我可以使用来自其他引用类库的 Java servlet Filter 类吗？

Question

I have five web applications in my project and want to filter HTTP requests, but I don't want to write a Filter class for each web application because there will be no application specific behaviour. What is the most practical way to do this?

I've tried creating only one Filter in another class library called MyClassLibrary but it doesn't work. Other classes in this library can be used by the web applications so I don't think there's a reference problem.

The web.xml filter part for one of the applications is:

<filter>
    <filter-name>SampleFilter</filter-name>
    <filter-class>MyClassLibrary.Filters.SampleFilter</filter-class>
</filter>
<filter-mapping>
    <filter-name>SampleFilter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

This causes an exception:

java.lang.ClassNotFoundException: MyClassLibrary.Filters.SampleFilter

Platform : Windows, NetBeans, GlassFish

Answer 1

Please check the following

• Make sure your class is compiled without any errors
• Make sure your deployment of those web applications is having reference to project/jar that contains your library
• From the name, it looks like SampleFilter is an inner class. If so is the case, make sure that Filters and SampleFilter are static inner class of MyClassLibrary and has no args constructor
• Are you missing package name in front of MyClassLibrary?

Answer 2

If the exception is ClassNotFoundException this means that you haven't set the class MyClassLibrary in the classpath of your application.

Make sure that your class MyClassLibrary is referenced from the app of this web.xml.

Regards.

Answer 3

I have a filter that works and just modifying the filter-class value to the same class but in a jar, including that jar, does not work out. The path was wrong, I had noClassDefFound error, so I changed it correctly. No error appears but the filter don't work anymore.

My class compiled without errors. The library is exported with the web app, the class is in the jar in the WEB-INF folder.

The only difference is that the class was in my app before for me to make it work. And now, after it worked, I moved it in an external library and only changed the filter-class. I built the library and included it in my app.

Even though I have no error, I see in the logs that the filter does not work anymore. Any idea?

** UPDATE I don't know why, but the filter works if I modify the web.xml in the tomcat directory but not if I modify the application web.xml in my project.