DispatcherServlet和ContextLoaderListener，还有spring+servlet3.0 无web.xml启动问题

上篇提到：

关于spring +springmvc中两个spring应用上下文（DispatcherServlet和ContextLoaderListener）的问题，挺让人迷糊的。

他们都是加载Bean。简单粗暴的理解就是spring的bean 用ContextLoaderListener加载，springmvc的用DispatcherServlet 加载。

《spring in action》一书中给了点解释，【我们希望DispatcherServlet 加载包含Web组件的bean，如控制器，视图解析器及处理映射，而ContextLoaderListener需要加载应用中的其他bean。这些bean通常是驱动应用后端的中间层和数据层组件】。

按道理说，反正都是bean的配置，所有的配置都配置到一起也是可以的？其实不然。

参看了网上几篇博客，解释的有的还算正常，有的就是可能是猜测的，当然也可能是spring版本不同导致的。

【Spring启动过程分析】（1）启动流程简介 http://blog.csdn.net/moshenglv/article/details/53517343

DispatcherServlet与ContextLoaderListener的对比 http://blog.csdn.net/sadfishsc/article/details/51027873

SpringMVC DispatcherServlet 初始化过程 http://blog.csdn.net/sadfishsc/article/details/51027809

SpringWeb ContextLoaderListener 初始化过程 http://blog.csdn.net/sadfishsc/article/details/51027840

Servlet 3 + Spring MVC零配置：去除所有xml http://blog.csdn.net/xiao__gui/article/details/46803193

如果想真正深入了解，估计得看源码了。

个人觉得，还是分开好。否则可能引起不必要的错误。那如果两个都配置了，都加载了所有的bean呢，会不会有bean重复加载的问题？

个人亲自写代码实验了一下，

1. 配置web.xml方式启动

为方便，先把普通的bean配置（service层，domain层，dao层，数据库等）成为application.xml， springmvc相关的bean配置（controller层，视图解析器等），称为springmvc.xml，

springmvc.xml中配置是：

  <mvc:annotation-driven /> 
   <mvc:default-servlet-handler/>
   <mvc:resources location="/WEB-INF/pages/" mapping="/pages/**"/>  
   <!-- 扫描controller（controller层注入） -->
   <context:component-scan base-package="com.zj.controller"/> 
   <!-- 对模型视图添加前后缀 -->
   <bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver" p:prefix="/WEB-INF/pages/" p:suffix=".jsp"/>

如果正常配置，应该是:

<context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>classpath:application.xml</param-value>
    </context-param>
<listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
    </listener>
<!-- springMVC核心配置 -->
    <servlet>
        <servlet-name>dispatcherServlet</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>classpath:springmvc/springmvc.xml</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>
    
    <!-- 拦截设置 -->
    <servlet-mapping>
        <servlet-name>dispatcherServlet</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>

UserServiceImpl------------------------------- 和 UserController==================== 是我写在构造函数中的System.out.println 输出的。

如果配置成这样呢：把正常的springmvc.xml 和 application.xml 放一起，让ContextLoaderListener 加载。DispatcherServlet 加载一个空的springmvc配置springmvc-empty.xml，

 <context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>classpath:application.xml,classpath:springmvc/springmvc.xml</param-value>
    </context-param>
   <servlet>
        <servlet-name>dispatcherServlet</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>classpath:springmvc/springmvc-empty.xml</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>

结果发现，还是可以正常加载controller的bean以及视图解析等，只是controller Bean加载的顺序变提前了。。不过应用访问和正常情况没啥两样。

所以，不像网上有些人说的controller 、视图解析器一定要DispatcherServlet加载。不过拦截器等东西，我没试验。

================

如果下面这样配置呢：

    <!-- 读取spring配置文件 -->
    <context-param>
        <param-name>contextConfigLocation</param-name>
        <param-value>classpath:application.xml,classpath:springmvc/springmvc.xml</param-value>
    </context-param>

 <servlet>
        <servlet-name>dispatcherServlet</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>classpath:springmvc/springmvc.xml</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet

可以发现 controller的bean确实加载了两遍。

不过web应用可以正常使用。

同理，如果把application.xml 也在DispatcherServlet里在配置一遍，那service等bean也是加载两遍。

===========

结论：配置web.xml 方式启动，最好还是最好把application.xml 配置和 springmvc.xml 配置分开，分别用ContextLoadListener加载和 DispatcherServlet加载。

