Socket Server problem
Hey all,
I'm working on a Socket Server that connects to a database, and then allows clients to connect to itself and process Database queries through the socket server. Currently my socket server works for the first client, but when I try to connect and run a query the second time I get the following error.
java.lang.NullPointerException
at SocketServerThread.sendStmt(SocketServerThread.java:84)
at SocketServerThread.run(SocketServerThread.java:37)
I assume this is probably having something to do with me not closing connections correctly.
Any advice would be greatly appreciated.
Thank you for your time.
Here is the server code:
import java.net.*;
import java.io.*;
import javax.naming.*;
import javax.sql.DataSource;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Hashtable;
/*
*
*/
publicclass SocketServer{
staticboolean listening =true;
publicfinalstatic String JNDI_FACTORY="weblogic.jndi.WLInitialContextFactory";
publicvoid endListening()
{
listening =false;
}
privatestaticvoid usage()
{
System.err.println("Usage: SocketServer " +"<hostname> <port number>");
System.exit(-1);
}
publicstaticvoid main(String[] argv)throws IOException
{
ServerSocket serverSocket =null;
// Get hostname and port from arguments
if (argv.length < 2)
{
usage();
}
String host = argv[0];
int port = 0;
InitialContext ic =null;
DataSource ds =null;
Connection conn =null;
try
{
port = Integer.parseInt(argv[1]);
}
catch (NumberFormatException nfe)
{
usage();
}
// Set up Socket Server on Port
try{
serverSocket =new ServerSocket(4444);
}catch (IOException e){
System.err.println("Could not listen on port: 4444.");
System.exit(-1);
}
//Set up connection to DB
try
{
ic = getInitialContext("t3://" + host +":" + port);
ds = (DataSource) ic.lookup("jdbc-database");
if ( ds !=null )
{
conn = ds.getConnection();
if (conn !=null )
System.out.println("Got a connection from datasource at " + host +" at port " + port );
else
{
thrownew Throwable("Connection is null");
}
}
else
System.out.println("DataSource is null");
}
catch (Throwable t)
{
t.printStackTrace();
System.exit(-1);
}
// Wait for connection from client, then create new thread to handle client
while(listening)
{
new SocketServerThread(serverSocket.accept(), conn).start();
}
serverSocket.close();
}
privatestatic InitialContext getInitialContext(String url)
throws NamingException
{
Hashtable env =new Hashtable();
env.put(Context.INITIAL_CONTEXT_FACTORY, JNDI_FACTORY);
env.put(Context.PROVIDER_URL, url);
returnnew InitialContext(env);
}
}
Here is the SocketServerThread code:
import java.net.*;
import java.io.*;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
/*
*
*/
publicclass SocketServerThreadextends Thread{
privatestatic Socket socket =null;
privatestatic Connection conn=null;
privatestatic PrintWriter out =null;
public SocketServerThread(Socket theSocket, Connection theConn){
super("SocketServerThread");
socket = theSocket;
conn = theConn;
}
publicvoid run(){
PreparedStatement stmt =null;
try
{
out =new PrintWriter(socket.getOutputStream(),true);
stmt = conn.prepareStatement("SELECT USER_NAME FROM LOGIN_INFO");
sendStmt(stmt);
}
catch( SQLException sqe)
{
sqe.printStackTrace();
}
catch(IOException e){e.printStackTrace();
}
//Send done response and close Connections
try
{
out.println("done");//Lets client know that it is done
socket.close();
conn.close();
out.close();
}catch(IOException e){e.printStackTrace();}
catch(SQLException e){e.printStackTrace();}
}
// Execute prepared statement and send back the results
publicvoid sendStmt(PreparedStatement statement)
{
try
{
ResultSet rs = statement.executeQuery();
while ( rs.next() )
{
out.println(rs.getString(1));
}
out.close();
}
catch( SQLException sqe)
{
sqe.printStackTrace();
}
finally
{
try
{
statement.close();
}catch(SQLException e){e.printStackTrace();}
}
}
}
