title: java.lang.NoClassDefFoundError: javax/validation/Validator
body: <p>I wonder why my app throws this error:</p>
  
  <blockquote>
    <p>[ERROR] java.lang.NoClassDefFoundError: javax/validation/Validator
    [ERROR]   at java.lang.ClassLoader.defineClass1(Native Method) [ERROR]
      at java.lang.ClassLoader.defineClass(ClassLoader.java:800) [ERROR]
      at
    java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
    [ERROR]   at
    java.net.URLClassLoader.defineClass(URLClassLoader.java:449) [ERROR]
      at java.net.URLClassLoader.access$100(URLClassLoader.java:71) [ERROR]
      at java.net.URLClassLoader$1.run(URLClassLoader.java:361) [ERROR]   at
    java.net.URLClassLoader$1.run(URLClassLoader.java:355) [ERROR]    at
    java.security.AccessController.doPrivileged(Native Method) [ERROR]    at
    java.net.URLClassLoader.findClass(URLClassLoader.java:354) [ERROR]    at
    java.lang.ClassLoader.loadClass(ClassLoader.java:425) [ERROR]     at
    com.google.appengine.tools.development.IsolatedAppClassLoader.loadClass(IsolatedAppClassLoader.java:215)
    [ERROR]   at java.lang.ClassLoader.loadClass(ClassLoader.java:358)
    [ERROR]   at
    org.jboss.resteasy.core.ResourceMethod.(ResourceMethod.java:162)
    [ERROR]   at
    org.jboss.resteasy.core.ResourceMethodRegistry.processMethod(ResourceMethodRegistry.java:280)
    [ERROR]   at
    org.jboss.resteasy.core.ResourceMethodRegistry.addResourceFactory(ResourceMethodRegistry.java:129)
    [ERROR]   at
    org.jboss.resteasy.core.ResourceMethodRegistry.addResourceFactory(ResourceMethodRegistry.java:111)
    [ERROR]   at
    org.jboss.resteasy.core.ResourceMethodRegistry.addResourceFactory(ResourceMethodRegistry.java:88)
    [ERROR]   at
    org.jboss.resteasy.plugins.guice.ModuleProcessor.processInjector(ModuleProcessor.java:66)
    [ERROR]   at
    org.jboss.resteasy.plugins.guice.ModuleProcessor.process(ModuleProcessor.java:45)
    [ERROR]   at
    org.jboss.resteasy.plugins.guice.GuiceResteasyBootstrapServletContextListener.contextInitialized(GuiceResteasyBootstrapServletContextListener.java:31)</p>
  </blockquote>
  
  <p>When it has this dependency in place:</p>
  
  <p>pom.xml</p>
  
  <pre><code>   &lt;dependency&gt;
         &lt;groupId&gt;javax.validation&lt;/groupId&gt;
         &lt;artifactId&gt;validation-api&lt;/artifactId&gt;
         &lt;version&gt;1.0.0.GA&lt;/version&gt;
         &lt;scope&gt;provided&lt;/scope&gt;
     &lt;/dependency&gt;
  
     &lt;dependency&gt;
         &lt;groupId&gt;javax.validation&lt;/groupId&gt;
         &lt;artifactId&gt;validation-api&lt;/artifactId&gt;
         &lt;version&gt;1.0.0.GA&lt;/version&gt;
         &lt;classifier&gt;sources&lt;/classifier&gt;
         &lt;scope&gt;provided&lt;/scope&gt;
     &lt;/dependency&gt;
  </code></pre>