EJB in REST service returns null pointer exception

Question

I'm trying to implement REST service with Resteasy and Jboss as7, I have session bean which gets data from DB through DAO(it works on JSF+managed bean), and I want to inject that session bean with @EJB, but it returns null, am I doing something wrong?

MyRESTApplication.java:

public class MyRESTApplication extends Application {

    private Set<Object> singletons = new HashSet<Object>();
    private Set<Class<?>> empty = new HashSet<Class<?>>();
    public MyRESTApplication(){
         singletons.add(new TablesResource());
    }
    @Override
    public Set<Class<?>> getClasses() {
         return empty;
    }
    @Override
    public Set<Object> getSingletons() {
         return singletons;
    }
}

TablesResource.java:

@Path("/RESTService")
public class TablesResource {

    @EJB
    private TablesSB tablesSB;

    @GET
    @Produces("application/xml")
    @Path("/table")
    public Tables getTable() {
        return tablesSB.getTable(28);
    }
}

session bean:

@Stateless
@LocalBean
public class TablesSB {

    @PersistenceContext
    private EntityManager em;

    private TablesDAO tablesDao;
    private TablesDAOxml tablesDaoXml;

    public TablesSB() {
    }

    @PostConstruct
    public void init(){
        //tablesDao = new TablesDAO(em);
        tablesDaoXml = new TablesDAOxml();
    }

    public Tables getTable(int tableId) {
        return tablesDaoXml.getTable(tableId);
    }
    ...
}

web.xml:

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
  <display-name>BarBar</display-name>
  <welcome-file-list>
    <welcome-file>index.xhtml</welcome-file>
  </welcome-file-list>
  <servlet>
    <servlet-name>Resteasy</servlet-name>
    <servlet-class>org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>Resteasy</servlet-name>
    <url-pattern>/*</url-pattern>
  </servlet-mapping>
  <context-param>
    <param-name>javax.ws.rs.Application</param-name>
    <param-value>ws.MyRESTApplication</param-value>
  </context-param>
  <listener>
    <listener-class>org.jboss.resteasy.plugins.server.servlet.ResteasyBootstrap</listener-class>
  </listener>
</web-app>

stack trace:

