在开发Web应用程序时，我应该在哪里放置外部JAR文件？

Question

I'm developing a dynamic web application with Java (Servlets/JSP) in Eclipse. I'm trying to use an external JAR (I'm using StringUtils from Apache Commons) and I'm confused as to where I should put the jar ( /lib , /WEB-INF/lib ?) and how do I need to configure my class path (in Eclipse).

I tried putting the JARs in both of the aforementioned places, and loading them to the classpath by clicking Add JAR in the project properties and both solution compile fine, but give a runtime error like so:

SEVERE: Servlet.service() for servlet UserList threw exception java.lang.NoClassDefFoundError: org/apache/commons/lang/StringUtils at cs236369.hw5.db.MySqlDbHandler.insert(MySqlDbHandler.java:58) at cs236369.hw5.servlets.UserList.doGet(UserList.java:50) at javax.servlet.http.HttpServlet.service(HttpServlet.java:617) 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:127) 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:298) at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859) at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588) at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489) at java.lang.Thread.run(Unknown Source)

So... how do I load external JARs?

Please take note that I am not that familiar with how external JARs are loaded in Java, the VM, or how Eclipse manages it all, so I would appreciate detailed solutions.

Answer 1

They must be placed in yourapp/WEB-INF/lib . (In eclipse you are adding them properly). So make sure the jar is really there. Note that if you are starting the app from within eclipse, you would have to configure deployment assembling.

The deployment assembly is configured through right click > properties > deployment assembly in eclipse. There you should "Add" your "Java build path entries"