Building a web application with embedded-jetty and jersey .. with request dispatching - html

Question

I am setting a web application with embedded jetty and jersey .As i am fairly new with concepts, it is difficult to load a sample webpage index.html. When i target it as localhost:8989/myServlet i see the code flow through my servlet . But request dispatcher always returns null.
Please let me know with this:
Main class:
import org.eclipse.jetty.server.Server;
import org.eclipse.jetty.servlet.ServletContextHandler;
import org.eclipse.jetty.servlet.ServletHandler;
import org.eclipse.jetty.servlet.ServletHolder;
public class MainApp {
public static void main(String[] args) throws Exception {
ServletContextHandler context = new ServletContextHandler(ServletContextHandler.SESSIONS);
context.setContextPath("/");
Server jettyServer = new Server(8989);
jettyServer.setHandler(context);
ServletHandler handler =new ServletHandler();
handler.addServletWithMapping(MyServletHandler.class,"/myServlet");
jettyServer.setHandler(handler);
ServletHolder jerseyServlet = context.addServlet(
org.glassfish.jersey.servlet.ServletContainer.class, "/*");
jerseyServlet.setInitOrder(0);
jerseyServlet.setInitParameter(
"jersey.config.server.provider.classnames",
Entry.class.getCanonicalName());
try {
jettyServer.start();
jettyServer.join();
} finally {
jettyServer.destroy();
}
}
}
Myservlet class:
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
public class MyServletHandler extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
System.out.println("Control is in servlet");
RequestDispatcher requestDispatcher = request.getRequestDispatcher("index.html"); // this returns null. hence i am unable to request dispatch to view the html webpage.
}
}
I use Maven to build the application and i have placed index.html in src/main/resources directory

