Question

我必须允许客户端为我的项目执行查询，但我不知道如何将我的客户端/服务器应用程序连接到MySQL。我只知道如何在一个单独的类中连接到MySQL。有什么建议？

服务器：

import java.io.BufferedWriter;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.net.ServerSocket;
import java.net.Socket;

public class Server {

private ServerSocket serverSocket;
private int port;

public Server(int port) {
    this.port = port;
}

public void start() throws IOException {
    System.out.println("Starting the socket server at port:" + port);
    serverSocket = new ServerSocket(port);

    //Listen for clients. Block till one connects

    System.out.println("Waiting for clients...");
    Socket client = serverSocket.accept();

    //A client has connected to this server. Send welcome message
    sendWelcomeMessage(client);
}

private void sendWelcomeMessage(Socket client) throws IOException {
    BufferedWriter writer = new BufferedWriter(new     OutputStreamWriter(client.getOutputStream()));
    writer.write("Hello. You are connected to Server. What is your name?");
    writer.flush();
}

/**
* Creates a SocketServer object and starts the server.
*
* @param args
*/
public static void main(String[] args) {
    // Setting a default port number.
    int portNumber = 1234;

    try {
        // initializing the Socket Server
        Server socketServer = new Server(portNumber);
        socketServer.start();

        } catch (IOException e) {
        e.printStackTrace();
    }
}
}

客户：

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.Socket;
import java.net.UnknownHostException;

public class Client {

private String hostname;
private int port;
Socket socketClient;

public Client(String hostname, int port){
    this.hostname = hostname;
    this.port = port;
}

public void connect() throws UnknownHostException, IOException{
    System.out.println("Attempting to connect to "+hostname+":"+port);
    socketClient = new Socket(hostname,port);
    System.out.println("Connection Established");
}

public void readResponse() throws IOException{
    String userInput;
    BufferedReader stdIn = new BufferedReader(new InputStreamReader(socketClient.getInputStream()));

    System.out.println("Response from server:");
    while ((userInput = stdIn.readLine()) != null) {
        System.out.println(userInput);
    }
}

public static void main(String arg[]){
    //Creating a SocketClient object
    Client client = new Client ("localhost",1234);
    try {
        //trying to establish connection to the server
        client.connect();
        //if successful, read response from server
        client.readResponse();

    } catch (UnknownHostException e) {
        System.err.println("Host unknown. Cannot establish connection");
    } catch (IOException e) {
        System.err.println("Cannot establish connection. Server may not be up."+e.getMessage());
    }
}
}

Answer 1

我不会给你所有的答案，但这里提示如何从服务器端建立连接：

 private Connection conn = null;
  public void connect(){
    try {
      Class.forName("com.mysql.jdbc.Driver").newInstance();
      conn = 
        DriverManager.getConnection("jdbc:mysql://mysql.agh.edu.pl/db_name",
                                    "username","password");

      ...

    } catch (SQLException ex) {
      // handle any errors
      System.out.println("SQLException: " + ex.getMessage());
      System.out.println("SQLState: " + ex.getSQLState());
      System.out.println("VendorError: " + ex.getErrorCode());
    }catch(Exception e){e.printStackTrace();}   
  }

这是从客户端站点连接的方式：

  private Connection conn = null;
  private Statement stmt = null;
  private ResultSet rs = null;
  ..... .......
  connect();
  stmt = conn.createStatement();

  rs = stmt.executeQuery("SELECT name FROM users");

  while(rs.next()){
    String name = rs.getString(1);
    System.out.println("User: "+name);
  }

将MySQL连接到Java客户端/服务器应用程序

1 个答案: