eclipse/tomcat: deploy doesn't work any more (

Question

I'm running Eclipse Helios Service Release 1, with Tomcat 7.0.12 in Linux Ubuntu Natty Narwhal.

I've been happily hot re-deploying my webapp until it stopped working for apparently no reason. The following exception is displayed:

SEVERE: Allocate exception for servlet Index
java.lang.ClassNotFoundException: obliquid.servlet.Index
    at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1676)
    at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1521)

• In Servers tab I've "Tomcat v7.0 Server at localhost [Started,Synchronized]
• My project appears as a child of Tomcat v7.0 Server
• In Properties, Java Build Path, Source I've Project/src Source folder
• In Properties, Web Deployment Assembly, I've the following mappings: /WebContent -> /, /src -> /WEB-INF/classes, /test -> /build/classes
• My src directory contains a Servlet in obliquid/servlet/Index.java
• I tried already to click on Clean Module Work Directory... and Publish
• I tried to stop and start the Server from within Eclipse Servers tab

What else should I check? Thank you.

UPDATE Despite now I'm working with the new project, I came back to check the old one, and mysteriously now it's working. I think I won't be able to find what has happened.

However today with the new project, I had 404 errors with no apparent reason and I found out that right clicking on the Tomcat server and selecting "Clean..." can be useful. Maybe it could have helped.

Selecting "Clean..." says: "Clean will discard all publish state and republish from scratch. Are you sure you want to clean all published resources?". Selecting yes, I solved the problem

UPDATE 2 It happened again on the new project. 404 errors, this time they don't go away.

Stop -> Clean... -> Start (404)
Stop -> Clean Tomcat Work Directory... -> Start (404)
Stop -> Clean Tomcat Work Directory... -> Clean... -> Start (404)
Stop -> Remove on the application ->  Clean... -> Run As -> Run on Server -> (404)  
Exit Eclipse, Start Eclipse
Start the server -> (404)

UPDATE 3 It turned out that this time I just didn't notice an exception caused by a listener-class during startup. After solving the problem, it worked. Guess I should stop working at 3 AM.

Answer 1

I wonder when I see the accepted answer with +25 is it really accurate?

First if you are going to delete the server then whats the point in cleaning it? It will take your time unnecessarily and nothing useful will you gain.

So i will say just 5, 6, 7 steps should do the magic

5 delete Servers folder

6 restart Eclipse

7 create new server, add project and start

Answer 2

I was running into the same problem - tried all of the above, Eclipse always freezed when i tried to start the server, even after i deleted all the server configs and created a new one with a freshly downloaded tomcat instance. Anyways, problem wasnt solved until i moved to a new workspace, reimported the projects and created a new server. Seems like an Eclipse bug to me...So in case nothing else works, this is the way to go...

Answer 3

This could be something I learned on con-fess 2011. For me this sounds like a classloader problem.

The theory behind:

• Java does not only use the type of the class but also the classloader which loaded it to identify the type of an instance. This means a simle operation could fail, e.g.

  ClassA a1 = new a1; ClassA a2 = SomeOtherClass.giveMeInstanceOfA(); a1 = a2;

This example would fail if SomeOtherClass uses a different classloader because Java would say that they are not the same.

• The speaker also mentioned that some servers use per default about 45 different classloaders.

What does this mean in practice:

You deploy your webapp to the server, everything runs fine. The server caches the classes and everything he needs to load them somewhere. Now you make a hot deploymen and the server may loads new classes with a new (or different) classloader. This is the point where it starts to become dangerous because from now on you have two different classes in the memory which should be the same. Simple operations like casts (ClassA a = (ClassA) new ClassA()) fail, new Methods within the class are not found (because the server takes a cached version without this method),....

This is the point where I restart the server, clean the working directory (to get rid of the cached versions) and start thinking about hot deployment as critical thing.

If it is possible to try Mikkos procedere and this solves the problem this explanation could help you understand why.

I know this does not solve your problem but could give you some hints what maybe could have happened.

Answer 4

I was able to solve this by disabling the maven nature (right click on project >> maven >> disable maven nature). Then re-enabling it (right click on project >> configure >> convert to maven project). I had tried all of the other tips and tricks above, but this is the one that finally worked.