一个简单JDK版动态代理

本文实例为大家分享了手动实现的一个简单JDK版动态代理，供大家参考，具体内容如下

一.实现步骤

1.根据目标类的接口类型生成代理类的java文件。
2.编译代理类java文件为.class字节码文件。
3.将编译好的字节码文件加载到jvm中。
4.生成代理类对象并返回。

二.代码实现

1.Proxy类

public class CLProxy  {
  private static final String ENTER= "\r\n";
  private static final String PAKAGE=CLProxy.class.getPackage().toString()+";";
  private static final String CLASS_NAME="$Proxy";
  private static final AtomicInteger NUMBER= new AtomicInteger(0);
  public static Object newProxyInstance(CLClassLoader classLoader, Class<?>[] interfaces,CLInvocationHandler h) throws Exception{
    String className =CLASS_NAME+NUMBER.getAndIncrement();
    //遍历所有的接口生成java 文件
    String javaString = createJavaString(interfaces, className);
    String parentPath = CLProxy.class.getResource("").getPath();
    File file =new File(parentPath,className+".java" );
    FileWriter writer  = new FileWriter(file);
    writer.write(javaString);
    writer.flush();
    writer.close();
    //System.out.println(file);
    //编译
    JavaCompiler systemJavaCompiler = ToolProvider.getSystemJavaCompiler();
    StandardJavaFileManager standardFileManager = systemJavaCompiler.getStandardFileManager(null, null, null);
    Iterable<? extends JavaFileObject> javaFileObjects = standardFileManager.getJavaFileObjects(file);
    JavaCompiler.CompilationTask task = systemJavaCompiler.getTask(null, standardFileManager, null, null, null, javaFileObjects);
    task.call();
    standardFileManager.close();
    //创建实例
    Class<?> aClass = classLoader.findClass(className);
    Constructor<?> constructor = aClass.getConstructor(CLInvocationHandler.class);
    Object instance = constructor.newInstance(h);
    //file.delete();
    return instance;
  }

  /**
   * 生成java 文件
   * @param interfaces
   * @return
   */
  private static String createJavaString(Class<?>[] interfaces , String className ){

    StringBuffer buffer  = new StringBuffer();
    buffer.append(PAKAGE+ENTER);
    buffer.append("import java.lang.reflect.Method;"+ ENTER);

    StringBuffer interfaceString= new StringBuffer();
    int length= interfaces.length;
    for (int i = 0; i<length ; ++i){
      interfaceString.append(interfaces[i].getName());
      if (i!=length-1){
        interfaceString.append(",");
      }
    }
    buffer.append("public final class ");
    buffer.append(className);
    buffer.append(" implements ");
    buffer.append(interfaceString);
    buffer.append(" {"+ENTER);
    buffer.append("private CLInvocationHandler handler;"+ENTER);
    buffer.append("public "+className+"(CLInvocationHandler handler) {"+ENTER);
    buffer.append(" this.handler= handler;"+ENTER);
    buffer.append("}"+ENTER);
    for (int i =0 ;i<length;++i){
      Class<?> clazz= interfaces[i];
      Method[] methods = clazz.getMethods();
      for (Method method : methods){
        String returnTypeString = method.getReturnType().getName();

        Class<?>[] parameterTypes = method.getParameterTypes();
        StringBuffer paramTypeString = new StringBuffer();
        StringBuffer methodParamString = new StringBuffer();
        StringBuffer invokeParamString = new StringBuffer();

        paramTypeString.append("new Class[]{");
        int paramLength= parameterTypes.length;
        for (int j =0 ; j<paramLength ;++j){
          Class<?> paramClazz= parameterTypes[j];
          paramTypeString.append(paramClazz.getName()+".class");
          String paramFieldName = "var"+j;
          methodParamString.append(paramClazz.getName() +" "+paramFieldName);
          invokeParamString.append(paramFieldName);
          if (j!= paramLength-1){
            paramTypeString.append(",");
            methodParamString.append(",");
            invokeParamString.append(",");
          }
        }
        paramTypeString.append("}");
        int modifiers = method.getModifiers();
        if (Modifier.isPublic(modifiers)){
          buffer.append("public");
        }else if (Modifier.isPrivate(modifiers)){
          buffer.append("private");
        }else if (Modifier.isProtected(modifiers)){
          buffer.append("protected");
        }
        buffer.append(" final "+returnTypeString+" "+ method.getName()+"("+methodParamString+"){"+ ENTER);
          buffer.append("try{"+ENTER);

