[FIXED] Why can I get null when I get a bean from spring?

Issue

My 'applicationContext.xml' file for spring is:

<bean id="gzipResponseInterceptor" class="my.interceptor.GzipResponseInterceptor"/>

<bean id="addResponseInterceptor" class="org.springframework.beans.factory.config.MethodInvokingFactoryBean">
    <property name="targetObject">
        <ref local="httpClient"/>
    </property>
    <property name="targetMethod">
        <value>addResponseInterceptor</value>
    </property>
    <property name="arguments">
        <list>
            <ref bean="gzipResponseInterceptor"/>
        </list>
    </property>
</bean>

<bean id="httpClient" class="org.apache.http.impl.client.DefaultHttpClient">
    <constructor-arg>
        <bean class="org.apache.http.impl.conn.tsccm.ThreadSafeClientConnManager" p:defaultMaxPerRoute="100"
              p:maxTotal="100"/>
    </constructor-arg>
</bean>

Then in my Java code:

ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
System.out.println(context.getBean("gzipResponseInterceptor"));
System.out.println(context.getBean("addResponseInterceptor"));
System.out.println(context.getBean("httpClient"));

And it prints:

my.interceptor.GzipResponseInterceptor@525f1e4e
null
org.apache.http.impl.client.DefaultHttpClient@75f9eccc

Notice the value of the bean 'addResponseInterceptor' is null! I can't understand why I can get null for a spring bean.

Solution

The addResponseInterceptor is a MethodInvokingFactoryBean which sole purpose is, as the name implies, to invoke a method. When doing context.getBean("addResponseInterceptor") what is being returned is the result of the getObject method of the FactoryBean.

The MethodInvokingFactoryBean returns the result of the invoked method.

Judging by the name of the method being invoked, addResponseInterceptor, that is void. void or Void results in a null result to be return from the MethodInvokingFactoryBean.

If you want the actual FactoryBean add a & to the name of the bean you want to retrieve. See last part of section 5.8.3 of the reference guide.

Answered By - M. Deinum
Answer Checked By - Gilberto Lyons (JavaFixing Admin)