java servlet project and android library project in eclipse - NoClassDefFoundError

问题

I have some projects in my workspace :

AndroidMonitoring # an android application
MonitoringModel # an android library project
DataServlet # servlet project

AndroidMonitoring (which depends on MonitoringModel,

)

compiles and runs just fine but I need the MonitoringModel classes to be available also in the DataServlet project. I added the Model as a dependency in the Java Build path of the DataServlet project but I get :

java.lang.NoClassDefFoundError: gr/uoa/di/monitoring/model/Battery
    gr.uoa.di.monitoring.server.servlets.DataCollectionServlet.doGet(DataCollectionServlet.java:20)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

I need the Model to be an Android library project as it contains android classes - but also contains the methods to parse the files in the servlet - is it possible ? How should I set this up ?

EDIT : MonitoringModel is here

回答1:

Solved !

remove the dependency from DataServlet's java build path
~~go to the MonitoringModel project and remove the library attribute, run it as an Android app remake it into a library (from here)~~ Clean the MonitoringModel project
grab the monitoringmodel.jar from bin/ and drop it into the DataServlet/WEB-INF/lib
refresh and run on server
done !

Will try and improve on this hack (linking to an external jar did not seem to work btw) - any better ideas will be accepted as an answer - however closing this for now.

EDIT : apparently step 3. can be substituted by creating a hard link from DataServlet/WEB-INF/lib/monitoringmodel.jar to monitoringmodel.jar - still testing this as some action sequences break the link methinks. Symbolic links do not seem to work though - reported this as a bug

EDIT2 : the steps below seem to work too - but I leave the manual procedure as it definitely works

remove the dependency from DataServlet's java build path
Hard link the monitoringmodel.jar from bin/ and to the DataServlet/WEB-INF/lib. I used shell link extension but this :
```
mklink /H c:\path\to\WebContent\WEB-INF\lib\monitoringmodel.jar c:\path\to\bin\monitoringmodel.jar
```
should also work
Now everytime you make a change in monitoring model the jar is updated. You only have to refresh the servlet project (will be redeployed on server on its own by default)

_{Clarification : of course the servlet project is not meant to use android.* classes - this was not my issue - my issue was to have the model code in one place and this place had to be an android library}

回答2:

First of all - I believe Java Web Project will not work with any of Android specific classes due to many reasons.
If your MonitoringModel contains some Java code that you want to share between Android and Web application you can extract it to separate Java project and use a Link Source option in Properties->Build Path to link it to both projects.

来源：https://stackoverflow.com/questions/18419425/java-servlet-project-and-android-library-project-in-eclipse-noclassdeffounderr

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