Classes not auto compiling in Eclipse - eclipse

Question

I am using Eclipse, In struts.xml, if I use:
<action name="hello">
<result>
/hello.jsp
</result>
</action>
This works when I access localhost:8080/app/hello
But if I add a self-defined action class like:
<action name="hello" class="com.hah">
<result>
/hello.jsp
</result>
</action>
The hah.java does not compile automatically, it gives me the exception:
Unable to load configuration. - action - file:/D:/workspace/.metadata/.plugins/org.eclipse.wst.server.core/tmp0/wtpwebapps/Struts2/WEB-INF/classes/struts.xml:17:46
at com.opensymphony.xwork2.config.ConfigurationManager.getConfiguration(ConfigurationManager.java:58)
at org.apache.struts2.dispatcher.Dispatcher.init_PreloadConfiguration(Dispatcher.java:360)
at org.apache.struts2.dispatcher.Dispatcher.init(Dispatcher.java:403)
at org.apache.struts2.dispatcher.ng.InitOperations.initDispatcher(InitOperations.java:69)
at org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.init(StrutsPrepareAndExecuteFilter.java:48)
at org.apache.catalina.core.ApplicationFilterConfig.initFilter(ApplicationFilterConfig.java:279)
at org.apache.catalina.core.ApplicationFilterConfig.getFilter(ApplicationFilterConfig.java:260)
at org.apache.catalina.core.ApplicationFilterConfig.<init>(ApplicationFilterConfig.java:105)
at org.apache.catalina.core.StandardContext.filterStart(StandardContext.java:4658)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5277)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:147)
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1408)
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1398)
at java.util.concurrent.FutureTask.run(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
Caused by: Action class [com.hah] not found - action - file:/D:/workspace/.metadata/.plugins/org.eclipse.wst.server.core/tmp0/wtpwebapps/Struts2/WEB-INF/classes/struts.xml:17:46
at com.opensymphony.xwork2.config.providers.XmlConfigurationProvider.verifyAction(XmlConfigurationProvider.java:405)
at com.opensymphony.xwork2.config.providers.XmlConfigurationProvider.addAction(XmlConfigurationProvider.java:355)
at com.opensymphony.xwork2.config.providers.XmlConfigurationProvider.addPackage(XmlConfigurationProvider.java:460)
at com.opensymphony.xwork2.config.providers.XmlConfigurationProvider.loadPackages(XmlConfigurationProvider.java:265)
at org.apache.struts2.config.StrutsXmlConfigurationProvider.loadPackages(StrutsXmlConfigurationProvider.java:111)
at com.opensymphony.xwork2.config.impl.DefaultConfiguration.reloadContainer(DefaultConfiguration.java:189)
at com.opensymphony.xwork2.config.ConfigurationManager.getConfiguration(ConfigurationManager.java:55)
... 16 more
But I can make it work properly by compiling the hah.java manually(by using javac hah.java) and move the compiled hah.class into /D:/workspace/.metadata/.plugins/org.eclipse.wst.server.core/tmp0/wtpwebapps/Struts2/WEB-INF/classes/ folder
I have checked Build Automatically and there is an entry "/src WEB-INF/classes " in Deployment Assembly.
So the problem is that the action class does not compile automatically. What can I do to make it compiled when Tomcat starts?
ps: Finally, I reinstall eclipse for Java EE and use struts-2.3.29, it works.
But I still do not know why..

Answer 1

Check if the Project > Build Automatically is selected.
Also
Right click open project property and select Deployment Assembly check if the project target classes are copied into web-inf/classes
If these does not solve, I suggest you create an empty project and select Dynamic Web Project template, and copy your files in this new project.

Answer 2

I finally found a solution to this:
Here's what was happening:
I had the exact same problem. Eclipse was not compiling the Java class into the .class file even if there were packages being created in the below path:
[workspace_root].metadata.plugins\org.eclipse.wst.server.core\tmp0\wtpwebapps\2_StrutsReadingProject\WEB-INF\classes\
I tried manually compiling the class in the cmd prompt. Turns out I was missing the JAR files in the BUILD PATH. All my JARs were correct, there was no duplication. But it seems like Eclipse needs these JARs both, in your build path as well in your WEB-INF/lib folder.
After I added the JARs in both places and built the project again from Eclipse, the classes were compiled properly.
So here is how to add JARs in your Eclipse Build Path:
Right click the project node in the "Project Explorer" > Build Path >
Configure Build Path > Switch to "Libraries" tab > Click "Add External
JARs" > Browse and select all your required JARs > Click "Apply" >
Click "OK".
Hopefully this will solve this error for many people! If it doesn't, try manually compiling the class and the CMD prompt will show exactly any errors.
MORAL OF THE STORY: Eclipse does not show any errors in such a scenario, where the source of error is in its own operations!

Answer 3

Had same problem and apparently this can be caused when deleting a library file (.jar) from disk (ie: in lib folder) but not removing it from the built path.
How I resolved it:
After deleting the .jar library from disk
Open Java Build Path. How:
In Project Explorer, right click on name of project and chose properties
In Properties window chose "Java Build Path"
Locate the respective entry (the file name you deleted)
And click on Remove
click on "Apply and close"
This will automatically rebuild the project if "Build Automatically" is selected (Menu: Project>"Build Automatically").