RequestDispatcher not redirecting in java servlet to JSP

I'm trying to redirect to another page from my servlet where string value is null. When I run the code it stays on the same page instead of redirecting to my error page. Here is my code:

public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException { 
  response.setContentType("text/html");
  String emp = request.getParameter("emp")!=null ? request.getParameter("emp"): "";
  MCenter mCenter = new MCenter();
  mCenter = mCenterDAO.getMCenterPocByEmp(emp);
  mCenter = mCenterDAO.getMCenterByObject(mCenter);

  PrintWriter pw = response.getWriter();
  String mPocName = mCenter.getMCenterPocName();
  String mCenter = mCenter.getMCenterName();
     if(mPocName == null || mCenter == null) {
        request.getRequestDispacher("error.jsp").forward(request, response);
     System.out.println("Null or not name " + mPocName + "center " + mCenter);
     }
   String json = getMCenterPoc(emp);
   pw.print(json);
   pw.close();
}

public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
   doPost(request, response); 
}

I get no error, and the print out give me null or value depending on whether or not there is value or not.

You must do following changes in your code. Request Dispatcher doesn't work with Ajax post.

public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
 String emp = request.getParameter("emp") != null ? request.getParameter("emp") : "";
 MCenter mCenter = new MCenter();
 mCenter = mCenterDAO.getMCenterPocByEmp(emp);
 mCenter = mCenterDAO.getMCenterByObject(mCenter);
 String mPocName = mCenter.getMCenterPocName();
 String mCenter = mCenter.getMCenterName();
 if (mPocName == null || mCenter == null) {
  request.sendRedirect("error.jsp");
  System.out.println("Null or not name " + mPocName + "center " + mCenter);
 } else {
  response.setContentType("text/html");
  PrintWriter pw = response.getWriter();
  String json = getMCenterPoc(emp);
  pw.print(json);
  pw.close();
 }
}

Or you can do with Ajax success. In this way you don't need to change code to mine. If you want to do with Ajax.

var emp = $('#emp').val();
$.ajax({
    type: "POST",
    url: "yourServletName",
    data: 'emp='+emp+'',
    success: function(response) {
        if(response='error'){
              window.location.href='error.jsp';
        }else{
              //What you want
        }
    }
});

Of course your servlet must change to following.

public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
 response.setContentType("text/html");
 PrintWriter pw = response.getWriter();
 String emp = request.getParameter("emp") != null ? request.getParameter("emp") : "";
 MCenter mCenter = new MCenter();
 mCenter = mCenterDAO.getMCenterPocByEmp(emp);
 mCenter = mCenterDAO.getMCenterByObject(mCenter);
 String mPocName = mCenter.getMCenterPocName();
 String mCenter = mCenter.getMCenterName();
 if (mPocName == null || mCenter == null) {
  String json = "error";
 } else {
  String json = getMCenterPoc(emp);
 }
 pw.print(json);
 pw.close();
}