        buffer.append("Method method = "+clazz.getName()+".class.getMethod(\""+method.getName()+"\","+paramTypeString+" );"+ENTER);

          if (!"void".equals(returnTypeString)){
            buffer.append("return ("+returnTypeString+")");

          }
          if (invokeParamString.toString().length()==0){
            invokeParamString.append("null");
          }else{
            invokeParamString = new StringBuffer("new Object[]{"+invokeParamString.toString()+"}");
          }
          buffer.append("this.handler.invoke(this,method,"+invokeParamString+");"+ENTER);
          buffer.append("}catch(Throwable e){"+ENTER);
          buffer.append("e.printStackTrace();"+ENTER);
          buffer.append("}"+ENTER);
          if (!"void".equals(returnTypeString)){
            buffer.append("return null;"+ENTER);
          }
        buffer.append("}"+ENTER);
      }
    }

    buffer.append("}");
    return buffer.toString();
  }

  public static void main(String[] args) throws Exception {
    Person person = (Person)CLProxy.newProxyInstance(new CLClassLoader(), XiaoMing.class.getInterfaces(), new CLInvocationHandler() {
      @Override
      public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        System.out.println("before");

        Object result= method.invoke(new XiaoMing(), args);
        System.out.println("after");
        return result;
      }
    });
    String laoxu = person.call("laoxu");
    System.out.println(laoxu);
    /* person.eat();
    Class<?>[] interfaces = person.getClass().getInterfaces();
    for (Class<?> in:interfaces){
      System.out.println(in.getName());
    }
*/
    Person person2= (Person)CLProxy.newProxyInstance(new CLClassLoader(), XiaoMing.class.getInterfaces(), new CLInvocationHandler() {
      @Override
      public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        System.out.println("before");

        Object result= method.invoke(new XiaoMing(), args);
        System.out.println("after");
        return result;
      }
    });

    System.out.println(person2.getClass());

  }
}

2.InvocationHandler接口

public interface CLInvocationHandler {

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

}

3.ClassLoader类加载器

public class CLClassLoader extends ClassLoader {

  private File classPathFile;

  public CLClassLoader(){

    String classPath = CLClassLoader.class.getResource("").getPath();

    this.classPathFile= new File(classPath);
  }

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

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

    if (classPathFile!= null ){

      File classFile = new File(classPathFile, name.replace("\\.", "/") + ".class");

      if (classFile.exists()){

        FileInputStream inputStream =null;

        ByteArrayOutputStream outputStream = null;
        try{
          inputStream=new FileInputStream(classFile);

          outputStream= new ByteArrayOutputStream();

          byte[] bytes = new byte[1024];
          int len;
          while ((len=inputStream.read(bytes))!=-1){
            outputStream.write(bytes,0,len);
          }
          return defineClass(className,outputStream.toByteArray(),0,outputStream.size());
        }catch (Exception e){
          e.printStackTrace();
        }finally {
          if (inputStream!= null){
            try {
              inputStream.close();
            } catch (IOException e) {
              e.printStackTrace();
            }
          }
          if (outputStream!=null){
            try {
              outputStream.close();
            } catch (IOException e) {
              e.printStackTrace();
            }
          }
        }

      }

    }
    return super.findClass(name);
  }
}

4.测试使用的接口与目标类

//测试使用的接口
public interface Person {

  void eat();

  String call(String name);
}

//测试使用目标类
public class XiaoMing implements Person {
  @Override
  public void eat() {
    System.out.println("吃东西");
  }

  //@Override
  public String call(String name) {
    return name;
  }
}

注意测试方法在CLProxy 的main 方法中。

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持我们。