SpringMvc三层架构注解详解@Controller@Service和@Repository

Posted 2022-04-21 虎子

• 1. @Controller控制层
• 2. @Service()
• 3. @Repository持久层

@Autowired依赖注入源码分析

1. @Controller控制层

@Controller用于标记在一个类上，使用它标记的类就是一个SpringMvc Controller对象，分发处理器会扫描使用该注解的类的方法，并检测该方法是否使用了@RequestMapping注解。
@Controller只是定义了一个控制器类，而使用@RequestMapping注解的方法才是处理请求的处理器。
@Controller标记在一个类上还不能真正意义上说它就是SpringMvc的控制器，应为这个时候Spring还不认识它，这个时候需要把这个控制器交给Spring来管理。有两种方式可以管理：

<span style="color:#000000"><span style="background-color:#f3f4f5"><code class="language-xml"><span style="color:#969896"><!--基于注解的装配--></span>
<span style="color:#969896"><!--方式一--></span>
<span style="color:#63a35c"><span style="color:#63a35c"><span style="color:#969896"><</span>bean</span> <span style="color:#795da3">class</span><span style="color:#df5000"><span style="color:#969896">=</span><span style="color:#969896">"</span>com.HelloWorld<span style="color:#969896">"</span></span><span style="color:#969896">/></span></span>
<span style="color:#969896"><!--方式二--></span>
<span style="color:#969896"><!--路径写到controller的上一层--></span>
<span style="color:#63a35c"><span style="color:#63a35c"><span style="color:#969896"><</span>context:component-scan</span> <span style="color:#795da3">base-package</span><span style="color:#df5000"><span style="color:#969896">=</span><span style="color:#969896">"</span>com<span style="color:#969896">"</span></span><span style="color:#969896">/></span></span>
</code></span></span>

Action层:

<span style="color:#000000"><span style="background-color:#f3f4f5"><code class="language-java"><span style="color:#a71d5d">package</span> com<span style="color:#969896">;</span>
<span style="color:#969896">@Controller</span>
<span style="color:#a71d5d">public</span> <span style="color:#a71d5d">class</span> HelloWorld<span style="color:#969896"></span>
	
	<span style="color:#969896">@RequestMapping</span><span style="color:#969896">(</span>value<span style="color:#df5000">=</span><span style="color:#df5000">"/showRegUser"</span><span style="color:#969896">)</span>
	<span style="color:#a71d5d">public</span> String <span style="color:#795da3">printHello</span><span style="color:#969896">(</span><span style="color:#969896">)</span> <span style="color:#969896"></span>
		<span style="color:#a71d5d">return</span> <span style="color:#df5000">"hello"</span><span style="color:#969896">;</span>
	<span style="color:#969896"></span>

    <span style="color:#969896">@Autowried</span>
    <span style="color:#a71d5d">private</span> IocSerevce service<span style="color:#969896">;</span>
    <span style="color:#a71d5d">public</span> <span style="color:#a71d5d">void</span> <span style="color:#795da3">add</span><span style="color:#969896">(</span><span style="color:#969896">)</span><span style="color:#969896"></span>
        service<span style="color:#969896">.</span><span style="color:#795da3">add</span><span style="color:#969896">(</span><span style="color:#969896">)</span><span style="color:#969896">;</span>
    <span style="color:#969896"></span>
<span style="color:#969896"></span>
</code></span></span>

component-scan默认扫描的注解类型是@Component,不过，在@Component的语义基础之上细化为@Reposity，@Service,@Controller.
有一个use-defaultbao'i-filters属性，属性默认是true,表示会扫描抱下所有的标有@Component的类，并注册为bean，也就是@Component的子注解@Service,@reposity等
如果只想扫描包下的@Controller或其他内容，则设置use-default-filters属性为false，表示不再按照scan指定的包进行扫描，而是按照指定包进行扫描

<span style="color:#000000"><span style="background-color:#f3f4f5"><code class="language-xml"><span style="color:#63a35c"><span style="color:#63a35c"><span style="color:#969896"><</span>context:component-scan</span> <span style="color:#795da3">base-package</span><span style="color:#df5000"><span style="color:#969896">=</span><span style="color:#969896">"</span>com<span style="color:#969896">"</span></span> <span style="color:#795da3">user-default-filters</span><span style="color:#df5000"><span style="color:#969896">=</span><span style="color:#969896">"</span>false<span style="color:#969896">"</span></span><span style="color:#969896">></span></span>
    <span style="color:#63a35c"><span style="color:#63a35c"><span style="color:#969896"><</span>context:include-filter</span> <span style="color:#795da3">type</span><span style="color:#df5000"><span style="color:#969896">=</span><span style="color:#969896">"</span>regex<span style="color:#969896">"</span></span> <span style="color:#795da3">expression</span><span style="color:#df5000"><span style="color:#969896">=</span><span style="color:#969896">"</span>com.tan.*<span style="color:#969896">"</span></span><span style="color:#969896">/></span></span>
<span style="color:#63a35c"><span style="color:#63a35c"><span style="color:#969896"></</span>context:component-scan</span><span style="color:#969896">></span></span>
</code></span></span>

