Question

I’m trying to create a simple webapp without any XML configuration using Spring 3.1 and an embedded Jetty 8 server.

However, I’m struggling to get Jetty to recognise my implementaton of the Spring WebApplicationInitializer interface.

Project structure:

src
 +- main
     +- java
     |   +- JettyServer.java
     |   +- Initializer.java
     | 
     +- webapp
         +- web.xml (objective is to remove this - see below).

The Initializer class above is a simple implementation of WebApplicationInitializer:

import javax.servlet.ServletContext;
import javax.servlet.ServletException;

import org.springframework.web.WebApplicationInitializer;

public class Initializer implements WebApplicationInitializer {

    @Override
    public void onStartup(ServletContext servletContext) throws ServletException {
        System.out.println("onStartup");
    }
}

Likewise JettyServer is a simple implementation of an embedded Jetty server:

import org.eclipse.jetty.annotations.AnnotationConfiguration;
import org.eclipse.jetty.server.Server;
import org.eclipse.jetty.webapp.Configuration;
import org.eclipse.jetty.webapp.WebAppContext;

public class JettyServer {

    public static void main(String[] args) throws Exception { 

        Server server = new Server(8080);

        WebAppContext webAppContext = new WebAppContext();
        webAppContext.setResourceBase("src/main/webapp");
        webAppContext.setContextPath("/");
        webAppContext.setConfigurations(new Configuration[] { new AnnotationConfiguration() });
        webAppContext.setParentLoaderPriority(true);

        server.setHandler(webAppContext);
        server.start();
        server.join();
    }
}

My understanding is that on startup Jetty will use AnnotationConfiguration to scan for
annotated implementations of ServletContainerInitializer; it should find Initializer and wire it in…

However, when I start the Jetty server (from within Eclipse) I see the following on the command-line:

2012-11-04 16:59:04.552:INFO:oejs.Server:jetty-8.1.7.v20120910
2012-11-04 16:59:05.046:INFO:/:No Spring WebApplicationInitializer types detected on classpath
2012-11-04 16:59:05.046:INFO:oejsh.ContextHandler:started o.e.j.w.WebAppContext{/,file:/Users/duncan/Coding/spring-mvc-embedded-jetty-test/src/main/webapp/}
2012-11-04 16:59:05.117:INFO:oejs.AbstractConnector:Started SelectChannelConnector@0.0.0.0:8080

The important bit is this:

No Spring WebApplicationInitializer types detected on classpath

Note that src/main/java is defined as a source folder in Eclipse, so should be on the classpath. Also note that the Dynamic Web Module Facet is set to 3.0.

I’m sure there’s a simple explanation, but I’m struggling to see the wood for the trees! I suspect the key is with the following line:

...
webAppContext.setResourceBase("src/main/webapp");
...

This makes sense with a 2.5 servlet using web.xml (see below), but what should it be when using AnnotationConfiguration?

NB: Everything fires up correctly if I change the Configurations to the following:

...
webAppContext.setConfigurations(new Configuration[] { new WebXmlConfiguration() });
...

In this case it finds the web.xml under src/main/webapp and uses it to wire the servlet using DispatcherServlet and AnnotationConfigWebApplicationContext in the usual way (completely bypassing the WebApplicationInitializer implementation above).

This feels very much like a classpath problem, but I’m struggling to understand quite how Jetty associates itself with implementations of WebApplicationInitializer – any suggestions would be most appreciated!

For info, I’m using the following:

Spring 3.1.1
Jetty 8.1.7
STS 3.1.0

Answer 1

The problem is that Jetty’s AnnotationConfiguration class does not scan non-jar resources on the classpath (except under WEB-INF/classes).

It finds my WebApplicationInitializer‘s if I register a subclass of AnnotationConfiguration which overrides configure(WebAppContext) to scan the host classpath in addition to the container and web-inf locations.

Most of the sub-class is (sadly) copy-paste from the parent. It includes:

• an extra parse call (parseHostClassPath) at the end of the configure method;
• the parseHostClassPath method which is largely copy-paste from
  AnnotationConfiguration‘s parseWebInfClasses;
• the getHostClassPathResource method which grabs the first non-jar URL
  from the classloader (which, for me at least, is the file url to my
  classpath in eclipse).

I am using slightly different versions of Jetty (8.1.7.v20120910) and Spring (3.1.2_RELEASE), but I imagine the same solution will work.

Edit: I created a working sample project in github with some modifications (the code below works fine from Eclipse but not when running in a shaded jar) – https://github.com/steveliles/jetty-embedded-spring-mvc-noxml

In the OP’s JettyServer class the necessary change would replace line 15 with:

webAppContext.setConfigurations (new Configuration []
{
        new AnnotationConfiguration() 
        {
            @Override
            public void configure(WebAppContext context) throws Exception
            {
                boolean metadataComplete = context.getMetaData().isMetaDataComplete();
                context.addDecorator(new AnnotationDecorator(context));   

                AnnotationParser parser = null;
                if (!metadataComplete)
                {
                    if (context.getServletContext().getEffectiveMajorVersion() >= 3 || context.isConfigurationDiscovered())
                    {
                        parser = createAnnotationParser();
                        parser.registerAnnotationHandler("javax.servlet.annotation.WebServlet", new WebServletAnnotationHandler(context));
                        parser.registerAnnotationHandler("javax.servlet.annotation.WebFilter", new WebFilterAnnotationHandler(context));
                        parser.registerAnnotationHandler("javax.servlet.annotation.WebListener", new WebListenerAnnotationHandler(context));
                    }
                }

