java.lang.ClassNotFoundException

java.lang.ClassNotFoundException: com.mysql.jdbc.Driver

at java.net.URLClassLoader$1.run(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at study.java.DBConnectUtils.(DBConnectUtils.java:46)
at study.java.DBOperateVoidUtils.operate(DBOperateVoidUtils.java:13)
at study.java.DatabaseFactoryImp.insert(DatabaseFactoryImp.java:20)
at study.java.test.Demo.main(Demo.java:26)
Exception in thread "main" java.lang.ExceptionInInitializerError
at study.java.DBOperateVoidUtils.operate(DBOperateVoidUtils.java:13)
at study.java.DatabaseFactoryImp.insert(DatabaseFactoryImp.java:20)
at study.java.test.Demo.main(Demo.java:26)
Caused by: java.lang.RuntimeException: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver

at study.java.DBConnectUtils.(DBConnectUtils.java:50)
... 3 more
Caused by: java.lang.ClassNotFoundException: com.mysql.jdbc.Driver

at java.net.URLClassLoader$1.run(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at study.java.DBConnectUtils.(DBConnectUtils.java:46)
... 3 more

jar放在lib下，已经buildpath了，突然这样了不知道为什么

没有找到这个类

他有脾气，不要理他。整个工程clear一下，再重新编译。

mysql相关的驱动包有没有呀？

如果之前是好的，现在启动出问题了，那就是环境的问题，那就clean项目；
如果首次启动就这样，那就看看你放入的是不是MySQL的jar包，或者是不是多放了引起的冲突。

找不到编译的尅，重新clean一下

很显然没有找到mysql驱动包

 java.lang.ClassNotFoundException: com.mysql.jdbc.Driver

这句话就说了没有找到com.mysql.jdbc.Driver类；你看下你工程里有没有把mysql驱动包加载进来；重新build下你的jar

mysql驱动找不到，楼上应该是正解，没有导mysql驱动包 ，