I've recently tried to install GeoServer with Tomcat7 on a Lubuntu 14.04 server, and had a lot of problems doing so, because Tomcat7's Java default version was set to 1.7. I've struggled a lot with this last night and I'd like to document how to fix it.
I installed GeoServer in my Lubuntu 14.04 machine following these steps:
1) Install Java 8, as documented here
sudo apt-add-repository ppa:webupd8team/java
sudo apt-get update
sudo apt-get install oracle-java8-installer
After that, running java -versionreturned:
java version "1.8.0_131"
Java(TM) SE Runtime Environment (build 1.8.0_131-b11)
Java HotSpot(TM) 64-Bit Server VM (build 25.131-b11, mixed mode)
2) Install Tomcat 7
sudo apt-get install tomcat7 tomcat7-admin
3) Install GeoServer's "Web Archive" version
cd ~/Downloads
wget http://sourceforge.net/projects/geoserver/files/GeoServer/2.11.0/geoserver-2.11.0-war.zip
unzip geoserver-2.11.0-war.zip geoserver.war
sudo mv geoserver.war /var/lib/tomcat7/webapps/
sudo service tomcat7 restart
After that, I could not access localhost:8080/geoserver. Trying to do so returned the HTTP Status 404 - /geoserver error, with "The requested resource is not available." as a description.
Trying to deploy the .war file through Tomcat's /manager page also did not work, returning the following error: Application at context path /geoserver could not be started.
I've looked in the error logs to see what was going wrong, and found the following exception:
Apr 29, 2017 12:32:49 PM org.apache.catalina.core.StandardContext listenerStart
SEVERE: Error configuring application listener of class org.geoserver.platform.GeoServerHttpSessionListenerProxy
java.lang.UnsupportedClassVersionError: org/geoserver/platform/GeoServerHttpSessionListenerProxy : Unsupported major.minor version 52.0 (unable to load class org.geoserver.platform.GeoServerHttpSessionListenerProxy)
at org.apache.catalina.loader.WebappClassLoader.findClassInternal(WebappClassLoader.java:2970)
at org.apache.catalina.loader.WebappClassLoader.findClass(WebappClassLoader.java:1209)
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1689)
[...]
Despite what the error message says, echoing $JAVA_HOME returned /usr/lib/jvm/java-8-oracle, so I was sure I had the necessary Java version.
Apparently Tomcat 7 ships with 1.7 JVM as the default. This can be checked on Tomcat Web Application Manager (usually at localhost:8080/manager), at the bottom of the page there is a table with the JVM version.
+-------------------------------+---------------+-------+
| Tomcat Version | JVM Version | [...] |
+-------------------------------+---------------+-------+
| Apache Tomcat/7.0.52 (Ubuntu) | 1.7.0_121-b00 | [...] |
+-------------------------------+---------------+-------+
Since GeoServer requires Java 1.8, this explains the UnsupportedClassVersionError. We must explicitly tell Tomcat to use JVM 1.8. This was documented here and the steps are the following:
First of all we need to find where JVM 1.8 is located. Open a console terminal and enter:
$ echo $JAVA_HOME
The path to Java 8's folder should be echoed back to you. In my case it's /usr/lib/jvm/java-8-oracle. Make sure to copy it.
Then we have to edit Tomcat's configurations and tell it to use this JVM. On the console terminal, type in:
$ sudo nano /etc/default/tomcat7
The configuration file for Tomcat 7 should be opened. Locate the following text in it:
# The home directory of the Java development kit (JDK). You need at least
# JDK version 1.5. If JAVA_HOME is not set, some common directories for
# OpenJDK, the Sun JDK, and various J2SE 1.5 versions are tried.
#JAVA_HOME=/usr/lib/jvm/openjdk-6-jdk
Find the line that starts with JAVA_HOME, and change the path to your Java 8 folder. Make sure to uncomment the line by removing the # before JAVA_HOME. In my case, the file ended up like this:
# The home directory of the Java development kit (JDK). You need at least
# JDK version 1.5. If JAVA_HOME is not set, some common directories for
# OpenJDK, the Sun JDK, and various J2SE 1.5 versions are tried.
JAVA_HOME=/usr/lib/jvm/java-8-oracle
After that we need to restart Tomcat with the following command:
$ sudo service tomcat7 restart
Then if we check localhost:8080/manager, in the bottom of the page there should be something like:
+-------------------------------+---------------+-------+
| Tomcat Version | JVM Version | [...] |
+-------------------------------+---------------+-------+
| Apache Tomcat/7.0.52 (Ubuntu) | 1.8.0_131-b11 | [...] |
+-------------------------------+---------------+-------+
And GeoServer should now be successfully started, and it should be accessible through localhost:8080/geoserver.