Java服务器将仅接受来自我的客户端的一项

Question

我已经制作了一个多线程服务器，该服务器连接到MySQL数据库并接受来自客户端的请求。 服务器应该始终在侦听客户端命令，但这不会发生。 它只接受一个命令将其发送到数据库并获取我需要的任何内容，然后就完成了。 它不再接受任何命令。 我为您提供客户端和服务器。

 import java.io.BufferedReader; import java.io.DataInputStream; import java.io.DataOutputStream; import java.io.IOException; import java.io.InputStreamReader; import java.io.PrintWriter; import java.net.ServerSocket; import java.net.Socket; import java.rmi.ConnectException; import java.sql.Connection; import java.sql.DriverManager; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Statement; import java.util.Scanner; public class Airlines { public static void main(String[] args) { ServerSocket serverSocket = null; Socket connection = null; int port = 1234; try{ serverSocket = new ServerSocket(port); while ((connection = serverSocket.accept())!=null){ System.out.println("Client connected!"); Thread client = new Thread (new AirlinesThread(connection)); client.start(); } }catch (IOException e){ System.out.println("Binding unsuccesful..."); } } } class AirlinesThread implements Runnable{ Socket connection = null; public AirlinesThread (Socket connection){ this.connection = connection; } private static Connection connect(String url, String user, String password){ Connection result = null; try{ result = DriverManager.getConnection(url, user, password); System.out.println("Database connection successful!"); } catch(SQLException e){ System.out.println("Could not connect to the database!"); } return result; } String url = "jdbc:mysql://localhost:3306/Airlines"; String user = "root"; String pass = "123456"; Connection link = AirlinesThread.connect(url, user, pass); Statement stmt = null; ResultSet resultSet = null; public void run() { PrintWriter socketOut = null; DataInputStream socketIn = null; try{ socketOut = new PrintWriter(this.connection.getOutputStream(),true); socketIn = new DataInputStream(this.connection.getInputStream()); int command; boolean exists = false; socketOut.flush(); loop:do{ socketOut.flush(); command = socketIn.readInt(); switch (command){ case 1: try{ stmt = link.createStatement(); resultSet = stmt.executeQuery("select Flight.id, Flight.Date, Flight.Time, Flight.Total_Flight_Time, Airports.Departure, Airports.Arrivals FROM Flight, Airports WHERE Flight.id = Airports.Flight"); socketOut.flush(); socketOut.println("FlightID\\tDate\\t\\tTime\\t\\tTotal Time\\tDeparture\\tArrivals"); while (resultSet.next()) { socketOut.println(resultSet.getString("Flight.id")+"\\t\\t"+resultSet.getDate("Flight.Date")+"\\t"+resultSet.getString("Flight.Time")+"\\t"+resultSet.getString("Flight.Total_Flight_Time")+"\\t\\t"+resultSet.getString("Airports.Departure")+"\\t"+resultSet.getString("Airports.Arrivals")); } } catch(SQLException e){ System.out.println("Something went wrong at 1"); } break; case 2: try{ stmt = link.createStatement(); resultSet = stmt.executeQuery("select Flight.id, Flight.Date, Flight.Time, Pilots.First_Name, Pilots.Last_Name from Flight RIGHT JOIN Pilots ON Flight.id = Pilots.FlightID;"); socketOut.flush(); socketOut.println("FlightID\\tDate\\t\\tTime\\t\\tFirst Name\\tLast Name"); exists = resultSet.next(); if(exists == false){ socketOut.flush(); socketOut.println("Wrong request!"); System.out.println("Wrong query at 2"); } while (resultSet.next()) { socketOut.flush(); socketOut.println(resultSet.getString("Flight.id")+"\\t\\t"+resultSet.getDate("Flight.Date")+"\\t"+resultSet.getString("Flight.Time")+"\\t"+resultSet.getString("Pilots.First_Name")+"\\t\\t"+resultSet.getString("Pilots.Last_Name")); } } catch(SQLException e){ System.out.println("Something went wrong at 2"); } break; case 3: try{ stmt = link.createStatement(); resultSet = stmt.executeQuery("select Food.Breakfast, Airplanes.Plane_Model FROM Food, Airplanes Where Food.FlightID=Airplanes.Plane_Model;"); exists = resultSet.next(); if(exists == false){ socketOut.flush(); socketOut.println("Wrong request!"); System.out.println("Wrong query at 3"); } while (resultSet.next()) { socketOut.flush(); socketOut.println(resultSet.getString("Food.Breakfast")+"\\t\\t"+resultSet.getString("Airplanes.Plane_Model")); } } catch(SQLException e){ System.out.println("Something went wrong at 3"); } break; case 0 : socketOut.flush(); socketOut.println("Exitting..."); break loop; default: System.out.println("Unknown command!"); socketOut.println("Unknown command!"); break; } }while(command!=0); System.out.println("Closing connection to the client!"); }catch (IOException e){ e.printStackTrace(); }finally{ try{ if (socketIn!=null) socketIn.close(); if (socketOut!=null) socketOut.close(); if (connection!=null) connection.close(); System.out.println("Connection to server closed!"); } catch(IOException e){ System.err.println("Could not close connection!"); } } try{ if(stmt != null) stmt.close(); if(resultSet != null) resultSet.close(); if(link != null) link.close(); System.out.println("Database connection closed successfully!"); }catch(SQLException ex){ System.out.println("Could not close connection to the database!"); } } } 

