模拟实现jdk动态代理

实现步骤

1、生成代理类的源代码

2、将源代码保存到磁盘

3、使用JavaCompiler编译源代码生成.class字节码文件

4、使用JavaCompiler编译源代码生成.class字节码文件

5、返回代理类的实例

实现代码

package com.lnjecit.proxy.custom;

import java.lang.reflect.Method;

/**

 * 自定义InvocationHandler

 */

public interface MyInvocationHandler {

    /**

     * 执行代理实例中目标方法，并返回结果

     * @param proxy 代理实例

     * @param method 目标方法

     * @param args 目标方法中的参数

     * @return

     */

    Object invoke(Object proxy, Method method, Object[] args) throws Throwable;

}

package com.lnjecit.proxy.custom;

import java.io.File;

import java.lang.reflect.Constructor;

/**

 * 自定义代理类

 *

 * @author

 * @create 2018-04-08 21:55

 **/

public class MyProxy {

    /**

     * 生成代理类实例

     *

     * @param classLoader 类加载器

     * @param interfaces  被代理类实现的接口数组

     * @param h

     * @return

     */

    public static Object newProxyInstance(MyClassLoader classLoader, Class<?>[] interfaces, MyInvocationHandler h) throws ClassNotFoundException {

        // 1、生成代理类的源代码

        String sourceFileStr = MyProxyGenerator.generateSourceFile("$Proxy0", interfaces);

        String filePath = MyProxy.class.getResource("/").getPath();

        try {

            // 2、将源代码保存到磁盘

            File sourceFile = MyProxyGenerator.saveGeneratedSourceFile(filePath, sourceFileStr);

            // 3、使用JavaCompiler编译源代码生成.class字节码文件

            MyProxyGenerator.generateProxyClass(sourceFile);

            // 4、使用ClassLoader将.class文件中的内容加载到JVM

            Class proxyClass = classLoader.findClass("$Proxy0");

            // 5、返回代理类的实例

            Constructor c = proxyClass.getConstructor(MyInvocationHandler.class);

            // 删除生成的源文件

            // sourceFile.delete();

            return c.newInstance(h);

        } catch (Exception e) {

            e.printStackTrace();

        }

        return null;

    }

}

package com.lnjecit.proxy.custom;

import javax.tools.*;

import java.io.File;

import java.io.FileWriter;

import java.io.IOException;

import java.lang.reflect.Method;

/**

 * 生成代理类

 *

 * @author

 * @create 2018-04-08 22:01

 **/

public class MyProxyGenerator {

    private static final String PROXY_PACKAGE = "com.lnjecit.proxy.custom";

    private static final String LINE_FEED = "\r\n";

    /**

     * 生成代理类的源代码

     * @param proxyName

     * @param interfaces

     * @return

     */

    public static String generateSourceFile(String proxyName, Class<?>[] interfaces) {

        StringBuffer buffer = new StringBuffer();

        buffer.append("package " + PROXY_PACKAGE + ";" + LINE_FEED);

        for (Class<?> intf : interfaces) {

            buffer.append("import " + intf.getName() + ";" + LINE_FEED);

        }

        buffer.append("import java.lang.reflect.Method;" + LINE_FEED);

        buffer.append("import com.lnjecit.proxy.custom.MyProxy;" + LINE_FEED);

        buffer.append("import com.lnjecit.proxy.custom.MyInvocationHandler;" + LINE_FEED);

        buffer.append("public final class " + proxyName + " extends MyProxy implements ");

        for (Class<?> intf : interfaces) {

            buffer.append(intf.getSimpleName());

        }

        buffer.append("{" + LINE_FEED);

        buffer.append("private MyInvocationHandler h;" + LINE_FEED);

        // 构造函数

        buffer.append("public " + proxyName + "(MyInvocationHandler h" + ") {" + LINE_FEED);

        buffer.append("this.h = h;" + LINE_FEED);

        buffer.append("}" + LINE_FEED);

        for (Class<?> intf : interfaces) {

            Method[] methods = intf.getMethods();

            for (int i = 0; i < methods.length; i++) {

                Method method = methods[i];

                buffer.append("public " + method.getReturnType() + " " + method.getName() + "()" + "{" + LINE_FEED);

                buffer.append("try {" + LINE_FEED);

                buffer.append("Method m = " + intf.getName() + ".class.getMethod(\"" + method.getName() + "\",new Class[]{});" + LINE_FEED);

                buffer.append("h.invoke(this, m, null);" + LINE_FEED);

                buffer.append("}  catch (Throwable e) {" + LINE_FEED);

                buffer.append("e.printStackTrace();" + LINE_FEED);

                buffer.append("}" + LINE_FEED);

                buffer.append("}" + LINE_FEED);

            }

        }

        buffer.append("}" + LINE_FEED);

        return buffer.toString();

