Getting java.lang.AbstractMethodError on implemented method

Question

As the title states, I get a java.lang.AbstractMethodError on a method that is definitively implemented by my class. The complete error message is:

java.lang.AbstractMethodError: htmlexport.HTMLExport.getParameterFormDescriptor()Ljava/util/List;

I have an interface that defines the method as follows:

List<ParamFormElement> getParameterFormDescriptor();

And as I said this method is implemented by the implementing class.

The interface is included in a jar that is in my local Maven repository. I already tried mvn clean and mvn install and bumping the version number, but this does not solve the problem.

The implementing class is in another jar file which I create using an ANT-script. The file is then loaded via a ClassLoader in the main application.

Any clues why I get this error? All other methods defined by the interface are working.

Here comes the code

I have a Wicket WebPage where I make the call to this method:

public class AddJobPage extends BasePage {

    public AddJobPage(final PageParameters params) {
        super(params);

        final Workable w =
                WorkableManager.getInstance().findWorkableByName(params.get("workableName").toString());
        w.getParameterFormDescriptor();
    }

}

The WorkableManager internally loads the jar-file which includes the implementing class using an URLClassLoader. This is working fine and I get an instance of the needed class.

The interface that defines the method is:

public interface Workable {

    List<ParamFormElement> getParameterFormDescriptor();

}

And the implementing class looks like this (Module extends Workable):

public class HTMLExport implements Module {

    @Override
    public final List<ParamFormElement> getParameterFormDescriptor() {
        final List<ParamFormElement> form = new ArrayList<>();
        form.add(new ParamFormElement(ParamFormElement.Type.TEXT, "Bitte eingeben:", "test"));
        return form;
    }

}

The interface is in a separate project and assembled as a jar-file in my local Maven repository. The HTMLExport class is in a different project, too and compiled and assembled using Ant. The resulting jar-file is in a folder next to my main application and as I said loading the class works. The main application is a Maven project and has the interface added as a dependency. In Eclipse I do not have any errors or warnings.

The stacktrace is following:

Root cause:

java.lang.AbstractMethodError: htmlexport.HTMLExport.getParameterFormDescriptor()Ljava/util/List;
    at web.pages.AddJobPage.<init>(AddJobPage.java:30)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:525)
    at org.apache.wicket.session.DefaultPageFactory.newPage(DefaultPageFactory.java:171)
    at org.apache.wicket.session.DefaultPageFactory.newPage(DefaultPageFactory.java:99)
    at org.apache.wicket.DefaultMapperContext.newPageInstance(DefaultMapperContext.java:137)
    at org.apache.wicket.core.request.handler.PageProvider.resolvePageInstance(PageProvider.java:268)
    at org.apache.wicket.core.request.handler.PageProvider.getPageInstance(PageProvider.java:166)
    at org.apache.wicket.request.handler.render.PageRenderer.getPage(PageRenderer.java:78)
    at org.apache.wicket.request.handler.render.WebPageRenderer.isPageStateless(WebPageRenderer.java:300)
    at org.apache.wicket.request.handler.render.WebPageRenderer.shouldRenderPageAndWriteResponse(WebPageRenderer.java:342)
    at org.apache.wicket.request.handler.render.WebPageRenderer.respond(WebPageRenderer.java:203)
    at org.apache.wicket.core.request.handler.RenderPageRequestHandler.respond(RenderPageRequestHandler.java:175)
    at org.apache.wicket.request.cycle.RequestCycle$HandlerExecutor.respond(RequestCycle.java:837)
    at org.apache.wicket.request.RequestHandlerStack.execute(RequestHandlerStack.java:64)
    at org.apache.wicket.request.cycle.RequestCycle.execute(RequestCycle.java:265)
    at org.apache.wicket.request.cycle.RequestCycle.processRequest(RequestCycle.java:222)
    at org.apache.wicket.request.cycle.RequestCycle.processRequestAndDetach(RequestCycle.java:293)
    at org.apache.wicket.protocol.http.WicketFilter.processRequestCycle(WicketFilter.java:261)
    at org.apache.wicket.protocol.http.WicketFilter.processRequest(WicketFilter.java:203)
    at org.apache.wicket.protocol.http.WicketFilter.doFilter(WicketFilter.java:284)
    at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1631)
    at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:549)
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:143)
    at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:568)
    at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:221)
    at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1111)
    at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:478)
    at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:183)
    at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1045)
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141)
    at org.eclipse.jetty.server.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:199)
    at org.eclipse.jetty.server.handler.HandlerCollection.handle(HandlerCollection.java:109)
    at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:97)
    at org.eclipse.jetty.server.Server.handle(Server.java:462)
    at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:279)
    at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:232)
    at org.eclipse.jetty.io.AbstractConnection$2.run(AbstractConnection.java:534)
    at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:607)
    at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:536)
    at java.lang.Thread.run(Thread.java:722)

