The AS Java system
consists of three logical layers:
●
Java Enterprise
Runtime – comprises
low-level subsystems that provide functions such as classloading, cluster
communication, persistent configuration data management, and so on.
●
AS Java System Components – consists of facades, interfaces, libraries
and services components that provide various runtime functions and programming
APIs.
●
Applications – refers to the applications that are deployed
and run on the AS Java.
Features
The AS Java system
architecture is based on the following general rule: components from a higher
level can use components from a lower level only through a set of defined APIs
– facades; whereas components from a lower level are not aware of the
APIs of the components from a higher level and therefore cannot use
them.
This rule is
reflected by the order of starting the system modules: the runtime is started
first, then the services (the libraries are loaded, the interfaces resolved at
this phase), and the applications are started last. The system is considered
as started when all runtime managers and core services components are started
properly.
The AS Java system
components use the Framework APIs to connect to the Java enterprise runtime.
Applications use the AS Java system components using the APIs that are defined
by Java EE 5 specification (and supporting specifications) and SAP-proprietary APIs.
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