JAVA客户端/服务器计算器示例

Question

我们获得了实现客户端/服务器项目的网络分配。我们给出的一个例子是一个客户端/服务器计算器程序。我已经发布了以下两个类的代码。我正在使用eclipse，并在我的运行配置设置中输入'ADD，5,6'作为客户端程序的参数，但输出为空。你们能看到为什么会发生这种情况吗？

客户端代码：

package networking; 

import java.io.BufferedReader; 
import java.io.IOException; 
import java.io.InputStreamReader; 
import java.io.PrintWriter; 
import java.net.Socket; 
import java.net.UnknownHostException; 

public class CalculatorClient { 

    /** 
    * @param args 
    * @throws IOException 
    * @throws UnknownHostException 
    */ 
    public static void main(String[] args) throws UnknownHostException, IOException { 
     String operation = args[0]; 

     // Create a new socket object and names it socket 
     // the constructor requires the name of the computer and the port number to which you want to connect 
     Socket socket = new Socket("localhost", CalculatorServer.PORT_NO); 

     // gets the socket's input stream and opens a BufferedReader on it. 
     BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream())); 

     // gets the socket's output stream and opens a PrintWriter on it 
     PrintWriter pw = new PrintWriter(socket.getOutputStream()); 

     pw.println(operation); 
     pw.flush(); 

     if (!"quit".equals(operation.trim())) { 
      String line = reader.readLine(); 
      reader.close(); 
      System.out.println("Line 36 in Client"); 
      System.out.println("result: " + line); 
      System.out.println("Line 38 in Client"); 
     } 
     socket.close(); 


    } 

} 

Server代码：

package networking; 

import java.io.BufferedReader; 
import java.io.IOException; 
import java.io.InputStreamReader; 
import java.io.PrintWriter; 
import java.net.ServerSocket; 
import java.net.Socket; 

/** 
* Support add, subtraction, multiplication, division 
* @author hluu 
* 
*/ 
public class CalculatorServer { 
    enum OPERATOR { ADD, SUB, MULT, DIV }; 

    public static final int PORT_NO = 8888; 

    /** 
    * @param args 
    * @throws IOException 
    * @throws InterruptedException 
    */ 
    public static void main(String[] args) throws IOException, InterruptedException { 

     ServerSocket serverSocket = new ServerSocket(PORT_NO); 
     System.out.println("... server is accepting request"); 

     while (true) { 
      Socket socket = serverSocket.accept(); 

      BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream())); 
      String line = reader.readLine(); 

      System.out.println("got request: " + line); 
      System.out.println("Right after getting request"); 

      if (line.trim().startsWith("quit")) { 
       System.out.println("... server shutting down ..."); 
       socket.close(); 
       break; 
      } else { 
       System.out.println("Entering Else"); 
       System.out.println(line); 
       processRequest(socket, line); 
      } 
     } 

     System.out.println("... closing server socket ..."); 
     serverSocket.close(); 
    } 

    private static void processRequest(Socket socket, String line) throws IOException, InterruptedException { 
     PrintWriter pw = new PrintWriter(socket.getOutputStream()); 

     String[] tokens = line.split(" "); 

     if (tokens.length != 2) { 
      pw.println("invalid command: " + line); 
      socket.close(); 
      return; 
     } 

     String[] operands = tokens[1].split(","); 

     if (operands.length != 2) { 
      pw.println("invalid command: " + line); 
      socket.close(); 
      return; 
     } 

     String operator = tokens[0].trim(); 

     try { 
      Double operand1 = Double.valueOf(operands[0].trim()); 
      Double operand2 = Double.valueOf(operands[1].trim()); 
      System.out.println(operand1);System.out.println(operand2); 

      double result = 0; 
      OPERATOR op = OPERATOR.valueOf(operator.toUpperCase()); 
      switch (op) { 
      case ADD: 
       result = operand1 + operand2; 
       break; 
      case SUB: 
       System.out.println("Entering SUB"); 
       result = operand1 - operand2; 
       break; 
      case MULT: 
       result = operand1 * operand2; 
       break; 
      case DIV: 
       result = operand1/operand2; 
       break; 
      default: 
       pw.println("invalid operand: " + line); 
       pw.flush(); 
       socket.close(); 
       return; 
      } 

      System.out.println("send back result: " + result); 
      pw.println(result); 
     } catch (NumberFormatException nfe) { 
      pw.println("invalid operand: " + line); 
     } 

     pw.flush(); 
     socket.close(); 
    } 

} 

Answer 1

调试是在大多数情况下的方式，看看发生了什么。 因为它出来你的观点的权利的格式是：

ADD 5,6

但operation串在你CalculatorClient争夺只有ADD一部分args内容居然是：{"ADD", "5,6"}。因此，要形成有效的请求，你应该Concat的你输入像一些方法：

String operation = args[0] + " " + args[1];