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From Rick Hillegas <rick.hille...@gmail.com>
Subject Re: Driver registration, Derby drivers and Derby versions
Date Wed, 08 Jul 2020 12:49:27 GMT
Hi Russell,

This is a little complicated because it involves a bit of history. Derby 
and Java grew up together. The core of Derby is the Cloudscape database 
engine, which appeared around 1996, close to the the appearance of Java 
itself. Two significant events in the evolution of Java have affected 
what happened to the Derby drivers. Where the code ended up is a little 
weird, but the aim all along has been to minimize disruption to legacy 
applications. The two events are:

1) The introduction of JDBC driver autoloading in Java 5 and the further 
refinement of driver autoloading in Java 6.

2) The introduction of the JPMS module architecture in Java 9.

If you are getting connections via 
java.sql.DriverManager.getConnection(), then you don't need to register 
drivers at all. That is because the JVM will load all of the JDBC 
drivers which are visible on the application classpath--that is, all of 
the drivers which have metadata recorded in the manifests of their 
respective jar files.

In Derby 10.15, the drivers around, in order to achieve the clean 
package partitioning required by JPMS. The original embedded driver now 
lives in the tools jar. The autoloading driver moved into another 
package in the engine jar. It is now called 
org.apache.derby.iapi.jdbc.AutoloadedDriver.

Hope this helps,
-Rick


On 7/7/20 6:00 PM, Russell Bateman wrote:
> How do the myriad Derby drivers work?
>
> I am using Apache Derby in-memory with no daemon or outside 
> dependencies in support of being called from JUnit tests. This is 
> working pretty well, but what it's going to be doing underneath will 
> eventually cause me to walk the following road, I think.
>
> I am using 10.15.2.0. I find myself needing to register a driver such 
> that a call to DriverManager.getConnection()will find it. (Or, I think 
> I do; I'm looking at some existing homespun mocking code that does 
> this and I'm trying to imitate then replace it with Derby.)
>
>     DriverManager.registerDriver( new 
> org.apache.derby.jdbc.AutoLoadedDriver() );
>
> Here and there, in examples on-line, I see references to drivers like:
>
>    org.apache.derby.jdbc.AutoloadedDriver
>    org.apache.derby.jdbc.EmbeddedDriver
>
> However, unless I'm mistaken, these do not exist in derby 10.15.2.0. I 
> am using derby-10.15.2.0.jar. I have also tried adding the same 
> version's shared and tools JARs.
>
> Any thoughts on this would help. I only discovered this phenomenon of 
> registering drivers today, so I'm stumbling around a bit.
>
> Thanks.
>


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