Question

1. Installed Tomcat 6
2. Installed Eclipse + GWT plugin
3. Created GWT project with sample
   generated code
4. Compliled GWT project (GWT compile)
5. Copied war (compiled) directory from
   eclipse’s workspace to TOMCAT
   webapps/ROOT folder
6. Run localhost:8080 at my browser

The sample.html page from the GWT project displays correct but when i try to make a server call an error occurs.

• No problem with jetty
  (Eclipse GWT develpment mode) – rpc
  work’s fine
• PROBLEM at TOMCAT.

The catalina.out log at TOMCAT says:

Error deploying web application
directory ROOT
java.lang.UnsupportedClassVersionError:
Bad version number in .class file
(unable to load class
com.tomcat.server.GreetingServiceImpl)

I guess there might be a problem at WEB_INF/web.xml at servlet definition, here’s my web.xml

<web-app xmlns="http://java.sun.com/xml/ns/javaee"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
   version="2.5">

  <display-name>Welcome to Tomcat</display-name>
  <description>
     Welcome to Tomcat
  </description>

  <!-- Servlets -->
  <servlet>
    <servlet-name>greetServlet</servlet-name>
    <servlet-class>com.tomcat.server.GreetingServiceImpl</servlet-class>
  </servlet>

  <servlet-mapping>
    <servlet-name>greetServlet</servlet-name>
    <url-pattern>/tomcat/greet</url-pattern>
  </servlet-mapping>

  <!-- Default page to serve -->
  <welcome-file-list>
    <welcome-file>Tomcat.html</welcome-file>
  </welcome-file-list>

</web-app>

Answer 1

I had this same issue when I deployed to my Godaddy hosting server. It worked fine on my local machine but not when I deployed. I got the same exact error message. The problem is you compiled your code with a version of java that is newer then that of which Tomcat is using.

Install jdk1.5.0_22 (Or whatever your tomcat server is using)
Probably need to restart your machine
Eclipse->Window->Preferences->Java->Installed JRES->Add
Standard VM->Next
Browse to the directory of your jdk
Finish
Clean the project
Compile the project
Redeploy and cross your fingers!

This worked for me, if it doesn’t for you then….ya…it should work. Good luck