代理模式

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代理设计模式：

代理对象 增强后的对象

目标对象 被增强的对象

分为静态代理和动态代理

静态代理

实现方式：继承或聚合（实现接口）

动态代理

模拟的动态代理
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package com.hu.proxy;

import javax.tools.JavaCompiler;
import javax.tools.StandardJavaFileManager;
import javax.tools.ToolProvider;
import java.io.File;
import java.io.FileWriter;
import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import java.lang.reflect.Parameter;
import java.net.URL;
import java.net.URLClassLoader;

public class Proxy {

    private static String LINE = "\n";
    private static String TAB = "\t";
    private static String PATH = "d:\\proxy\\com\\hu\\";

    /**
     * 步骤：
     * 1、通过拼接字符串生成（io）Java代码文件
     * 2、动态编译
     * 3、类加载
     * 4、反射生成代理对象
     * <p>
     * 注：此处处理实现一个接口的代理
     */
    public static Object newInstance(Object target) throws Exception {
        Object proxy = null;
        StringBuilder code = new StringBuilder();

        Class targetInterface = target.getClass().getInterfaces()[0];
        Method methods[] = targetInterface.getDeclaredMethods();

        String className = target.getClass().getSimpleName() + "$Proxy";
        PATH += className + ".java";

        String targetInterfaceName = targetInterface.getSimpleName();
        //生成类字符串
        code.append("package com.hu;" + LINE);
        code.append("import " + targetInterface.getName() + ";" + LINE);
        code.append("public class " + className + " implements " + targetInterfaceName + "{" + LINE);

        code.append(TAB + "private " + targetInterfaceName + " target;" + LINE);
        code.append(TAB + "public " + className + " (" + targetInterfaceName + " target){" + LINE);
        code.append(TAB + TAB + "this.target =target;");
        code.append(LINE + TAB + "}" + LINE);

        String methodStr = getMethods(methods);
        code.append(methodStr);
        code.append("}");

        //创建类
        File java = cteateFile(code.toString(), PATH);
        //编译
        compiler(java);
        //加载字节码
        URL[] urls = new URL[]{new URL("file:D:\\proxy\\\\")};
        URLClassLoader urlClassLoader = new URLClassLoader(urls);
        Class clazz = urlClassLoader.loadClass("com.hu." + className);

        //创建代理对象
        Constructor constructor = clazz.getConstructor(targetInterface);
        proxy = constructor.newInstance(target);
        return proxy;
    }

    /**
     * 获取类方法
     */
    private static String getMethods(Method[] methods) {
        StringBuilder methodStr = new StringBuilder();
        for (Method method : methods) {
            String returnTypeName = method.getReturnType().getSimpleName();
            String methodName = method.getName();

            Class args[] = method.getParameterTypes();
            Parameter[] parameters = method.getParameters();
            String argsContent = "";
            String paramsContent = "";
            int flag = 0;
            for (Class arg : args) {
                argsContent += arg.getSimpleName() + " " + parameters[flag].getName() + ",";
                paramsContent += parameters[flag].getName() + ",";
                flag++;
            }
            if (argsContent.length() > 0) {
                argsContent = argsContent.substring(0, argsContent.length() - 1);
                paramsContent = paramsContent.substring(0, paramsContent.length() - 1);
            }
            methodStr.append(TAB + "public " + returnTypeName + " " + methodName + "(" + argsContent + ") {" + LINE);
            methodStr.append(TAB + TAB + "System.out.println(\"日志输出！！！！！！！！！\");" + LINE);

            if ("void".equals(returnTypeName)) {
                methodStr.append(TAB + TAB + "target." + methodName + "(" + paramsContent + ");" + LINE);
            } else {
                methodStr.append(TAB + TAB + "return target." + methodName + "(" + paramsContent + ");" + LINE);
            }
            methodStr.append(TAB + "}" + LINE);

        }
        return methodStr.toString();
    }

    /**
     * 创建类
     */
    private static File cteateFile(String code, String pathName) throws Exception {
        File file = new File(pathName);
        if (!file.exists()) {
            file.createNewFile();
        }
        FileWriter fw = new FileWriter(file);
        fw.write(code);
        fw.flush();
        fw.close();
        return file;
    }

    /**
     * 编译
     */
    private static void compiler(File file) throws Exception {
        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();

        StandardJavaFileManager fileMgr = compiler.getStandardFileManager(null, null, null);
        Iterable units = fileMgr.getJavaFileObjects(file);

        JavaCompiler.CompilationTask t = compiler.getTask(null, fileMgr, null, null, null, units);
        t.call();
        fileMgr.close();
    }
}

测试：

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public class Test {
    public static void main(String[] args) throws Exception {
        UserDao proxy = (UserDao) Proxy.newInstance(new UserDaoImpl());
        System.out.println("return "+proxy.query("001", "胡"));
    }
}

这种方式实现由缺点：要生成文件、动态编译文件 class、需要一个URLclassloader、软件性能的最终体现在IO操作。

升级版，简单模拟jdk动态代理

Proxy.java

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package com.hu.proxy1;

import javax.tools.JavaCompiler;
import javax.tools.StandardJavaFileManager;
import javax.tools.ToolProvider;
import java.io.File;
import java.io.FileWriter;
import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
import java.lang.reflect.Parameter;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.Random;

public class Proxy {

    private static String LINE = "\n";
    private static String TAB = "\t";
    private static String PATH = "d:\\proxy\\com\\hu\\";

    public static Object newInstance(Class targetInterface, MyInvocationHandler h) throws Exception {
        Object proxy = null;
        StringBuilder code = new StringBuilder();

        Method methods[] = targetInterface.getDeclaredMethods();

