Can't show value with json format on apache tomcat server <p>I've been trying to make a certain API and I need it to show result of a method on server in JSON format. If I try simple </p> <pre><code>import javax.ws.rs.GET; import javax.ws.rs.Path; import javax.ws.rs.Produces; import javax.ws.rs.core.MediaType; @Path("/messages") public class MessageResource { @GET @Produces(MediaType.TEXT_PLAIN) public String getMessages() { return "Hello World!"; } } </code></pre> <p>it works but when I try to use my class where I return values in JSON format it shows some errors on the server (it works in ordinary console). </p> <p>I'm new to this, hope I explained it well enough.</p> <pre><code>type Exception report message org.glassfish.jersey.server.ContainerException: java.lang.NoClassDefFoundError: org/codehaus/jackson/map/ObjectMapper description The server encountered an internal error that prevented it from fulfilling this request. exception javax.servlet.ServletException: org.glassfish.jersey.server.ContainerException: java.lang.NoClassDefFoundError: org/codehaus/jackson/map/ObjectMapper org.glassfish.jersey.servlet.WebComponent.serviceImpl(WebComponent.java:489) org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:427) org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:388) org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:341) org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:228) org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) root cause org.glassfish.jersey.server.ContainerException: java.lang.NoClassDefFoundError: org/codehaus/jackson/map/ObjectMapper org.glassfish.jersey.servlet.internal.ResponseWriter.rethrow(ResponseWriter.java:278) org.glassfish.jersey.servlet.internal.ResponseWriter.failure(ResponseWriter.java:260) org.glassfish.jersey.server.ServerRuntime$Responder.process(ServerRuntime.java:509) org.glassfish.jersey.server.ServerRuntime$2.run(ServerRuntime.java:334) org.glassfish.jersey.internal.Errors$1.call(Errors.java:271) org.glassfish.jersey.internal.Errors$1.call(Errors.java:267) org.glassfish.jersey.internal.Errors.process(Errors.java:315) org.glassfish.jersey.internal.Errors.process(Errors.java:297) org.glassfish.jersey.internal.Errors.process(Errors.java:267) org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:317) org.glassfish.jersey.server.ServerRuntime.process(ServerRuntime.java:305) org.glassfish.jersey.server.ApplicationHandler.handle(ApplicationHandler.java:1154) org.glassfish.jersey.servlet.WebComponent.serviceImpl(WebComponent.java:473) org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:427) org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:388) org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:341) org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:228) org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) root cause java.lang.NoClassDefFoundError: org/codehaus/jackson/map/ObjectMapper valendor.messenger.ReturnJson.main(ReturnJson.java:27) sun.reflect.GeneratedMethodAccessor19.invoke(Unknown Source) sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) java.lang.reflect.Method.invoke(Unknown Source) org.glassfish.jersey.server.model.internal.ResourceMethodInvocationHandlerFactory$1.invoke(ResourceMethodInvocationHandlerFactory.java:81) org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher$1.run(AbstractJavaResourceMethodDispatcher.java:144) org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.invoke(AbstractJavaResourceMethodDispatcher.java:161) org.glassfish.jersey.server.model.internal.JavaResourceMethodDispatcherProvider$VoidOutInvoker.doDispatch(JavaResourceMethodDispatcherProvider.java:143) org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.dispatch(AbstractJavaResourceMethodDispatcher.java:99) org.glassfish.jersey.server.model.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:389) org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:347) org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:102) org.glassfish.jersey.server.ServerRuntime$2.run(ServerRuntime.java:326) org.glassfish.jersey.internal.Errors$1.call(Errors.java:271) org.glassfish.jersey.internal.Errors$1.call(Errors.java:267) org.glassfish.jersey.internal.Errors.process(Errors.java:315) org.glassfish.jersey.internal.Errors.process(Errors.java:297) org.glassfish.jersey.internal.Errors.process(Errors.java:267) org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:317) org.glassfish.jersey.server.ServerRuntime.process(ServerRuntime.java:305) org.glassfish.jersey.server.ApplicationHandler.handle(ApplicationHandler.java:1154) org.glassfish.jersey.servlet.WebComponent.serviceImpl(WebComponent.java:473) org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:427) org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:388) org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:341) org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:228) org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) note The full stack trace of the root cause is available in the Apache Tomcat/8.0.36 logs. </code></pre> <p>thats the error</p>