BadPractice13 - SpotBugsExtensionForSpringFrameWork/CS5098 GitHub Wiki

Bug Pattern Name: COLLECTION_TYPE_INEXPLICIT_INJECTION
Short Description: Use @Resource over @Autowire + @Qualifier for collection type injection (to shorten your code).

Description

"If you intend to express annotation-driven injection by name, do not primarily use @Autowired - even if is technically capable of referring to a bean name through @Qualifier values. Instead, prefer the JSR-250 @Resource annotation which is semantically defined to identify a specific target component by its unique name, with the declared type being irrelevant for the matching process." spring docs


"You may wonder why the annotation @Resource is used instead of @Autowired. It’s because the @Autowired annotation is semantically defined in a way that it always treats arrays, collections, and maps as sets of corresponding beans, with the target bean type derived from the declared collection value type. So, **for example**, if a class has an attribute of type List and has the @Autowired annotation defined, **Spring will try to inject all beans of type ContentHolder** within the current ApplicationContext into that attribute (instead of the declared in the configuration file), **which will result in either the unexpected dependencies being injected or Spring throwing an exception if no bean of type ContentHolder was defined**. So, for collection type injection, we have to explicitly instruct Spring to perform injection by specifying the bean name, which the @Resource annotation supports." (Pro Spring 5) 
@Service("injectCollection")
public class CollectionInjection {
    //@Resource(name="map") is equivalent with @Autowired @Qualifier("map")
    @Autowired
    @Qualifier("map") 
    private Map<String, Object> map; 

    @Resource(name="props")
    private Properties props;

    @Resource(name="set")
    private Set set;
    
    @Resource(name="list")
    private List list;
}
<beans ...>
	<bean id="lyricHolder"
 lass="com.apress.prospring5.ch3.xml.LyricHolder"/>
	<bean id="injectCollection"
 class="com.apress.prospring5.ch3.xml.CollectionInjection">
		<property name="map">
			<map>
				<entry key="someValue">
					<value>It's a Friday, we finally made it</value>
				</entry>
				<entry key="someBean">
					<ref bean="lyricHolder"/>
				</entry>
			</map>
		</property>
		<property name="props">
			<props>
				<prop key="firstName">John</prop>
				<prop key="secondName">Mayer</prop>
			</props>
		</property>
		<property name="set">
			<set>
				<value>I can't believe I get to see your face</value>
				<ref bean="lyricHolder"/>
			</set>
		</property>
		<property name="list">
			<list>
				<value>You've been working and I've been waiting</value>
				<ref bean="lyricHolder"/>
			</list>
		</property>
	</bean>
</beans>

Reference List

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