Description

JIRA versions 6.2.x and below do not support JDK 1.8.x as per JIRA's Supported Platforms. To use Java 8/JDK 1.8, you would need to upgrade/install JIRA 6.3 or above.

This can be detected because the following will appear in the atlassian-jira.log:

java.version                                  : 1.8.x

Resolution

If you are using JIRA 6.2.x or below, JIRA may appear to be working on this platform, however it is recommended to migrate off JDK 1.8 and have JIRA running on JDK 1.7 since JIRA 6.2.x and below are not tested on JDK1.8 and could result in unpredictable stability of the application.

 OpenJDK is not supported in Jira versions up and including Jira 7. Recently Atlassian announced that support for OpenJDK is coming so stay tuned!