From 9a088b8128cb1a8027a13645a7e4d400d767aabb Mon Sep 17 00:00:00 2001
From: Chris Beams <cbeams@vmware.com>
Date: Tue, 17 Aug 2010 09:50:22 +0000
Subject: [PATCH] Document BeanFactoryPostProcessor implementation constraints
 (SPR-7466)

JavaDoc and reference docs now warn developers against interacting with
bean instances within BeanFactoryPostProcessor implementations in order
to avoid premature bean instantiation.

See SPR-7450 for an example of a third-party BFPP
(OAuthTokenLifecycleRegistryPostProcessor) prematurely instantiating
a FactoryBean instance, such that bean post-processing is bypassed
and autowired injection (via @Inject) never occurs.
---
 .../beans/factory/config/BeanFactoryPostProcessor.java    | 6 ++++++
 spring-framework-reference/src/beans.xml                  | 8 +++++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/org.springframework.beans/src/main/java/org/springframework/beans/factory/config/BeanFactoryPostProcessor.java b/org.springframework.beans/src/main/java/org/springframework/beans/factory/config/BeanFactoryPostProcessor.java
index c61ce8272d..1619505c1f 100644
--- a/org.springframework.beans/src/main/java/org/springframework/beans/factory/config/BeanFactoryPostProcessor.java
+++ b/org.springframework.beans/src/main/java/org/springframework/beans/factory/config/BeanFactoryPostProcessor.java
@@ -31,6 +31,12 @@ import org.springframework.beans.BeansException;
  * <p>See PropertyResourceConfigurer and its concrete implementations
  * for out-of-the-box solutions that address such configuration needs.
  *
+ * <p>A BeanFactoryPostProcessor may interact with and modify bean
+ * definitions, but never bean instances. Doing so may cause premature bean
+ * instantiation, violating the container and causing unintended side-effects.
+ * If bean instance interaction is required, consider implementing
+ * {@link BeanPostProcessor} instead.
+ *
  * @author Juergen Hoeller
  * @since 06.07.2003
  * @see BeanPostProcessor
diff --git a/spring-framework-reference/src/beans.xml b/spring-framework-reference/src/beans.xml
index f6669f8378..dabb662d2e 100644
--- a/spring-framework-reference/src/beans.xml
+++ b/spring-framework-reference/src/beans.xml
@@ -4149,7 +4149,13 @@ org.springframework.scripting.groovy.GroovyMessenger@272961</programlisting>
         <emphasis>instances</emphasis> (the objects that are created from the
         configuration metadata), then you instead need to use a
         <interfacename>BeanPostProcessor</interfacename> (described above in
-        <xref linkend="beans-factory-extension-bpp" />.</para>
+        <xref linkend="beans-factory-extension-bpp"/>.  While it is technically
+        possible to work with bean instances within a
+        <interfacename>BeanFactoryPostProcessor</interfacename> (e.g. using
+        <methodname>BeanFactory.getBean()</methodname>), doing so causes
+        premature bean instantiation, violating the usual containter lifecycle.
+        This may cause negative side effects such as bypassing bean post
+        processing.</para>
 
         <para>Also, <literal>BeanFactoryPostProcessors</literal> are scoped
         <emphasis>per-container</emphasis>. This is only relevant if you are
-- 
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