Confluence plugin servlet and JDBC classpath issue
Asked by Paul Guthrie:

I'm having a problem getting a servet (part of a plugin) to connect to an external datasource. The datasource is a postgresql DB, and is defined in server.xml and can be accessed through the (wonderful) SQL plugin.

However, I cannot get to the DB through my servlet. I've tried three things:

1) By the standard Class.forName("org.postgresql.Driver"); syntax. I get a "no class found" error.

2) By directly instantiating a postgresql Driver object (Driver d = new org.postgresql.Driver()) and registering it. I get a java.lang.NoClassDefFoundError: org/postgresql/Driver error.

3) By getting an initial context within the servlet's init method ( Context ctx = InitialContext() ) and going after the datasource since clearly the SQL plugin can read the data source.

Nothing has worked to date. First, how is it that the postgresql libs appear to not be within the servlet's classpath? They are obviously accessible to Confluence as it is the database for the instance as well as for the SQL plugin calls.

Second, I'd rather use the datasource approach to raw JDBC connections. Does anyone have a code snippet that shows how that can work within the context of a servlet?

Thanks!

Paul

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Answers:
author: Paul Guthrie
body: To answer this there are three ways I've found.1. Yes, it is possible to bundle the .jar file with my own plugin. I did get that working.2. Not liking that solution, I wrote a custom classloader which loaded the postgresql drivers jar from the server. That too worked.3. Not liking that solution, I grabbed the source for the SQL plugin, and it has a good source-code example of how to use the datasource through the InitialContext. There was a little magic in there I would never have figured out. That's what I'm going with.

comments: author: Joe Clark
body: Nice work digging to find an answer to your own solution! I admit that it's an area I haven't messed around with much, so I'm glad you were able to find a good solution.


author: Sandro H?rler
body: And how did you do that:

Yes, it is possible to bundle the .jar file with my own plugin.

Pls share, thx


author: Chris Kent
body: Hi,

Has anyone got the Class.forName("org.postgresql.Driver"); to work in a plugin.

I want to use this method for connecting to a database, I know the drivers jar file exists as I am using the same database as the confluence external database, so I know it's there.

Why does my plugin throw the exception " java.lang.ClassNotFoundException: org.postgresql.Driver"

Paul you said you found some magic, can you please share, although I'm not interested if I need to define the datasource in the server.xml file -\> not very flexible solution when distributing a plugin. I know the SQL plugin can dynamically do this through its Configure menu, so I'm sure this can be achieved - please help.


author: Joe Clark
body: The Atlassian plugin system uses OSGi to help keep plugins and the core app separate from each other - this means that each plugin can have a different 'effective' classpath and not everything from the host application is exposed to plugins by default.

The easiest solution is to bundle the database driver within your plugin.

**Edit:**That is to say, there is probably a way to configure your plugin to request the driver be provided to it by the host application, but I haven't dug into it to see exactly what would be required :)

comments: author: Paul Guthrie
body: Is there anyway to override the classpath within the manifest to include other server-hosted jars? Java doesn't handle jars within jars well and it doesn't really make sense to have to include a jar which is already part of the confluence installation.


author: Eric Koepfle
body: I kind of agree with the above poster. Including multiple jars of the \~same\~ classes is generally a very bad idea in Java.   

Yet another reason for me to dislike OSGi. It is a framework for administrators, not developers. Unfortunately we are forced to comply.


Tags: confluence-app

servlet