java.lang.IllegalStateException: getWriter() has already been called for this response

This fault comes when a Servlet calls the getOutputStream() method on answer object for writing something afterward calling the include() method. Suppose a Servlet calls the include() method to charge the answer of a JSP. Since JSP has already written the answer on it thus 1 time to a greater extent than opening OutputStream on answer object is illegal, yous acquire the java.lang.IllegalStateException: getWriter() has already been called for this response error. This fault too comes when yous endeavour to include answer of but about other Servlet too than tries to write something on output flow again. In short, your Servlet should never write anything on answer object afterward calling the include() method.

Here is the detailed stack draw of exception :
java.lang.IllegalStateException: getWriter() has already been called for this response
org.apache.catalina.connector.Response.getOutputStream(Response.java:580)
org.apache.catalina.connector.ResponseFacade.getOutputStream(ResponseFacade.java:183)
HelloServlet.doGet(HelloServlet.java:20)
javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
javax.servlet.http.HttpServlet.service(HttpServlet.java:723)

This a perfect beginner fault who tries to acquire Servlet too JSP past times lawsuit too error. If yous know the right agency to role the include() too forward() method too so yous won't aspect upwards this type of problem. That 1 time to a greater extent than highlights the of import of learning novel applied scientific discipline from a adept majority similar Head First Servlet too JSP. The majority volition no dubiety instruct yous the basics, which is quite of import inwards the long journeying of learning novel characteristic every day.

This fault comes when a Servlet calls the java.lang.IllegalStateException: getWriter() has already been called for this response

java.lang.IllegalStateException: getWriter() has already been called for this answer Solution

If yous await at the fault carefully, yous tin laissez passer the axe run into it pointing to HelloServlet.doGet() method at work 20, let's run into the HelloServlet aeroplane to detect out what's happening at work 20.

import java.io.IOException;  import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse;  public class HelloServlet extends HttpServlet {     private static in conclusion long serialVersionUID = 1L;      public void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {         String userAgent = req.getHeader("user-agent");         String clientBrowser = "Not known!";         if (userAgent != null)             clientBrowser = userAgent;         req.setAttribute("client.browser", clientBrowser);         req.getRequestDispatcher("/hello.jsp").include(req, resp);         resp.getOutputStream().println("This is written from Servlet");     }  }

You tin laissez passer the axe run into that at work xx nosotros are calling the getOutputStream() afterward calling the include() method of RequestDispather, this is causing the problem. Remove this work too your computer program volition run fine. The bottom work is yous should endeavour to write anything on output flow of Servlet afterward calling the include() too forward() method because the answer is already committed.