客户端：

 import java.io.BufferedReader; import java.io.DataInputStream; import java.io.DataOutputStream; import java.io.IOException; import java.io.InputStreamReader; import java.io.PrintWriter; import java.net.ConnectException; import java.net.Socket; import java.util.Scanner; public class AirlinesClient { public static void main(String[] args) { Socket connection = null; Scanner socketIn = null; DataOutputStream socketOut = null; int port = 1234; String host = "localhost"; Scanner keyIn = new Scanner(System.in); try{ try{ connection = new Socket(host,port); socketIn = new Scanner(new BufferedReader(new InputStreamReader(connection.getInputStream()))); socketOut = new DataOutputStream(connection.getOutputStream()); }catch(ConnectException e){ System.out.println("Could not connect to the host!"); return; } System.out.println("Successfully connected to the server!"); System.out.println("Select from the options below:\\n1: Check schedules\\n2: Check pilots shifts\\n3: Check corresponding airplanes and food offered\\n4: Possible pilot shift changes"); loop:do{ int command; socketOut.flush(); command = keyIn.nextInt(); socketOut.flush(); socketOut.writeInt(command); while (socketIn.hasNext()){ System.out.println(socketIn.nextLine()); } }while(keyIn.nextInt()!=0); System.out.println("Closing connection to server!"); }catch(IOException e){ e.printStackTrace(); } finally{ try{ if(socketIn!=null) socketIn.close(); if(socketOut!=null) socketOut.close(); if(connection!=null) connection.close(); } catch(IOException e){ System.err.println("Socket could not be closed!"); } } } } 

Answer 1

问题是您在客户端中使用Scanner 。 执行挂在socketIn.hasNext() ，因为

public boolean hasNext()

如果此扫描程序的输入中包含另一个令牌，则返回true。 等待输入扫描时，此方法可能会阻塞。 扫描仪不会前进超过任何输入。

如果有新输入或底层流关闭（并且我们不希望这样做），则将继续执行代码。 您必须有一种无需关闭流即可知道传输结束的方法。 在下面查找非常简单的一个。

在服务器中每个try-catch block的末尾放置

socketOut.println("$$$");

在客户端中，将socketIn声明为BufferedReader并实例化为

socketIn = new BufferedReader(new InputStreamReader(connection.getInputStream()));

在客户端中也将您的loop循环更改为

int command = keyIn.nextInt();
do {
    socketOut.flush();
    socketOut.writeInt(command);
    String line;
    while (!(line = socketIn.readLine()).equals("$$$"))
        System.out.println(line);
} while ((command = keyIn.nextInt()) != 0);

这也将修复您对keyIn.nextInt()双重检查。 在您的代码中，每个循环调用两次（除了第一次迭代）。