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Thread: Nullpointer exception when sending string

  1. #1
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    Default 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


  2. #2
    Super Moderator Norm's Avatar
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    Default Re: Nullpointer exception when sending string

    java.lang.NullPointerException
    com.jennifersoft.client.lib.Client.sendCommand(Cli ent.java:38)
    What variable at line 38 is null?

  3. #3
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    Default Re: Nullpointer exception when sending string

    It's a request parameter which is a string that is send from the JSP page.
    client.sendCommand(command.toString());

  4. #4
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    Default Re: Nullpointer exception when sending string

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

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