Learn Spring - Spring MVC

1. 处理流程

• 请求提交给DispatchServlet

• 查找HandlerMapping

• 调用由HandlerAdapter封装后的Handler

• 返回ModelAndView到DispatcherServlet

• 借由ViewResolver完成逻辑视图到真实视图的转换

• 返回响应

2. 配置DispatcherServlet

• web.xml

<web-app>
    <!-- 父容器配置 -->
    <context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>
            /WEB-INF/applicationServlet.xml,
        </param-value>
    </context-param>
    <listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
    </listener>

    <!-- 子容器配置 -->
    <servlet>
        <servlet-name>app</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <param-name>logLevel</param-name>
            <param-value>FINE</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>

    <!-- url映射 -->
    <servlet-mapping>
        <servlet-name>app</servlet-name>
        <url-pattern>/api/*</url-pattern>
    </servlet-mapping>
</web-app>

• 子容器可以访问父容器的bean，父容器不能访问子容器的bean

• 默认采用org.springframework.web.context.ContextLoaderListener

• 默认使用/WEB-INF/{servlet-name}-*.xml加载子容器

3. DispatcherServlet的初始化

• DispatcherServlet初始化

protected void initStrategies(ApplicationContext context) {
    initMultipartResolver(context);
    initLocaleResolver(context);
    initThemeResolver(context);
    initHandlerMappings(context);
    initHandlerAdapters(context);
    initHandlerExceptionResolvers(context);
    initRequestToViewNameTranslator(context);
    initViewResolvers(context);
    initFlashMapManager(context);
}

• 默认配置: DispatcherServlet.properties

# Default implementation classes for DispatcherServlet's strategy interfaces.
# Used as fallback when no matching beans are found in the DispatcherServlet context.
# Not meant to be customized by application developers.

org.springframework.web.servlet.LocaleResolver=org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolver

org.springframework.web.servlet.ThemeResolver=org.springframework.web.servlet.theme.FixedThemeResolver

org.springframework.web.servlet.HandlerMapping=org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping,\
    org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping

org.springframework.web.servlet.HandlerAdapter=org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter,\
    org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter,\
    org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter

org.springframework.web.servlet.HandlerExceptionResolver=org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerExceptionResolver,\
    org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver,\
    org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver

org.springframework.web.servlet.RequestToViewNameTranslator=org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator

org.springframework.web.servlet.ViewResolver=org.springframework.web.servlet.view.InternalResourceViewResolver

org.springframework.web.servlet.FlashMapManager=org.springframework.web.servlet.support.SessionFlashMapManager

4. Controller注解

4.1 类注解

• @Controller(由Spring识别Handler实例)

• @RequestMapping(value=, method=, params=)

4.2 方法注解

• @RequestMapping(value=, method=, params=)

• @PathVariable，配合占位符{parameter}

• @RequestParam(value=, required=, defaultValue=)

• @CookieValue(value=, required=, defaultValue=)

• @RequestHeader(value=, required=, defaultValue=)

5. 封装入参

• HttpServletRequest, WebRequest, ServletRequest的InputStream / Reader

• HttpServeltResponse, ServletResponse的OutputStream / Writer

6. 请求信息和对象的转换

6.1 基本

• HttpMessageConverter<T>

• 使用@RequestBody / @ResponseBody；使用HttpEntity<T> / ResponseEntity<T>

• Spring根据HTTP报文头部的Accept指定的MIME类型，查找匹配的HttpMessageConverter

• Spring MVC默认装配AnnotationMethodHandlerAdapter，调用HttpMessageConverter

• mvc命名空间的<mvc:annotation-driven/>标签会创建并注册一个默认的DefaultAnnotationHandlerMapping和一个AnnotationMethodHandlerAdapter实例，如果上下文中存在自定义的对应组件bean，则覆盖默认配置

6.2 样例

• app-servlet.xml

<bean id="handlerMapping" class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping">
    <property name="alwaysUseFullPath" value="true"/>
    <property name="interceptors">
        <list>
            <ref bean="monitorInterceptor"/>
            <ref bean="commonOutLogInterceptor"/>
            <ref bean="serverTraceInterceptor"/>
        </list>        
    </property>
</bean>

