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Recommend ObjectProvider as alternative to @Lazy for optional dependencies 

Closes gh-27649
This commit is contained in:
Juergen Hoeller 2021-11-09 22:29:56 +01:00
parent 39be572a7a
commit 9bc09631d6
2 changed files with 12 additions and 5 deletions
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7
spring-context/src/main/java/org/springframework/context/annotation/Lazy.java
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@ -1,5 +1,5 @@
/* /*
* Copyright 2002-2013 the original author or authors. * Copyright 2002-2021 the original author or authors.
* *
* Licensed under the Apache License, Version 2.0 (the "License"); * Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License. * you may not use this file except in compliance with the License.
@ -47,6 +47,11 @@ import java.lang.annotation.Target;
* or {@link javax.inject.Inject}: In that context, it leads to the creation of a * or {@link javax.inject.Inject}: In that context, it leads to the creation of a
* lazy-resolution proxy for all affected dependencies, as an alternative to using * lazy-resolution proxy for all affected dependencies, as an alternative to using
* {@link org.springframework.beans.factory.ObjectFactory} or {@link javax.inject.Provider}. * {@link org.springframework.beans.factory.ObjectFactory} or {@link javax.inject.Provider}.
* Please note that such a lazy-resolution proxy will always be injected; if the target
* dependency does not exist, you will only be able to find out through an exception on
* invocation. As a consequence, such an injection point results in unintuitive behavior
* for optional dependencies. For a programmatic equivalent, allowing for lazy references
* with more sophistication, consider {@link org.springframework.beans.factory.ObjectProvider}.
* *
* @author Chris Beams * @author Chris Beams
* @author Juergen Hoeller * @author Juergen Hoeller

10
src/docs/asciidoc/core/core-beans.adoc
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@ -3039,7 +3039,7 @@ constructor or setter argument or autowired field) as `ObjectFactory<MyTargetBea
allowing for a `getObject()` call to retrieve the current instance on demand every allowing for a `getObject()` call to retrieve the current instance on demand every
time it is needed -- without holding on to the instance or storing it separately. time it is needed -- without holding on to the instance or storing it separately.
As an extended variant, you may declare `ObjectProvider<MyTargetBean>`, which delivers As an extended variant, you may declare `ObjectProvider<MyTargetBean>` which delivers
several additional access variants, including `getIfAvailable` and `getIfUnique`. several additional access variants, including `getIfAvailable` and `getIfUnique`.
The JSR-330 variant of this is called `Provider` and is used with a `Provider<MyTargetBean>` The JSR-330 variant of this is called `Provider` and is used with a `Provider<MyTargetBean>`
@ -6675,9 +6675,11 @@ factory method and other bean definition properties, such as a qualifier value t
the `@Qualifier` annotation. Other method-level annotations that can be specified are the `@Qualifier` annotation. Other method-level annotations that can be specified are
`@Scope`, `@Lazy`, and custom qualifier annotations. `@Scope`, `@Lazy`, and custom qualifier annotations.
TIP: In addition to its role for component initialization, you can also place the `@Lazy` annotation TIP: In addition to its role for component initialization, you can also place the `@Lazy`
on injection points marked with `@Autowired` or `@Inject`. In this context, it annotation on injection points marked with `@Autowired` or `@Inject`. In this context,
leads to the injection of a lazy-resolution proxy. it leads to the injection of a lazy-resolution proxy. However, such a proxy approach
is rather limited. For sophisticated lazy interactions, in particular in combination
with optional dependencies, we recommend `ObjectProvider<MyTargetBean>` instead.
Autowired fields and methods are supported, as previously discussed, with additional Autowired fields and methods are supported, as previously discussed, with additional
support for autowiring of `@Bean` methods. The following example shows how to do so: support for autowiring of `@Bean` methods. The following example shows how to do so: