学步园

随着服务器的压力不断的上升，rmi的重要性日益突出

今天就简单的剖析以下RMI的底层实现原理

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（1）rmi调用承载对象：call

import java.io.*;
public class Call implements Serializable{
  private String className;  //表示类名
  private String methodName; //表示方法名
  private Class[] paramTypes; //表示方法参数类型
  private Object[] params; //表示方法参数值
  private Object result;  //表示方法的返回值或者方法抛出的异常
  
  public Call(){}
  public Call(String className,String methodName,Class[] paramTypes,
                            Object[] params){
    this.className=className;
    this.methodName=methodName;
    this.paramTypes=paramTypes;
    this.params=params;
  }
  
  public String getClassName(){return className;}
  public void setClassName(String className){this.className=className;}

  public String getMethodName(){return methodName;}
  public void setMethodName(String methodName){this.methodName=methodName;}

  public Class[] getParamTypes(){return paramTypes;}
  public void setParamTypes(Class[] paramTypes){this.paramTypes=paramTypes;}

  public Object[] getParams(){return params;}
  public void setParams(Object[] params){this.params=params;}

  public Object getResult(){return result;}
  public void setResult(Object result){this.result=result;}

  public String toString(){
    return "className="+className+" methodName="+methodName;
  }
} 

（2）客户端执行rmi调用

import java.io.*;
import java.net.*;
import java.util.*;
public class SimpleClient {
  public void invoke()throws Exception{
    Socket socket = new Socket("localhost",8000);
    OutputStream out=socket.getOutputStream();
    ObjectOutputStream oos=new ObjectOutputStream(out);
    InputStream in=socket.getInputStream();
    ObjectInputStream ois=new ObjectInputStream(in);
 
    //Call call=new Call("remotecall.HelloService","getTime",new Class[]{},new Object[]{});
    Call call=new Call("remotecall.HelloService","echo",new Class[]{String.class},new Object[]{"Hello"}); 
    oos.writeObject(call);
    call=(Call)ois.readObject(); 
    System.out.println(call.getResult());

    ois.close();
    oos.close();
    socket.close();
  }
  public static void main(String args[])throws Exception {
    new SimpleClient().invoke(); 
  }
}

（服务器端更具call对象的相关信息，通过反射调用方法，并将结果返回给客户端）

import java.io.*;
import java.net.*;
import java.util.*;
import java.lang.reflect.*;
public class SimpleServer {
  private Map remoteObjects=new HashMap();
  
  public void register(String className,Object remoteObject){
    remoteObjects.put( className,remoteObject);
  } 
  public void service()throws Exception{
    ServerSocket serverSocket = new ServerSocket(8000);
    System.out.println("服务器启动.");
    while(true){
      Socket socket=serverSocket.accept();
      InputStream in=socket.getInputStream();
      ObjectInputStream ois=new ObjectInputStream(in);
      OutputStream out=socket.getOutputStream();
      ObjectOutputStream oos=new ObjectOutputStream(out);

      Call call=(Call)ois.readObject();
      System.out.println(call);
      call=invoke(call);
      oos.writeObject(call);
      
      ois.close();
      oos.close();
      socket.close();
    }
  }

  public Call invoke(Call call){
    Object result=null;
    try{
      String className=call.getClassName();
      String methodName=call.getMethodName();
      Object[] params=call.getParams();
      Class classType=Class.forName(className); 
      Class[] paramTypes=call.getParamTypes();
      Method method=classType.getMethod(methodName,paramTypes);  
      Object remoteObject=remoteObjects.get(className);------>>>至于这边为什么不用class  newInstance得到一个新对象————>>>必须式注册的组件才能被访问
      if(remoteObject==null){
        throw new Exception(className+"的远程对象不存在");
      }else{
        result=method.invoke(remoteObject,params);
      }
    }catch(Exception e){result=e;}

    call.setResult(result);
    return call;
  }

  public static void main(String args[])throws Exception {
    SimpleServer server=new SimpleServer();
    server.register("remotecall.HelloService",new HelloServiceImpl());
    server.service();
  }
}