How to define a List bean in Spring?
I'm using Spring to define stages in my application. It's configured that the necessary class (here called Configurator ) is injected with the stages.
Now I need the List of Stages in another class, named LoginBean . The Configurator doesn't offer access to his List of Stages.
I cannot change the class Configurator .
My Idea:
Define a new bean called Stages and inject it to Configurator and LoginBean . My problem with this idea is that I don't know how to transform this property:
<property ...>
<list>
<bean ... >...</bean>
<bean ... >...</bean>
<bean ... >...</bean>
</list>
</property>
into a bean.
Something like this does not work:
<bean id="stages" class="java.util.ArrayList">
Can anybody help me with this?
Import the spring util namespace. Then you can define a list bean as follows:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:util="http://www.springframework.org/schema/util"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/util
http://www.springframework.org/schema/util/spring-util-2.5.xsd">
<util:list id="myList" value-type="java.lang.String">
<value>foo</value>
<value>bar</value>
</util:list>
The value-type is the generics type to be used, and is optional. You can also specify the list implementation class using the attribute list-class .
以下是一种方法：
<bean id="stage1" class="Stageclass"/>
<bean id="stage2" class="Stageclass"/>
<bean id="stages" class="java.util.ArrayList">
<constructor-arg>
<list>
<ref bean="stage1" />
<ref bean="stage2" />
</list>
</constructor-arg>
</bean>
Another option is to use JavaConfig. Assuming that all stages are already registered as spring beans you just have to:
@Autowired
private List<Stage> stages;
and spring will automatically inject them into this list. If you need to preserve order (upper solution doesn't do that) you can do it in that way:
@Configuration
public class MyConfiguration {
@Autowired
private Stage1 stage1;
@Autowired
private Stage2 stage2;
@Bean
public List<Stage> stages() {
return Lists.newArrayList(stage1, stage2);
}
}
The other solution to preserve order is use a @Order annotation on beans. Then list will contain beans ordered by ascending annotation value.
@Bean
@Order(1)
public Stage stage1() {
return new Stage1();
}
@Bean
@Order(2)
public Stage stage2() {
return new Stage2();
}