How to Call a Servlet in GWT

Sometimes you may need a HttpServlet other than GWT Rpc Service in a real life application. If needed then how to call the Servlet from your GWT client? Here you will find the answer.

Here is a simple HelloServlet

public class HelloServlet extends HttpServlet {
@Override
public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
{ 
String name = request.getParameter("name");
response.getWriter().write("Hello "+name+", Welcome in My Servlet");
}
}

The Servlet uses a request a parameter 'name' and writes it in the response writer.

To call the Servlet from the client first configure the web.xml (war/WEB-INF/web.xml) file to let your GWT client know about the HelloServlet.

 HelloServlet
 org.ratul.servlettest.server.HelloServlet


 HelloServlet
 /hello

Value of the url-pattern node will be used later to call the Servlet.

Now make a simple UI with a TextBox and a Button.

final Button sendButton = new Button("Send");
final TextBox nameField = new TextBox();
RootPanel.get().add(nameField);
RootPanel.get().add(sendButton);

In the Click Handler of the sendButton call the Servlet with the 'name' parameter in the following way

sendButton.addClickHandler(new ClickHandler() {
  public void onClick(ClickEvent event) {
    Window.Location.replace("/hello?name="+nameField.getText());
    //the url-pattern value is used here
  }
});

Thats' all for today. Happy coding with GWT :-)