JSP页面的Tomcat 500错误-唯一的JSP内容是if / else

Question

i hope everyone is well.

I come from a PHP background and recently I have had to do some work on a project based on Java - I then found out about JSP pages which was quite similar to PHP. I have tried to make a page which has a "String" variable declared, which is called account. I then check if the account is an administrator, if so they can see the admin menus. However, it works fine for me in firefox and chrome, but customers using the same browser are seeing a 500 error. Please see details below from the logs, i have no idea what it means but i do know a simple if statement shouldn't cause it (stupid language).

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Mar 06, 2014 8:51:59 AM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [jsp] in context with path [/test] threw exception [An exception occurred processing JSP page /test.jsp at line 126

123:                </ul>       
124:            </li>
125: <% 
126: if (account.equals("sysadmin")) { %>
127:            <li>
128:                <a href="#" target="_gts">AssetTrack</a>
129:                <ul>


Stacktrace:] with root cause
java.lang.NullPointerException
    at org.apache.jsp.test_jsp._jspService(test_jsp.java:203)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:409)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1044)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:607)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:315)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:744)

Any ideas let me know, before i go insane! Thanks,

Paul

Answer 1

Try this ,

if ((null!=account) && (account.equals("sysadmin")))

because it says , you have null pointer exception . so you should check whether account is not null

Hope it helps !

Answer 2

使用此方法可以避免空指针欺骗：

if(account!=null && !account.toString().equalsIgnoreCase(""))

Answer 3

When ever you get a NullPointerException as in this case, you must be calling some function on a null. In your code

if (account.equals("sysadmin")) {

NullPointerException has occured because account may be null.

so before using this line

if (account.equals("sysadmin")) {

You should check if account is not null Like below

if(account!=null) { if (account.equals("sysadmin")) {

Means you should call equals function only after confirming account is not null.

Hope it helps!