Thread: Nullpointer exception when sending string

Hi there,

I hope someone can help me because I'm struggeling to solve this issue.

I have a client/server application where I send a command to a server where is executes a certain method. The client is a JSp page which initializes a Client class where the command is send to. It is this Client class which gives me a nullpointer exception where I can't lay my finger on.

The issue comes when I use the "sendCommand(String c)" method from the Client class which gives the following error in Tomcat 7:
-----------------------------------------------------------------------------------
HTTP Status 500 -

--------------------------------------------------------------------------------

type Exception report

message

description The server encountered an internal error () that prevented it from fulfilling this request.

exception

org.apache.jasper.JasperException: java.lang.NullPointerException
org.apache.jasper.servlet.JspServletWrapper.handle JspException(JspServletWrapper.java:548)
org.apache.jasper.servlet.JspServletWrapper.servic e(JspServletWrapper.java:471)
org.apache.jasper.servlet.JspServlet.serviceJspFil e(JspServlet.java:389)
org.apache.jasper.servlet.JspServlet.service(JspSe rvlet.java:333)
javax.servlet.http.HttpServlet.service(HttpServlet .java:722)


root cause

java.lang.NullPointerException
com.jennifersoft.client.lib.Client.sendCommand(Cli ent.java:38)
org.apache.jsp.JANEClient_jsp._jspService(JANEClie nt_jsp.java:75)
org.apache.jasper.runtime.HttpJspBase.service(Http JspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet .java:722)
org.apache.jasper.servlet.JspServletWrapper.servic e(JspServletWrapper.java:433)
org.apache.jasper.servlet.JspServlet.serviceJspFil e(JspServlet.java:389)
org.apache.jasper.servlet.JspServlet.service(JspSe rvlet.java:333)
javax.servlet.http.HttpServlet.service(HttpServlet .java:722)


note The full stack trace of the root cause is available in the Apache Tomcat/7.0.20 logs.
-----------------------------------------------------------------------------------

The JSP page contains the following code:
Code:

<%
	//String req = request.getParameter("command");
 
	if(request.getParameter("command") != null || request.getParameter("command") != ""){
 
		String command = request.getParameter("command");
		Client client = new Client();
 
		//client.connectServer();
		out.println(command);
		client.sendCommand(command.toString());
		client.disconnect();
	}
%>

The Client class code:
Code:

public class Client {
 
	private static final String HOSTNAME = "127.0.0.1";
	private static final int PORT = 20000;
 
	private Socket socket = null;
	private BufferedWriter wr = null;
 
	public Client(){
		try {
			socket = new Socket(HOSTNAME, PORT);
			Thread.sleep(2000);
		} catch (UnknownHostException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
 
	}
 
	public void sendCommand(String c){
 
		try{
			if(socket != null){
				socket = new Socket(HOSTNAME, PORT);
			}
			wr = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
		    wr.write(c);
		    wr.flush();
		    wr.close();
		}catch(IOException iex){
 
		}
	}
 
	public boolean getConnectionStatus(){
		return socket.isConnected();
	}
 
	public void disconnect(){
		if(socket != null){
			try {
				socket.close();
			} catch (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
 
	}
}

I've been searching for hours now and I hope that somebody can help me.

With kind regards,

Sander

java.lang.NullPointerException
com.jennifersoft.client.lib.Client.sendCommand(Cli ent.java:38)

What variable at line 38 is null?

It's a request parameter which is a string that is send from the JSP page.

client.sendCommand(command.toString());

i solved the issue. Was due a piece of code which closed the server connections.