eclipse和tomcat编译时错误信息Exception in thread "main" java.lang.NoClassDefFoundError

Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/tools/ant/Project
at java.lang.Class.getDeclaredMethods0(Native Method)
at java.lang.Class.privateGetDeclaredMethods(Class.java:2442)
at java.lang.Class.getMethod0(Class.java:2685)
at java.lang.Class.getMethod(Class.java:1620)
at sun.launcher.LauncherHelper.getMainMethod(LauncherHelper.java:484)
at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:476)
Caused by: java.lang.ClassNotFoundException: org.apache.tools.ant.Project
at java.net.URLClassLoader$1.run(URLClassLoader.java:366)
at java.net.URLClassLoader$1.run(URLClassLoader.java:355)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:354)
at java.lang.ClassLoader.loadClass(ClassLoader.java:423)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:308)
at java.lang.ClassLoader.loadClass(ClassLoader.java:356)
... 6 more
环境变量设了很多次了，还是不对，求指教