Derby, Java: Trouble with "CREATE_TYPE" statement

Question

I've been messing around with Apache Derby inside Eclipse. I've booted up a Network Server, and I've been working with servlets. In my Eclipse project, I have a class called "User", inside the package "base.pack". I have an SQL script open, and I've been trying to convert User, which implements Serializable, into a custom type. When I run the following lines, everything works fine:

CREATE TYPE CARTEBLANCHE.bee
EXTERNAL NAME 'base.pack.User'
LANGUAGE JAVA

This follows the general format they identify here: http://db.apache.org/derby/docs/10.7/ref/rrefsqljcreatetype.html#rrefsqljcreatetype

Now, when I try to create a table using this new type, I get an error. I run the following line:

CREATE TABLE CARTEBLANCHE.TestTabel (ID INTEGER NOT NULL, NAME CARTEBLANCHE.bee, PRIMARY KEY(ID));

And I receive the following error:

The class 'base.pack.User' for column 'NAME' does not exist or is inaccessible. This can happen if the class is not public.

Now, the class is in fact public, and as I noted before, it does implement Serializable. I don't think I'm stating the package name incorrectly, but I could be wrong. I'm wondering, is this an issue with my classpath? If so, how would you suggest I fix this? I admit that I do not know much about the classpath.

Thank you.

(For reference, I have configured my project build path to include derby.jar, derbyclient.jar, derbytools.jar, and derbynet.jar, and I have put these files into my project's lib folder as well).

Answer 1

As politely as I can, may I suggest that if you are uncomfortable with Java's CLASSPATH notion, then writing your own custom data types in Derby is likely to be a challenging project?

In the specific case you describe here, one issue that will arise is that your custom Java code has to be available not only to your client application, but also to the Derby Network Server, which means you will need to be modifying the server's CLASSPATH as well as your application's CLASSPATH.

It's all possible, it's just not a beginner-level project.

To get started with customizing your Derby Network Server, the first topic involves how you are starting it. Here's an overview of the general process: http://db.apache.org/derby/docs/10.11/adminguide/tadmincbdjhhfd.html

Depending on how precisely you are starting the Derby Network Server, you'll possibly be editing the CLASSPATH settting in the startNetworkServer or startNetworkServer.bat script, or you'll be editing the CLASSPATH setting in your own script that you have written to start the server.

If it's a tool like Eclipse or Netbeans which is starting the Derby Network Server, you'll need to dig into the details of that tool to learn more about how to configure its CLASSPATH.

And if you've written a custom Java application to start the Derby Network Server (e.g., as described here: http://db.apache.org/derby/docs/10.11/adminguide/tadminconfig814963.html) then you'd be configuring the CLASSPATH of your custom application.

Regardless, as a basic step, you're going to want to be deploying your custom Java extension classes in the Derby Network Server's classpath, which means you'll want to build them into a .jar file and put that .jar file somewhere that the Derby Network Server has access to, and you'll want to make that build-a-jar-and-copy-it-to-the-right-location process straightforward, so you should integrate it into whatever build tool you're using (Apache Ant?).

And, you'll need to consider Java security policy, because the default security policy will prevent you from trivially loading custom Java classes into your Derby Network Server as that would seem like a malware attack and the Derby Network Server is going to try to prevent that. So study this section of the Security manual: http://db.apache.org/derby/docs/10.11/security/tsecnetservrun.html