How to make Jetty dynamically load "static" pages

Question

I am building Java web applications, and I hate the traditional "code-compile-deploy-test" cycle. I want to type in one tiny change, then see the result INSTANTLY, without having to compile and deploy.

Fortunately, Jetty is great for this. It is a pure-java web server. It comes with a really nice maven plugin which lets you launch Jetty reading directly from your build tree -- no need to package a war file or deploy. It even has a scanInterval setting: put this to a non-zero value and it will watch your java files and various config files for changes and automatically re-deploy a few seconds after you make a change.

There's just one thing keeping me from nirvana. I have javascript and css files in my src/main/webapp directory which just get served up by Jetty. I would like to be able to edit these and have the changes show up when I refresh the page in the browser. Unfortunately, Jetty holds these files open so I can't (on Windows) modify them while it is running.

Does anyone know how to make Jetty let go of these files so I can edit them, then serve up the edited files for subsequent requests?

Answer 1

Jetty uses memory-mapped files to buffer static content, which causes the file-locking in Windows. Try setting useFileMappedBuffer for DefaultServlet to false.

Troubleshooting Locked files on Windows (from the Jetty wiki) has instructions.

Answer 2

While one of the answers above is exactly right for configuring jetty by xml, if you want to configure this option in code (for an embedded server) the answer is different and not found on that page.

You'll find a number of suggestions online including

context.getInitParams().put("useFileMappedBuffer", "false");

Or overriding the WebAppContext, or using a fully qualified name for the init parameter. None of these suggestions worked for me (using Jetty 7.2.2). Part of the problem was that the useFileMappedBuffer option needs to be set on the servlet that the WebAppContext is using to serve the static files, rather than on the context.

In the end I did something like this on a straightforward ServletContextHandler

// Startup stuff
final Server server = new Server(port);
ServletContextHandler handler = new ServletContextHandler();
handler.setResourceBase(path);

SessionManager sm = new HashSessionManager();
SessionHandler sh = new SessionHandler(sm);
handler.setSessionHandler(sh);

DefaultServlet defaultServlet = new DefaultServlet();
ServletHolder holder = new ServletHolder(defaultServlet);
holder.setInitParameter("useFileMappedBuffer", "false");
handler.addServlet(holder, "/");

server.setHandler(handler);
server.start();
server.join();

Answer 3

Although this is a Old problem but i found this post very helpful, in short just change your config to

            <plugin>
                <groupId>org.mortbay.jetty</groupId>
                <artifactId>jetty-maven-plugin</artifactId>
                <configuration>
                <connectors>
                    <connector implementation="org.eclipse.jetty.server.bio.SocketConnector">
                        <port>8080</port>
                    </connector>
                </connectors>
                </configuration>
            </plugin>

This disables the NIO support in Jetty ( but it should not be problem for debug puropse for simple cases ).