The reason: no lead on jar.
Solution: someone else's project into your own project, you need to rejoin his tomcat into the environment. As follows:
1, first introduced in other people's projects in eclipse, you can see the project hit a red cross, the document is also being given.
2, double-click the file error, his own and some tomcat join in: Right-click the project -build path-configure build path, and then double-click the tomcat.
3, double-click, the pop-up box, select tomcat their own existence (there are some basic built-jar, because of the lack of these jar before the error).
4. After selecting, click Apply to apply just fine.
5, so that the project to normal.
Transfer from Baidu know the answer
https://zhidao.baidu.com/question/454412996732586005.html