20:59:06,820 ERROR [org.apache.catalina.core.ContainerBase.[jboss.web].[default-host].[/BarBar].[Resteasy]] (http-localhost-127.0.0.1-8080-1) Servlet.service() for servlet Resteasy threw exception: org.jboss.resteasy.spi.UnhandledException: java.lang.NullPointerException
    at org.jboss.resteasy.core.ExceptionHandler.handleApplicationException(ExceptionHandler.java:76) [resteasy-jaxrs-3.0.6.Final.jar:]
    at org.jboss.resteasy.core.ExceptionHandler.handleException(ExceptionHandler.java:212) [resteasy-jaxrs-3.0.6.Final.jar:]
    at org.jboss.resteasy.core.SynchronousDispatcher.writeException(SynchronousDispatcher.java:149) [resteasy-jaxrs-3.0.6.Final.jar:]
    at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:372) [resteasy-jaxrs-3.0.6.Final.jar:]
    at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:179) [resteasy-jaxrs-3.0.6.Final.jar:]
    at org.jboss.resteasy.plugins.server.servlet.ServletContainerDispatcher.service(ServletContainerDispatcher.java:220) [resteasy-jaxrs-3.0.6.Final.jar:]
    at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:56) [resteasy-jaxrs-3.0.6.Final.jar:]
    at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:51) [resteasy-jaxrs-3.0.6.Final.jar:]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:847) [jboss-servlet-api_3.0_spec-1.0.0.Final.jar:1.0.0.Final]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:329) [jbossweb-7.0.13.Final.jar:]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:248) [jbossweb-7.0.13.Final.jar:]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:275) [jbossweb-7.0.13.Final.jar:]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:161) [jbossweb-7.0.13.Final.jar:]
    at org.jboss.as.jpa.interceptor.WebNonTxEmCloserValve.invoke(WebNonTxEmCloserValve.java:50) [jboss-as-jpa-7.1.1.Final.jar:7.1.1.Final]
    at org.jboss.as.web.security.SecurityContextAssociationValve.invoke(SecurityContextAssociationValve.java:153) [jboss-as-web-7.1.1.Final.jar:7.1.1.Final]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:155) [jbossweb-7.0.13.Final.jar:]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) [jbossweb-7.0.13.Final.jar:]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) [jbossweb-7.0.13.Final.jar:]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:368) [jbossweb-7.0.13.Final.jar:]
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:877) [jbossweb-7.0.13.Final.jar:]
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:671) [jbossweb-7.0.13.Final.jar:]
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:930) [jbossweb-7.0.13.Final.jar:]
    at java.lang.Thread.run(Unknown Source) [rt.jar:1.7.0_45]
Caused by: java.lang.NullPointerException
    at ws.TablesResource.getTable(TablesResource.java:30) [classes:]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) [rt.jar:1.7.0_45]
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) [rt.jar:1.7.0_45]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) [rt.jar:1.7.0_45]
    at java.lang.reflect.Method.invoke(Unknown Source) [rt.jar:1.7.0_45]
    at org.jboss.resteasy.core.MethodInjectorImpl.invoke(MethodInjectorImpl.java:137) [resteasy-jaxrs-3.0.6.Final.jar:]
    at org.jboss.resteasy.core.ResourceMethodInvoker.invokeOnTarget(ResourceMethodInvoker.java:280) [resteasy-jaxrs-3.0.6.Final.jar:]
    at org.jboss.resteasy.core.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:234) [resteasy-jaxrs-3.0.6.Final.jar:]
    at org.jboss.resteasy.core.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:221) [resteasy-jaxrs-3.0.6.Final.jar:]
    at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:356) [resteasy-jaxrs-3.0.6.Final.jar:]
    ... 19 more

Answer 1

Please add bean.xml file in WEB-INF folder and paste the below code in bean.xml file.

<?xml version="1.0" encoding="UTF-8"?>

    <beans 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/beans_1_0.xsd">

</beans>

Answer 2

Hints from Nikos are completely true. However it's strange that code works for you. In your code You create reference of TablesResource class "manually". You call constructor explicit.

public MyRESTApplication(){
     singletons.add(new TablesResource());
}

The class MyRESTApplication should be change as follow. The point is to show container which classes it should use. And it has to call constructor(s) itself.

public class MyRESTApplication extends Application {

   private Set<Object> singletons = new HashSet<Object>();
   private Set<Class<?>> classes = new HashSet<Class<?>>();

   public MyRESTApplication(){
        classes.add(TablesResource.class); 
        // singletons.add(new TablesResource());
   }

   @Override
   public Set<Class<?>> getClasses() {
        return classes;
    }

   @Override
   public Set<Object> getSingletons() {
        return singletons;
   }
}

(I had similar problem and I solved it with above changes. The problem is the code automatically generated from Eclipse JBoss Tool "Create Sample RESTful Service".)

Answer 3

I believe the cause of this is because you are using RestEasy explicitly. It cannot inject the EJB because it doesn't know about it. Can you try replacing the entire web.xml above with:

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
    <display-name>BarBar</display-name>
    <welcome-file-list>
        <welcome-file>index.xhtml</welcome-file>
    </welcome-file-list>

    <servlet-mapping>
        <servlet-name>yourcompany.yourpackage.MyRESTApplication</servlet-name>
        <url-pattern>/*</url-pattern>
    </servlet-mapping>
</web-app>

(i.e. substituted all the RestEasy stuff with the standard servlet mapping for JAX-RS - see JAX-RS 1.1 specs, ch. 2.3.2; obviously replace yourcompany.yourpackage.MyRESTApplication with the real fully quallified name of MyRESTApplication)

Alternatively, annotate your application class with javax.ws.rs.ApplicationPath and remove all relevant configuration from web.xml:

@ApplicationPath("/*")
public class MyRESTApplication extends Application {
    ...
}