我正在尝试使用套接字来对客户端和服务器交互进行编程。用户可以阅读他们的消息、给某人撰写消息，然后退出。一切正常，除了“没有消息”打印两次而不是一次，我不明白为什么。我将把相关代码放在下面，任何帮助都会很棒。谢谢!
客户端.java
import java.io.*;
import java.net.*;
public class Client {
public static void main(String[] args) {
String messages = "";
// Makes sure there are only two arguments entered
if(args.length != 2) {
System.err.println("Usage: java Client <host name> <port number>");
System.exit(1);
}
// Stores the command line arguments for readability further in the program
String host = args[0];
int port = Integer.parseInt(args[1]);
try (
// Creates the socket to be used
Socket s = new Socket(host, port);
// Reader and Writer to talk with Server
PrintWriter pw =
new PrintWriter(s.getOutputStream(), true);
BufferedReader bf = new BufferedReader(
new InputStreamReader(s.getInputStream()));
) {
// Reader to read from standard input (keyboard)
BufferedReader keyboard =
new BufferedReader(new InputStreamReader(System.in));
// User interface
while (true) {
System.out.println("Please enter your username: ");
String username = keyboard.readLine();
// Check that the login is valid
if (username == null) {
System.out.println("No username entered");
}
else if (username.contains(" ")) {
System.out.println("Username cannot contain spaces");
}
// Send username to server and return number of messages
else {
pw.println(username);
messages = bf.readLine();
System.out.println("You have " + Integer.parseInt(messages) + " messages");
break;
}
}
// Enable the user to continue reading and composing messages until
// they choose to exit
while (true) {
System.out.println("Would you like to READ, COMPOSE or EXIT?");
String choice = keyboard.readLine();
// Shows the messages left for the user
if (choice.equals("READ")) {
pw.println("READ");
messages = bf.readLine();
if (Integer.parseInt(messages) == 0) {
System.out.println("NO MESSAGES");
}
else {
String incoming = bf.readLine();
System.out.println(incoming);
incoming = bf.readLine();
System.out.println(incoming);
}
}
// Allows user to write a message to another user
else if (choice.equals("COMPOSE")) {
pw.println("COMPOSE");
// I've separated this into two lines for readability
System.out.println("Enter message recipient");
String recipient = keyboard.readLine();
if (recipient == null) {
System.out.println("No recipient username entered");
}
else if (recipient.contains(" ")) {
System.out.println("Recipient username cannot contain spaces");
}
else {
pw.println(recipient);
System.out.println("Enter message to be sent");
String im = keyboard.readLine();
pw.println(im);
System.out.println(bf.readLine());
}
}
else if (choice.equals("EXIT")) {
pw.println("EXIT");
System.exit(1);
}
else {
System.out.println("Error: you must either READ, COMPOSE or EXIT");
}
}
}
// Catches the exception in which the server cannot be found
catch(IOException e) {
System.out.println("Error, could not connect to Server");
System.exit(1);
}
}
}
服务器.java
import java.io.*;
import java.net.*;
public class Server {
public static void main(String[] args) {
String request;
// Makes sure that the user has specified the correct number of command line arguments
if(args.length != 1) {
System.err.println("Usage: java Server <port number>");
System.exit(1);
}
int port = Integer.parseInt(args[0]);
try (
// Creates a server socket and waits for a connection
ServerSocket ss = new ServerSocket(port);
// A socket to communicate with the client
Socket cs = ss.accept();
// Reader and Writer to talk with Client
PrintWriter pw =
new PrintWriter(cs.getOutputStream(), true);
BufferedReader bf = new BufferedReader(
new InputStreamReader(cs.getInputStream()));
)
// Links the server to the protocol
{
Protocol protocol = new Protocol();
protocol.storeUsername(bf.readLine());
pw.println(protocol.messagesNumber());
// Loop through user input until EXIT is entered
while (true) {
request = bf.readLine();
// Controls output if user inputs READ
if (request.equals("READ")) {
pw.println(protocol.messagesNumber());
if (protocol.messagesNumber() != 0) {
pw.println(protocol.readSender());
pw.println(protocol.readMessage());
}
}
// Controls input if user inputs COMPOSE
else if (request.equals("COMPOSE")) {
String sender = bf.readLine();
String message = bf.readLine();
if (protocol.append(sender, message)) {
pw.println("MESSAGE SENT");
}
else {
pw.println("MESSAGE FAILED");
}
}
// Exits the server
else {
System.exit(1);
}
}
}
// Catches the exception in which the server cannot find a client
catch(IOException e) {
System.out.println("Failed to find a client");
System.exit(1);
}
}
}
协议(protocol).java
import java.net.*;
import java.io.*;
import java.util.*;
public class Protocol {
private String username;
private String recipient;
private String sender;
private HashMap<String, ArrayList<String>> senderMap = new HashMap<String, ArrayList<String>>();
private HashMap<String, ArrayList<String>> messageMap = new HashMap<String, ArrayList<String>>();
// Stores the username for the logged in user
public void storeUsername(String user) {
username = user;
}
// Stores the recipient name
public void storeRecipient(String name) {
recipient = name;
}
// Returns how many messages the logged in user has
public int messagesNumber() {
if(messageMap.containsKey(username))
return messageMap.get(username).size();
else
return 0;
}
public boolean append(String recipient, String message) {
boolean success = false;
// If there is an entry for that name, just add the message to the end
if(messageMap.containsKey(recipient)) {
senderMap.get(recipient).add(username);
messageMap.get(recipient).add(message);
success = true;
}
// If there is no entry for that name, create a new entry with a list of messages and add the first message
else {
senderMap.put(recipient, new ArrayList<String>());
senderMap.get(recipient).add(username);
messageMap.put(recipient, new ArrayList<String>());
messageMap.get(recipient).add(message);
success = true;
}
return success;
}
public String readSender() {
// If the user has an entry and has at least 1 sender, return the least recent sender and then remove it (the sender first in the list)
if(senderMap.containsKey(username)) {
if(senderMap.get(username).size() > 0) {
String temp = senderMap.get(username).get(0);
senderMap.get(username).remove(0);
return temp;
}
else
// If there are no messages left to read
return "NO MESSAGES";
}
else
// If the login hasn't been created yet
return "NO MESSAGES";
}
public String readMessage() {
// If the user has an entry and has at least 1 unread message, return the least recent unread message and then remove it (the first message in the list)
if(messageMap.containsKey(username)) {
if(messageMap.get(username).size() > 0) {
String temp = messageMap.get(username).get(0);
messageMap.get(username).remove(0);
return temp;
}
else
// If there are no messages left to read
return "NO MESSAGES";
}
else
// If the login hasn't been created yet
return "NO MESSAGES";
}
}
最佳答案
原因是您两次获取“NO MESSAGES”。
看一下 server.java
if (request.equals("READ")) {
pw.println(protocol.messagesNumber());
pw.println(protocol.readSender());
pw.println(protocol.readMessage());
}
这将调用 readSender() 和 readMessage() 方法。
现在看一下这两个方法的返回语句 - return "NO MESSAGES";
只需在这两个方法中设置调试断点并进行调试和检查即可!
关于java - 输出被打印两次，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/43165090/