springmvc学习笔记 1 --- helloworld

步骤：

加入 jar – 包

commons-logging-1.1.3.jar –
spring-aop-4.0.0.RELEASE.jar –
spring-beans-4.0.0.RELEASE.jar –
spring-context-4.0.0.RELEASE.jar –
spring-core-4.0.0.RELEASE.jar –
spring-expression-4.0.0.RELEASE.jar –
spring-web-4.0.0.RELEASE.jar –
spring-webmvc-4.0.0.RELEASE.jar

在 web.xml 中配置 DispatcherServlet –

[code=java]

<!-- 配置DispatcherServlet -->
<servlet>
<servlet-name>springDispatcherServlet</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<!-- 配置DispatcherServlet的初始化参数：配置springmvc 配置文件的位置和名称 -->
<init-param>
<param-name>contextConfigLocation</param-name>
<param-value>classpath:springmvc.xml</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>


<!-- Map all requests to the DispatcherServlet for handling -->
<servlet-mapping>
<servlet-name>springDispatcherServlet</servlet-name>
<url-pattern>/</url-pattern>
</servlet-mapping>

[/code]

加入 Spring MVC 的配置文件 –

编写处理请求的处理器，并标识为处理器 –

编写视图

思考：<load-on-startup>1</load-on-startup>，那么这个配置有什么作用呢？

贴一段英文原汁原味的解释如下：
Servlet specification:
The load-on-startup element indicates that this servlet should be loaded (instantiated and have its init() called) on the startup of the web application. The optional contents of these element must be an integer indicating the order in which the servlet should be loaded. If the value is a negative integer, or the element is not present, the container is free to load the servlet whenever it chooses.   If the value is a positive integer or 0, the container must load and initialize the servlet as the application is deployed. The container must guarantee that servlets marked with lower integers are loaded before servlets marked with higher integers. The container may choose the order of loading of servlets with the same load-on-start-up value.

翻译过来的意思大致如下：
1)load-on-startup元素标记容器是否在启动的时候就加载这个servlet(实例化并调用其init()方法)。

2)它的值必须是一个整数，表示servlet应该被载入的顺序

2)当值为0或者大于0时，表示容器在应用启动时就加载并初始化这个servlet；

3)当值小于0或者没有指定时，则可以由server容器自行决定何时load该servlet. 句中的it应该指的是container而不是servlet.

4)正数的值越小，该servlet的优先级越高，应用启动时就越先加载。

5)当值相同时，容器就会自己选择顺序来加载。

所以，<load-on-startup>x</load-on-startup>，中x的取值1，2，3，4，5代表的是优先级，而非启动延迟时间。