2. spring +servlet3.0 无web.xml方式启动

我用的是继承WebApplicationInitializer ，通过OnStartup 启动的方式。

我用的Tomact 7.0环境，发现如果web.xml 中存在Servlet的那些配置，就不会按照WebApplicationInitializer 启动，除非web.xml 中不要Servlet的那些配置，几乎一个空的web.xml。

这个没有深究，估计和 Servlet3.0启动方式顺序有关吧。

第一种写法:

public class MyWebAppInitializer implements WebApplicationInitializer {

    public void onStartup(ServletContext servletContext) throws ServletException {
        System.out.println("startUP=++++=+++++++++++++++++++++++++++++");
         servletContext.setInitParameter("contextConfigLocation", "classpath:application.xml,classpath:springmvc/springmvc.xml");  
        // servletContext.setInitParameter("contextConfigLocation", "classpath:application.xml"); 
        ServletRegistration.Dynamic registration = servletContext.addServlet("dispatcher", new DispatcherServlet());  
            
        registration.setLoadOnStartup(1);  
        //registration.addMapping("/");  
        registration.addMapping(new String[]{"*.html"});  
        registration.setInitParameter("contextConfigLocation", "classpath:springmvc/springmvc.xml");  
        servletContext.addListener(new ContextLoaderListener( ));
      
        
    }
}

运行结果：

结果：可以正常访问。不过第一次访问的时候，会再出现一次UserController Bean的初始化。

代码改一下， servletContext.setInitParameter("contextConfigLocation", "classpath:application.xml,classpath:springmvc/springmvc.xml");

改成 servletContext.setInitParameter("contextConfigLocation", "classpath:application.xml");

结果：可以正常访问。 UserController的bean 第一次访问的时候才生成，有点懒加载的意思。

=========

如果 servletContext.setInitParameter("contextConfigLocation", "classpath:application.xml,classpath:springmvc/springmvc.xml");

把 //registration.setInitParameter("contextConfigLocation", "classpath:springmvc/springmvc.xml"); 注释掉。

会出现什么情况呢。

结果：可以正常启动。但是不能正常访问。 DispatcherServlet 会找默认的配置。找不到，就发飙了。

第二种写法：

public void onStartup(ServletContext servletContext) throws ServletException {
        System.out.println("startUP=++++=+++++++++++++++++++++++++++++");
        // servletContext.setInitParameter("contextConfigLocation", "classpath:application.xml,classpath:springmvc/springmvc.xml");  
        // servletContext.addListener(new ContextLoaderListener()); 
        // AnnotationConfigWebApplicationContext rootContext = new AnnotationConfigWebApplicationContext();  
        XmlWebApplicationContext rootContext = new XmlWebApplicationContext();
        List<String> locationList = new ArrayList<String>();
        locationList.add("classpath:application.xml");
        //locationList.add("classpath:springmvc/springmvc.xml");
        rootContext.setConfigLocations((String[])locationList.toArray(new String[locationList.size()]));
//        ContextLoader contextLoader = new ContextLoader(rootContext);
//        contextLoader.initWebApplicationContext(servletContext);
        servletContext.addListener(new ContextLoaderListener( rootContext));
            
        //AnnotationConfigWebApplicationContext webContext = new AnnotationConfigWebApplicationContext();  
       // webContext.register(WebConfig.class);
        ServletRegistration.Dynamic registration = servletContext.addServlet("dispatcher", new DispatcherServlet());  
            
        registration.setLoadOnStartup(1);  
        //registration.addMapping("/");  
        registration.addMapping(new String[]{"*.html"});  
        registration.setInitParameter("contextConfigLocation", "classpath:springmvc/springmvc.xml");  
        //servletContext.addListener(new ContextLoaderListener( ));
      
        
    }

结果：

信息: Spring WebApplicationInitializers detected on classpath: [com.zj.controller.MyWebAppInitializer@5794495e]
startUP=++++=+++++++++++++++++++++++++++++
log4j:WARN No appenders could be found for logger (org.springframework.web.context.support.StandardServletEnvironment).
log4j:WARN Please initialize the log4j system properly.
四月 13, 2017 1:38:20 下午 org.apache.catalina.core.ApplicationContext log
信息: Initializing Spring root WebApplicationContext
UserServiceImpl------------------------调用初始化方法....
四月 13, 2017 1:38:21 下午 org.apache.coyote.AbstractProtocolHandler start
信息: Starting ProtocolHandler ["http-bio-8080"]
四月 13, 2017 1:38:21 下午 org.apache.coyote.AbstractProtocolHandler start
信息: Starting ProtocolHandler ["ajp-bio-8009"]
四月 13, 2017 1:38:21 下午 org.apache.catalina.startup.Catalina start
信息: Server startup in 4462 ms
四月 13, 2017 1:38:31 下午 org.apache.catalina.core.ApplicationContext log
信息: Initializing Spring FrameworkServlet 'dispatcher'
UserController=====================
3333333333333333333333333333

