Consider that we are developing an application that will store users and their authorities (roles). In this application, there will be two Data Access Objects (DAO) to deal with User and Authority entity classes, and a service class that depends on these two DAO classes.
In this scenario without using the auto-wire feature our configuration file will look like:
<?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:p="http://www.springframework.org/schema/p"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">
<!-- DAO Beans -->
<bean id="userDao"
class="org.hoydaa.autowire.dao.impl.UserDaoImpl" />
<bean id="authorityDao"
class="org.hoydaa.autowire.dao.impl.AuthorityDaoImpl" />
<!-- Service Beans -->
<bean id="userService"
class="org.hoydaa.autowire.service.impl.UserServiceImpl"
p:userDao-ref="userDao"
p:authorityDao-ref="authorityDao" />
</beans>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:p="http://www.springframework.org/schema/p"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">
<!-- DAO Beans -->
<bean id="userDao"
class="org.hoydaa.autowire.dao.impl.UserDaoImpl" />
<bean id="authorityDao"
class="org.hoydaa.autowire.dao.impl.AuthorityDaoImpl" />
<!-- Service Beans -->
<bean id="userService"
class="org.hoydaa.autowire.service.impl.UserServiceImpl"
p:userDao-ref="userDao"
p:authorityDao-ref="authorityDao" />
</beans>
However, when the auto-wire feature is enabled, configuration file will be as simple as:
<?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:p="http://www.springframework.org/schema/p"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd"
default-autowire="byName">
<!-- DAO Beans -->
<bean id="userDao"
class="org.hoydaa.autowire.dao.impl.UserDaoImpl" />
<bean id="authorityDao"
class="org.hoydaa.autowire.dao.impl.AuthorityDaoImpl" />
<!-- Service Beans -->
<bean id="userService"
class="org.hoydaa.autowire.service.impl.UserServiceImpl" />
</beans>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:p="http://www.springframework.org/schema/p"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd"
default-autowire="byName">
<!-- DAO Beans -->
<bean id="userDao"
class="org.hoydaa.autowire.dao.impl.UserDaoImpl" />
<bean id="authorityDao"
class="org.hoydaa.autowire.dao.impl.AuthorityDaoImpl" />
<!-- Service Beans -->
<bean id="userService"
class="org.hoydaa.autowire.service.impl.UserServiceImpl" />
</beans>
Although the XML file is way more simple, the dependency information between the beans is lost. In my opinion, it is very good to have such a place listing all the dependency between the beans clearly. By looking at this simple configuration file I cannot say that the User Service depends on User DAO and Authority DAO. When the auto-wire feature is enabled, the only way to learn this information is to inspect all the Java classes.
