Tuesday, May 18, 2010

Enhanced POM for JBoss RESTEasy Twitter API Client Sample

I recently looked at JBOSS RESTEasy as a way to create and test RESTful APIs. The platform looks very promising with a lot of praise from developers. Also the documentation seems very extensive and precise.

I started by downloading RESTEasy 1.2.1 GA and tried the sample code. I started with a java client to access existing RESTful Web Services and APIs. Among the api-clients, there is a Twitter small client that works out-of-the box (located under /RESTEASY_1_2_1_GA/examples/api-clients/src/main/java/org/jboss/resteasy/examples/twitter).

However when I started to extract the code and wanted to create a Maven 2 based stand-alone project, I encountered some issues related to JAR dependency conflicts, including the following error message also described here.

java.lang.NoClassDefFoundError: Could not initialize class com.sun.xml.bind.v2.model.impl.RuntimeBuiltinLeafInfoImpl 

The project (eclipse) structure looks as below:

I managed to fix these issues by modifying the POM file as follow:

<?xml version="1.0" encoding="UTF-8"?>
    <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
    <!-- Resteasy Core -->
    <!-- JAXB support -->
   <!-- Build Settings --> 
  <!-- Environment Settings -->
      <name>jboss repo</name>

The most important piece, beside the cleaning of the POM file, was to include a pom that can be imported so the versions of the individual modules do not have to be specified (see RESTEasy documentation - Chapter 43. Maven and RESTEasy).

I also made sure to have correct dependencies for resteasy-jaxrs and resteasy-jaxb-provider.

As a result, I was able to compile the whole project without any errors (mvn clean compile) and run it to access the Twitter REST API

mvn exec:java -Dexec.mainClass="org.jboss.resteasy.examples.twitter.TwitterClient" -Dexec.args="<userid> <password>"
(Replace last parameters by your twitter user and password).

The small client in question leverages JAX-RS annotations to read and write the Twitter API resources:

package org.jboss.resteasy.examples.twitter;

import java.util.Date;
import java.util.List;

import javax.ws.rs.FormParam;
import javax.ws.rs.GET;
import javax.ws.rs.POST;
import javax.ws.rs.Path;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;
import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;

import org.apache.commons.httpclient.Credentials;
import org.apache.commons.httpclient.HttpClient;
import org.apache.commons.httpclient.UsernamePasswordCredentials;
import org.apache.commons.httpclient.auth.AuthScope;
import org.jboss.resteasy.client.ProxyFactory;
import org.jboss.resteasy.client.ClientExecutor;
import org.jboss.resteasy.client.core.executors.ApacheHttpClientExecutor;
import org.jboss.resteasy.plugins.providers.RegisterBuiltin;
import org.jboss.resteasy.spi.ResteasyProviderFactory;

public class TwitterClient
   static final String friendTimeline = "http://twitter.com/statuses/friends_timeline.xml";

   public static void main(String[] args) throws Exception
      final ClientExecutor clientExecutor = new ApacheHttpClientExecutor(createClient(args[0], args[1]));
      TwitterResource twitter = ProxyFactory.create(TwitterResource.class,
            "http://twitter.com", clientExecutor);
      System.out.println("===> first run");
      .updateStatus("I programmatically tweeted with the RESTEasy Client at "
            + new Date());
      System.out.println("===> second run");

   public static interface TwitterResource
      Statuses getFriendsTimelines();

      Status updateStatus(@FormParam("status") String status);

   private static void printStatuses(Statuses statuses)
      for (Status status : statuses.status)

   private static HttpClient createClient(String userId, String password)
      Credentials credentials = new UsernamePasswordCredentials(userId,
      HttpClient httpClient = new HttpClient();
      httpClient.getState().setCredentials(AuthScope.ANY, credentials);
      return httpClient;

   public static class Statuses
      public List<Status> status;

   public static class Status
      public String text;
      public User user;

      @XmlElement(name = "created_at")
      @XmlJavaTypeAdapter(value = DateAdapter.class)
      public Date created;

      public String toString()
         return String.format("== %s: %s (%s)", user.name, text, created);

   public static class User
      public String name;


The small DateAdapter class is a utility class for date formatting:

package org.jboss.resteasy.examples.twitter;

import java.util.Date;
import java.util.List;
package org.jboss.resteasy.examples.twitter;
import java.util.Date;
import javax.xml.bind.annotation.adapters.XmlAdapter;
import org.jboss.resteasy.util.DateUtil;

public class DateAdapter extends XmlAdapter<String, Date> {

   public String marshal(Date date) throws Exception {
       return DateUtil.formatDate(date, "EEE MMM dd HH:mm:ss Z yyyy");

   public Date unmarshal(String string) throws Exception {
       try {
           return DateUtil.parseDate(string);
       } catch (IllegalArgumentException e) {
                   "Could not parse date string '%s'", string));
           return null;