写一个jar文件实用程序

Question

I am writing a utility jar file to be shared into multiple project. Basically it handles establishing database connection and making calculations and later return the values. Other projects will import my jar file and call my function.

Right now i am having problem when i tried to call one of the functions in the jar file.In eclipse there are no compile error but as i test it at app server i receives this error

22:16:35,177 DEBUG ExecutionContext:187 - Transitioning to lifecycle stage RequestComplete
22:16:35,178  WARN DefaultExceptionHandler:94 - Unhandled exception caught by the Stripes default exception handler.
net.sourceforge.stripes.exception.StripesServletException: ActionBean execution threw an exception.
    at net.sourceforge.stripes.controller.DispatcherServlet.service(DispatcherServlet.java:183)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at net.sourceforge.stripes.controller.StripesFilter.doFilter(StripesFilter.java:247)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:224)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:185)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:151)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:929)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:405)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:269)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:515)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:302)
    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: java.lang.NoClassDefFoundError: com/my/rnd/test/utils/SimplePing
    at com.app.action.JbpmProcessInstanceActionBean.testTrigger(JbpmProcessInstanceActionBean.java:83)
    at com.app.action.JbpmProcessInstanceActionBean.loadProcInstanceList(JbpmProcessInstanceActionBean.java:72)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)

I export the jar file using eclipse and here's the sample function of the SimplePing

public class SimplePing {

     /**
      * @param args
      */
     public  void testSimplePing() {
        // TODO Auto-generated method stub
        System.out.println("This is a simple ping .");
     }

}

It seems that the appserver unable to find my class even to it exists in the jar file.Any help is welcomed

Answer 1

If you look closely to the error stack you can see the following:

Caused by: java.lang.NoClassDefFoundError: com/my/rnd/test/utils/SimplePing

Which is a common error when you have one of the following conditions:

1. You have a jar(s) missing in your lib
2. You have some jar(s) missing from your classpath

3. You have some dependencies missing from your MANIFEST file:

   ...
Main-Class: fully.qualified.MainClass
Class-Path: lib/dependency1-XYjar lib/dependency2-WZjar
...

4. You have a JDK problem

Eventually all connect to the same problem: A missing jar ( JDK or third-party related jar)
You can also use maven plugin for eclipse which will manage your dependancies of your current project and your jar able one which is needed by your project, ofcourse if you are fond of Maven.

Answer 2

This is a good question

There are 2 ways I can think of

1. Try to use Maven (m2e plugin) - this will manage the dependencies for you If you do this, remember to add Maven Dependencies to the project Deployment Assembly (right click - properties)

2. Use Deployment Assembly and add the other project

Answer 3

使用7-zip或winzip等程序打开jar，并验证您是否在其中看到此目录结构和文件：com / my / rnd / test / utils / SimplePing.class