我要最简单的解释。我的 Java TCP 项目有一个服务器和三个客户端。
服务器有一个 ClientThread。每个客户端都有一个 ServerThread 和一个 UserThread。
工作流程是：
1. 客户端（例如，client_0）的 UserThread 获取用户输入，然后向服务器发送消息。
2. 服务器的 ClientThread 捕获来自 client_0 的消息，并将另一条消息发送到不同客户端（例如，client_1）的 ServerThread。
3、client_1的ServerThread再发回一条消息给运行在服务器端的ClientThread；
第 3 步的消息未到达服务器。
总共有 3 个客户端，比如 client_0、client_1 和 client_2。
最初的想法是，如果 client_0 请求服务器，则服务器与 client_1 和 client_2 通信。这就是if(i==cid) continue;服务器中 for 循环中的行的原因。但是，如果我注释掉这一行，服务器将与 client_0 通信（这在语义上是不必要的）并且不会发生消息传递问题。之后服务器与client_1通信，问题再次出现。
服务器可以接收来自客户端（client_0）的 ServerThread 的消息，该客户端从其 UserThread 发送原始请求（msgToServer.println("get list");）以启动整个过程。但是 Server 无法从任何其他客户端的 ServerThread 获取消息，即使它可以向其他客户端发送消息并且所有客户端程序都是相同的，并且所有 ServerThreads 和 UserThreads 应该以相同的方式工作。怎么可能？
服务器：
package serverftp;
import java.io.*;
import java.net.*;
public class ServerFTP {
static String[] id = {"cp 1","cp 2","cp 3"};
static String[] pass = {"123","456","789"};
static BufferedReader[] msgFromClient = new BufferedReader[3];
static PrintWriter[] msgToClient = new PrintWriter[3];
static InputStream[] fileFromClient = new InputStream[3];
static OutputStream[] fileToClient = new OutputStream[3];
public static void main(String[] args) throws Exception {
ServerSocket welcome = new ServerSocket(6789);
// connecting the three clients
for(int i=0; i<3; i++) {
System.out.println("Waiting for Client "+i);
Socket clientSocket;
clientSocket = welcome.accept();
while(true) {
System.out.println("Connecting Client "+i);
BufferedReader fromClient = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
PrintWriter toClient = new PrintWriter(clientSocket.getOutputStream(),true);
// get id pass from client
String clientId = fromClient.readLine();
System.out.println(clientId);
String clientPass = fromClient.readLine();
System.out.println(clientPass);
// check id pass and feedback
if(clientId.equals(id[i]) && clientPass.equals(pass[i])) {
toClient.println("ok");
msgFromClient[i] = fromClient;
msgToClient[i] = toClient;
fileFromClient[i] = clientSocket.getInputStream();
fileToClient[i] = clientSocket.getOutputStream();
break;
} else {
toClient.println("error");
}
}
ClientThread ct = new ClientThread(i);
ct.start();
System.out.println("Client "+i+" connected!");
}
welcome.close();
}
}
class ClientThread extends Thread {
int cid;
String msg;
public ClientThread(int client_id) {
cid = client_id;
try {
// telling client it's serial
ServerFTP.msgToClient[cid].println(Integer.toString(cid));
} catch(Exception ex) {
ex.printStackTrace();
}
}
@Override
public void run() {
while(true) {
try {
// get request from receiver
msg = ServerFTP.msgFromClient[cid].readLine();
if(msg.equals("get list")) {
System.out.println(cid+" "+msg);
msg = ServerFTP.msgFromClient[cid].readLine();
System.out.println(cid+" "+msg);
for(int i=0; i<3; i++) {
if(i==cid) continue;
// send sender request for file list
ServerFTP.msgToClient[i].println("give list");
System.out.println("request sent to client "+i);
// get file count from sender
msg = ServerFTP.msgFromClient[i].readLine();
System.out.println("file count caught!!!"); // THIS LINE NEVER EXECUTES
System.out.println("File count "+msg);
}
}
} catch(Exception ex) {
ex.printStackTrace();
}
}
}
}
该线路System.out.println("file count caught!!!");永远不会被调用。
客户：
package clientftp_1;
import java.io.*;
import java.net.*;
public class ClientFTP_1 {
static String[] allPaths = { "...path...\\client_1_folder",
"...path...\\client_2_folder",
"...path...\\client_3_folder"};
