在Spring XML中使用任意数量的参数调用Java构造函数

Question

Assume that there is a class having constructor with arbitrary number of arguments like this:

public ClassA(URI ... uri){
    //contruct object
}

The number of URI objects to pass into ClassA's constructor may varies depending on number of values defined in config file (can be one to many URIs).

How should I define a ClassA bean in Spring XML?

Answer 1

Use the FactoryBean interface:

public interface FactoryBean<T> {
  T getObject() throws Exception;
  Class<T> getObjectType();
  boolean isSingleton();
}

Basically define of bean of that type. Something like this:

<bean id="classA" class="ClassAFactoryBean"/>

And then:

public class ClassAFactoryBean implements FactoryBean<ClassA> {

   @Value("${uris}")
   URI[] uris;

   ClassA getObject() throws Exception {
       return new ClassA(uris);
   }

   Class<T> getObjectType() {
       return ClassA.class;
   }

   boolean isSingleton() {
       return true;
   }
}

You may have to inject the "uris" properties as String and then converting if there's no converter provided by Spring. Or hook your own URI converter.

Answer 2

The following configuration works fine:

<beans>
  <bean id="ClassA" class="ClassA">
      <constructor-arg ref="uri"/>
   </bean>

   <bean id="uri" class="URI"/>
</beans>