java - 客户端无法向服务器发送第二次执行

Question

我有一个 Java 的服务器客户端程序。服务器进行一些基本计算并将结果发送给客户端。在此之前，客户端必须发送操作和值。我可以成功运行一次，但是当我插入第二个操作和值时，我得到 null 的结果。为什么会出现这种情况？

服务器

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

public class Server {

private static final int PORT = 9001;

public static void main(String[] args) throws IOException {
    // TODO Auto-generated method stub
    System.out.println("O servidor está a correr...");
    ServerSocket listener = new ServerSocket(PORT);
    listener.setSoTimeout(0);
    try{
        while(true){
            new Handler(listener.accept()).start();
        }
    }finally{
        listener.close();
        System.out.println("Servidor fechou!");
    }
}

private static class Handler extends Thread{
    private Socket socket;
    private BufferedReader in;
    private PrintWriter out;

    public Handler(Socket socket){
        this.socket = socket;
    }

    public void run(){
        try{
            in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            out = new PrintWriter(socket.getOutputStream(), true);
            while(true){
                String line = in.readLine();
                System.out.print(line);
                double result = parseExecution(line);
                out.write("" + result + "\n");
                out.close();
                in.close();
            }
        }catch(IOException e){
            e.printStackTrace();
        }
        out.flush();


    }

    private double parseExecution(String line) throws IllegalArgumentException{
        // TODO Auto-generated method stub
                double result = 0;
                String [] elements = line.split(":");
                if (elements.length != 3){
                    throw new IllegalArgumentException("parsing error!");
                }
                double firstValue = 0;
                double secondValue = 0;
                try{
                    firstValue = Double.parseDouble(elements[1]);
                    secondValue = Double.parseDouble(elements[2]);
                } catch(Exception e){
                    throw new IllegalArgumentException("Invalid arguments!");
                }
            switch (elements[0].charAt(0)) {
            case '+':
                result = firstValue + secondValue;
                break;
            case '-':
                result = firstValue - secondValue;
                break;
            case '*':
                result = firstValue * secondValue;
                break;
            case '/':
                if(secondValue != 0)
                result = firstValue / secondValue;
                break;
            default: 
                throw new IllegalArgumentException("Invalid math operation!");
            }
            return result;
        }
}
}

客户端

import java.io.*;
import java.net.Socket;
import java.net.UnknownHostException;

import javax.swing.JOptionPane;
import javax.xml.bind.helpers.ParseConversionEventImpl;

public class MathClient {

private String getServerAddress(){
    return JOptionPane.showInputDialog("Introduza IP do Servidor", JOptionPane.QUESTION_MESSAGE);
}

private void run() throws IOException {
    String serverAddress = getServerAddress();
    int port = 9001;

    // criar a socket

    Socket socket = new Socket(serverAddress, port);
    BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
    BufferedReader op = new BufferedReader(new InputStreamReader(System.in));
    BufferedReader valor1 = new BufferedReader(new InputStreamReader(System.in));
    BufferedReader valor2 = new BufferedReader(new InputStreamReader(System.in));
    BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
    while(true){
        System.out.println("Operação(+,-,*,/): ");
        String operacao = op.readLine();
        System.out.println("Primeiro valor: ");
        String primeiroValor = valor1.readLine();
        System.out.println("Segundo valor: ");
        String segundoValor = valor2.readLine();
        writer.write(operacao+":"+primeiroValor+":"+segundoValor);
        writer.newLine();
        writer.flush();
        //double resultado = Double.parseDouble(reader.readLine());
        System.out.println(reader.readLine());

    }

}

public static void main(String[] args) throws UnknownHostException, IOException {
    MathClient client = new MathClient();
    client.run();
}

}

谢谢!

编辑:在 run() 方法中我正在执行一个 while 循环。但现在我收到一条错误消息，提示“流已关闭”。当我尝试将 in.close() 放在 while 循环之外时，它给了我另一个错误并删除了 in.close()。

java.io.IOException: Stream closed
at java.io.BufferedReader.ensureOpen(Unknown Source)
at java.io.BufferedReader.readLine(Unknown Source)
at java.io.BufferedReader.readLine(Unknown Source)
at MathFinal.Server$Handler.run(Server.java:41)

第 41 行是:String line = in.readLine();

Answer 1

我修复了您的代码，它可以使用 Java 7 try-with-resources 运行。这是重要的片段:

private static class Handler extends Thread{
    private Socket socket;

    public Handler(Socket socket){
        this.socket = socket;
    }

    public void run(){
        try(BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
                PrintWriter out = new PrintWriter(socket.getOutputStream(), true)) {
            while(true){
                String line = in.readLine();
                System.out.print(line);
                double result = parseExecution(line);
                out.write("" + result + "\n");
                out.flush();
            }
        }catch(IOException e){
            e.printStackTrace();
        }

    }

这样做，您无需担心自己关闭资源。