Spring DispatcherServlet 请求映射

在项目中，我们通常会在web.xml文件中配置一个DispatcherServlet进行请求转发

<servlet><servlet-name>springMVC</servlet-name><servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class><init-param><param-name>contextConfigLocation</param-name><param-value>classpath:spring/spring-mvc.xml</param-value></init-param><load-on-startup>1</load-on-startup><async-supported>true</async-supported>
</servlet>
<servlet-mapping><servlet-name>springMVC</servlet-name><url-pattern>/</url-pattern>
</servlet-mapping>

http://localhost:8080/demo/service/model/{modelId}/json

{modelId}在实际环境中替换为对应modelId的值

当有如上请求时，Controller的RequestMapping注解的value值为/service/model/{modelId}/json

修改DispatcherServlet的<url-pattern>的值为/service/*，此时Controller的RequestMapping注解的value值应该改为/model/{modelId}/json

dispatcherServlet对象在进行请求转发时，会将请求中的url与已知的url进行匹配，以便确定对应的Controller和Method。

如何确定已知的url呢？
dispatcherServlet对象初始化时会读取默认的配置文件({servlet-name}-servlet.xml)，当dispatcherServlet的<init-param>元素指定了contextConfigLocation参数，则会读取该参数中指定的配置文件而不再读取默认配置文件({servlet-name}-servlet.xml)，这些配置文件中会指定待扫描Controller的包名，这些Controller中指定的url会被这个dispatcherServlet对象进行请求转发时与接收的url进行比较。没有被扫描到的Controller，其指定的映射url不会被当前dispatcherServlet对象用于请求分发时的比较。

由于dispatcherServlet对象进行请求分发与其指定的配置文件中可扫描到的Controller有关，故不同的dispatcherServlet对象中允许不同的Controller拥有相同的映射url(这些Controller被不同的dispatcherServlet扫描)，而同一个dispatcherServlet对象中不允许有相同的映射url

例子：
web.xml

<servlet><servlet-name>springMVC</servlet-name><servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class><init-param><param-name>contextConfigLocation</param-name><param-value>classpath:spring/spring-mvc.xml</param-value></init-param><load-on-startup>1</load-on-startup><async-supported>true</async-supported>
</servlet>
<servlet-mapping><servlet-name>springMVC</servlet-name><url-pattern>/LoginController/*</url-pattern>
</servlet-mapping><servlet><servlet-name>sysCore</servlet-name><servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class><init-param><param-name>contextConfigLocation</param-name><param-value>classpath:spring/sys-core.xml</param-value></init-param><load-on-startup>2</load-on-startup><async-supported>true</async-supported>
</servlet>
<servlet-mapping><servlet-name>sysCore</servlet-name><url-pattern>/UserController/*</url-pattern>
</servlet-mapping>	

spring-mvc.xml

<context:component-scan base-package="com.example.controller" />

sys-core.xml

<context:component-scan base-package="com.example.sysCore.controller" />

com.example.controller.LoginController.java

@Controller
//@RequestMapping("/LoginController")
public class LoginController extends BaseController {
    @RequestMapping(value = "/intoLoginPage.web", method = {
    RequestMethod.GET})public ModelAndView intoLoginPage(HttpServletRequest req, HttpServletResponse resp) {
    log.info("<==============LoginController#intoLoginPage==============>");ModelAndView mav = new ModelAndView();mav.setViewName("/login");return mav;}
}

com.example.sysCore.controller.UserController.java

@Controller
//@RequestMapping("/UserController")
public class UserController extends BaseController {
    @RequestMapping(value = "/intoLoginPage.web", method = {
    RequestMethod.GET})public ModelAndView user() {
    log.info("<==============UserController#user==============>");ModelAndView mav = new ModelAndView();mav.setViewName("/login");return mav;}
}

Request URL

http://localhost:8080/demo/LoginController/intoLoginPage.web
http://localhost:8080/demo/UserController/intoLoginPage.web