I am running my app on google app engine. All I have is a simple servlet that is trying to use Jsoup. However when I run the application I get java.lang.ClassNotFoundException: org.jsoup.Jsoup.
I am using Eclipse so I added the jsoup jar file in the Java Build Path -> Libraries
You need to put the Jsoup JAR file in the /WEB-INF/lib folder of the webapp. That folder is covered by webapp's default classpath. Also, Eclipse will automagically put all libraries in /WEB-INF/lib folder in the buildpath of the project, you shouldn't need to do that manually. Of course I assume that the project is been created as Dynamic Web Project.
Another way to add the .jar is to right click on your project, and choose Properties -> Java Build Path, click the Libraries tab, then click Add External JARs... This will allow you to browse to the path of the .jar file you wish to add.
Also make sure your import org.jsoup.Jsoup; imports are after all the application imports such as
import com.google.gwt.core.client.GWT;
Having the JSOUP imports before those other imports caused errors for deploying an application at one point for me.
I had the same error now on my Android project. To Fix this on Android, you need to create a lib folder and put the .jar file there
来源：https://stackoverflow.com/questions/4235855/getting-a-java-lang-classnotfoundexception-org-jsoup-jsoup