KNOX-3051: Ability to extend classpath with configurable paths

[hanicz]

What changes were proposed in this pull request?

Classpath extension for patches

It would be convenient to have the ability to easily pre-pend classes/JARs to the Knox classpath for quickly applying/testing patches. This approach is completely configurable and multiple locations can be configured although their order has to be kept in mind to avoid overrides. Placing any class or JAR in these locations will take precedence on the classpath as it will come first. These locations can be within the Knox installation, external to it or even a mix of them.

The logic is checking the gateway-site.xml file for 'gateway.server.classpath.extension' property, if it is there it will extend the classpath with its value. The launcher only modifies the classpath for the GatewayServer. There is a check for the main class that's in the properties and if it is 'org.apache.knox.gateway.GatewayServer' only then the classpath is extended.

Example extension:

<property>
    <name>gateway.server.classpath.extension</name>
    <value>/new/classpath/jars/*.jar;../patch/*;/new/classpath/classes;</value>
</property>

• The different locations should be separated by ',' or ';'.
• '*.jar': picks up all jar files in the folder.
• '*': picks up all files in the folder.
• '/folder': class files are picked up from various folder hierarchies (eq. put GatewayServer.class in org/apache/knox/gateway folder)

How was this patch tested?

• Unit tests
• Tested locally with class and JAR files

[smolnar82]

LGTM

[smolnar82]

Hi @moresandeep , @pzampino - Could you please review this one? Thanks!

[pzampino]

LGTM