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Clarify environment property precedence rules 

Issue: SPR-13845
This commit is contained in:
Juergen Hoeller 2016-01-25 20:23:25 +01:00
parent 64d83e78ea
commit ebad8db8d5
1 changed files with 11 additions and 2 deletions
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src/asciidoc/core-beans.adoc
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@ -7519,7 +7519,7 @@ is populated with additional default property sources including servlet config a
context parameters. {api-spring-framework}/web/portlet/context/StandardPortletEnvironment.html[`StandardPortletEnvironment`]
similarly has access to portlet config and portlet context parameters as property sources.
Both can optionally enable a {api-spring-framework}/jndi/JndiPropertySource.html[`JndiPropertySource`].
See Javadoc for details.
See the javadocs for details.
====
Concretely, when using the `StandardEnvironment`, the call to `env.containsProperty("foo")`
@ -7531,7 +7531,16 @@ runtime.
The search performed is hierarchical. By default, system properties have precedence over
environment variables, so if the `foo` property happens to be set in both places during
a call to `env.getProperty("foo")`, the system property value will 'win' and be returned
preferentially over the environment variable.
preferentially over the environment variable. Note that property values will not get merged
but rather completely overridden by a preceding entry.
For a common `StandardServletEnvironment`, the full hierarchy looks as follows, with the
highest-precedence entries at the top:
* ServletConfig parameters (if applicable, e.g. in case of a `DispatcherServlet` context)
* ServletContext parameters (web.xml context-param entries)
* JNDI environment variables ("java:comp/env/" entries)
* JVM system properties ("-D" command-line arguments)
* JVM system environment (operating system environment variables)
====
Most importantly, the entire mechanism is configurable. Perhaps you have a custom source