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Document common use cases for @Order vs @Priority vs @DependsOn

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Issue: SPR-16213

(cherry picked from commit 84699c8)
This commit is contained in:
Juergen Hoeller
2017-11-20 12:53:37 +01:00
parent 122a3fe9fd
commit 1d060ecff0
4 changed files with 98 additions and 42 deletions
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34
spring-core/src/main/java/org/springframework/core/annotation/Order.java
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@@ -1,5 +1,5 @@
/*
* Copyright 2002-2015 the original author or authors.
* Copyright 2002-2017 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
@@ -27,21 +27,29 @@ import org.springframework.core.Ordered;
/**
* {@code @Order} defines the sort order for an annotated component.
*
* <p>The {@link #value} is optional and represents an order value as defined
* in the {@link Ordered} interface. Lower values have higher priority. The
* default value is {@code Ordered.LOWEST_PRECEDENCE}, indicating
* lowest priority (losing to any other specified order value).
* <p>The {@link #value} is optional and represents an order value as defined in the
* {@link Ordered} interface. Lower values have higher priority. The default value is
* {@code Ordered.LOWEST_PRECEDENCE}, indicating lowest priority (losing to any other
* specified order value).
*
* <p>Since Spring 4.1, the standard {@link javax.annotation.Priority}
* annotation can be used as a drop-in replacement for this annotation.
* <p><b>NOTE:</b> Since Spring 4.0, annotation-based ordering is supported for many
* kinds of components in Spring, even for collection injection where the order values
* of the target components are taken into account (either from their target class or
* from their {@code @Bean} method). While such order values may influence priorities
* at injection points, please be aware that they do not influence singleton startup
* order which is an orthogonal concern determined by dependency relationships and
* {@code @DependsOn} declarations (influencing a runtime-determined dependency graph).
*
* <p><b>NOTE</b>: Annotation-based ordering is supported for specific kinds
* of components only &mdash; for example, for annotation-based AspectJ
* aspects. Ordering strategies within the Spring container, on the other
* hand, are typically based on the {@link Ordered} interface in order to
* allow for programmatically configurable ordering of each <i>instance</i>.
* <p>Since Spring 4.1, the standard {@link javax.annotation.Priority} annotation
* can be used as a drop-in replacement for this annotation in ordering scenarios.
* Note that {@code Priority} may have additional semantics when a single element
* has to be picked (see {@link AnnotationAwareOrderComparator#getPriority}).
*
* <p>Consult the Javadoc for {@link org.springframework.core.OrderComparator
* <p>Alternatively, order values may also be determined on a per-instance basis
* through the {@link Ordered} interface, allowing for configuration-determined
* instance values instead of hard-coded values attached to a particular class.
*
* <p>Consult the javadoc for {@link org.springframework.core.OrderComparator
* OrderComparator} for details on the sort semantics for non-ordered objects.
*
* @author Rod Johnson