Solr Search - java.util.Map$Entry cannot be resolved

I have Solr 3.6.2 running and powering the search for a Magento Enterprise site, and it's all working well, with no errors on startup etc.

However when trying to access the following admin pages:

• /solr/admin/stats.jsp
• /solr/admin/registry.jsp
• /solr/admin/analysis.jsp
• /solr/admin/distributiondump.jsp

I am getting the following error:

Problem accessing /solr/admin/stats.jsp. Reason:

PWC6033: Unable to compile class for JSP

PWC6197: An error occurred at line: 41 in the jsp file: /admin/stats.jsp
PWC6199: Generated servlet error:
The type java.util.Map$Entry cannot be resolved. It is indirectly referenced from required .class files



org.apache.jasper.JasperException: PWC6033: Unable to compile class for JSP

PWC6197: An error occurred at line: 41 in the jsp file: /admin/stats.jsp
PWC6199: Generated servlet error:
The type java.util.Map$Entry cannot be resolved. It is indirectly referenced from required .class files


at org.apache.jasper.compiler.DefaultErrorHandler.javacError(DefaultErrorHandler.java:123)
at org.apache.jasper.compiler.ErrorDispatcher.javacError(ErrorDispatcher.java:296)
at org.apache.jasper.compiler.Compiler.generateClass(Compiler.java:376)
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:437)
at org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:608)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:360)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:486)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:380)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:820)
at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:511)
at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:401)
at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:766)
at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:450)
at org.mortbay.jetty.servlet.Dispatcher.forward(Dispatcher.java:327)
at org.mortbay.jetty.servlet.Dispatcher.forward(Dispatcher.java:126)
at org.apache.solr.servlet.SolrDispatchFilter.doFilter(SolrDispatchFilter.java:283)
at org.mortbay.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1212)
at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:399)
at org.mortbay.jetty.security.SecurityHandler.handle(SecurityHandler.java:216)
at org.mortbay.jetty.servlet.SessionHandler.handle(SessionHandler.java:182)
at org.mortbay.jetty.handler.ContextHandler.handle(ContextHandler.java:766)
at org.mortbay.jetty.webapp.WebAppContext.handle(WebAppContext.java:450)
at org.mortbay.jetty.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:230)
at org.mortbay.jetty.handler.HandlerCollection.handle(HandlerCollection.java:114)
at org.mortbay.jetty.handler.HandlerWrapper.handle(HandlerWrapper.java:152)
at org.mortbay.jetty.Server.handle(Server.java:326)
at org.mortbay.jetty.HttpConnection.handleRequest(HttpConnection.java:542)
at org.mortbay.jetty.HttpConnection$RequestHandler.headerComplete(HttpConnection.java:928)
at org.mortbay.jetty.HttpParser.parseNext(HttpParser.java:549)
at org.mortbay.jetty.HttpParser.parseAvailable(HttpParser.java:212)
at org.mortbay.jetty.HttpConnection.handle(HttpConnection.java:404)
at org.mortbay.jetty.bio.SocketConnector$Connection.run(SocketConnector.java:228)
at org.mortbay.thread.QueuedThreadPool$PoolThread.run(QueuedThreadPool.java:582)

It is always the same error, with java.util.Map$Entry. The other pages in the admin panel seem to be working fine.

This is most probably because in your JSP file you are referencing a class file compiled with Java 8, and Solr itself is run with Java 7.

Solution: either recompile the referenced class with Java 7 or run Solr with Java 8.