    }

    /**

     * 将代理类源文件便以为.class文件

     * @param sourceFile 源文件

     * @throws IOException

     */

    public static void generateProxyClass(File sourceFile) throws IOException {

        // 获取JavaCompiler

        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();

        // DiagnosticListener用于获取Diagnostic信息，Diagnostic信息包括：错误，警告和说明性信息

        DiagnosticListener<JavaFileObject> diagnostics = new DiagnosticCollector<JavaFileObject>();

        // StandardJavaFileManager:用于管理与工具有关的所有文件

        StandardJavaFileManager manager = compiler.getStandardFileManager(diagnostics, null, null);

        // avaFileObjects: 是java源码文件(.java)和class文件(.class)的抽象

        Iterable iterable = manager.getJavaFileObjects(sourceFile);

        // 编译任务

        JavaCompiler.CompilationTask task = compiler.getTask(null, manager, diagnostics, null, null, iterable);

        task.call();

        manager.close();

    }

    /**

     * 将代理类的源代码保存到本地磁盘

     * @param filePath   文件保存路径

     * @param sourceFileStr 源代码

     * @throws IOException

     */

    public static File saveGeneratedSourceFile(String filePath, String sourceFileStr) throws IOException {

        File sourceFile = new File(filePath + PROXY_PACKAGE.replaceAll("\\.", "/") + "/" + "$Proxy0.java");

        FileWriter fw = new FileWriter(sourceFile);

        fw.write(sourceFileStr);

        fw.flush();

        fw.close();

        return sourceFile;

    }

}

package com.lnjecit.proxy.custom;

import java.io.ByteArrayOutputStream;

import java.io.File;

import java.io.FileInputStream;

import java.io.IOException;

/**

 * 自定义ClassLoader

 * @author

 * @create 2018-04-08 21:57

 **/

public class MyClassLoader extends ClassLoader {

    private File baseDir;

    public MyClassLoader(){

        String basePath = MyClassLoader.class.getResource("").getPath();

        this.baseDir = new java.io.File(basePath);

    }

    @Override

    protected Class<?> findClass(String name) throws ClassNotFoundException {

        String className = MyClassLoader.class.getPackage().getName() + "." + name;

        if(baseDir != null){

            File classFile = new File(baseDir,name.replaceAll("\\.", "/") + ".class");

            if(classFile.exists()){

                FileInputStream in = null;

                ByteArrayOutputStream out = null;

                try{

                    in = new FileInputStream(classFile);

                    out = new ByteArrayOutputStream();

                    byte [] buff = new byte[1024];

                    int len;

                    while ((len = in.read(buff)) != -1) {

                        out.write(buff, 0, len);

                    }

                    return defineClass(className, out.toByteArray(), 0,out.size());

                }catch (Exception e) {

                    e.printStackTrace();

                }finally{

                    if(null != in){

                        try {

                            in.close();

                        } catch (IOException e) {

                            e.printStackTrace();

                        }

                    }

                    if(null != out){

                        try {

                            out.close();

                        } catch (IOException e) {

                            e.printStackTrace();

                        }

                    }

                    classFile.delete();

                }

            }

        }

        return null;

    }

}

package com.lnjecit.proxy.custom;

import java.lang.reflect.Method;

/**

 * @author

 * @create 2018-04-08 21:59

 **/

public class JDKDynamicProxy implements MyInvocationHandler {

    Object target;

    public <T> T getInstance(Object target) throws Exception {

        this.target = target;

        return (T) MyProxy.newProxyInstance(new MyClassLoader(), target.getClass().getInterfaces(), this);

    }

    @Override

    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {

        System.out.println("Before invoke");

        Object result = method.invoke(target, args);

        System.out.println("After invoke");

        return result;

    }

}

测试代码

package com.lnjecit.proxy;

/**

 * Subject

 * 抽象主题接口

 * @author

 * @create 2018-03-29 14:16

 **/

public interface Subject {

    void doSomething();

}

package com.lnjecit.proxy;

/**

 * RealSubject

 * 真实主题类

 * @author

 * @create 2018-03-29 14:21

 **/

public class RealSubject implements Subject {

    @Override

    public void doSomething() {

        System.out.println("RealSubject do something");

    }

}

import com.lnjecit.proxy.RealSubject;

import com.lnjecit.proxy.Subject;

/**

 * 测试类

 * @author

 * @create 2018-04-08 23:07

 **/

public class Client {

    public static void main(String[] args) {

        try {

            Subject subject = new JDKDynamicProxy().getInstance(new RealSubject());

            subject.doSomething();

        } catch (Exception e) {

            e.printStackTrace();

        }

    }

}

测试结果：

Before invoke
RealSubject do something
After invoke

在调试过程中可看到：在classpath路径下生成了$Proxy0.java和$Proxy0.class两个文件

以上仅仅实现了代理一个接口并且方法无参数的简单代理，只是为了更好理解jdk动态代理。

巴特西

模拟实现jdk动态代理

实现步骤

实现代码

测试代码

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