Mikhail Pochatkin created IGNITE-19475:
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Summary: Implement class loaders hierarchy
Key: IGNITE-19475
URL: https://issues.apache.org/jira/browse/IGNITE-19475
Project: Ignite
Issue Type: New Feature
Reporter: Mikhail Pochatkin
Attachments: image-2023-05-15-14-09-41-734.png
h3. Class loaders hierarchy
!image-2023-05-15-14-09-41-734.png!
For user defined classes loading and execution are responsible class loaders.
The class loaders are built in the hierarchy pictured above.
The Bootstrap, the extension and the system class loaders are provided by the
runtime environment and each class loader first delegates class loading logic
to the parent class loader.
Such an approach is not suitable for all user use cases. For example it is
impossible to override behavior of some classes. Apache Ignite 3 provides more
flexible behavior of class loaders which could be managed by a user - Ignite
chained class loader. In general, the Ignite class loader behave like web
application classloader in popular web application containers (e.g. Apache
Tomcat):
* Ignite class loader disallows to override classes from the following
packages:
* org.java.*
* org.javax.*
* org.apache.ignite.*
* org.gridgain.* (for GridGain 9 only)
If the system tries to find a class from packages listed above then the Ignite
class loader should delegate this logic to the parent class loader first (in
our hierarchy it is the system class loader).
* Ignite class loader allows to override any non-system and non-Ignite class.
If the system tries to find class from any package that is not listed in the
previous item then Ignite class loader should try to find class over
corresponding deployment unit and delegate this logic to the parent class
loader in case of failure.
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