Embedded tomcat 7 servlet 3.0 annotations not working

Question

I have a stripped down test project which contains a Servlet version 3.0, declared with annotations like so:

    @WebServlet("/test")
public class TestServlet extends HttpServlet {

    private static final long serialVersionUID = -3010230838088656008L;

    @Override
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException{
        response.getWriter().write("Test");
        response.getWriter().flush();
        response.getWriter().close();
    }
}

I also have a web.xml file like so:

<web-app xmlns="http://java.sun.com/xml/ns/javaee"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
      version="3.0">

      <servlet>
        <servlet-name>testServlet</servlet-name>
        <servlet-class>g1.TestServlet</servlet-class>
      </servlet>      

      <servlet-mapping>
        <servlet-name>testServlet</servlet-name>
        <url-pattern>/testWebXml</url-pattern>
      </servlet-mapping>

</web-app> 

I've tried to make a JUnit test using Embedded Tomcat 7. When I start the Embedded Tomcat I can only access the servlet via the url-pattern declared in web.xml (/testWebXml). If I try to access it via the url-pattern declared via annotation (/test) it sais 404 page not found.

Here's the code for my test:

    String webappDirLocation = "src/main/webapp/";
    Tomcat tomcat = new Tomcat();
    tomcat.setPort(8080);

    tomcat.addWebapp("/jerseyTest", new File(webappDirLocation).getAbsolutePath());

    tomcat.start();
    tomcat.getServer().await();

Just to make sure I've set up my project correctly, I've also installed an actual Tomcat 7 and deployed the war. This time, both web.xml declared url and annotation url for my servlet work ok.

So my question is: does anyone know how to make Embedded Tomcat 7 take into account my Servlet 3.0 annotations?

I should also state that it's a Maven project, and the pom.xml contains the following dependencies:

    <dependency>
        <groupId>org.apache.tomcat</groupId>
        <artifactId>tomcat-catalina</artifactId>
        <version>7.0.29</version>
        <scope>test</scope>
    </dependency>
    <dependency>
        <groupId>org.apache.tomcat.embed</groupId>
        <artifactId>tomcat-embed-core</artifactId>
        <version>7.0.29</version>
        <scope>provided</scope>
    </dependency>
    <dependency>
        <groupId>org.apache.tomcat</groupId>
        <artifactId>tomcat-jasper</artifactId>
        <version>7.0.29</version>
        <scope>test</scope>
    </dependency>
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.8.1</version>
        <scope>test</scope>
    </dependency>

== UPDATE ==

Here's an issue that seems similar to this (except the Servlet 3.0 annotation that is not working is on Listener, not Servlet), which has a suggested fix:

https://issues.apache.org/bugzilla/show_bug.cgi?id=53903

I've tried it and it didn't work:

Changed the Embedded Tomcat start code to:

String webappDirLocation = "src/main/webapp/";
Tomcat tomcat = new Tomcat();

tomcat.enableNaming();
tomcat.setPort(8080);


Context ctx = tomcat.addWebapp(tomcat.getHost(), "/embeddedTomcat", new File(webappDirLocation).getAbsolutePath());
((StandardJarScanner) ctx.getJarScanner()).setScanAllDirectories(true);

tomcat.start();

tomcat.getServer().await();

Other things I've tried, also without success:

• specifically setting metadata-complete="false" in web.xml "web-app" tag

• updating the Maven dependencies to version 7.0.30

• debugging the org.apache.catalina.startup.ContextConfig class. There's code there that checks for @WebServlet annotations, it's just that it never gets executed (line 2115). This may be a good way to get to the root of the issue, but the class is pretty big, and I don't have time to do this now. Maybe if someone would be willing to look how this class works, and under which conditions (config params) does it get to correctly check your project's classes for that annotation, it might get to a valid answer.

Answer 1

Well I finally solved it by looking in the Tomcat7 sources, namely in the unit tests that deal with EmbeddedTomcat and servlet 3.0 annotations.

Basically, you must start your Embedded Tomcat 7 like this to make it aware of your annotated classes:

String webappDirLocation = "src/main/webapp/";
Tomcat tomcat = new Tomcat();
tomcat.setPort(8080);

StandardContext ctx = (StandardContext) tomcat.addWebapp("/embeddedTomcat",
                new File(webappDirLocation).getAbsolutePath());

//declare an alternate location for your "WEB-INF/classes" dir:     
File additionWebInfClasses = new File("target/classes");
VirtualDirContext resources = new VirtualDirContext();
resources.setExtraResourcePaths("/WEB-INF/classes=" + additionWebInfClasses);
ctx.setResources(resources);

tomcat.start();
tomcat.getServer().await();

For the sake of clarity I should mention that this works for a standard Maven project where your "web resources" (such as static and dynamic pages, WEB-INF directory etc) are found in:

[your project's root dir]/src/main/webapp

and your classes get compiled into

[your project's root dir]/target/classes

(such that you'd have [your project's root dir]/target/classes/[some package]/SomeCompiledServletClass.class)

For other directories layouts, these locations need to be changed accordingly.

==== UPDATE: Embedded Tomcat 8 ====

Thanks to @kwak for noticing this.

The APIs have changed a bit, here how the above example changes when using Embedded Tomcat 8:

String webappDirLocation = "src/main/webapp/";
Tomcat tomcat = new Tomcat();
tomcat.setPort(8080);

StandardContext ctx = (StandardContext) tomcat.addWebapp("/embeddedTomcat",
                new File(webappDirLocation).getAbsolutePath());

//declare an alternate location for your "WEB-INF/classes" dir:     
File additionWebInfClasses = new File("target/classes");
WebResourceRoot resources = new StandardRoot(ctx);
resources.addPreResources(new DirResourceSet(resources, "/WEB-INF/classes", additionWebInfClasses.getAbsolutePath(), "/"));
ctx.setResources(resources);

tomcat.start();
tomcat.getServer().await();

Answer 2

    Tomcat tomcat = new Tomcat();
    tomcat.setPort(port);

    Context ctx = tomcat.addWebapp("/", new File(docBase).getAbsolutePath());
    StandardJarScanner scan = (StandardJarScanner) ctx.getJarScanner();
    scan.setScanClassPath(true);
    scan.setScanBootstrapClassPath(true); // just guessing here
    scan.setScanAllDirectories(true);
    scan.setScanAllFiles(true);

    tomcat.start();
    tomcat.getServer().await();

it works well for me using Tomcat Embed 7.0.90 from MVN

Answer 3

Given the JNDI magic in the snippet you posted:

try {
    listBindings = context.getResources().listBindings(
            "/WEB-INF/classes");
} catch (NameNotFoundException ignore) {
    // Safe to ignore
}

could you maybe set up the same sort of entries in JNDI yourself?

Context ctx = tomcat.addWebapp(...);
FileDirContext fdc = new FileDirContext();
fdc.setDocBase(new File("/path/to/my/classes").getAbsolutePath());
ctx.getResources().createSubcontext("/WEB-INF/classes").bind("myclasses", fdc);

Answer 4

I think in 8.5 and later it's just one liner:

Context.setAddWebinfClassesResources(true);

Sets the flag that indicates if /WEB-INF/classes should be treated like an exploded JAR and JAR resources made available as if they were in a JAR.

http://tomcat.apache.org/tomcat-8.5-doc/api/org/apache/catalina/core/StandardContext.html#setAddWebinfClassesResources(boolean)