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Re: [jetty-users] Avoiding file-locking when developing with embedded Jetty

Hi Jan

Thanks for the reply and sorry about my "thinking out loud" emails. Things are getting clearer as we speak and I now actually know what change I want (to contribute). I write this mail to hear if you're interested in a patch for this or if I would be wasting my time.

On Thu, Jan 8, 2015 at 2:06 PM, Jan Bartel <janb@xxxxxxxxxxx> wrote:

Sheesh, we already give you so many ways to start jetty, and its still
not enough :) :) :)

Actually, you're right - there are enough ways. The approach that I am using is the same as the one from the Heroku sample application. It is also the way described under "Setting a Web Application Context" under I personally thing these are the best ways of using Jetty.

The example code from Heroku is similar to the one I showed: However, I also need static resources like HTML, CSS and _javascript_. It can look like this (provided that the resources are included in the jar-file):

WebAppContext webapp = new WebAppContext("/webapp", "/app");

This approach works great on the server, but it is very cumbersome during development if the project also contains static resources (HTML. CSS, JS). If I start Jetty with a WebAppContext in the IDE I will encounter a problem:
  • If I change a static file (HTML, CSS, JS) and save, the IDE will try and copy this file to the output directory. Since the file has been opened with useFileMappedBuffers, this copy will fail. In Eclipse, the project will get an error and I have to stop Jetty and cleanly build it to continue.
You can change this behavior by changing the line above to use the source folder instead. If I'm using Maven, it will probably look like this:

WebAppContext webapp = new WebAppContext("/webapp", "src/main/resources/app");

This avoids leaving the project in an invalid state, but it leads to two other problems:
What I really want is to be able to say something to the effect of the first line:

WebAppContext webapp = new WebAppContext("/webapp", "/app");

This can probably not be made to be backwards compatible, but I can do something like this:

WebAppContext webapp = new WebAppContext("/webapp", Resource.newProjectResource("/app", new String[] { "src/main/resource" }));

What this would do:
  • Look for /app in the classpath. If it is in a directory (and not a JAR), this means we're running in exploded mode. In that case, try to substitute the source directories (in this case src/main/resource). If that works, make sure file mapped buffers are not used.
  • If /app is in a jar-file or not in the source folders, it works exactly as Resource.newResource("/app")
On more thing: org.eclipse.jetty.annotations.AnnotationConfiguration doesn't currently work with classpath resources, only with WAR-files.

I have made an experimental implementation of the above code. In order to make it work, I had to fight org.eclipse.jetty.server.ResourceCache.getDirectBuffer pretty hard. I can fool this code "if (_useFileMappedBuffer && resource.getFile()!=null)" by making my resource return null for a file, but it would probably be more meaningful to create a new method org.eclipse.jetty.util.resource.Resource.isSupportingDirectBuffer.

The resulting code would look something like this:

public class SimpleServer {
    public static void main(String[] args) throws Exception {
        HandlerList handlers = new HandlerList();
        handlers.addHandler(new ShutdownHandler("randomtoken", false, true));
        handlers.addHandler(new WebApplication("/app", Resource.newProjectResource("/app")));
        Server server = new Server(5000);
        System.out.println("Started " + server.getURI());

Again: This is the same way of starting the Jetty as Heroku and on the Emdedding Jetty documentation pages, with additional ease of use during development. So it is not a new method, but an improvement to what I personally feel is the current best method. It also addresses the section "Setting a Web Application Context" under, where there are currently two examples. This approach unifies them. (This section seems to be missing from the new documentation at

The changes I would contribute are as follows:
  • ResourceBuffer.getDirectBuffer() would use the new method Resource.isSupportingDirectBuffer() instead of checking for Resource.getFile() == null
  • A new method Resource.newProjectResource would check if the classpath resource should be treated as a source resource and return a subclass of Resource which does not support direct buffer if so
  • A new constructor to WebAppContext would take contextPath and baseResource
In addition, I would like to contribute a subclass of WebAppContext (ClasspathWebAppContext) with a new method scanForAnnotations which mimics AnnotationConfiguration when you're not dealing with a WAR-file.