public static void main(String[] args) throws Exception {
InetAddress inetAddress = InetAddress.getLocalHost();
Socket server = new Socket(inetAddress,6789);
int myId;
// login phase
BufferedReader fromUser = new BufferedReader(new InputStreamReader(System.in));
BufferedReader fromServer = new BufferedReader(new InputStreamReader(server.getInputStream()));
PrintWriter toServer = new PrintWriter(server.getOutputStream(),true);
InputStream getFile = server.getInputStream();
OutputStream sendFile = server.getOutputStream();
while(true) {
System.out.println("id: ");
String msg = fromUser.readLine();
toServer.println(msg);
System.out.println("password: ");
msg = fromUser.readLine();
toServer.println(msg);
msg = fromServer.readLine();
if(msg.equals("ok")) {
System.out.println("Connection Successful!");
myId = Integer.parseInt(fromServer.readLine());
System.out.println("Client serial is: "+myId);
System.out.println("Folder path is: "+allPaths[myId]);
break;
} else {
System.out.println("Error! Try again please.");
}
}
ServerThread st = new ServerThread(allPaths[myId],fromUser,fromServer,toServer,getFile,sendFile);
st.start();
UserThread ut = new UserThread(allPaths[myId],fromUser,fromServer,toServer,getFile,sendFile);
ut.start();
}
}
class ServerThread extends Thread {
String folderPath;
String msg;
BufferedReader msgFromServer,msgFromUser;
PrintWriter msgToServer;
InputStream fileFromServer;
OutputStream fileToServer;
public ServerThread(String path,BufferedReader fromUser,BufferedReader fromServer,PrintWriter toServer,InputStream getFile,OutputStream sendFile) throws Exception {
folderPath = path;
msgFromUser = fromUser;
msgFromServer = fromServer;
msgToServer = toServer;
fileFromServer = getFile;
fileToServer = sendFile;
}
@Override
public void run() {
System.out.println("Server Thread Started");
while(true) {
try {
// receive request
msg = msgFromServer.readLine();
System.out.println("request received from server");
if(msg.equals("give list")) {
// get filenames
File folder = new File(folderPath);
File[] fileList = folder.listFiles();
int cnt = fileList.length;
System.out.println("count calculated");
// sned file count to server
msgToServer.println(Integer.toString(cnt));
System.out.println("count sent to server"); // THIS LINE PRINTS
}
} catch(Exception ex) {
ex.printStackTrace();
}
}
}
}
class UserThread extends Thread {
String folderPath;
String msg;
BufferedReader msgFromServer,msgFromUser;
PrintWriter msgToServer;
InputStream fileFromServer;
OutputStream fileToServer;
public UserThread(String path,BufferedReader fromUser,BufferedReader fromServer,PrintWriter toServer,InputStream getFile,OutputStream sendFile) throws Exception {
folderPath = path;
msgFromUser = fromUser;
msgFromServer = fromServer;
msgToServer = toServer;
fileFromServer = getFile;
fileToServer = sendFile;
}
@Override
public void run() {
System.out.println("USer Thread Started");
while(true) {
try {
// input from user
msg = msgFromUser.readLine();
if(msg.equals("get list")) {
// send request to server
msgToServer.println("get list");
msgToServer.println("fahim list");
}
} catch(Exception ex) {
ex.printStackTrace();
}
}
}
}
该行System.out.println("count sent to server");已打印。这意味着之前的消息发送行已经执行没有问题。
我知道服务器中的登录系统很愚蠢。但是对于这项工作来说“还可以”。上面解释的一切都发生在所有客户端都连接并登录到服务器之后。
我想我已经找到了问题所在。我对客户端程序的 ServerThread 和 UserThread 使用了相同的套接字。因此，当 ServerThread 尝试响应服务器时，消息很可能会通过同一套接字发送到服务器中正在侦听消息的另一个不同线程（认为消息来自 UserThread）。
本文收集自互联网，转载请注明来源。
如有侵权，请联系[email protected] 删除。
我来说两句