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Polish "Clarify edge case docs on ConditionalOnClass"

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Closes gh-8185
This commit is contained in:
Stephane Nicoll 2017-04-10 16:12:11 +02:00
parent 08f8219248
commit 0a55e3e736
2 changed files with 17 additions and 18 deletions
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13
spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/condition/ConditionalOnClass.java
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@ -1,5 +1,5 @@
/*
* Copyright 2012-2015 the original author or authors.
* Copyright 2012-2017 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.
@ -36,14 +36,11 @@ import org.springframework.context.annotation.Conditional;
public @interface ConditionalOnClass {
/**
* <p>
* The classes that must be present. Since this annotation parsed by loading class
* bytecode it is safe to specify classes here that may ultimately not be on the
* The classes that must be present. Since this annotation is parsed by loading class
* bytecode, it is safe to specify classes here that may ultimately not be on the
* classpath, only if this annotation is directly on the affected component and
* <b>not</b> if this annotation is used as a composed, meta-annotation. If this
* is used as a meta annotation and the given class is not available at runtime
* then this {@link @Conditional} will effectively be ignored. In order to use
* this annotation as a meta-annotation, only use the {@link #name} attribute.
* <b>not</b> if this annotation is used as a composed, meta-annotation. In order to
* use this annotation as a meta-annotation, only use the {@link #name} attribute.
* @return the classes that must be present
*/
Class<?>[] value() default {};

22
spring-boot-docs/src/main/asciidoc/spring-boot-features.adoc
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@ -5839,16 +5839,18 @@ code by annotating `@Configuration` classes or individual `@Bean` methods.
[[boot-features-class-conditions]]
==== Class conditions
The `@ConditionalOnClass` and `@ConditionalOnMissingClass` annotations allows
configuration to be included based on the presence or absence of specific classes.
If you are using the `@ConditionalOnClass` annotation directly on the class you are conditionally
registering, you can actually use the `value` attribute to refer to the real class,
even though that class might not actually appear on the running application classpath.
This is due to the fact that annotation metadata directly on a class is parsed
using http://asm.ow2.org/[ASM]. You can also use the `name` attribute if you prefer to
specify the class name using a `String` value, which is required if you are using
`@ConditionalOnClass` or `@ConditionalOnMissingClass` as apart of a meta-annotation to
compose your own composed annotations or in an `@Bean` method as neither of these cases
are handled by ASM.
configuration to be included based on the presence or absence of specific classes. Due to
the fact that annotation metadata is parsed using http://asm.ow2.org/[ASM] you can
actually use the `value` attribute to refer to the real class, even though that class
might not actually appear on the running application classpath. You can also use the
`name` attribute if you prefer to specify the class name using a `String` value.
[TIP]
====
If you are using `@ConditionalOnClass` or `@ConditionalOnMissingClass` as apart of a
meta-annotation to compose your own composed annotations you must use `name` as referring
to the class in such a case is not handled.
====