Allow specification of the classloader for [de]serialisation

[gravelld]

See also #377 .

When MapDB [de]serialises objects, it needs to load the classes each object implements.

In a Java app running in a vanilla application container, using Class.forName is sufficient for this, because there is no class scope and all classes are known to all classes.

In an OSGi container, the scope is far more constrained. MapDB is deployed as its own "bundle" and using Class.forName will only work to load classes in the packages that the MapDB bundle has been pre-configured to know about.

This is a problem common with ORMs. The problem is more eloquently and authoritatively described in http://njbartlett.name/2010/08/30/osgi-readiness-loading-classes.html . Three solutions are suggested.

For my own use, I have hacked MapDB to have a setClassloader method on DBMaker which is passed through to the serialisation layer. This is then used for loading classes, and it works well. However, whoever does this work for MapDB should consider which of the three options presented above makes most sense from MapDB's perspective.

[jankotek]

I will have a look, thanks for good documentation.

On August 7, 2015 5:57:25 PM CEST, gravelld notifications@github.com wrote:

See also #377 .

When MapDB [de]serialises objects, it needs to load the classes each
object implements.

In a Java app running in a vanilla application container, using
Class.forName is sufficient for this, because there is no class scope
and all classes are known to all classes.

In an OSGi container, the scope is far more constrained. MapDB is
deployed as its own "bundle" and using Class.forName will only work to
load classes in the packages that the MapDB bundle has been
pre-configured to know about.

This is a problem common with ORMs. The problem is more eloquently and
authoritatively described in
http://njbartlett.name/2010/08/30/osgi-readiness-loading-classes.html .
Three solutions are suggested.

For my own use, I have hacked MapDB to have a setClassloader method
on DBMaker which is passed through to the serialisation layer. This
is then used for loading classes, and it works well. However, whoever
does this work for MapDB should consider which of the three options
presented above makes most sense from MapDB's perspective.

---

Reply to this email directly or view it on GitHub:
#555

[jankotek]

MapDB now allows to set custom global class loader and per-class class loader.

There are new methods in DBMaker:

This will set default Class Loader for all classes instantiated during deserialization:
serializerClassLoader(loader)

And this will set Class Loader for specific class:
.serializerRegisterClass(classname,loader)

[gravelld]

Thanks, that will be very easy for me to port to.