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！！！
javax.servlet.ServletException: Error instantiating servlet class Compiler 错误
原文：http://www.cnblogs.com/a294098789/p/5307728.html