Develop Reference

Tomcat home page showing error

I can't open my tomcat server home page it is showing the following error:
HTTP Status 500 -
type Exception report
message
description The server encountered an internal error () that prevented it from fulfilling this request.
exception
org.apache.jasper.JasperException: Unable to compile class for JSP:
An error occurred at line: 1 in the generated java file
The type java.util.Map$Entry cannot be resolved. It is indirectly referenced from required .class files
Stacktrace:
org.apache.jasper.compiler.DefaultErrorHandler.javacError(DefaultErrorHandler.java:102)
org.apache.jasper.compiler.ErrorDispatcher.javacError(ErrorDispatcher.java:331)
org.apache.jasper.compiler.JDTCompiler.generateClass(JDTCompiler.java:457)
org.apache.jasper.compiler.Compiler.compile(Compiler.java:378)
org.apache.jasper.compiler.Compiler.compile(Compiler.java:353)
org.apache.jasper.compiler.Compiler.compile(Compiler.java:340)
org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:646)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:357)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
note The full stack trace of the root cause is available in the Apache Tomcat/7.0.23 logs.
Apache Tomcat/7.0.23

This is caused by a compatibility problem because you are using different Java versions. Likely you are using Java8 only as:
JRE for your Tomcat OR
compiling your code
Make a decision on which Java version would you like to use and ensure that your environment is consistently uses that specific version.

Java 8 error: HTTP Status 500 - Unable to compile class for JSP

I have installed java 8 and removed previously installed java 7 and its folders, and also re-installed Apache Tomcat 7 with security options, I did all the environment variables settings and my tomcat 7 started with no problem, but when I tried to open the localhost http://localhost:8080 then i am getting the following error.
org.apache.jasper.JasperException: Unable to compile class for JSP:
An error occurred at line: 1 in the generated java file
The type java.util.Map$Entry cannot be resolved. It is indirectly referenced from required .class files
Stacktrace:
org.apache.jasper.compiler.DefaultErrorHandler.javacError(DefaultErrorHandler.java:102)
org.apache.jasper.compiler.ErrorDispatcher.javacError(ErrorDispatcher.java:331)
org.apache.jasper.compiler.JDTCompiler.generateClass(JDTCompiler.java:469)
org.apache.jasper.compiler.Compiler.compile(Compiler.java:378)
org.apache.jasper.compiler.Compiler.compile(Compiler.java:353)
org.apache.jasper.compiler.Compiler.compile(Compiler.java:340)
org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:646)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:357)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
The error have a some description: The server encountered an internal error that prevented it from fulfilling this request.
It seems i did nothing wrong, but are there an issues with Java 8 and Apache Tomcat 7.

