title: What happen Http Status 500 Error instantiating servlet class
body: <p>exception </p>
  
  <pre><code>javax.servlet.ServletException: Error instantiating servlet class SAA.Servlet.Addrest
      org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
      org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:936)
      org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
      org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1004)
      org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
      org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
      java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
      java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
      java.lang.Thread.run(Unknown Source)
  
  
  root cause 
  
  java.lang.ClassNotFoundException: SAA.Servlet.Addrest
      org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1713)
      org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1558)
      org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
      org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:936)
      org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
      org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1004)
      org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
      org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
      java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
      java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
      java.lang.Thread.run(Unknown Source)
  </code></pre>