[英]TCP Server and Client in Java
我尝试使用 Java 构建 TCP 服务器和客户端。 他们可以连接,运行良好,但我有一个错误。
这是服务器端:
package com.company;
import java.io.*;
import java.net.*;
public class Main {
public static void main (String[] args) throws IOException {
System.out.println("The server is ready");
ServerSocket serverSocket = new ServerSocket (1234);
Socket clientSocket = serverSocket.accept ();
BufferedReader in = new BufferedReader (new InputStreamReader (clientSocket.getInputStream ()));
PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true);
String message, modifiedMessage;
message = in.readLine ();
System.out.print("The received message from client: " + message);
modifiedMessage = message.toUpperCase();
out.print(modifiedMessage);
System.out.println ("\nModified message which is sent to client: " + modifiedMessage);
}
}
服务器必须从客户端接收消息,然后将其转换为大写字符串。
客户端是:
package com.company;
import java.io.*;
import java.net.*;
public class Main {
public static void main(String[] args) throws IOException {
Socket socket = new Socket("127.0.0.1", 1234);
PrintWriter out = new PrintWriter(socket.getOutputStream(), true);
System.out.println("Enter a lowercase sentence: ");
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
BufferedReader in = new BufferedReader((new InputStreamReader(socket.getInputStream())));
String messageSent = reader.readLine();
System.out.println("The message sent is: " + messageSent);
out.println(messageSent);
String messageReceived = in.readLine();
System.out.println("The modified message is: " + messageReceived);
}
}
我希望客户端能够打印小写句子和接收到的(修改后的)大写句子。 问题是,当我输入一个简单的单词 say hello 时,我的客户端只会打印原始字符串,而不是修改后的字符串。
服务器的输出是:
The received message from client: hello
The modified message sent to the client is: HELLO
但是客户端的输出是:
The message sent is: hello
The modified message is: null
我知道服务器能够将字符串转换为大写版本并连接到我的客户端。 为什么我的客户端不打印收到的消息? 它真的没有收到吗?
您需要刷新消息。 PrintWriter 在 println 中调用 flush,print 不调用。
在服务器端,您需要更改为: out.println(modifiedMessage); 而不是 out.print(modifiedMessage);
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