import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.ServerSocket;
import java.net.Socket;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import com.mysql.jdbc.Driver;
public class ClientHandler {
static ServerSocket providerSocket;
static Socket connection = null;
static ObjectOutputStream out;
static ObjectInputStream in;
static String message;
static DBProvider dbProvider;
public static void main(String args[]) {
// while (true) {
ClientHandler.run();
// }
}
static void run() {
try {
// 1. creating a server socket
providerSocket = new ServerSocket(4001, 10);
// 2. Wait for connection
System.out.println("Waiting for connection at "
+ providerSocket.getLocalPort());
connection = providerSocket.accept();
System.out.println("Connection received from "
+ connection.getInetAddress().getHostAddress());
// 3. get Input and Output streams
out = new ObjectOutputStream(connection.getOutputStream());
out.flush();
in = new ObjectInputStream(connection.getInputStream());
sendMessage("Connection successful");
// 4. The two parts communicate via the input and output streams
message = (String) in.readObject();
dbProvider.connect();
// gets the messages from client here
dbProvider.insert_delete_entries(message);
} catch (ClassNotFoundException e) {
System.out.println(e.toString());
e.printStackTrace();
} catch (NullPointerException e) {
System.out.println(e.toString());
e.printStackTrace();
} catch (IOException ioException) {
System.out.println(ioException.toString());
ioException.printStackTrace();
} catch (SQLException e) {
System.out.println(e.toString());
e.printStackTrace();
} catch (IllegalAccessException e) {
// TODO Auto-generated catch block
System.out.println(e.toString());
e.printStackTrace();
} finally {
// 4: Closing connection
try {
dbProvider.disconnect();
in.close();
out.close();
providerSocket.close();
} catch (IOException ioException) {
ioException.printStackTrace();
} catch (NullPointerException e) {
System.out.println(e.toString());
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
static void sendMessage(String... msg) {
try {
out.writeObject(msg);
out.flush();
System.out.println("server>" + msg);
} catch (IOException ioException) {
ioException.printStackTrace();
}
}
static void sendMessage(String msg) {
try {
out.writeObject(msg);
out.flush();
} catch (IOException ioException) {
ioException.printStackTrace();
}
}
public class DBProvider {
final static String userName = "root";
final static String password = "password";
final static String url = "jdbc:mysql://localhost:3306/central_server";
protected Connection conn = null;
DBProvider() {
}
public void connect() throws ClassNotFoundException, SQLException,
IllegalAccessException {
// TODO Auto-generated method stub
Class.forName("com.mysql.jdbc.Driver");
conn = DriverManager.getConnection(url, userName, password);
System.out.println("Database connection established");
System.out.println(conn.toString());
}
public void disconnect() throws SQLException {
// TODO Auto-generated method stub
if (conn != null) {
conn.close();
System.out.println("Database connection terminated");
}
}
public void insert_delete_entries(String string) throws SQLException {
// TODO Auto-generated method stub
Statement delete = conn.createStatement();
int i = delete.executeUpdate(string);
System.out.println(i + " row(s) affected");
}
public ResultSet display_results(String string) throws SQLException {
// TODO Auto-generated method stub
Statement displayStatement = conn.createStatement();
ResultSet result = displayStatement.executeQuery(string);
System.out.println(result.toString());
return result;
}
}
}
我在打开端口 4001 的 Amazon EC2 上运行它。
我在套接字通信中成功，但是当我连接到本地运行的 mysql 时，出现空指针异常
dpProvider.connect();
我使用名为 mysql_conn.jar 的 jdbc mysql 连接器调用它：
javac -classpath ./mysql_conn.jar ClientHandler.java
编译得很好。
但是当我打电话时：java ClientHandler
出现空指针异常。。
请帮忙..！