Is this a bug in RequestFactory when a collection has a null? Resolver.class ...

[Brandon Donnelson]

Is this a bug or as designed?

Having a collection of java.util.List<Long> [31021, null, 87001] cause the resolver to throw an exception on return from the server to the client.  While I can see this is probably poor design to have a collection with a null, but still, this causes it to break with a generic warning too.

The effected class with my notes where I found the error below:

package com.google.web.bindery.requestfactory.server;
// ...

class Resolver {

//...

 /**
   * Creates a Resolution object that holds a client value that represents the
   * given domain value. The resolved client value will be assignable to
   * {@code clientType}.
   */
  private Resolution resolveClientValue(Object domainValue, Type clientType) {
    if (domainValue == null) {
      return null;
    }

    boolean anyType = clientType == null;
    if (anyType) {
      clientType = Object.class;
    }

    Class<?> assignableTo = TypeUtils.ensureBaseType(clientType);
    ResolutionKey key = new ResolutionKey(domainValue, clientType);

    Resolution previous = resolved.get(key);
    if (previous != null && assignableTo.isInstance(previous.getClientObject())) {
      return previous;
    }

    Class<?> returnClass = service.resolveClientType(domainValue.getClass(), assignableTo, true);

    if (anyType) {
      assignableTo = returnClass;
    }

    // Pass simple values through
    if (ValueCodex.canDecode(returnClass)) {
      return makeResolution(domainValue);
    }

    // Convert entities to EntityProxies or EntityProxyIds
    boolean isProxy = BaseProxy.class.isAssignableFrom(returnClass);
    boolean isId = EntityProxyId.class.isAssignableFrom(returnClass);
    if (isProxy || isId) {
      Class<? extends BaseProxy> proxyClass = returnClass.asSubclass(BaseProxy.class);
      return resolveClientProxy(domainValue, proxyClass, key);
    }

    // Convert collections
    if (Collection.class.isAssignableFrom(returnClass)) {
      Collection<Object> accumulator;
      if (List.class.isAssignableFrom(returnClass)) {
        accumulator = new ArrayList<Object>();
      } else if (Set.class.isAssignableFrom(returnClass)) {
        accumulator = new HashSet<Object>();
      } else {
        throw new ReportableException("Unsupported collection type" + returnClass.getName());
      }

      Type elementType = TypeUtils.getSingleParameterization(Collection.class, clientType);
      for (Object o : (Collection<?>) domainValue) {
        
        // this throws when the collection is java.util.List<Long> [31021, null, 87001] // <<<<<<<<< Here
        accumulator.add(resolveClientValue(o, elementType).getClientObject());

      }
      return makeResolution(accumulator);
    }

    throw new ReportableException("Unsupported domain type " + returnClass.getCanonicalName());
  }
}

Here is the trace: for the error:

May 7, 2012 9:03:22 PM com.google.web.bindery.requestfactory.server.RequestFactoryServlet doPost
SEVERE: Unexpected error
java.lang.NullPointerException
        at com.google.web.bindery.requestfactory.server.Resolver.resolveClientValue(Resolver.java:618)
        at com.google.web.bindery.requestfactory.server.Resolver.access$400(Resolver.java:50)
        at com.google.web.bindery.requestfactory.server.Resolver$PropertyResolver.visitReferenceProperty(Resolver.java:139)
        at com.google.web.bindery.autobean.shared.AutoBeanVisitor.visitCollectionProperty(AutoBeanVisitor.java:229)
        at com.google.web.bindery.autobean.vm.impl.ProxyAutoBean.traverseProperties(ProxyAutoBean.java:300)
        at com.google.web.bindery.autobean.shared.impl.AbstractAutoBean.traverse(AbstractAutoBean.java:166)
        at com.google.web.bindery.autobean.shared.impl.AbstractAutoBean.accept(AbstractAutoBean.java:101)
        at com.google.web.bindery.requestfactory.server.Resolver.resolveClientValue(Resolver.java:395)
        at com.google.web.bindery.requestfactory.server.SimpleRequestProcessor.processInvocationMessages(SimpleRequestProcessor.java:483)
        at com.google.web.bindery.requestfactory.server.SimpleRequestProcessor.process(SimpleRequestProcessor.java:225)
        at com.google.web.bindery.requestfactory.server.SimpleRequestProcessor.process(SimpleRequestProcessor.java:127)
        at com.google.web.bindery.requestfactory.server.RequestFactoryServlet.doPost(RequestFactoryServlet.java:133)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
        at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
        at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1166)
        at com.google.appengine.tools.development.HeaderVerificationFilter.doFilter(HeaderVerificationFilter.java:35)
        at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
        at com.google.appengine.api.blobstore.dev.ServeBlobFilter.doFilter(ServeBlobFilter.java:60)
        at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
        at com.google.apphosting.utils.servlet.TransactionCleanupFilter.doFilter(TransactionCleanupFilter.java:43)
        at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
        at com.google.appengine.tools.development.StaticFileFilter.doFilter(StaticFileFilter.java:122)
        at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
        at com.google.appengine.tools.development.BackendServersFilter.doFilter(BackendServersFilter.java:97)
        at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1157)
        at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:388)
        at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
        at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
        at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:765)
        at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:418)
        at com.google.appengine.tools.development.DevAppEngineWebAppContext.handle(DevAppEngineWebAppContext.java:78)
        at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
        at com.google.appengine.tools.development.JettyContainerService$ApiProxyHandler.handle(JettyContainerService.java:369)
        at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
        at org.mortbay.jetty.Server.handle(Server.java:326)
        at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
        at org.mortbay.jetty.HttpConnection$RequestHandler.content(HttpConnection.java:938)
        at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:755)
        at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:218)
        at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
        at org.mortbay.io.nio.SelectChannelEndPoint.run(SelectChannelEndPoint.java:409)
        at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582)

Thoughts?

Brandon Donnelson

http://c.gwt-examples.com

[Brandon Donnelson]

Seems I'm not the only one that found this one:

http://code.google.com/p/google-web-toolkit/issues/detail?id=6809 - Issue for it.

[Stephen Nelson]

As you know from the bug report you linked to this bug has been marked as fixed, not released. Posting a new comment on a bug that has been closed is not very helpful -- it only distracts busy developers from fixing actual bugs. Wait for the fix to be released in the next version of GWT then check that it solves your bug.