Java EE project can't find Gson

Question

I'm building a Java EE project for class, and am attempting to use Google's Gson package to send JSON to another part of my project inside of a Servlet. When I visit the URL mapped to the aforementioned Servlet, I expect to see the raw JSON, however I get a ClassNotFoundException.

import com.google.gson.Gson;
import edu.neumont.writingCenter.json.Event;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;


@WebServlet("/user/appointments/json")
public class UserAppointmentsJsonServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, 
                         HttpServletResponse response) 
                                        throws ServletException, IOException {
        response.setContentType("application/json");
        PrintWriter out = response.getWriter();

        List<Event> events = new ArrayList<Event>();
        for (int i =0; i < 10; i++) {
            Event event = new Event();
            event.setId(i);
            event.setTitle("Test " + i);
            event.setAllDay(false);
            event.setStart(new Date());
            event.setEnd(new Date());
            events.add(event);
        }

        Gson gson = new Gson();
        out.print(gson.toJson(events));
        out.flush();

    }
}

java.lang.NoClassDefFoundError: com/google/gson/Gson at edu.neumont.writingCenter.servlets.user.appointments.UserAppointmentsJsonServlet.doGet(UserAppointmentsJsonServlet.java:35) at javax.servlet.http.HttpServlet.service(HttpServlet.java:734) at javax.servlet.http.HttpServlet.service(HttpServlet.java:847) at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1539) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:343) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:217) at edu.neumont.writingCenter.filters.SetRootFilter.doFilter(SetRootFilter.java:43) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:256) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:217) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:279) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175) at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:655) at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:595) at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:98) at com.sun.enterprise.web.PESessionLockingStandardPipeline.invoke(PESessionLockingStandardPipeline.java:91) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:162) at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:330) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:231) at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:174) at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:828) at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:725) at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:1019) at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:225) at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:137) at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:104) at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:90) at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:79) at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:54) at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:59) at com.sun.grizzly.ContextTask.run(ContextTask.java:71) at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:532) at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:513) at java.lang.Thread.run(Thread.java:662) Caused by: java.lang.ClassNotFoundException: com.google.gson.Gson at org.glassfish.web.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1519) at org.glassfish.web.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1369) ... 33 more

Answer 1

CNF exception means you're missing a JAR from your CLASSPATH. Try putting it in the WEB-INF/lib of your WAR file, repackage, and redeploy.

If you get another CNF exception, keep adding JARs until they go away.