Java Spring - 使用其他方式設定DispatcherServlet及ContextLoaderListener

•  透過其他方式set up DispatcherServlet and ContextLoaderListener
• 可能需要額外的Servlet、filter
• 需要對DispatcherServlet做額外config
• 自行定義個DispatcherServlet configuration
• 除了以下三種必須被override的method以外，其實還有更多可以被override的method
• getRootConfigClasses
• getServletConfigClasses
• getServletMappings

• 如：
• customizeRegistration()
• 當DispatcherServlet註冊到Servlet container後，就會呼叫customizeRegistration，並將Servlet註冊以後得到的Registration.Dynamic 傳遞進去。透過override此method，可以對DispatcherServlet進行額外config

@Override
protected void customizeRegistration(Dynamic registration) {
 registration.setMultipartConfig(
  new MultipartConfigElement("/tmp/spittr/uploads")); //設定暫存目錄
}

• 透過setLoadOnStartup()設定load-on-startup優先權
• 透過setInitParameter()設定初始化parameter
• 透過setMultipartConfig() config Servlet3.0對multipart的support
• Adding additional Servlet & Filter
• AbstractAnnotationConfigDispatcherServletInitializer會自行create DispatcherServlet和ContextLoaderListener.
• 問：如果想要建立Servlet、Filter及Listener時
• 使用Java的initializer可以定義任意數量的initializer classes。因此如果想要註冊其他component，則只需create一個新的initializer
• 最簡單的方法: implement Spring WebApplicationInitializer interface

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRegistration.Dynamic;
import org.springframework.web.WebApplicationInitializer;
import com.myapp.MyServlet;

public class MyServletInitializer implements WebApplicationInitializer {

    @Override
    public void onStartup(ServletContext servletContext) throws ServletException {
        Dynamic myServlet = servletContext.addServlet("myServlet", MyServlet.class); // 註冊servlet
        myServlet.addMapping("/custom/**"); // mapping servlet
    }
}

• 也可以註冊Listener & Filter

@Override
public void onStartup(ServletContext servletContext) throws ServletException {
 javax.servlet.FilterRegistration.Dynamic filter = servletContext.addFilter("myFilter", MyFilter.class); // 註冊filter
 filter.addMappingForUrlPatterns(null, false, "/custom/*"); // mapping servlet
}

• 若只是register Filter，且此filter會mapping至DispatcherServlet，則AbstractAnnotationConfigDispatcherServletInitializer提供一個簡單override的方法

@Override
protected Filter[] getServletFilters() {
 return new Filter[] {
  new MyFilter() // 不需要特別mapping，因為override這個method的所有return filter都會mapping到DispatcherServlet內
 };
}

• 傳統使用web.xml declare DispatcherServlet

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
      http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
  <context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>/WEB-INF/spring/root-context.xml</param-value>
  </context-param>
  <listener>
    <listener-class>
      org.springframework.web.context.ContextLoaderListener</listener-class>
  </listener>
  <servlet>
    <servlet-name>appServlet</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>appServlet</servlet-name>
    <url-pattern>/</url-pattern>
  </servlet-mapping>
</web-app>

• context-param: 設定root context config file
• listener-class: register ContextLoader Listener
• servlet: register Dispatcher servlet
• ContextLoaderListener& DispatcherServlet都有各自的Spring application context
• ContextLoaderListener會從/WEB-INF/spring/root-context.xml load bean definition
• DispatcherServlet會根據Servlet名字找到文件，因此會從/WEB-INF/appServlet-context.xml file中load application context
• 也可以自行指定config location

<servlet>
  <servlet-name>appServlet</servlet-name>
  <servlet-class>
    org.springframework.web.servlet.DispatcherServlet
  </servlet-class>
  <init-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>
      /WEB-INF/spring/appServlet/servlet-context.xml
    </param-value>
  </init-param>
  <load-on-startup>1</load-on-startup>
</servlet>

• 要在Spring MVC中使用基於Java的配置，需要告訴ContextLoaderListener及DispatcherServlet使用AnnotationConfigWebApplicationContext，這是一個WebApplicationContext的implement class，他會load Java config class，而不是使用XML
• 方法：設定contextClass context parameter
• DispatcherServlet的initial parameters
• 以下範例使用基於Java的Spring configuration 

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5"
  xmlns="http://java.sun.com/xml/ns/javaee"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://java.sun.com/xml/ns/javaee
      http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
  <context-param>
    <param-name>contextClass</param-name>
    <param-value>org.springframework.web.context.support.AnnotationConfigWebApplicationContext //使用Java config
  </param-value>
</context-param>
<context-param>
  <param-name>contextConfigLocation</param-name>
  <param-value>com.habuma.spitter.config.RootConfig</param-value>
 </context-param>//指定root config class
<listener>
  <listener-class>
    org.springframework.web.context.ContextLoaderListener
  </listener-class>
</listener>
<servlet>
  <servlet-name>appServlet</servlet-name>
  <servlet-class>
    org.springframework.web.servlet.DispatcherServlet
  </servlet-class>
  <init-param>
    <param-name>contextClass</param-name>
    <param-value>org.springframework.web.context.support.AnnotationConfigWebApplicationContext//使用Java config

      </param-value>
    </init-param>
    <init-param>
      <param-name>contextConfigLocation</param-name>
      <param-value> // 指定DispatcherServlet config
        com.habuma.spitter.config.WebConfigConfig
      </param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>appServlet</servlet-name>
    <url-pattern>/</url-pattern>
  </servlet-mapping>
</web-app>