GAE 500 server error - google-app-engine

Question

I'm developing app on GAE, I test the website locally fine however, every time I tried to deploy it to the GAE it reports with
Error: Server Error
The server encountered an error and could not complete your request.
Please try again in 30 seconds.
I searched a lot in google, seems no answer could solve my question. When I look for the log in the GAE app, following is the major problem I found so far. Initially, I thought it's due to JDK8 but when I set JDK8 I can't even run the app locally!
Uncaught exception from servlet
java.lang.UnsupportedClassVersionError: org/apache/jsp/index_jsp : Unsupported major.minor version 52.0
at com.google.appengine.runtime.Request.process-aea5c804a9f29902(Request.java)
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:795)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:449)
at sun.reflect.GeneratedMethodAccessor5.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at java.lang.ClassLoader.loadClass(ClassLoader.java:360)
at org.mortbay.util.Loader.loadClass(Loader.java:91)
at org.mortbay.util.Loader.loadClass(Loader.java:71)
at org.mortbay.jetty.servlet.Holder.doStart(Holder.java:73)
at org.mortbay.jetty.servlet.ServletHolder.doStart(ServletHolder.java:242)
at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
at org.mortbay.jetty.servlet.ServletHandler.initialize(ServletHandler.java:685)
at org.mortbay.jetty.servlet.Context.startContext(Context.java:140)
at org.mortbay.jetty.webapp.WebAppContext.startContext(WebAppContext.java:1250)
at org.mortbay.jetty.handler.ContextHandler.doStart(ContextHandler.java:517)
at org.mortbay.jetty.webapp.WebAppContext.doStart(WebAppContext.java:467)
at org.mortbay.component.AbstractLifeCycle.start(AbstractLifeCycle.java:50)
at com.google.tracing.TraceContext$TraceContextRunnable.runInContext(TraceContext.java:437)
at com.google.tracing.TraceContext$TraceContextRunnable$1.run(TraceContext.java:444)
at com.google.tracing.CurrentContext.runInContext(CurrentContext.java:188)
at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContextNoUnref(TraceContext.java:308)
at com.google.tracing.TraceContext$AbstractTraceContextCallback.runInInheritedContext(TraceContext.java:300)
at com.google.tracing.TraceContext$TraceContextRunnable.run(TraceContext.java:441)
at java.lang.Thread.run(Thread.java:724)

Answer 1

This is the telltale: Unsupported major.minor version 52.0. This happens when you compile on higher version JDK (52 = java8) and then execute it on lower JRE version (GAE uses java7).
GAE does not yet support Java8, so you should compile under Java7.

Answer 2

I had the same problem on Windows when Java 8 was installed.
I tried modifying the project/workspace settings but it didn't help me.
So, I created the following batch file as a workaround for GAE projects:
eclipse_gae.bat:
SET JAVA_HOME="C:\Program Files\Java\jdk1.7.0_55"
SET PATH="%JAVA_HOME%\bin"
START eclipse.exe

Answer 3

there is no need to fully remove Java 8 from MacOS. Just reconfigure Eclipse as shown here to force it to compile JSPs as Java 7:
http://java.wildstartech.com/Java-Platform-Standard-Edition/mac-os-x-java-development/how-to-configure-eclipse-to-run-with-java-7-when-java-8-is-installed

Answer 4

Make sure, that the version of Project Properties -> Project Facets -> Java is set to 1.7 and not to 1.8.
This is also nicely explained in the plugin's documentation section 'Changing the JDK Compliance Level'

Answer 5

I ran into a similar issue now. My setup is OS X + JDKs 6, 7 and 8, and in my eclipse.ini I had:
-vm
/Library/Java/JavaVirtualMachines/jdk1.8.0_20.jdk/Contents/Home/bin/java
Apparently it will use that compiler no matter what you set in global/project preferences (I even removed JDK 8 from the Installed JRE list, no success).
Once I've changed that to use JDK 7 and redeployed my GAE app, it worked.

Answer 6

You have to compile with Java 1.7. But if you have *.jsp files, you should also completely remove Java 1.8 from the system. If you use Mac, here is how you can do it.

Answer 7

If you are using gradle (e.g. Android Studio) on a mac, you can work around this problem by adding the following lines to the top of your gradlew script:
# Insist on java 7
JAVA_HOME=$(/usr/libexec/java_home -v 1.7)
Variations of this method should work on other platforms.

Answer 8

I'm sure this has been resolved, but here is the solution
GAE runs on java7 (as indicated by Mr. Knego) so maven must be compiling with java7. Do the following:
I prefer to do all this in the terminal
Edit bash profile:
touch ~/.bash_profile; open ~/.bash_profile
Set Java Home Directory
#set JAVA_HOME
JAVA_HOME=/Library/Java/JavaVirtualMachines/jdk1.7.0_79.jdk/Contents/Home
export JAVA_HOME
# For Apache Maven Commands
export M2_HOME=/Users/your-username/your/path/to/maven/apache-maven-3.3.3
export PATH=$PATH:$M2_HOME/bin
Navigate to your project folder (with pom.xml) and reinstall a clean version of maven
mvn clean install
Navigate to EAR or WAR directory and deploy with a new runtime
mvn appengine:update
If you are using endpoints, you should update your endpoint libraries