结果发现：可以正常访问，第一次访问加载UserController bean

如果： ServletRegistration.Dynamic registration = servletContext.addServlet("dispatcher", new DispatcherServlet());
改成 ServletRegistration.Dynamic registration = servletContext.addServlet("dispatcher", new DispatcherServlet(rootContext));

结果：可以正常启动，但是无法正常访问。提示 The requested resource () is not available.，不知道咋回事儿。

=============

如果代码改成这样：

public void onStartup(ServletContext servletContext) throws ServletException {
        System.out.println("startUP=++++=+++++++++++++++++++++++++++++");
        // servletContext.setInitParameter("contextConfigLocation", "classpath:application.xml,classpath:springmvc/springmvc.xml");  
        // servletContext.addListener(new ContextLoaderListener()); 
        // AnnotationConfigWebApplicationContext rootContext = new AnnotationConfigWebApplicationContext();  
        XmlWebApplicationContext rootContext = new XmlWebApplicationContext();
        List<String> locationList = new ArrayList<String>();
        locationList.add("classpath:application.xml");
        locationList.add("classpath:springmvc/springmvc.xml");
        rootContext.setConfigLocations((String[])locationList.toArray(new String[locationList.size()]));
//        ContextLoader contextLoader = new ContextLoader(rootContext);
//        contextLoader.initWebApplicationContext(servletContext);
        servletContext.addListener(new ContextLoaderListener( rootContext));
            
        //AnnotationConfigWebApplicationContext webContext = new AnnotationConfigWebApplicationContext();  
       // webContext.register(WebConfig.class);
        ServletRegistration.Dynamic registration = servletContext.addServlet("dispatcher", new DispatcherServlet(rootContext));  
            
        registration.setLoadOnStartup(1);  
        //registration.addMapping("/");  
        registration.addMapping(new String[]{"*.html"});  
        //registration.setInitParameter("contextConfigLocation", "classpath:springmvc/springmvc.xml");  
        //servletContext.addListener(new ContextLoaderListener( ));
      
        
    }

结果：正常启动，可以正常访问。controller bean提前加载。

信息: Spring WebApplicationInitializers detected on classpath: [com.zj.controller.MyWebAppInitializer@6710bb13]
startUP=++++=+++++++++++++++++++++++++++++
log4j:WARN No appenders could be found for logger (org.springframework.web.context.support.StandardServletEnvironment).
log4j:WARN Please initialize the log4j system properly.
四月 13, 2017 1:48:46 下午 org.apache.catalina.core.ApplicationContext log
信息: Initializing Spring root WebApplicationContext
UserServiceImpl------------------------调用初始化方法....
UserController=====================
四月 13, 2017 1:48:47 下午 org.apache.coyote.AbstractProtocolHandler start
信息: Starting ProtocolHandler ["http-bio-8080"]
四月 13, 2017 1:48:47 下午 org.apache.coyote.AbstractProtocolHandler start
信息: Starting ProtocolHandler ["ajp-bio-8009"]
四月 13, 2017 1:48:47 下午 org.apache.catalina.startup.Catalina start
信息: Server startup in 4797 ms
四月 13, 2017 1:49:02 下午 org.apache.catalina.core.ApplicationContext log
信息: Initializing Spring FrameworkServlet 'dispatcher'
3333333333333333333333333333

