[springMVC学习]1、springmvc设置spring配置文件

        我们给springmvc设置配置文件，实际上就是让某个类在tomcat启动时，自动的去读取配置文件，完成ioc容器的创建，完成初始化工作。在spring中，我们是手动new出来，但是在springMVC中就是通过配置了，配置文件路径后就会自己创建spring容器。

        DispathcerServlet是springMVC的核心，这个类用于所有请求的处理，分发等等，这个类非常的复杂，如果是第一次学springMVC，那么现在会用即可。该类的类图和功能如下

        DispatcherServlet为springMVC的核心控制器，用于请求的分发，本质还是一个Servlet，我们在web.xml中配置该Servlet，让其拦截所有请求。

    <servlet>
        <servlet-name>springConfig</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <load-on-startup>1</load-on-startup>
    </servlet>
    <servlet-mapping>
        <servlet-name>springConfig</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>

        我们在配置好DiapatcherServlet之后，需要配置spring的配置文件，将其传给DispathcerServlet。常见的有2种方式，一种是通过init-param进行设置，步骤如下：

        第一步先在src下面创建spring配置文件

        接下来就是通过init-param进行配置 

    <servlet>
        <servlet-name>springConfig</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>classpath:applicationContext.xml</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>
    <servlet-mapping>
        <servlet-name>springConfig</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>

        另外一种方式就是通过名称来进行配置，相对比较方便。

        配置之前，先来看下DiapatcherServlet的源代码，下面的代码为DiapatcherServlet类的父类的一部分

/**
 * Base servlet for Spring's web framework. Provides integration with
 * a Spring application context, in a JavaBean-based overall solution.
 *
 * <p>This class offers the following functionality:
 * <ul>
 * <li>Manages a {@link org.springframework.web.context.WebApplicationContext
 * WebApplicationContext} instance per servlet. The servlet's configuration is determined
 * by beans in the servlet's namespace.
 * <li>Publishes events on request processing, whether or not a request is
 * successfully handled.
 * </ul>
 *
 * <p>Subclasses must implement {@link #doService} to handle requests. Because this extends
 * {@link HttpServletBean} rather than HttpServlet directly, bean properties are
 * automatically mapped onto it. Subclasses can override {@link #initFrameworkServlet()}
 * for custom initialization.
 *
 * <p>Detects a "contextClass" parameter at the servlet init-param level,
 * falling back to the default context class,
 * {@link org.springframework.web.context.support.XmlWebApplicationContext
 * XmlWebApplicationContext}, if not found. Note that, with the default
 * {@code FrameworkServlet}, a custom context class needs to implement the
 * {@link org.springframework.web.context.ConfigurableWebApplicationContext
 * ConfigurableWebApplicationContext} SPI.
 *
 * <p>Accepts an optional "contextInitializerClasses" servlet init-param that
 * specifies one or more {@link org.springframework.context.ApplicationContextInitializer
 * ApplicationContextInitializer} classes. The managed web application context will be
 * delegated to these initializers, allowing for additional programmatic configuration,
 * e.g. adding property sources or activating profiles against the {@linkplain
 * org.springframework.context.ConfigurableApplicationContext#getEnvironment() context's
 * environment}. See also {@link org.springframework.web.context.ContextLoader} which
 * supports a "contextInitializerClasses" context-param with identical semantics for
 * the "root" web application context.
 *
 * <p>Passes a "contextConfigLocation" servlet init-param to the context instance,
 * parsing it into potentially multiple file paths which can be separated by any
 * number of commas and spaces, like "test-servlet.xml, myServlet.xml".
 * If not explicitly specified, the context implementation is supposed to build a
 * default location from the namespace of the servlet.
 *
 * <p>Note: In case of multiple config locations, later bean definitions will
 * override ones defined in earlier loaded files, at least when using Spring's
 * default ApplicationContext implementation. This can be leveraged to
 * deliberately override certain bean definitions via an extra XML file.
 *
 * <p>The default namespace is "'servlet-name'-servlet", e.g. "test-servlet" for a
 * servlet-name "test" (leading to a "/WEB-INF/test-servlet.xml" default location
 * with XmlWebApplicationContext). The namespace can also be set explicitly via
 * the "namespace" servlet init-param.
 *
 * <p>As of Spring 3.1, {@code FrameworkServlet} may now be injected with a web
 * application context, rather than creating its own internally. This is useful in Servlet
 * 3.0+ environments, which support programmatic registration of servlet instances. See
 * {@link #FrameworkServlet(WebApplicationContext)} Javadoc for details.
**/

         上面的注释就说明我们前面的第一种方式就是显示指定配置文件，当然，我们也可以不指定，默认就会在/WEB-INF/下寻找  xxx-servlet.xml的文件作为配置文件，xxx就是我们在web.xml中配置的DispatcherServlet的servlet-name

    <servlet>
        <servlet-name>springConfig</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <load-on-startup>1</load-on-startup>
    </servlet>
    <servlet-mapping>
        <servlet-name>springConfig</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>

         这里我们的servlet-name配置的是springConfig，那么当项目启动时，默认就会去读取springConfig-servlet.xml作为spring的配置文件，我们只需要在/WEB-INF/下创建该文件即可

         由于这个是springmvc了，所以我们在spring配置文件中加入以下的基本配置

    <!--开启注解驱动-->
    <mvc:annotation-driven/>
    <!--springmvc不能处理的交由tomcat处理-->
    <mvc:default-servlet-handler/>