在访问servlet时，在Tomcat java.lang.NoClassDefFoundError下？

Question

I'm writing a web applicaion in Eclipse, and I'm using the XStream Serialization Library to generate My JSON.

I've encapsulated the Code that builds up the JSON in a class which is called by my servelet. Then encapsulated class has a main method for testing and when I run it everything seems to work fine.

However when I use the call the class from my servelet I get a java.lang.NoClassDefFoundError error, sayying that I've not loaded the XStream libraries. I assume I've got my build path wrong, but I've set the XStream libraries to be in the build path for the project, so as far as I know it should work.

What is likely to be going wrong here?

Following is the exact exception:

java.lang.ClassNotFoundException: com.thoughtworks.xstream.io.HierarchicalStreamDriver
    at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1387)
    at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1233)
    at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:320)
    at SecurePaymentAjaxData.doPost(SecurePaymentAjaxData.java:44)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:845)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
    at java.lang.Thread.run(Thread.java:619)

And here is the relavant code that uses the xstream class:

XStream xstream = new XStream(new JettisonMappedXmlDriver());
xstream.setMode(XStream.NO_REFERENCES);
xstream.alias("CallDataUpdate", CallDataUpdate.class);
xstream.alias("CardStatus", CardStatus.class);
String jsonData = xstream.toXML(updateData);

I stress that this code works fine when run as a java application, I'm sure it's something to do with loading the libraries, I just don't know where I've gone wrong.

Answer 1

Don't forget that there's a difference between how you build and how you deploy . That is, you may be building against XStream, but you should also package it in the .war file for deployment.

Explode your resultant .war file ( jar tvf {filename} to see the contents) and check whether it's there (a .jar file under WEB-INF/lib ). I suspect it's not.

Answer 2

I found the issue:

If you right click on the project and select properties you can set the "Java EE Module dependencies" to include the modules you are using.

Hey Presto it works.

Answer 3

Java EE Module Dependencies seem to be the way to go. However, menus names changed in Eclipse Helios: that particular menu is now under "Deployment Assembly".

Answer 4

一个容易犯的错误就是错误地命名WEB_INF下的目录，我把它命名为libs而不是lib，编译得很好但是tomcat会抛出错误。