//代码也可以改成这样，自己写 ContextLoader  加载bean
public void onStartup(ServletContext servletContext) throws ServletException {
        System.out.println("startUP=++++=+++++++++++++++++++++++++++++");
        XmlWebApplicationContext rootContext = new XmlWebApplicationContext();
        List<String> locationList = new ArrayList<String>();
        locationList.add("classpath:application.xml");
        locationList.add("classpath:springmvc/springmvc.xml");
        rootContext.setConfigLocations((String[])locationList.toArray(new String[locationList.size()]));
        ContextLoader contextLoader = new ContextLoader(rootContext);
        contextLoader.initWebApplicationContext(servletContext);
        //servletContext.addListener(new ContextLoaderListener( rootContext));
        ServletRegistration.Dynamic registration = servletContext.addServlet("dispatcher", new DispatcherServlet(rootContext));  
            
        registration.setLoadOnStartup(1);  
        //registration.addMapping("/");  
        registration.addMapping(new String[]{"*.html"});  
        //registration.setInitParameter("contextConfigLocation", "classpath:springmvc/springmvc.xml");  
        //servletContext.addListener(new ContextLoaderListener( ));
      
        
    }

=============

或者采用注解方式。这里只给mvc配置采用了注解。

@Configuration  
@EnableWebMvc  
@ComponentScan(basePackages = "com.zj.controller")  
public class WebConfig {  
      
    @Bean  
    public InternalResourceViewResolver internalResourceViewResolver() {  
        InternalResourceViewResolver viewResolver = new InternalResourceViewResolver();  
        viewResolver.setPrefix("/WEB-INF/pages/");  
        viewResolver.setSuffix(".jsp");  
        return viewResolver;  
    }  
    
    public void configureDefaultServletHandling(final DefaultServletHandlerConfigurer configurer) {
        configurer.enable();
      }
}

    public void onStartup(ServletContext servletContext) throws ServletException {
        System.out.println("startUP=++++=+++++++++++++++++++++++++++++");
    
        XmlWebApplicationContext rootContext = new XmlWebApplicationContext();
        List<String> locationList = new ArrayList<String>();
        locationList.add("classpath:application.xml");
        //locationList.add("classpath:springmvc/springmvc.xml");
        rootContext.setConfigLocations((String[])locationList.toArray(new String[locationList.size()]));
        ContextLoader contextLoader = new ContextLoader(rootContext);
        contextLoader.initWebApplicationContext(servletContext);
         
        AnnotationConfigWebApplicationContext webContext = new AnnotationConfigWebApplicationContext();  
        webContext.register(WebConfig.class);
        ServletRegistration.Dynamic registration = servletContext.addServlet("dispatcher", new DispatcherServlet(webContext));  
            
        registration.setLoadOnStartup(1);  
        //registration.addMapping("/");  
        registration.addMapping(new String[]{"*.html"});  
        //registration.setInitParameter("contextConfigLocation", "classpath:springmvc/springmvc.xml");  
        //servletContext.addListener(new ContextLoaderListener( ));
      
        
    }

结果：正常启动，正常访问。controller bean 延迟加载。

信息: Spring WebApplicationInitializers detected on classpath: [com.zj.controller.MyWebAppInitializer@5a278fe0]
startUP=++++=+++++++++++++++++++++++++++++
log4j:WARN No appenders could be found for logger (org.springframework.web.context.support.StandardServletEnvironment).
log4j:WARN Please initialize the log4j system properly.
四月 13, 2017 1:58:09 下午 org.apache.catalina.core.ApplicationContext log
信息: Initializing Spring root WebApplicationContext
UserServiceImpl------------------------调用初始化方法....
四月 13, 2017 1:58:09 下午 org.apache.coyote.AbstractProtocolHandler start
信息: Starting ProtocolHandler ["http-bio-8080"]
四月 13, 2017 1:58:09 下午 org.apache.coyote.AbstractProtocolHandler start
信息: Starting ProtocolHandler ["ajp-bio-8009"]
四月 13, 2017 1:58:09 下午 org.apache.catalina.startup.Catalina start
信息: Server startup in 4644 ms
四月 13, 2017 1:58:18 下午 org.apache.catalina.core.ApplicationContext log
信息: Initializing Spring FrameworkServlet 'dispatcher'
UserController=====================
3333333333333333333333333333

综上： springmvc配置和普通的bean的配置分开加载，可以延迟加载controller 的Bean。

不过我感觉很奇怪，<load-on-startup>1</load-on-startup>应该是启动时候立即加载。 0 及0 以上应该是容器启动时候加载，负数为懒加载，

在web.xml起作用，但是在代码方式registration.setLoadOnStartup(1) 为啥还是第一次访问才加载呢？是我版本问题，还是代码问题呢？

posted on 2017-04-13 09:25 aji2014 阅读(356) 评论(0) 编辑收藏举报

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aji2014

DispatcherServlet和ContextLoaderListener，还有spring+servlet3.0 无web.xml启动问题

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