Overview

This interface layer handles the communication between charms needing a Java runtime (JRE or JDK) and subordinate charms which deliver that runtime.

Usage

Charms needing a Java runtime

Charms needing a Java runtime must provide a relation endpoint using the java interface protocol in their metadata.yaml file and include this interface layer in their layer.yaml file. Then, they can watch for the following reactive states:

• {relation_name}.connected indicates that a Java relation is present (this is mainly used for reporting if the relation is missing, via status)
• {relation_name}.ready indicates that Java is installed and ready

The relation also provides the following methods for getting information about the Java runtime:

• java_home() provides the path that the JAVA_HOME env var should be set to
• java_version() provides the major version of Java that was installed

An example of how a charm might use this would be:

@when_not('java.ready')
def missing_java():
    hookenv.status_set('blocked', 'Missing JRE')

@when('java.ready')
@when_not('mysoftware.installed')
def install_software(java):
    mysoftware.install(java.java_home(), java.java_version())
    set_state('mysoftware.installed')
    hookenv.status_set('active', 'Ready')

Charms delivering a Java runtime

Charms delivering a Java runtime must be subordinate, and they must require a relation endpoint using the java interface protocol in their metadata.yaml file and include this interface layer in their layer.yaml file. Then, they can watch for the following reactive states:

• {relation_name}.connected indicates that a Java relation is present. The charm should then perform the installation and call the following methods to provide the necessary information about the Java runtime that was installed:
  • set_ready(java_home, java_version)
  • set_version(java_version) (for upgrades)

An example of how a charm might use this would be:

@when('java.connected')
@when_not('java.installed')
def install(client):
    status_set('maintenance', 'Installing JRE')
    java.install_jre()
    client.set_ready(java.get_home(), java.get_version())
    reactive.set_state('java.installed')
    hookenv.status_set('active', 'JRE is installed')

@when('java.connected', 'java.installed')
def configure(client):
    # update /etc/environment, call update-alternatives, etc
    java.configure_jre()
    hookenv.status_set('active', 'JRE is ready')

@when_not('java.connected')
@when('java.installed')
def uninstall():
    java.uninstall_jre()
    reactive.remove_state('java.installed')
    hookenv.status_set('blocked', 'No JRE available')

Contact Information

• bigdata@lists.ubuntu.com

OpenJDK

• OpenJDK home page