                List<ServletContainerInitializer> nonExcludedInitializers = getNonExcludedInitializers(context);
                parser = registerServletContainerInitializerAnnotationHandlers(context, parser, nonExcludedInitializers);

                if (parser != null)
                {
                    parseContainerPath(context, parser);
                    parseWebInfClasses(context, parser);
                    parseWebInfLib (context, parser);
                    parseHostClassPath(context, parser);
                }                  
            }

            private void parseHostClassPath(final WebAppContext context, AnnotationParser parser) throws Exception
            {
                clearAnnotationList(parser.getAnnotationHandlers());
                Resource resource = getHostClassPathResource(getClass().getClassLoader());                  
                if (resource == null)
                    return;

                parser.parse(resource, new ClassNameResolver()
                {
                    public boolean isExcluded (String name)
                    {           
                        if (context.isSystemClass(name)) return true;                           
                        if (context.isServerClass(name)) return false;
                        return false;
                    }

                    public boolean shouldOverride (String name)
                    {
                        //looking at webapp classpath, found already-parsed class of same name - did it come from system or duplicate in webapp?
                        if (context.isParentLoaderPriority())
                            return false;
                        return true;
                    }
                });

                //TODO - where to set the annotations discovered from WEB-INF/classes?    
                List<DiscoveredAnnotation> annotations = new ArrayList<DiscoveredAnnotation>();
                gatherAnnotations(annotations, parser.getAnnotationHandlers());                 
                context.getMetaData().addDiscoveredAnnotations (annotations);
            }

            private Resource getHostClassPathResource(ClassLoader loader) throws IOException
            {
                if (loader instanceof URLClassLoader)
                {
                    URL[] urls = ((URLClassLoader)loader).getURLs();
                    for (URL url : urls)
                        if (url.getProtocol().startsWith("file"))
                            return Resource.newResource(url);
                }
                return null;                    
            }
        },
    });

Update: Jetty 8.1.8 introduces internal changes that are incompatible with the code above. For 8.1.8 the following seems to work:

webAppContext.setConfigurations (new Configuration []
    {
        // This is necessary because Jetty out-of-the-box does not scan
        // the classpath of your project in Eclipse, so it doesn't find
        // your WebAppInitializer.
        new AnnotationConfiguration() 
        {
            @Override
            public void configure(WebAppContext context) throws Exception {
                   boolean metadataComplete = context.getMetaData().isMetaDataComplete();
                   context.addDecorator(new AnnotationDecorator(context));   


                   //Even if metadata is complete, we still need to scan for ServletContainerInitializers - if there are any
                   AnnotationParser parser = null;
                   if (!metadataComplete)
                   {
                       //If metadata isn't complete, if this is a servlet 3 webapp or isConfigDiscovered is true, we need to search for annotations
                       if (context.getServletContext().getEffectiveMajorVersion() >= 3 || context.isConfigurationDiscovered())
                       {
                           _discoverableAnnotationHandlers.add(new WebServletAnnotationHandler(context));
                           _discoverableAnnotationHandlers.add(new WebFilterAnnotationHandler(context));
                           _discoverableAnnotationHandlers.add(new WebListenerAnnotationHandler(context));
                       }
                   }

                   //Regardless of metadata, if there are any ServletContainerInitializers with @HandlesTypes, then we need to scan all the
                   //classes so we can call their onStartup() methods correctly
                   createServletContainerInitializerAnnotationHandlers(context, getNonExcludedInitializers(context));

                   if (!_discoverableAnnotationHandlers.isEmpty() || _classInheritanceHandler != null || !_containerInitializerAnnotationHandlers.isEmpty())
                   {           
                       parser = createAnnotationParser();

                       parse(context, parser);

                       for (DiscoverableAnnotationHandler h:_discoverableAnnotationHandlers)
                           context.getMetaData().addDiscoveredAnnotations(((AbstractDiscoverableAnnotationHandler)h).getAnnotationList());      
                   }

            }

            private void parse(final WebAppContext context, AnnotationParser parser) throws Exception
            {                   
                List<Resource> _resources = getResources(getClass().getClassLoader());

                for (Resource _resource : _resources)
                {
                    if (_resource == null)
                        return;

                    parser.clearHandlers();
                    for (DiscoverableAnnotationHandler h:_discoverableAnnotationHandlers)
                    {
                        if (h instanceof AbstractDiscoverableAnnotationHandler)
                            ((AbstractDiscoverableAnnotationHandler)h).setResource(null); //
                    }
                    parser.registerHandlers(_discoverableAnnotationHandlers);
                    parser.registerHandler(_classInheritanceHandler);
                    parser.registerHandlers(_containerInitializerAnnotationHandlers);

                    parser.parse(_resource, 
                                 new ClassNameResolver()
                    {
                        public boolean isExcluded (String name)
                        {
                            if (context.isSystemClass(name)) return true;
                            if (context.isServerClass(name)) return false;
                            return false;
                        }

                        public boolean shouldOverride (String name)
                        {
                            //looking at webapp classpath, found already-parsed class of same name - did it come from system or duplicate in webapp?
                            if (context.isParentLoaderPriority())
                                return false;
                            return true;
                        }
                    });
                }
            }

            private List<Resource> getResources(ClassLoader aLoader) throws IOException
            {
                if (aLoader instanceof URLClassLoader)
                {
                    List<Resource> _result = new ArrayList<Resource>();
                    URL[] _urls = ((URLClassLoader)aLoader).getURLs();                      
                    for (URL _url : _urls)
                        _result.add(Resource.newResource(_url));

                    return _result;
                }
                return Collections.emptyList();                 
            }
        }
    });