java.lang.UnsupportedClassVersionError - jdk version

I developed an API in Eclipse using jdk 1.7.0_03 on the Windows 7 platform. It works fine when deployed on other Windows 7 systems.
On deploying it on a Windows 8 system using jdk 1.6 it gave the following exception:
HTTP Status 500 - Servlet.init() for servlet MediaPlayer-Backend-API threw exception
type Exception report
message Servlet.init() for servlet MediaPlayer-Backend-API threw exception
description The server encountered an internal error that prevented it from fulfilling this request.
exception
javax.servlet.ServletException: Servlet.init() for servlet MediaPlayer-Backend-API threw exception
org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:931)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1004)
org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:1822)
java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
java.lang.Thread.run(Thread.java:662)
root cause
java.lang.UnsupportedClassVersionError: favorite/api/VideoManager : Unsupported major.minor version 51.0 (unable to load class favorite.api.VideoManager)
org.apache.catalina.loader.WebappClassLoader.findClassInternal(WebappClassLoader.java:2908)
org.apache.catalina.loader.WebappClassLoader.findClass(WebappClassLoader.java:1173)
org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1681)
org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1559)
java.lang.Class.forName0(Native Method)
java.lang.Class.forName(Class.java:247)
com.sun.jersey.core.reflection.ReflectionHelper$3.run(ReflectionHelper.java:284)
com.sun.jersey.core.reflection.ReflectionHelper$3.run(ReflectionHelper.java:279)
java.security.AccessController.doPrivileged(Native Method)
com.sun.jersey.spi.scanning.AnnotationScannerListener$AnnotatedClassVisitor.getClassForName(AnnotationScannerListener.java:224)
com.sun.jersey.spi.scanning.AnnotationScannerListener$AnnotatedClassVisitor.visitEnd(AnnotationScannerListener.java:188)
org.objectweb.asm.ClassReader.accept(Unknown Source)
org.objectweb.asm.ClassReader.accept(Unknown Source)
com.sun.jersey.spi.scanning.AnnotationScannerListener.onProcess(AnnotationScannerListener.java:138)
com.sun.jersey.core.spi.scanning.uri.FileSchemeScanner$1.f(FileSchemeScanner.java:86)
com.sun.jersey.core.util.Closing.f(Closing.java:71)
com.sun.jersey.core.spi.scanning.uri.FileSchemeScanner.scanDirectory(FileSchemeScanner.java:83)
com.sun.jersey.core.spi.scanning.uri.FileSchemeScanner.scan(FileSchemeScanner.java:71)
com.sun.jersey.core.spi.scanning.PackageNamesScanner.scan(PackageNamesScanner.java:226)
com.sun.jersey.core.spi.scanning.PackageNamesScanner.scan(PackageNamesScanner.java:142)
com.sun.jersey.api.core.ScanningResourceConfig.init(ScanningResourceConfig.java:80)
com.sun.jersey.api.core.PackagesResourceConfig.init(PackagesResourceConfig.java:104)
com.sun.jersey.api.core.PackagesResourceConfig.<init>(PackagesResourceConfig.java:78)
com.sun.jersey.api.core.PackagesResourceConfig.<init>(PackagesResourceConfig.java:89)
com.sun.jersey.spi.container.servlet.WebComponent.createResourceConfig(WebComponent.java:696)
com.sun.jersey.spi.container.servlet.WebComponent.createResourceConfig(WebComponent.java:674)
com.sun.jersey.spi.container.servlet.WebComponent.init(WebComponent.java:205)
com.sun.jersey.spi.container.servlet.ServletContainer.init(ServletContainer.java:376)
com.sun.jersey.spi.container.servlet.ServletContainer.init(ServletContainer.java:559)
javax.servlet.GenericServlet.init(GenericServlet.java:160)
org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:931)
org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1004)
org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:1822)
java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
java.lang.Thread.run(Thread.java:662)
note The full stack trace of the root cause is available in the Apache Tomcat/7.0.33 logs.
Apache Tomcat/7.0.33
I referred to this answer and changed the Installed JRE and Compiler compliance level of the API Eclipse project to jdk 1.5.0_15.
Yet on deploying the API I got the same error.
Any help on whats going wrong and how I make the API compatible with all systems?

You are using two different JDK's to run the program. Java is not backward compatible and so you must run on the same version you compiled with.
jdk 1.7.0_03
and
jdk 1.6

If you were able to compile the API in JDK 1.5 then the UnsupportedClassVersionError error couldn't have come up.
Make sure the compiler version settings is correct in Eclipse and also clean up the directory where .class files are generated. Make some trivial changes in some or all the java files using eclipse editor and generate the new class files and check the timestamp of the generated class files / jar before deploying.

Change eclipse java version as jdk 1.7 and compile it. or check VideoManager.class has build by which version ? Get that version and build your project using that version.

PermGen Space error on hot deploys on Tomcat

I am seeing the following messages in the logs after each redeploys.
INFO: Reloading Context with name [/x1Application] has started
SEVERE: The web application [/x1Application] appears to have started a thread named [Mojarra-WebResourceMonitor-1-thread-1] but has failed to stop it. This is very likely to create a memory leak.
SEVERE: The web application [/x1Application] appears to have started a thread named [Hector.me.prettyprint.cassandra.connection.CassandraHostRetryService-1] but has failed to stop it. This is very likely to create a memory leak.
Eventually after 1-2 hot deploys the server stops responding & I get the PermGen space error
17 Mar, 2012 1:40:01 AM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [jsp] in context with path [] threw exception [The HTTP Monitor server side component intercepted and rethrew an error while processing a JSP or servlet. Please see the stack trace under the root cause message below to identify the problem.] with root cause
java.lang.OutOfMemoryError: PermGen space
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClassCond(ClassLoader.java:632)
at java.lang.ClassLoader.defineClass(ClassLoader.java:616)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:283)
at java.net.URLClassLoader.access$000(URLClassLoader.java:58)
at java.net.URLClassLoader$1.run(URLClassLoader.java:197)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:382)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:333)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:240)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:164)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:164)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:563)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:399)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:317)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:204)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:182)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:311)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
17 Mar, 2012 1:40:12 AM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [jsp] in context with path [] threw exception [The HTTP Monitor server side component intercepted and rethrew an error while processing a JSP or servlet. Please see the stack trace under the root cause message below to identify the problem.] with root cause
java.lang.OutOfMemoryError: PermGen space
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:382)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:333)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:304)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393)
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:240)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:164)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:164)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:100)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:563)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:399)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:317)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:204)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:182)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:311)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
at java.lang.Thread.run(Thread.java:662)
How can I get more information about the source of bug?

