I.Spring源码分析之web入口

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee 
	http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
	<display-name>Archetype Created Web Application</display-name>
	<!-- 初始化 -->
	<context-param>
		<param-name>contextConfigLocation</param-name>
		<param-value>classpath:applicationContext.xml</param-value>
	</context-param>
	<!-- 监听器 -->
	<listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
    </listener>
	<!-- 定义struts2的核心filter -->
	<filter>
		<filter-name>struts2</filter-name>
		<filter-class>
			org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter
		</filter-class>
	</filter>
	<!-- 让struts定义的核心filter拦截所有请求 -->
	<filter-mapping>
		<filter-name>struts2</filter-name>
		<url-pattern>*.do</url-pattern>
	</filter-mapping>

	<filter>
		<filter-name>encodingFilter</filter-name>
		<filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
		<init-param>
			<param-name>encoding</param-name>
			<param-value>UTF-8</param-value>
		</init-param>
	</filter>

	<!-- druid数据库监控 -->
	<filter>
		<filter-name>DruidWebStatFilter</filter-name>
		<filter-class>com.alibaba.druid.support.http.WebStatFilter</filter-class>
		<init-param>
			<param-name>exclusions</param-name>
			<param-value>*.js,*.gif,*.jpg,*.png,*.css,*.ico,/druid/*</param-value>
		</init-param>
	</filter>
	<filter-mapping>
		<filter-name>DruidWebStatFilter</filter-name>
		<url-pattern>/*</url-pattern>
	</filter-mapping>

	<servlet>
		<servlet-name>DruidStatView</servlet-name>
		<servlet-class>com.alibaba.druid.support.http.StatViewServlet</servlet-class>
	</servlet>
	<servlet-mapping>
		<servlet-name>DruidStatView</servlet-name>
		<url-pattern>/druid/*</url-pattern>
	</servlet-mapping>

	<!-- 项目欢迎界面 -->
	<welcome-file-list>
		<welcome-file>index.jsp</welcome-file>
	</welcome-file-list>
	<error-page>
		<error-code>404</error-code>
		<location>/404.html</location>
	</error-page>
	<error-page>
		<error-code>500</error-code>
		<location>/500.html</location>
	</error-page>
	<error-page>
		<error-code>502</error-code>
		<location>/502.html</location>
	</error-page>
	<error-page>
		<error-code>504</error-code>
		<location>/504.html</location>
	</error-page>
</web-app>

Spring 的入口 org.springframework.web.context.ContextLoaderListener

这个类继承了 org.springframework.web.context.ContextLoader

实现了javax.servlet.ServletContextListener接口

在ContextLoader中有一个静态语句块

static {
		// Load default strategy implementations from properties file.
		// This is currently strictly internal and not meant to be customized
		// by application developers.
		try {
			ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, ContextLoader.class);
			defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
		}
		catch (IOException ex) {
			throw new IllegalStateException("Could not load 'ContextLoader.properties': " + ex.getMessage());
		}
	}

注意这个private static final String DEFAULT_STRATEGIES_PATH = "ContextLoader.properties";

我找了一下这个文件

是在ContextLoader.class一个目录下

来看看这个文件

# Default WebApplicationContext implementation class for ContextLoader.
# Used as fallback when no explicit context implementation has been specified as context-param.
# Not meant to be customized by application developers.

org.springframework.web.context.WebApplicationContext=org.springframework.web.context.support.XmlWebApplicationContext

注释:默认的WebApplicationContext接口的实现类

在上面的静态语句块的作用是把这个文件读到Properties(defaultStrategies)对象里

ContextLoaderListener实现了ServletContextListener接口

那么启动服务的入口是这个方法contextInitialized

ContextLoader#initWebApplicationContext(ServletContext servletContext)

--》configureAndRefreshWebApplicationContext(cwac, servletContext);

注意看这一行代码String configLocationParam = sc.getInitParameter(CONFIG_LOCATION_PARAM);

public static final String CONFIG_LOCATION_PARAM = "contextConfigLocation";

这个就是获取web.xml中的内容

<context-param>
		<param-name>contextConfigLocation</param-name>
		<param-value>classpath:applicationContext.xml</param-value>
	</context-param>

获取配置文件的内容找到spring文件的路径

接下来看wac.setConfigLocation(configLocationParam);

我们直接进这2个方法发现了一个严重的问题 2个方法的实现里面都是直接抛出异常的！！！

说明这个是被禁止调用的？

我再看了下ConfigurableWebApplicationContext 这是一个接口

再回来看到了ConfigurableWebApplicationContext cwac = (ConfigurableWebApplicationContext) this.context; 这个

接着向上找 this.context = createWebApplicationContext(servletContext);

也就是我们找到了创建 wac具体实例的地方

Class<?> contextClass = determineContextClass(sc);

protected Class<?> determineContextClass(ServletContext servletContext) {
		String contextClassName = servletContext.getInitParameter(CONTEXT_CLASS_PARAM);
		if (contextClassName != null) {
			try {
				return ClassUtils.forName(contextClassName, ClassUtils.getDefaultClassLoader());
			}
			catch (ClassNotFoundException ex) {
				throw new ApplicationContextException(
						"Failed to load custom context class [" + contextClassName + "]", ex);
			}
		}
		else {
			contextClassName = defaultStrategies.getProperty(WebApplicationContext.class.getName());
			try {
				return ClassUtils.forName(contextClassName, ContextLoader.class.getClassLoader());
			}
			catch (ClassNotFoundException ex) {
				throw new ApplicationContextException(
						"Failed to load default context class [" + contextClassName + "]", ex);
			}
		}
	}

最重要的是这一行代码：

contextClassName = defaultStrategies.getProperty(WebApplicationContext.class.getName());

我们上面提到在静态语句块里面解析了ContextLoader.properties

得到了

org.springframework.web.context.WebApplicationContext=org.springframework.web.context.support.XmlWebApplicationContext

根据代码我们知道XmlWebApplicationContext就是

wac.setConfigLocation(configLocationParam);

中wac的实例

果然我们在它的父类的父类(AbstractRefreshableConfigApplicationContext)中找到了setConfigLocation方法的实现

看里面的实现是把路径解析到configLocations中

AbstractApplicationContext#refresh()

开始加载解析和加载相关的文件

来源：oschina

链接：https://my.oschina.net/u/2347196/blog/516831

标签

Spring

ContextLoaderListener

contextConfigLocation