当没有设置use-default-filters属性或属性为true时，表示基于base-package包下指定扫描的具体路径。

2. @Service()

此注注解属于业务逻辑层，service或者manager层
默认按照名称进行装配，如果名称可以通过name属性指定，如果没有name属性，注解写在字段上时，默认去字段名进行查找，如果注解写在setter方法上，默认按照方法属性名称进行装配。当找不到匹配的bean时，才按照类型进行装配，如果name名称一旦指定就会按照名称进行装配
Service层：

<span style="color:#000000"><span style="background-color:#f3f4f5"><code class="language-java"><span style="color:#969896">@Service</span><span style="color:#969896">(</span><span style="color:#969896">)</span>
<span style="color:#a71d5d">public</span> <span style="color:#a71d5d">class</span> IocService<span style="color:#969896"></span>

    <span style="color:#969896">@Resource</span>
    <span style="color:#a71d5d">private</span> IIocDao iiocDao<span style="color:#969896">;</span>
    <span style="color:#a71d5d">public</span> <span style="color:#a71d5d">void</span> <span style="color:#795da3">add</span><span style="color:#969896">(</span><span style="color:#969896">)</span><span style="color:#969896"></span>
        iiocDao<span style="color:#969896">.</span><span style="color:#795da3">add</span><span style="color:#969896">(</span><span style="color:#969896">)</span><span style="color:#969896">;</span>
    <span style="color:#969896"></span>
<span style="color:#969896"></span>
</code></span></span>

3. @Repository持久层

此注解式持久层组件，用于标注数据访问组件，即DAO组件
DAO层
先定义一个接口

<span style="color:#000000"><span style="background-color:#f3f4f5"><code class="language-java"><span style="color:#a71d5d">public</span> <span style="color:#a71d5d">interface</span> IIocDao<span style="color:#969896"></span>
    <span style="color:#a71d5d">public</span> <span style="color:#a71d5d">void</span> <span style="color:#795da3">add</span><span style="color:#969896">(</span><span style="color:#969896">)</span><span style="color:#969896">;</span>
<span style="color:#969896"></span>
</code></span></span>

然后实现类

<span style="color:#000000"><span style="background-color:#f3f4f5"><code class="language-java"><span style="color:#969896">//Dao层中定义了一些接口</span>
<span style="color:#969896">//表示将Dao类声明为bean</span>
<span style="color:#969896">@Repository</span>
<span style="color:#a71d5d">public</span> <span style="color:#a71d5d">class</span> IocDao <span style="color:#a71d5d">implements</span> IIocDao<span style="color:#969896"></span>
    <span style="color:#a71d5d">public</span> <span style="color:#a71d5d">void</span> <span style="color:#795da3">add</span><span style="color:#969896">(</span><span style="color:#969896">)</span><span style="color:#969896"></span>
        System<span style="color:#969896">.</span>out<span style="color:#969896">.</span><span style="color:#795da3">println</span><span style="color:#969896">(</span><span style="color:#df5000">"调用了Dao"</span><span style="color:#969896">)</span><span style="color:#969896">;</span>
    <span style="color:#969896"></span>
<span style="color:#969896"></span>
</code></span></span>

另外一种解释： @Repository对应数据访问层Bean

<span style="color:#000000"><span style="background-color:#f3f4f5"><code class="language-java"><span style="color:#969896">@Repository</span><span style="color:#969896">(</span>value<span style="color:#df5000">=</span><span style="color:#df5000">"userDao"</span><span style="color:#969896">)</span>
<span style="color:#a71d5d">public</span> <span style="color:#a71d5d">class</span> UserDaoImpl <span style="color:#a71d5d">extends</span> BeansDaoImpl<span style="color:#795da3"><span style="color:#969896"><</span>User<span style="color:#969896">></span></span><span style="color:#969896"></span>
    <span style="color:#969896">.</span><span style="color:#969896">.</span><span style="color:#969896">.</span><span style="color:#969896">.</span><span style="color:#969896">.</span><span style="color:#969896">.</span>
<span style="color:#969896"></span>
</code></span></span>

@Repository(value=“userDao”)注解告诉Spring ,让Spring创建一个名字叫做"userDao"的UserDapImpl实例。
当Service需要使用Spring创建的名字叫“userDao”的UserDaoImpl实例时，就可以使用@Resource(name=“userDao”)注解告诉Spring,Spring把创建好的userDao注入给Service即可。

<span style="color:#000000"><span style="background-color:#f3f4f5"><code class="language-java"> <span style="color:#969896">//注入userDao，从数据库中根据用户Id取出指定用户时需要用到</span>
 <span style="color:#969896">@Resource</span><span style="color:#969896">(</span>name <span style="color:#df5000">=</span> <span style="color:#df5000">"userDao"</span><span style="color:#969896">)</span>
 <span style="color:#a71d5d">private</span> BaseDao<span style="color:#795da3"><span style="color:#969896"><</span>User<span style="color:#969896">></span></span> userDao<span style="color:#969896">;</span>
</code></span></span>