I'd report it to Hector guys. It's their bug that their code is not properly shutting down running threads on webapp's shutdown. In the meanwhile, you could consider to pick a better development server (favourite is Glassfish; it hotdeploys in a subsecond) or to install JRebel to transform Tomcat into a real hotdeployer instead of a hotrestarter.
As to the background information about Tomcat's memory leak protection, read the following wikis:
Tomcat wiki - Memory leak protection
Tomcat wiki - How to deal with out of memory

Shortly I had to deal with a leaking Thread named "Mojarra-WebResourceMonitor-1-thread-1" on
Apacht Tomcat 8.0.26 with
Mojarra 2.2.12
in my web app using servlet sepc 3.0.
The root cause was that two instances of com.sun.faces.config.ConfigureListener had been added to the ServletContext.
First instance (A) was added by Tomcat's container SCI
org.apache.jasper.servlet.JasperInitializer.onStartup(...)
as it is configured in javax.faces-2.2.12.jar!/META-INF/jsf_core.tld
Second instance (B) was added by
com.sun.faces.config.FacesInitializer.onStartup(...)
Workaround was to prevent JapserInitializer from invokation by editing my web app context.xml and add the containerSciFilter attribute to the context element:
<Context containerSciFilter="org.apache.jasper.servlet.JasperInitializer|org.apache.tomcat.websocket.server.WsSci">
Both SCIs are not needed for my web app. So this work around won't help if you depend on JSP and JSF.
This is what happend wrong here:
On Servlet initialization, tomcat called
A.contextInitialized(...)
Initialize JSF
Start the threadPool
B.contextInitialized(...)
As JSF is running ...nothing to do
On Shutdown, tomcal calls:
B.contextDestroyed(...)
Shutdown JSF
Don't know of any threadPool as I haven't started one.
A.contextDestroyed(...)
As JSF is stopped, nothing to do.
Thus As' threadPool remains up and running, preventing GC on WebAppClassloader.
But whose fault is this?
Did Tomcat fail to reject multiple listeners of same Class?
Did JSF Mojarra fail to stop the threadPool due to its' implication of threadPool absence when there's no JSF up and running?
Is it wrong that the listener is declared twice:
Programmaticalli thru SCI
Declared in core TLD taglib.
Edit: It was problematic for me to completely skip the JasperInitializer. I had to remove it from containerSciFilter and add javax.faces-*.jar to Tomcat tldSkip filter like this:
<JarScanner>
<JarScanFilter defaultPluggabilityScan="false"
pluggabilityScan="${tomcat.util.scan.StandardJarScanFilter.jarsToScan}, javax.faces-*.jar"
tldSkip="${tomcat.util.scan.StandardJarScanFilter.jarsToSkip}, , javax.faces-*.jar" />
</JarScanner>

exception while integrating mahout recommender engine in java web application

I am trying to implement recoemmender code in java dynamic web application using direct approach. i can compile the code but when i run the application on server i am getting following error:
type
Exception report
message
description The server encountered an internal error () that prevented it from fulfilling this request.
exception
javax.servlet.ServletException: Servlet execution threw an exception
root cause
java.lang.NoClassDefFoundError: org/apache/mahout/cf/taste/model/DataModel
com.demoMahout.HelperRecommender.getUserBasedRecommendation(HelperRecommender.java:96)
com.demoMahout.HelperRecommender.doPost(HelperRecommender.java:53)
javax.servlet.http.HttpServlet.service(HttpServlet.java:641)
javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
root cause
java.lang.ClassNotFoundException: org.apache.mahout.cf.taste.model.DataModel
org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1676)
org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1521)
java.lang.ClassLoader.loadClassInternal(ClassLoader.java:332)
com.demoMahout.HelperRecommender.getUserBasedRecommendation(HelperRecommender.java:96)
com.demoMahout.HelperRecommender.doPost(HelperRecommender.java:53)
javax.servlet.http.HttpServlet.service(HttpServlet.java:641)
javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
How can i resolve this issue?

It means just what it says: you don't have the Mahout classes included in your web app! put the JAR files in WEB-INF/lib as you need to do with any other library a web app needs.