前言
最近打算花点时间好好看看spring的源码,然而现在Spring的源码经过迭代的版本太多了,比较庞大,看起来比较累,所以准备从最初的版本(interface21)开始入手,仅用于学习,理解其设计思想,后续慢慢研究其每次版本变更的内容。。。
先从interface21的一个典型web工程例子看起,宠物诊所 - petclinic,因为该工程基本涵盖了Spring的APO、IOC、JDBC、Web MVC、事务、国际化、主题切换、参数校验等主要功能。。。
先从简单的走起,看下该web工程中, Log4j是如何加载的吧~~~~~~~
对应的web.xml配置
<context-param>
<param-name>webAppRootKey</param-name>
<param-value>petclinic.root</param-value>
</context-param> <context-param>
<param-name>log4jConfigLocation</param-name>
<param-value>/WEB-INF/classes/log4j.properties</param-value>
</context-param> <listener>
<listener-class>com.interface21.web.util.Log4jConfigListener</listener-class>
</listener>
执行时序图(看不清的话可以点击查看原图)
时序图中的各个步骤简要分析
执行的入口在Log4jConfigListener类的contextInitialized方法,由于Log4jConfigListener类实现了ServletContextListener接口,所以在Servlet容器(tomcat)启动时,会自动调用contextInitialized方法。
步骤描述:
- 进入Log4jConfigListener类的contextInitialized方法,该类只有一句代码,执行Log4jWebConfigurer.initLogging方法;
public void contextInitialized(ServletContextEvent event) {
Log4jWebConfigurer.initLogging(event.getServletContext());
} - 进入Log4jWebConfigurer类的initLogging方法,首先,调用WebUtils.setWebAppRootSystemProperty方法,内部调用servletContext.getRealPath("/")方法获取工程实际运行的绝对路径(如:F:\004_SVN\IBP\springweb\target\spring-web-1.0-SNAPSHOT\),设置到系统变量中(System.setProperty),注意这里的key值是可以配置的,通过webAppRootKey参数配置,如在本例子的web.xml中配成了petclinic.root;
public static void setWebAppRootSystemProperty(ServletContext servletContext) {
String param = servletContext.getInitParameter(WEB_APP_ROOT_KEY_PARAM);
String key = (param != null ? param : DEFAULT_WEB_APP_ROOT_KEY);
String oldValue = System.getProperty(key);
if (oldValue != null) {
servletContext.log("WARNING: Web app root system property already set: " + key + " = " + oldValue);
servletContext.log("WARNING: Choose unique webAppRootKey values in your web.xml files!");
} else {
String root = servletContext.getRealPath("/");
System.setProperty(key, root);
servletContext.log("Set web app root system property: " + key + " = " + root);
}
} - 获取日志配置文件路径、刷新间隔等配置信息,日志配置文件路径可根据log4jConfigLocation参数配置,这里配置的是相对路径,通过调用ServletContext.getRealPath()获得完整路径,注意getRealPath方法的参数要以“/”开头;刷新间隔可根据log4jRefreshInterval参数配置,默认为60s;
public static void initLogging(ServletContext servletContext) {
// set the web app root system property
WebUtils.setWebAppRootSystemProperty(servletContext); // only perform custom Log4J initialization in case of a config file
String location = servletContext.getInitParameter(CONFIG_LOCATION_PARAM);
if (location != null) { // interpret location as relative to the web application root directory
if (location.charAt(0) != '/') {
location = "/" + location;
}
location = servletContext.getRealPath(location); // use default refresh interval if not specified
long refreshInterval = Log4jConfigurer.DEFAULT_REFRESH_INTERVAL;
String intervalString = servletContext.getInitParameter(REFRESH_INTERVAL_PARAM);
if (intervalString != null) {
refreshInterval = Long.parseLong(intervalString);
} // write log message to server log
servletContext.log("Initializing Log4J from " + location); // perform actual Log4J initialization
try {
Log4jConfigurer.initLogging(location, refreshInterval);
} catch (FileNotFoundException ex) {
throw new IllegalArgumentException("Invalid log4jConfigLocation parameter: " + ex.getMessage());
}
}
} - 进入Log4jConfigurer类的initLogging方法,initLogging比较简单,根据配置文件后缀名,使用相应的解析器解析配置文件中的元素。
public static void initLogging(String location, long refreshInterval) throws FileNotFoundException {
if (!(new File(location)).exists()) {
throw new FileNotFoundException("Log4j config file [" + location + "] not found");
}
if (location.toLowerCase().endsWith(XML_FILE_EXTENSION)) {
DOMConfigurator.configureAndWatch(location, refreshInterval);
} else {
PropertyConfigurator.configureAndWatch(location, refreshInterval);
}
}
另外补充下,当Servlet容器销毁时,会调用Log4jConfigListener的contextDestroyed方法,最终是调用LogManager.shutdown,执行一些资源关闭等操作;