt+
            "       }catch(Exception e ){" +rt+
            "           e.printStackTrace();" +rt+
            "       }"+rt+
            "   }";
        }
        /*
         * 总的java代码
         */
        String javaCode=
        "package  "+packageName+";"+rt+
        "import "+InHanderPackage+".InvocationHander;"+rt+

        "import java.lang.reflect.Method;"+rt+
        "public class "+proxyClassName+" implements "+inter.getName()+" {"+rt+
        "   public "+proxyClassName+"("+InHanderPackage+".InvocationHander h) {"+rt+
        "       super();"+rt+
        "       this.h = h;"+rt+
        "   }"+rt+
        "   private "+InHanderPackage+".InvocationHander h;"+rt+
        methodCode+rt+
        "}";
        /*
         *  生成java文件
         */
        // 生成文件路径
        String filename =  System.getProperty("user.dir")+"/bin/"+packageName.replace(".", "//")+"/"+proxyClassName+".java";
        File file = new File(filename);
        try {
            // 需要commons-io的jar方便的操作文件
            FileUtils.writeStringToFile(file, javaCode);
        } catch (IOException e) {
            e.printStackTrace();
        }


        // 编译  拿到编译器
        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
        // 文件管理
        StandardJavaFileManager fileMgr = compiler.getStandardFileManager(null, null, null);
        //获取文件
        Iterable units = fileMgr.getJavaFileObjects(filename);

        // 编译任务
        CompilationTask t  = compiler.getTask(null, fileMgr, null, null, null, units);
        // call进行编译
        t.call();
        try {
            fileMgr.close();
        } catch (IOException e) {
            e.printStackTrace();
        }

        // load到内存
        ClassLoader cl = ClassLoader.getSystemClassLoader();
        try {
            Class c = cl.loadClass(packageName+"."+proxyClassName);
            Constructor ctr = c.getConstructor(InvocationHander.class);
            return ctr.newInstance(h);
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }
}

4 测试

import org.junit.After;
import org.junit.Before;
import org.junit.Test;
public class TestProxy {
    @Before
    public void  before(){
        System.out.println("-----------------start-------------------");
    }
    @Test
    public  void test() {
        Book book = new Book();
        InvocationHander h = new ProxyHander(book);
        BookInterface bi = (BookInterface)Proxy.newProxyInstance(BookInterface.class,h);
        bi.selling(); // 没有日志打印

        System.out.println("==================分割==============================");

        PhoneInterface car = new VivoPhone();
        h = new ProxyHander(car);
        PhoneInterface pi = (PhoneInterface)Proxy.newProxyInstance(PhoneInterface.class,h);
        pi.selling(); // 有日志打印
    }
    @After
    public void  after(){
        System.out.println("-----------------end-------------------");
    }
}

 Proxy类里面生成代理类名称的方法是根据包名来的，全类名长度加起来超过250多个长度可能会让java类无法编译，那就需要特殊处理了。超过250个长度的全类名那种项目没见过，不考虑

上面是他的原理，spring中如何使用aop呢？

 请参考

 参考文章