Answer 1

This works, but you'll have to properly setup the ServletContext so that the request.getRequestDispatcher() can do something.
For starters, your ServletContextHandler MUST have a Resource Base setup.
You'll have to setup a DefaultServlet so that the request dispatcher can be returned properly.
You'll also have to use embedded-jetty properly, don't use ServletHandler directly like that. Use the ServletHolder if you must, but otherwise just use the ServletContextHandler directly.
Here's an example of this behavior.
Run with a System Property of baseResource pointing to a directory where you have a index.html.
package jetty.dispatching;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URI;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.eclipse.jetty.server.Server;
import org.eclipse.jetty.server.handler.DefaultHandler;
import org.eclipse.jetty.server.handler.HandlerList;
import org.eclipse.jetty.servlet.DefaultServlet;
import org.eclipse.jetty.servlet.ServletContextHandler;
import org.eclipse.jetty.servlet.ServletHolder;
import org.eclipse.jetty.util.IO;
import org.eclipse.jetty.util.resource.Resource;
import static java.nio.charset.StandardCharsets.UTF_8;
public class DispatchingToDefaultServletDemo
{
public static void main(String[] args) throws Exception
{
DispatchingToDefaultServletDemo demo = new DispatchingToDefaultServletDemo();
try
{
demo.startServer();
demo.makeRequests();
}
finally
{
demo.stopServer();
}
}
private Server server;
public void startServer() throws Exception
{
server = new Server(8989);
ServletContextHandler context = new ServletContextHandler(ServletContextHandler.SESSIONS);
context.setContextPath("/");
// Must have Resource Base for proper ServletContext (even if it points to an empty URI directory in a JAR file)
context.setBaseResource(getBaseResource());
// Don't use ServletHandler directly!
context.addServlet(MyServletHandler.class, "/myServlet");
// Add DefaultServlet last on ServletContextHandler to be able to serve content from resource base.
// It must be named "default" (per servlet spec)
ServletHolder defaultHolder = new ServletHolder("default", DefaultServlet.class);
defaultHolder.setInitParameter("dirAllowed", "true");
context.addServlet(defaultHolder, "/"); // this is the default url-pattern
HandlerList handlers = new HandlerList();
handlers.addHandler(context);
handlers.addHandler(new DefaultHandler()); // always last in handler tree
server.setHandler(handlers);
server.start();
}
public Resource getBaseResource() throws IOException
{
String baseResourceLocation = System.getProperty("baseResource");
if (baseResourceLocation == null)
{
baseResourceLocation = System.getProperty("user.dir");
}
Resource resource = Resource.newResource(baseResourceLocation);
System.out.println("Base Resource is " + resource);
return resource;
}
private void stopServer() throws Exception
{
server.stop(); // use .stop() NOT .destroy()
}
private void makeRequests()
{
performGET("/myServlet");
performGET("/");
}
private void performGET(String requestPath)
{
try
{
URI uri = server.getURI().resolve(requestPath);
System.out.println("Requesting GET on " + uri);
HttpURLConnection http = (HttpURLConnection) uri.toURL().openConnection();
System.out.println(" Response Status code = " + http.getResponseCode());
try (InputStream in = http.getInputStream())
{
System.out.println(" Response Body: " + IO.toString(in, UTF_8));
}
}
catch (IOException e)
{
e.printStackTrace();
}
}
public static class MyServletHandler extends HttpServlet
{
#Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
{
RequestDispatcher requestDispatcher = request.getRequestDispatcher("/index.html");
System.out.println("request Dispatcher = " + requestDispatcher);
requestDispatcher.forward(request, response);
}
}
}
The output ...
$ java -DbaseResource=/home/joakim/code/jetty/bases/listing-base/rez/welcomish/ -classpath <..snip..> jetty.dispatching.DispatchingToDefaultServletDemo
2019-04-18 15:15:15.595:INFO::main: Logging initialized #180ms to org.eclipse.jetty.util.log.StdErrLog
Base Resource is file:///home/joakim/code/jetty/bases/listing-base/rez/welcomish/
2019-04-18 15:15:15.678:INFO:oejs.Server:main: jetty-9.4.15.v20190215; built: 2019-02-15T16:53:49.381Z; git: eb70b240169fcf1abbd86af36482d1c49826fa0b; jvm 1.8.0_192-b12
2019-04-18 15:15:15.725:INFO:oejs.session:main: DefaultSessionIdManager workerName=node0
2019-04-18 15:15:15.726:INFO:oejs.session:main: No SessionScavenger set, using defaults
2019-04-18 15:15:15.727:INFO:oejs.session:main: node0 Scavenging every 660000ms
2019-04-18 15:15:15.736:INFO:oejsh.ContextHandler:main: Started o.e.j.s.ServletContextHandler#482f8f11{/,file:///home/joakim/code/jetty/bases/listing-base/rez/welcomish/,AVAILABLE}
2019-04-18 15:15:15.747:INFO:oejs.AbstractConnector:main: Started ServerConnector#3ffc5af1{HTTP/1.1,[http/1.1]}{0.0.0.0:8989}
2019-04-18 15:15:15.747:INFO:oejs.Server:main: Started #333ms
Requesting GET on http://127.0.1.1:8989/myServlet
request Dispatcher = Dispatcher#0x5d8c6ff2{null,/index.html}
Response Status code = 200
Response Body: <h1>My welcomish HTML</h1>
Requesting GET on http://127.0.1.1:8989/
Response Status code = 200
Response Body: <h1>My welcomish HTML</h1>
2019-04-18 15:15:15.827:INFO:oejs.AbstractConnector:main: Stopped ServerConnector#3ffc5af1{HTTP/1.1,[http/1.1]}{0.0.0.0:8989}
2019-04-18 15:15:15.827:INFO:oejs.session:main: node0 Stopped scavenging
2019-04-18 15:15:15.829:INFO:oejsh.ContextHandler:main: Stopped o.e.j.s.ServletContextHandler#482f8f11{/,file:///home/joakim/code/jetty/bases/listing-base/rez/welcomish/,UNAVAILABLE}
Process finished with exit code 0