<bean id="handlerAdapter" class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter">
    <property name="messageConverters">
        <list>
            <bean class="org.springframework.http.converter.ByteArrayHttpMessageConverter"/>
            <bean class="org.springframework.http.converter.StringHttpMessageConverter">
                <property name="writeAcceptCharset" value="false"/>
            </bean>
            <bean class="org.springframework.http.converter.xml.SourceHttpMessageConverter"/>
            <bean class="org.springframework.http.converter.xml.XmlAwareFormHttpMessageConverter"/>
            <bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
                <property name="supportedMediaTypes">
                    <list>
                        <bean class="org.springframework.http.MediaType">
                            <constructor-arg value="text"/>
                            <constructor-arg value="json"/>
                            <constructor-arg>
                                <map>  
                                    <entry key="charset" value="UTF-8" />  
                                </map>
                            </constructor-arg>
                        </bean>
                    </list>
                </property>
            </bean>
        </list>
    </property>
</bean>

7. 处理模型数据

• Spring MVC在调用方法前会创建一个隐含的模型对象

• ModelAndView：返回值类型为ModelAndView时，方法体通过该对象添加模型数据

• @ModelAttribute：入参对象添加到数据模型中

• Map和Model：入参为org.springframework.ui.Model、org.springframework.ui.ModelMap或java.util.Map时，处理方法返回时，Map中的数据会自动添加到模型中

• @SessionAttributes：将模型中的某个属性暂存到HttpSession中，以便多个请求共享

8. 数据绑定

8.1 基本

• Spring MVC将ServletRequest对象及处理方法的入参实例传递给DataBinder；

• DataBinder调用ConversionService组件进行数据类型转换、数据格式化等工作，将ServletRequest中的消息填充到入参对象中；

• 然后再调用Validator组件对已经绑定了请求消息数据的入参对象进行数据合法性校验，并最终生成绑定结果BindingResult对象，其中还包含相应的校验错误对象

• 抽取BindingResult中的入参对象及校验错误对象，赋给处理方法的相应入参

8.2 数据转换

• 例如：将请求信息中A类型参数转换并绑定到Controller对应的处理方法的B类型入参中

• 基于ConversionService接口，Spring将自动识别其实现类，用于入参类型转换，类似于C++中的自定义类型转换。例如，将http请求信息中的字符串格式参数转换为Controller对应方法中的类类型入参

• 可通过ConversionServiceFactoryBean的converters属性注册自定义转换器。可接受Converter，ConverterFacotory，GenericConverter或ConditionalConverterFactory的实现类，并统一封装到一个ConversionService的实例（即GenericConversionService）中

<bean id="conversionService" class="org.springframework.context.support.ConversionServiceFactoryBean">
    <property name="converters">
        <list>
            <bean class="MyConverters" />
        </list>
    </property>
</bean>

• <mvc:annotation-driven/>标签还会注册一个默认的ConversionService，即FormattingConversionServiceFactoryBean

8.3 数据格式化

• 例如：将请求信息中字符串类型参数转换并绑定到Controller对应的处理方法入参中的Date类型属性中

• 格式化框架定义了Formatter<T>接口，扩展于Printer<T>和Parser<T>接口

• Srping提供AnnotationFormatterFactory<A extends Annotation>接口及两个实现类：NumberFormatAnnotationFormatterFactory和JodaDateTimeFormatAnnotationFormatterFactory

• 在入参类属性上使用注解：@DateTimeFormat，@NumberFormat

• Spring通过<mvc:annotation-driven/>标签创建FormattingConversionServiceFactoryBean作为FormattingConversionService的实例，自动装配NumberFormatAnnotationFormatterFactory和JodaDateTimeFormatAnnotationFormatterFactory

8.4 数据验证

• <mvc:annotation-driven/>标签会默认装配LocalValidatorFactoryBean，实现了Spring的Validator接口，通过在入参上标注@Valid注解即可让Spring在完成数据绑定后执行数据校验

• @Valid注解标注的入参和其后的BindingResult或Errors入参成对出现，后者保存前者的校验结果

• 校验结果也保存在MVC的隐含模型中

• 样例

public Class User {
    private String userId;

