Why is Restlet unable to Register the JSON Converter?

Question

I'm at my wit's end here - never seemed to have faced this problem. I find it relatively easy to set up quick HelloWorld applications to ensure Restlet 2.0 is up and running. However, I'm facing a strange exception which I've never encountered before. I have the jars in my classpath as well as the WEB-INF/lib folder but for some reason I keep getting the following exception:

INFO: Unable to register the helper org.restlet.ext.json.JsonConverter
java.lang.NoClassDefFoundError: org/json/JSONException
    at java.lang.Class.getDeclaredConstructors0(Native Method)
    at java.lang.Class.privateGetDeclaredConstructors(Class.java:2389)
    at java.lang.Class.getConstructor0(Class.java:2699)
    at java.lang.Class.newInstance0(Class.java:326)
    at java.lang.Class.newInstance(Class.java:308)
    at org.restlet.engine.Engine.registerHelper(Engine.java:718)
    at org.restlet.engine.Engine.registerHelpers(Engine.java:753)
    at org.restlet.engine.Engine.registerHelpers(Engine.java:793)
    at org.restlet.engine.Engine.discoverConverters(Engine.java:501)
    at org.restlet.engine.Engine.<init>(Engine.java:337)
    at org.restlet.engine.Engine.register(Engine.java:248)
    at org.restlet.engine.Engine.register(Engine.java:237)
    at org.restlet.engine.Engine.getInstance(Engine.java:149)
    at org.restlet.engine.Engine.getLogger(Engine.java:204)
    at org.restlet.Context.<init>(Context.java:160)
    at org.restlet.Context.<init>(Context.java:133)
    at org.restlet.ext.servlet.ServerServlet.createComponent(ServerServlet.java:422)
    at org.restlet.ext.servlet.ServerServlet.getComponent(ServerServlet.java:763)
    at org.restlet.ext.servlet.ServerServlet.init(ServerServlet.java:881)
    at javax.servlet.GenericServlet.init(GenericServlet.java:242)
    at org.apache.catalina.core.StandardWrapper.initServlet(StandardWrapper.java:1428)
    at org.apache.catalina.core.StandardWrapper.allocate(StandardWrapper.java:1060)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:187)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:188)
    at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:641)
    at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:97)
    at com.sun.enterprise.web.PESessionLockingStandardPipeline.invoke(PESessionLockingStandardPipeline.java:85)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:185)
    at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:325)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:226)
    at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:165)
    at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:791)
    at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:693)
    at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:954)
    at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:170)
    at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:135)
    at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:102)
    at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:88)
    at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:76)
    at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:53)
    at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:57)
    at com.sun.grizzly.ContextTask.run(ContextTask.java:69)
    at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:330)
    at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:309)
    at java.lang.Thread.run(Thread.java:662)
Caused by: java.lang.ClassNotFoundException: org.json.JSONException
    at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
    at org.glassfish.web.loader.WebappClassLoader.findClass(WebappClassLoader.java:959)
    at org.glassfish.web.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1430)
    ... 45 more

The following jars are in my classpath and the WEB-INF/lib folders:

org.json.jar
org.restlet.jar
org.restlet.ext.servlet
org.restlet.ext.json

I'm building the project using Eclipse and deploying on Glassfish. The web.xml etc are all fine and no deployment errors...however, this one has had me scratching my head for a while.

Any ideas?

Answer 1

I had the same or a similar problem. I want to override the jackson representation and remove some dependencies it imports but when I do, the jackson converter is not discovered. Then I've found why in my case: the jar contains a META-INF/services folder with a file called org.restlet.engine.converter.ConverterHelper. That's how discovery works.

I've tried to add that files to my path and it didn't work, don't know. So I ended up registering the Jackson converter

Engine.getInstance().getRegisteredConverters().add(new JacksonConverter());

Answer 2

For some reason the error went away when I swapped the file with that from the Restlet Distribution - in the org.json folder of the Restlet Java EE version.

Seems maybe something was missing in the org.json.jar that I had from the json website, don't know...

Answer 3

It looks like your application isn't able to find a library. If you're building your app in Eclipse, have you made sure that the libraries are being exported? Go to the Build Path section, and make sure the checkbox for exporting libraries is checked.