Issue
I need help understanding the concept behind @Autowired and @Service. I have a DAO defined with @Service and controller with @Autowired and everything seems fine, however, I use the same @Autowired in a different class then it does not work.
Example:
Service
@Service
public class MyService {
private JdbcTemplate jdbcTemplate;
@Autowired
public void setDataSource (DataSource myDataSource) {
this.jdbcTemplate = new JdbcTemplate(myDataSource);
}
public void testUpdate(){
jdbcTemplate.update("some query");
}
}
Controller
package com.springtest.mywork.controller;
@Controller
@RequestMapping(value = "/test.html")
public class MyController
{
@Autowired
MyService myService;
@RequestMapping(method = RequestMethod.GET)
public String test(Model model)
{
systemsService.testUpdate();
return "view/test";
}
}
The above all works fine. However, If I want to use MyService in a POJO then it just doesn't work. Example:
package com.springtest.mywork.pojos;
public class MyPojo {
@Autowired
MyService myService;
public void testFromPojo () {
myService.someDataAccessMethod(); //myService is still null
}
}
Spring Config:
<beans>
<mvc:annotation-driven />
<bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
<property name="prefix" value="/WEB-INF/views/"/>
<property name="suffix" value=".jsp"/>
</bean>
<context:component-scan base-package="com.springtest.mywork" />
<bean id="dataSource" destroy-method="close" class="org.apache.commons.dbcp.BasicDataSource">
<property name="driverClassName" value="com.mysql.jdbc.Driver" />
<property name="url" value="jdbc:mysql://127.0.0.1:3306/mydb" />
<property name="username" value="hello" />
<property name="password" value="what" />
</bean>
<bean name="jdbcTemplate" class="org.springframework.jdbc.core.simple.SimpleJdbcTemplate">
<constructor-arg ref="dataSource"/>
</bean>
</beans>
Solution
It is because your POJO class is not managed by spring container.
@Autowire annotation will work only those objects which are managed by spring (ie created by the spring container).
In your case the service and controller object are managed by spring, but your POJO class is not managed by spring, that is why the @Autowire is not producing the behavior expected by you.
Another problem I noticed is, you are using the @Service annotation in the DAO layer when spring has the @Repository annotation specifically created for this purpose.
Also it is not desirable to allow spring to manage the POJO classes since normally it will be data storage elements which has to be created outside the container.
Answered By - Arun P Johny
Answer Checked By - Timothy Miller (JavaFixing Admin)
