可能重复:
为什么我的应用程序没有进入我的 if 语句
我正在尝试用 Java 编写控制台客户端-服务器应用程序;使用套接字,我目前有一个简单的登录系统和一个简单的命令系统。登录系统似乎工作,连接似乎工作。
但是,命令系统似乎根本不起作用,当服务器收到命令时,它似乎没有发回任何东西。
所以我的主要问题是为什么我的服务器在收到命令时不向客户端发送任何内容?
这是我的服务器:
import java.io.*;
import java.net.*;
class TCPServer2
{
public static void main(String argv[]) throws Exception
{
//error is caused by command being used differently to login & username/password strings.
//consider removing command as a set string and adding a statement which takes
//the readLine value, adds it to a string and the command is the value of said string.
//If string is = "listLanguages" do this else if = "getcost" do this else "invalid cmd".
ServerSocket welcomeSocket = new ServerSocket(6789);
Map<String, String> userDetails = new HashMap<String, String>();
userDetails.put("JOHN","UNCP");
userDetails.put("MATT","UNCP");
String Command;
String username;
String username1;
String password;
String password1;
String cmd;
while(true)
{
Socket connectionSocket = welcomeSocket.accept();
BufferedReader inFromClient =
new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));
DataOutputStream outToClient = new DataOutputStream(connectionSocket.getOutputStream());
username = inFromClient.readLine();
System.out.println("\nUsername received: " + username);
password = inFromClient.readLine();
System.out.println("\nPassword received: " + password);
username1=username.toUpperCase();
password1=password.toUpperCase();
if (userDetails.get(username1).equals(password1))
{
outToClient.writeBytes("Hello " + username1);
outToClient.writeBytes("\nOther users registered on the server currently include: \n");
for (String str : userDetails.keySet())
{
outToClient.writeBytes(str);
}
}
else
{
outToClient.writeBytes("Invalid Username and/or password.\n");
}
BufferedReader inFromClient2 =
new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));
DataOutputStream outToClient2 = new DataOutputStream(connectionSocket.getOutputStream());
Command = inFromClient2.readLine();
System.out.println("\nCommand received: " + Command);
if(Command.equals("listTranslations"))
{
outToClient2.writeBytes("English,Thai,Geordie,etc.");
}
else
{
if(Command.equals("getCost"))
{
outToClient2.writeBytes("£100\n");
}
else
{
outToClient2.writeBytes("Invalid Command");
}
}
}
}
}
这是我的客户:
import java.io.*;
import java.net.*;
class TCPClient2
{
public static void main(String argv[]) throws Exception
{
String userName;
String passWord;
String loginInfo;
String loginInfo2;
String loginInfo3;
String command;
String commandInfo;
String commandInfo2;
BufferedReader inFromUser = new BufferedReader( new InputStreamReader(System.in));
Socket clientSocket = new Socket("localhost", 6789);
DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());
BufferedReader inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
System.out.println("Username: ");
userName = inFromUser.readLine();
outToServer.writeBytes(userName + "\n");
System.out.println("Password: ");
passWord = inFromUser.readLine();
outToServer.writeBytes(passWord + "\n");
loginInfo = inFromServer.readLine();
System.out.println(loginInfo);
loginInfo2 = inFromServer.readLine();
System.out.println(loginInfo2);
loginInfo3 = inFromServer.readLine();
System.out.println(loginInfo3);
System.out.println("Please enter a command: ");
command = inFromUser.readLine();
outToServer.writeBytes(command);
commandInfo = inFromServer.readLine();
System.out.println(commandInfo);
commandInfo2 = inFromServer.readLine();
System.out.println(commandInfo);
clientSocket.close();
}
}
它的工作原理如下:客户端连接到服务器,客户端要求用户登录,用户输入他的登录信息,服务器检查登录信息,服务器告诉客户端它已成功登录,客户端询问用户输入命令,用户输入命令(请求价格),命令被发送到服务器,服务器发回所需的信息,然后它应该循环回被要求输入命令的用户。
但是,它不这样做。用户登录后卡在“当前在服务器上注册的其他用户包括:”行,没有打印任何数据。
为什么要这样做?