java - 如何使用 I/O 将 double 从客户端发送到服务器并返回客户端

Question

我无法使用扫描仪或打印机

我有一个客户端和一个服务器。

我运行服务器，输出是，

Creating Server Socket 5095 . . . 
SUCCESS!!!
in while loop
Waiting for connection.

然后我运行客户端，输出是，

Creating Client Socket 
SUCCESS!!!
initializing variables
variables flushed
initializing input
java.io.EOFException
at java.io.DataInputStream.readFully(Unknown Source)
at java.io.DataInputStream.readLong(Unknown Source)
at java.io.DataInputStream.readDouble(Unknown Source)
at Client.runClient(Client.java:38)
at Client.main(Client.java:51)

我想在客户端初始化一些 double ，并将它们发送到服务器，在服务器上对它们进行解析和操作，然后将结果发送回客户端。

客户端因 EOFException 失败，服务器因 ClassCastException 失败

我做错了什么？

import java.io.*;
import java.net.*;
import java.util.*;

public class Client {

static void pStr(String p) {
    System.out.println(p);
}

static void runClient() {

    Socket client;
    DataOutputStream output;
    DataInputStream input;

    try {
        pStr("Creating Client Socket ");
        client = new Socket("127.0.0.1", 5095);
        pStr("SUCCESS!!!");

        input = new DataInputStream(client.getInputStream());
        output = new DataOutputStream(client.getOutputStream());

        System.out.println("initializing variables");
        double arg1 = 5;
        output.writeDouble(arg1);
        output.flush();

        double arg2 = 3;
        output.writeDouble(arg2);
        output.flush();

        System.out.println("variables flushed");

        System.out.println("initializing input");
        // error occurs at next line
        double ans = input.readDouble();
        System.out.println("input has been read");
        System.out.println(ans);

        input.close();
        output.close();
        client.close();
    } catch (IOException e) {
        e.printStackTrace();
    }
}
 // this is second class file
public static void main(String args[]) {
    Client.runClient();
}
}
public class SimpleServer {

static void pStr(String p) {
    System.out.println(p);
}

static void runServer() {
    ServerSocket server;

    try {
        // Create a ServerSocket.
        pStr("Creating Server Socket " + 5095 + " . . . ");
        server = new ServerSocket(5095);
        pStr("SUCCESS!!!");

        while (true) {
            System.out.println("in while loop");
            Socket connection;
            DataOutputStream output = null;
            DataInputStream input = null;

            pStr("Waiting for connection.");
            connection = server.accept();
            pStr("Done");

            System.out.println("entering try");

            try {
                // Get input and output streams.
                input = (DataInputStream) connection.getInputStream();
                output = (DataOutputStream) connection.getOutputStream();

                String ansStr;

                double arg1, arg2;
                try {
                    System.out.println("int try block");
                    arg1 = input.readDouble();
                    arg2 = input.readDouble();

                    ansStr = "" + arg1 + "," + arg2;
                    System.out.println(ansStr);

                    output.writeDouble(arg1);
                    output.writeDouble(arg2);

                } catch (Exception e) {
                    ansStr = e.getMessage();
                }
                output.flush();
            } catch (Exception e) {
                pStr("Error in Protocol: " + e.getMessage());
            } finally {
                try {
                    input.close();
                } catch (Exception e) {
                }
                try {
                    output.close();
                } catch (Exception e) {
                }
                try {
                    connection.close();
                } catch (Exception e) {
                }
            }
        }
    } catch (Exception e) {
        pStr("Error making ServerSocket");
    }
}

public static void main(String args[]) {
    runServer();
}
}

Answer 1

您的服务器代码因 ClassCastException 崩溃，而您却莫名其妙地没有提及。因此，连接被关闭而没有发送任何数据，因此出现客户端异常。

仅通过强制转换无法从套接字获取 DataInputStream 或 DataOutputStream。您必须使用在客户端中使用的相同流程。