How can I insert a List instance in Spring?

Question

What works

Suppose I have a definition for spring bean ArrayList:

<bean id="availableLanguages" class="java.util.ArrayList"> <constructor-arg> <bean class="java.util.Arrays" factory-method="asList"> <constructor-arg> <list> <value>de</value> <value>en</value> </list> </constructor-arg> </bean> </constructor-arg> </bean> 

Now I can insert this into all kinds of beans, for example. eg:

 @Controller class Controller { @Autowired public Controller(ArrayList<String> availableLanguages) { // ... } } 

This works great.

How will it break

However, if I change my controller to a small bit and use the List type instead of ArrayList as follows:

 @Controller class Controller { @Autowired public Controller(List<String> availableLanguages) { // ... } } 

Then instead, I get a list of all beans of type String , not the bean that I defined. However, I really want my list to be placed on an unmodifiable List, but this will only be possible if I lower my dependency to a list.

So far, a workaround has been found

The following XML file:

 <bean id="availableLanguages" class="java.util.Collections" factory-method="unmodifiableList"> <constructor-arg> <bean class="java.util.Arrays" factory-method="asList"> <constructor-arg> <list> <value>de</value> <value>en</value> </list> </constructor-arg> </bean> </constructor-arg> </bean> 

works together with this controller:

 @Controller class Controller { @Autowired public Controller(Object availableLanguages) { List<String> theList = (List<String>)availableLanguages; } } 

While this works, adding an extra type is ugly.

conclusions

I realized that there is special handling for collections in spring 4.2.5 (the latest version) , which seems to cause all the problems. This creates special behavior when a parameter is an interface that extends Collection . That way, I can work around using Object or a specific implementation as a parameter type.

Question

Is there a way to directly insert a list into a bean? How?

Answer 1

Using @Qualifier will insert a bean with the given qualifier. You can name the list that you want to bean, and this will work fine.