Trying to understand dependency injection with spring - newbie.

**SparkySpider** · Oct 1st, 2011, 01:03 PM

Hi there,

I'm trying to create a simple Spring example using beans and annotations, but my @Autowired does not seem to work, nor does the container seem to instantiate my bean automatically. This is what I did:

1. In web.xml, set up a org.springframework.web.context.ContextLoaderListe ner and pointed the contextConfigLocation listener to by XML doc, /WEB-INF/spring-context.xml

2. Created spring-context.xml in such a way that the entire system uses annotation-based configuration and set up the "base-package" as the lowest common denominator as follows:

Code:

<beans xmlns="http://www.springframework.org/schema/beans"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xmlns:context="http://www.springframework.org/schema/context"
     xsi:schemaLocation="http://www.springframework.org/schema/beans
         http://www.springframework.org/schem...-beans-3.0.xsd
         http://www.springframework.org/schema/context
         http://www.springframework.org/schema/context/spring-context-3.0.xsd">
             

    <context:annotation-config base-package="com.foxbomb.springtest"/>

</beans>

3. Set up a @Service Service Bean - which doesn't get instantiated...

as such:

Code:

package com.foxbomb.springtest.domain.time;

import java.util.Date;
import org.springframework.stereotype.Service;

@Service
public class TimeService {

    public TimeService() {
        System.out.println("Instantiating Time Service");
    }    
    
    public Date getTime() {
        return new Date();
    }
}

4. Then I set up a class, that every time I instantiate it, realizes that it's a Spring configured class (annotated with @configurable), and injects the dependencies automatically. This is TimeManager.class. Here the @Autowired dependency seems to fail:

Code:

package com.foxbomb.springtest;

import com.foxbomb.springtest.domain.time.TimeService;
import java.util.Date;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

@Configurable
public class TimeManager {
    
    public TimeManager() {
        System.out.println("Instantiating Time Manager");
    }
    
    @Autowired
    protected TimeService timeService;
    
    public Date getTime() {
        return timeService.getTime();
    }
    
}

5. Then I created a JSP, for the simple purpose of interrogating the TimeManager class. Instantiating the TimeManager class in the JSP I hoped, would wake up Spring (cause it's @configurable) and quickly inject the protected TimeService timeService dependency in for me. Alas, the JSP reports a NullPointerException at return timeService.getTime();

Code:

<%@page import="com.foxbomb.springtest.ApplicationContextImpl"%>
<%@page import="com.foxbomb.springtest.TimeManager"%>
<%! TimeManager manager = new TimeManager(); %>
<html>
    <body>
        <h1>Autowired Dependencies....</h1>
        <p>
            Time is now <%=manager.getTime()%>!
        </p>
        
    </body>
</html>

What am I doing wrong? Your help is greatly appreciated...

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