    @Pattern(regexp="w{4,30}")
    private String userName;

    @Length(min=2, max=100)
    private String nickName;

    @Past
    @DateTimeFormat(pattern = "yyyy-MM-dd")
    private Date birthday;

    @DecimalMin(value = "1000.00")
    @DecimalMax(value = "10000.00")
    @NumberFormat(pattern = "#,###.##")
    pirvate Long salary;
}


@RequestMapping(value = "/handle")
public void handle(@Valid User uer, BindingResult bindingResult) {
    //do something
}

9. 视图解析

9.1 基本

• 视图对象是一个bean，由视图解析器负责实例化。

• 不同的视图实现技术对应于不同的View实现类

• 所有的视图解析器都实现了ViewResolver接口

9.2 样例

• app-servlet.xml

<!-- For multipart encoding support -->
<bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver">
    <property name="maxUploadSize" value="209715200"/>
</bean>

<bean id="beanNameResolver" class="org.springframework.web.servlet.view.BeanNameViewResolver"/>

<!--VM模板文件解析 -->
<bean id="viewResolver" class="org.springframework.web.servlet.view.velocity.VelocityViewResolver">
    <property name="cache" value="true" />
    <property name="prefix" value="" />
    <property name="suffix" value=".vm" />
    <property name="contentType">
        <value>text/html; charset=UTF-8</value>
    </property>
    <property name="toolboxConfigLocation" value="/WEB-INF/toolbox.xml"/>
</bean>

<bean id="velocityConfig" class="org.springframework.web.servlet.view.velocity.VelocityConfigurer">
    <property name="resourceLoaderPath" value="/WEB-INF/vm/" />
    <property name="velocityPropertiesMap">
        <props>
            <prop key="input.encoding">UTF-8</prop>
            <prop key="output.encoding">UTF-8</prop>
            <prop key="velocimacro.library"></prop>
            <prop key="velocimacro.library.autoreload">true</prop>
            <prop key="directive.foreach.counter.name">loopCursor</prop>
            <prop key="directive.foreach.counter.initial.value">0</prop>
        </props>
    </property>
</bean>

10. 静态资源处理

• 需要对项目中的图片、html静态资源等单独处理

• 配置<mvc:default-servlet-handler>后，会装配一个DefaultServletHttpRequestHandler，对静态资源做检查

• 配置<mvc:resources/>，允许对静态资源文件路径作映射，并提供文件在浏览器端的缓存控制，例如

<mvc:resources mapping="/resources/**" location="/,classpath:/META-INF/publicResources" />

11. 拦截器

11.1 基本

• DispatcherServlet将请求交给处理器映射(HandlerMapping)，找到对应的HandlerExecutionChain

• 找到对应的HandlerExecutionChain包含若干HandlerInterceptor，和一个Handler

• HandlerInterceptor接口：

public interface HandlerInterceptor {

  boolean preHandle (HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception;

  void postHandle (HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception;

  void afterCompletion (HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception;
}

11.2 样例

• app-servlet.xml:

<mvc:interceptors>
    <mvc:interceptor>
      <mvc:mapping path="/api/**" />
      <bean class="outfox.ynote.webserver.web.HttpsInterceptor" />
    </mvc:interceptor>
</mvc:interceptors>

12. 异常处理

12.1 基本

• Spring MVC通过HandlerExceptionResolver处理异常

• HandlerExceptionResolver接口：

public interface HandlerExceptionResolver {
  ModelAndView resolveException (HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex);
}

• Spring MVC默认装配了DefaultHandlerExceptionResolver

• Spring MVC默认注册了AnnotationMethodHandlerExceptionResolver，允许通过@ExceptionHandler指定处理特定异常

12.2 样例

• web.xml

<web-app>
    <!-- 对各种异常和错误，交由ErrorController处理 -->
    <error-page>
        <error-code>404</error-code>
        <location>/error</location>
    </error-page>
    <error-page>
        <error-code>403</error-code>
        <location>/error</location>
    </error-page>
    <error-page>
        <exception-type>java.lang.Throwable</exception-type>
        <location>/error</location>
    </error-page>
</web-app>