Rick,
This is helpful to understand. I have noticed as I perused myriad
examples of third-party use-Derby examples that how Derby is set up
seems to have changed in past versions. Some authors have pointed out
Java versions and Derby versions in relevance to their samples. (And, I
prefer using the latest Derby, of course.)
However, it's an unstable state for me. I was able to get connections
via java.sql.DriverManager.getConnection()for several days, but then it
stopped working. Debugging through this method, I see in (private)
DriverManager.getConnection(), when it doesn't work, that the
registeredDriverslist is empty whereupon I get:
java.sql.SQLException: No suitable driver found for
jdbc:derby:memory:sampledb;create=true
Given that I don't/can't/need not do DriverManager.register()in using
Derby, I am mystified as to why I get away with it sometimes, then find
it not working.
What is my formal responsibility to ensure the presence of Derby's
driver in DriverManager.registeredDriverslist? I'm encouraged to believe
that this is what calls to DriverManager.registerDriver()accomplish.
My earlier impression was that the simple presence in /pom.xml/ of
/derby-10.15.2.0.jar/ was sufficient. When it did work, that's all I had
done (or so I think).
This morning, I have experimented adding Derby dependencies (it doesn't
even work with derby, derbysharedand derbytoolsJARs present). I fear I
skipped a step as soon as, last week, it began working thinking I was
home and free. I'm sure I have done something to break that in the
meantime. As noted, I'm trying to replace /ad hoc/ mocking code with
something more "live" that I can use to regress and debug my JDBC code
and have chosen Derby to accomplish this.
Many thanks,
Russ
On 7/8/20 6:49 AM, Rick Hillegas wrote:
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.
