将MySQL连接到Java客户端/服务器应用程序

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。我只知道如何在单独的类中连接到MySQL。有什么建议么？

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，但这里是一个关于如何建立从服务器端的连接提示：

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();} 
    } 

这就是如何从客户端连接：

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); 
    }