javax.servlet.ServletException: Error instantiating servlet class Compiler 错误

javax.servlet.ServletException: Error instantiating servlet class Compiler
	org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:505)
	org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
	org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:957)
	org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:423)
	org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1079)
	org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:620)
	org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.doRun(AprEndpoint.java:2516)
	org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:2505)
	java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
	java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
	org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	java.lang.Thread.run(Thread.java:619)

root cause

java.lang.ClassNotFoundException: Compiler
	org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1722)
	org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1573)
	org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:505)
	org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
	org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:957)
	org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:423)
	org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1079)
	org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:620)
	org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.doRun(AprEndpoint.java:2516)
	org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:2505)
	java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
	java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
	org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	java.lang.Thread.run(Thread.java:619)

错误是因为修改了Servlet的位置，而没有去修改Web.XML中对应的位置！！！