Would you be interested in patches to this effect? If so, I can create a bug report with the modifications to Resource, WebAppContext and ResourceBuffer.


> On Fri, Jan 2, 2015 at 6:04 PM, Jan Bartel <janb@xxxxxxxxxxx> wrote:
>> Hi Johannes,
>> Have you considered using the jetty-runner? Here's the doc:
>> You could point it at your src/main/resources/webapp dir as the webapp
>> to deploy. However, as it seems you're running on windows, you'll need
>> to use a context xml file instead to set the context param to turn off
>> fileMappedBuffers, and to point to your webapp and context path.
>> OTOH, your main is a pretty simple class ... it could be made more
>> generic by using system properties to set the context path, webapp to
>> deploy and the fileMappedBuffers property.
>> cheers
>> Jan
>> On 2 January 2015 at 16:15, Johannes Brodwall <johannes@xxxxxxxxxxxx>
>> wrote:
>> > Hi
>> >
>> > I would like to hear if someone could suggest how to scratch this itch I
>> > often have when using Jetty embedded in applications.
>> >
>> > I am often using Jetty during development. I'd like for static files
>> > that
>> > are normally packaged into a war or jar file to be easy to edit when I
>> > am
>> > developing (that is, when the files are not packaged). At the same time,
>> > I
>> > want my code to be as similar as possible during development and in
>> > production.
>> >
>> > My best attempt so far has been to place the static content under
>> > src/main/resources/webapp and package it into the Jar-file.
>> >
>> > In order to avoid locking the files when I'm running the server in the
>> > debugger, I've implemented the following:
>> >
>> >     public static WebAppContext createApplicationContext() {
>> >         WebAppContext webapp = new WebAppContext("/webapp", "/app");
>> >
>> >         if
>> >
>> > (SimpleServer.class.getResource(webapp.getWar()).getProtocol().equals("file"))
>> > {
>> >             // Avoid locking static content when running exploded
>> >             webapp.setWar("src/main/resources/webapp");
>> >
>> >
>> > webapp.setInitParameter("org.eclipse.jetty.servlet.Default.useFileMappedBuffer",
>> > "false");
>> >         }
>> >         return webapp;
>> >     }
>> >
>> > This runs in a main method like so:
>> >
>> > public class SimpleServer {
>> >
>> >     public static void main(String[] args) throws Exception {
>> >         HandlerList handlers = new HandlerList();
>> >         handlers.addHandler(new ShutdownHandler("randomtoken", false,
>> > true));
>> >         handlers.addHandler(createApplicationContext());
>> >
>> >         Server server = new Server(5000);
>> >         server.setHandler(handlers);
>> >         server.start();
>> >
>> >         System.out.println("Started " + server.getURI());
>> >     }
>> > }
>> >
>> > As the rest of the code is extremely simple, the magic replacement of
>> > the
>> > target file with the source file and the setting of the very poorly
>> > documented "org.eclipse.jetty.servlet.Default.useFileMappedBuffer"
>> > parameter
>> > both feel really frustrating. The code is magic enough that I've ended
>> > up
>> > creating a "framework" to run it which is clearly not what I want.
>> >
>> >
>> > 1. Are there currently better ways of doing this?
>> > 2. Is there any way something that accomplishes the same could be added
>> > to
>> > Jetty itself?
>> >
>> >
>> > ~Johannes
>> >
>> >
>> >
>> > _______________________________________________
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>> > this list, visit
>> >
>> --
>> Jan Bartel <janb@xxxxxxxxxxx>
>> 'Expert Jetty/CometD developer,production,operations advice'
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Jan Bartel <janb@xxxxxxxxxxx>
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