Install Multiple Java versions and Setup Maven to Use one – Java 1.7

Problem

I was running Java 1.8 by default but I needed to build some modules that require Java 1.7

Solution

Check the default version of Java installed as well as the version of Java that maven is using:


implementer@whiscardz ~ $ java -version
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)

implementer@whiscardz ~ $ mvn -v
Java HotSpot(TM) 64-Bit Server VM warning: ignoring option MaxPermSize=512m; support was removed in 8.0
Apache Maven 3.3.9
Maven home: /usr/share/maven
Java version: 1.8.0_131, vendor: Oracle Corporation
Java home: /usr/lib/jvm/java-8-oracle/jre
Default locale: en_US, platform encoding: UTF-8
OS name: "linux", version: "4.4.0-78-generic", arch: "amd64", family: "unix" 
  • Install Java 1.7 as instructed in this link.
  • Create a .mavenrc file in your home directory and then add the JAVA_HOME of Java 1.7 In my case this would be JAVA_HOME=/usr/lib/jvm/java-7-oracle/jre
implementer@whiscardz ~ $ vim .mavenrc

JAVA_HOME=/usr/lib/jvm/java-7-oracle/jre
  • Optional, Run the maven file to assign the JAVA variable on the current terminal
implementer@whiscardz ~ $ source .mavenrc
  • Check version of Java Maven is now using:
implementer@whiscardz ~ $ mvn -version
Apache Maven 3.3.9
Maven home: /usr/share/maven
Java version: 1.7.0_80, vendor: Oracle Corporation
Java home: /usr/lib/jvm/java-7-oracle/jre
Default locale: en_US, platform encoding: UTF-8
OS name: "linux", version: "4.4.0-78-generic", arch: "amd64", family: "unix"

References

Create .mavenrc file

How to change maven java home

Java Heap Size Exception

Problem

I was getting this error after setting up a new instance of Tomcat7, using Java 1.7 and running OpenMRS2:

Exception in thread “ActiveMQ Journal Checkpoint Worker” java.lang.OutOfMemoryError: Java heap space
at java.lang.Class.getDeclaredMethods0(Native Method)
at java.lang.Class.privateGetDeclaredMethods(Class.java:2701)
at java.lang.Class.getDeclaredMethod(Class.java:2128)
at java.io.ObjectStreamClass.getInheritableMethod(ObjectStreamClass.java:1442)
Exception in thread “ActiveMQ Broker[localhost] Scheduler” at java.io.ObjectStreamClass.access$2200(ObjectStreamClass.java:72)
at java.io.ObjectStreamClass$2.run(ObjectStreamClass.java:510)
at java.io.ObjectStreamClass$2.run(ObjectStreamClass.java:472)
at java.security.AccessController.doPrivileged(Native Method)
at java.io.ObjectStreamClass.<init>(ObjectStreamClass.java:472)
at java.io.ObjectStreamClass.lookup(ObjectStreamClass.java:369)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1134)
at java.io.ObjectOutputStream.defaultWriteFields(ObjectOutputStream.java:1548)
at java.io.ObjectOutputStream.writeSerialData(ObjectOutputStream.java:1509)
at java.io.ObjectOutputStream.writeOrdinaryObject(ObjectOutputStream.java:1432)
at java.io.ObjectOutputStream.writeObject0(ObjectOutputStream.java:1178)
at java.io.ObjectOutputStream.writeObject(ObjectOutputStream.java:348)
at org.apache.activemq.store.kahadb.MessageDatabase.checkpointProducerAudit(MessageDatabase.java:1250)
at org.apache.activemq.store.kahadb.MessageDatabase.checkpointUpdate(MessageDatabase.java:1134)
at org.apache.activemq.store.kahadb.MessageDatabase$10.execute(MessageDatabase.java:698)
at org.apache.kahadb.page.Transaction.execute(Transaction.java:728)
at org.apache.activemq.store.kahadb.MessageDatabase.checkpointCleanup(MessageDatabase.java:696)
at org.apache.activemq.store.kahadb.MessageDatabase$3.run(MessageDatabase.java:293)
java.lang.OutOfMemoryError: Java heap space
at java.util.HashMap.newNode(HashMap.java:1734)
at java.util.HashMap.putVal(HashMap.java:630)
at java.util.HashMap.putMapEntries(HashMap.java:514)
at java.util.HashMap.<init>(HashMap.java:489)
at org.apache.activemq.broker.region.AbstractRegion.getDestinationMap(AbstractRegion.java:223)
at org.apache.activemq.broker.region.RegionBroker.getDestinationMap(RegionBroker.java:134)
at org.apache.activemq.broker.region.RegionBroker.purgeInactiveDestinations(RegionBroker.java:922)
at org.apache.activemq.broker.region.RegionBroker$1.run(RegionBroker.java:110)
at org.apache.activemq.thread.SchedulerTimerTask.run(SchedulerTimerTask.java:33)
at java.util.TimerThread.mainLoop(Timer.java:555)
at java.util.TimerThread.run(Timer.java:505)

A Java Heap Size error occurs because of certain memory intensive actions (like Data Exporting). The new Spring managed API uses a lot of memory to cache the xml beans. You may need to increase the default memory allocation.

Solution

According to this wiki page, the solution was to adjust the memory settings. Depending on your OS, I was using Ubuntu 16.04.1 LTS.

vim /etc/default/tomcat7

Then change the JAVA_OPTS variable to:

JAVA_OPTS=”-Djava.awt.headless=true -Xmx1024M -Xms1024M -XX:PermSize=256m -XX:MaxPermSize=256m -XX:NewSize=128m”

You can adjust the memory as per your needs, in my case this was multiplying everything by 2:

JAVA_OPTS=”-Djava.awt.headless=true -Xmx2048M -Xms2048M -XX:PermSize=512m -XX:MaxPermSize=512m -XX:NewSize=256m”

Resources

Troubleshooting Memory Errors

Java heap space errors when starting a new installation