Complete stack:

org.apache.wicket.WicketRuntimeException: Can't instantiate page using constructor 'public web.pages.AddJobPage(org.apache.wicket.request.mapper.parameter.PageParameters)' and argument 'workableName=[HTML Export]'. An exception has been thrown during construction!
    at org.apache.wicket.session.DefaultPageFactory.newPage(DefaultPageFactory.java:194)
    at org.apache.wicket.session.DefaultPageFactory.newPage(DefaultPageFactory.java:99)
    at org.apache.wicket.DefaultMapperContext.newPageInstance(DefaultMapperContext.java:137)
    at org.apache.wicket.core.request.handler.PageProvider.resolvePageInstance(PageProvider.java:268)
    at org.apache.wicket.core.request.handler.PageProvider.getPageInstance(PageProvider.java:166)
    at org.apache.wicket.request.handler.render.PageRenderer.getPage(PageRenderer.java:78)
    at org.apache.wicket.request.handler.render.WebPageRenderer.isPageStateless(WebPageRenderer.java:300)
    at org.apache.wicket.request.handler.render.WebPageRenderer.shouldRenderPageAndWriteResponse(WebPageRenderer.java:342)
    at org.apache.wicket.request.handler.render.WebPageRenderer.respond(WebPageRenderer.java:203)
    at org.apache.wicket.core.request.handler.RenderPageRequestHandler.respond(RenderPageRequestHandler.java:175)
    at org.apache.wicket.request.cycle.RequestCycle$HandlerExecutor.respond(RequestCycle.java:837)
    at org.apache.wicket.request.RequestHandlerStack.execute(RequestHandlerStack.java:64)
    at org.apache.wicket.request.cycle.RequestCycle.execute(RequestCycle.java:265)
    at org.apache.wicket.request.cycle.RequestCycle.processRequest(RequestCycle.java:222)
    at org.apache.wicket.request.cycle.RequestCycle.processRequestAndDetach(RequestCycle.java:293)
    at org.apache.wicket.protocol.http.WicketFilter.processRequestCycle(WicketFilter.java:261)

java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:525)
    at org.apache.wicket.session.DefaultPageFactory.newPage(DefaultPageFactory.java:171)
    at org.apache.wicket.session.DefaultPageFactory.newPage(DefaultPageFactory.java:99)
    at org.apache.wicket.DefaultMapperContext.newPageInstance(DefaultMapperContext.java:137)
    at org.apache.wicket.core.request.handler.PageProvider.resolvePageInstance(PageProvider.java:268)
    at org.apache.wicket.core.request.handler.PageProvider.getPageInstance(PageProvider.java:166)
    at org.apache.wicket.request.handler.render.PageRenderer.getPage(PageRenderer.java:78)
    at org.apache.wicket.request.handler.render.WebPageRenderer.isPageStateless(WebPageRenderer.java:300)
    at org.apache.wicket.request.handler.render.WebPageRenderer.shouldRenderPageAndWriteResponse(WebPageRenderer.java:342)
    at org.apache.wicket.request.handler.render.WebPageRenderer.respond(WebPageRenderer.java:203)
    at org.apache.wicket.core.request.handler.RenderPageRequestHandler.respond(RenderPageRequestHandler.java:175)
    at org.apache.wicket.request.cycle.RequestCycle$HandlerExecutor.respond(RequestCycle.java:837)
    at org.apache.wicket.request.RequestHandlerStack.execute(RequestHandlerStack.java:64)
    at org.apache.wicket.request.cycle.RequestCycle.execute(RequestCycle.java:265)
    at org.apache.wicket.request.cycle.RequestCycle.processRequest(RequestCycle.java:222)
    at org.apache.wicket.request.cycle.RequestCycle.processRequestAndDetach(RequestCycle.java:293)
    at org.apache.wicket.protocol.http.WicketFilter.processRequestCycle(WicketFilter.java:261)

Answer 1

The problem was that the implementing class was not compiled correctly and the Ant script did not copy the correct class into the jar-file. I converted it to a maven project and now the method can be found.

Answer 2

Make sure you have the latest jar file in your class path not a older copy. If you are seeing this at run time this happens due to incompatible binaries

From Oracle java site

Thrown when an application tries to call an abstract method. Normally, this error is caught by the compiler; this error can only occur at run time if the definition of some class has incompatibly changed since the currently executing method was last compiled.

Link to Class AbstractMethodError

Also try the -U flag forces to update dependencies.

mvn clean install -U

Answer 3

if your implementing class's jar is not in the classpath or not sure

try like below code

    YourInterfaceName obj = (YourInterfaceName)Class.forName
("yourPackageName.YourInterfaceImplClassName").newInstance();