        String className = targetInterface.getSimpleName() + "$Proxy" + new Random().nextInt(1);
        PATH += className + ".java";

        String targetInterfaceName = targetInterface.getSimpleName();
        //生成类字符串
        code.append("package com.hu;" + LINE);
        code.append("import " + targetInterface.getName() + ";" + LINE);

        code.append("import com.hu.proxy1.MyInvocationHandler;" + LINE);
        code.append("import java.lang.reflect.Method;" + LINE);

        code.append("public class " + className + " implements " + targetInterfaceName + "{" + LINE);

        code.append(TAB + "private " + MyInvocationHandler.class.getSimpleName() + " h;" + LINE);
        code.append(TAB + "public " + className + " (MyInvocationHandler h){" + LINE);
        code.append(TAB + TAB + "this.h =h;");
        code.append(LINE + TAB + "}" + LINE);

        String methodStr = getMethods(methods, targetInterface, h);
        code.append(methodStr);
        code.append("}");

        //创建类 这里可以直接生成字节码文件，就不需要编译。
        File java = cteateFile(code.toString(), PATH);
        //编译
        compiler(java);
        //加载字节码
        URL[] urls = new URL[]{new URL("file:D:\\proxy\\\\")};
        URLClassLoader urlClassLoader = new URLClassLoader(urls);
        Class clazz = urlClassLoader.loadClass("com.hu." + className);

        //创建代理对象
        Constructor constructor = clazz.getConstructor(MyInvocationHandler.class);
        proxy = constructor.newInstance(h);
        return proxy;
    }

    /**
     * 获取类方法
     */
    private static String getMethods(Method[] methods, Class targetInterface, MyInvocationHandler h) {
        StringBuilder methodStr = new StringBuilder();
        for (Method method : methods) {
            String returnTypeName = method.getReturnType().getSimpleName();
            String methodName = method.getName();

            Class args[] = method.getParameterTypes();
            Parameter[] parameters = method.getParameters();
            String argsContent = "";
            String paramsContent = "";
            String methodParamsTypes="";
            int flag = 0;
            for (Class arg : args) {
                argsContent += arg.getSimpleName() + " " + parameters[flag].getName() + ",";
                paramsContent += parameters[flag].getName() + ",";
                methodParamsTypes += arg.getTypeName() +".class,";
                flag++;
            }
            if (argsContent.length() > 0) {
                argsContent = argsContent.substring(0, argsContent.length() - 1);
                paramsContent = paramsContent.substring(0, paramsContent.length() - 1);
                methodParamsTypes = methodParamsTypes.substring(0, methodParamsTypes.length() - 1);
            }
            methodStr.append(TAB + "public " + returnTypeName + " " + methodName + "(" + argsContent + ") throws Exception {" + LINE);

            methodStr.append(TAB + TAB + "Object[] args={" + paramsContent + "};" + LINE);

            methodStr.append(TAB + TAB + "Method method=Class.forName(\"" + targetInterface.getName() + "\").getDeclaredMethod(\"" + methodName + "\""+
                    (methodParamsTypes==""?"":(","+methodParamsTypes))
                    + ");" + LINE);

            if ("void".equals(returnTypeName)) {
                methodStr.append(TAB + TAB + "h.invoke(method,args);" + LINE);
            } else {
                methodStr.append(TAB + TAB + "return (" + returnTypeName + ")h.invoke(method,args);" + LINE);
            }
            methodStr.append(TAB + "}" + LINE);

        }
        return methodStr.toString();
    }

    /**
     * 创建类 这里可以直接生成字节码文件，就不需要编译。
     */
    private static File cteateFile(String code, String pathName) throws Exception {
        File file = new File(pathName);
        if (!file.exists()) {
            file.createNewFile();
        }
        FileWriter fw = new FileWriter(file);
        fw.write(code);
        fw.flush();
        fw.close();
        return file;
    }

    /**
     * 编译
     */
    private static void compiler(File file) throws Exception {
        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();

        StandardJavaFileManager fileMgr = compiler.getStandardFileManager(null, null, null);
        Iterable units = fileMgr.getJavaFileObjects(file);

        JavaCompiler.CompilationTask t = compiler.getTask(null, fileMgr, null, null, null, units);
        t.call();
        fileMgr.close();
    }
}

MyInvocationHandler

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package com.hu.proxy1;

import java.lang.reflect.Method;

public interface MyInvocationHandler {
    public Object invoke(Method method, Object[] args) throws Exception;
}

MyInvocationHandlerImpl

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package com.hu.proxy1;

import java.lang.reflect.Method;

public class MyInvocationHandlerImpl implements MyInvocationHandler {

    private UserDao dao;

    public MyInvocationHandlerImpl(UserDao userDao) {
        this.dao = userDao;
    }

    @Override
    public Object invoke(Method method, Object[] args) throws Exception {
        System.out.println("proxy 自定义动态代理");
        return method.invoke(dao, args);
    }
}

测试：

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package com.hu.proxy1;

public class Test {
    public static void main(String[] args) throws Exception {
        UserDao proxy = (UserDao) Proxy.newInstance(UserDao.class, new MyInvocationHandlerImpl(new UserDaoImpl()));
        //UserDao proxy = (UserDao) java.lang.reflect.Proxy.newProxyInstance(Test.class.getClassLoader(), new Class[]{UserDao.class},new InvocationHandlerImpl(new UserDaoImpl()));
        System.out.println("return " + proxy.query("001", "胡"));
        System.out.println("-----------------------------------------------");
        proxy.query("ddddd");
    }
}
JDK动态代理

实现方法：通过Proxy的静态方法，通过接口反射得到得到字节码文件，使用ClassLoader将字节码文件加载到JVM，调用native方法生成代理对象。

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