Question

我们获得了一个网络分配来实现客户端/服务器项目。我们给出的一个例子是客户端/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，在我的运行配置设置中，我输入'ADD，5,6'作为客户端程序的参数，但输出结果为null。你们能看出为什么会这样吗？

客户代码：

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();


    }

}

服务器代码：

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

在大多数情况下，调试是一种查看正在发生的事情的方法。因为它出现了正确的参数格式：

ADD 5,6

但operation中的CalculatorClient字符串只抓取ADD部分args内容实际为：{"ADD", "5,6"}。因此，要形成有效的请求，您应该以某种方式连接您的输入：

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

JAVA客户端/服务器计算器示例

1 个答案: