以前研究过slf4j-log4j的使用，但具体初始化过程不是很清楚，今天闲下来，翻了一下源码，一探究竟。
日志组件介绍：[url]http://www.blogjava.net/daiyongzhi/archive/2014/04/13/412364.html[/url]
Log4j包使用说明：[url]http://www.360doc.com/content/10/1224/19/573136_81037906.shtml[/url]
Log4j配置：[url]http://blog.csdn.net/azheng270/article/details/2173430/[/url]
Log4j初始化详解：[url]http://donald-draper.iteye.com/blog/2332385[/url]
相关log4j的jar包，配置，使用上面链接已经说明，这里就不做介绍，今天来探究一下，与Spring的集成过程分析：
1.在web.xml配置log4属性文件位置：
<context-param>
<param-name>log4jConfigLocation</param-name>
<param-value>classpath*:log4j.properties</param-value>
</context-param>
2.添加监听器：
<listener>
<listener-class>
org.springframework.web.util.Log4jConfigListener
</listener-class>
</listener>
到这里配置完毕。
下面分析过程：
配置文件加载通过Tomcat-StandardContext
protected synchronized void startInternal() throws LifecycleException {
try {
// Create context attributes that will be required
if (ok) {
getServletContext().setAttribute(
JarScanner.class.getName(), getJarScanner());
}
//此函数初始化Web上下文变量，log4j属性文件位置
// Set up the context init params
mergeParameters();
// Call ServletContainerInitializers
for (Map.Entry<ServletContainerInitializer, Set<Class<?>>> entry :
initializers.entrySet()) {
try {
entry.getKey().onStartup(entry.getValue(),
getServletContext());
} catch (ServletException e) {
log.error(sm.getString("standardContext.sciFail"), e);
ok = false;
break;
}
}
//添加web监听器
// Configure and call application event listeners
if (ok) {
if (!listenerStart()) {
log.error(sm.getString("standardContext.listenerFail"));
ok = false;
}
}
}
上下文变量初始化
private void mergeParameters() {
Map<String,String> mergedParams = new HashMap<String,String>();
String names[] = findParameters();
for (int i = 0; i < names.length; i++) {
mergedParams.put(names[i], findParameter(names[i]));
}
ApplicationParameter params[] = findApplicationParameters();
for (int i = 0; i < params.length; i++) {
if (params[i].getOverride()) {
if (mergedParams.get(params[i].getName()) == null) {
mergedParams.put(params[i].getName(),
params[i].getValue());
}
} else {
mergedParams.put(params[i].getName(), params[i].getValue());
}
}
ServletContext sc = getServletContext();
for (Map.Entry<String,String> entry : mergedParams.entrySet()) {
//将上下文变量放在ServletContext中
sc.setInitParameter(entry.getKey(), entry.getValue());
}
}
监听器添加
public boolean listenerStart() {
ApplicationListener listeners[] = applicationListeners;
// Sort listeners in two arrays
ArrayList<Object> eventListeners = new ArrayList<Object>();
ArrayList<Object> lifecycleListeners = new ArrayList<Object>();
for (int i = 0; i < results.length; i++) {
if ((results[i] instanceof ServletContextAttributeListener)
|| (results[i] instanceof ServletRequestAttributeListener)
|| (results[i] instanceof ServletRequestListener)
|| (results[i] instanceof HttpSessionAttributeListener)) {
eventListeners.add(results[i]);
}
if ((results[i] instanceof ServletContextListener)
|| (results[i] instanceof HttpSessionListener)) {
lifecycleListeners.add(results[i]);
}
}
// Listener instances may have been added directly to this Context by
// ServletContextInitializers and other code via the pluggability APIs.
// Put them these listeners after the ones defined in web.xml and/or
// annotations then overwrite the list of instances with the new, full
// list.
for (Object eventListener: getApplicationEventListeners()) {
eventListeners.add(eventListener);
}
setApplicationEventListeners(eventListeners.toArray());
for (Object lifecycleListener: getApplicationLifecycleListeners()) {
//添加监听器
lifecycleListeners.add(lifecycleListener);
if (lifecycleListener instanceof ServletContextListener) {
noPluggabilityListeners.add(lifecycleListener);
}
}
setApplicationLifecycleListeners(lifecycleListeners.toArray());
// Send application start events
if (getLogger().isDebugEnabled())
getLogger().debug("Sending application start events");
// Ensure context is not null
getServletContext();
context.setNewServletContextListenerAllowed(false);
Object instances[] = getApplicationLifecycleListeners();
if (instances == null || instances.length == 0) {
return ok;
}
ServletContextEvent event = new ServletContextEvent(getServletContext());
ServletContextEvent tldEvent = null;
if (noPluggabilityListeners.size() > 0) {
noPluggabilityServletContext = new NoPluggabilityServletContext(getServletContext());
tldEvent = new ServletContextEvent(noPluggabilityServletContext);
}
for (int i = 0; i < instances.length; i++) {
if (instances[i] == null)
continue;
if (!(instances[i] instanceof ServletContextListener))
continue;
ServletContextListener listener =
(ServletContextListener) instances[i];
try {
fireContainerEvent("beforeContextInitialized", listener);
if (noPluggabilityListeners.contains(listener)) {
listener.contextInitialized(tldEvent);
} else {
listener.contextInitialized(event);
}
fireContainerEvent("afterContextInitialized", listener);
} catch (Throwable t) {
ExceptionUtils.handleThrowable(t);
fireContainerEvent("afterContextInitialized", listener);
getLogger().error
(sm.getString("standardContext.listenerStart",
instances[i].getClass().getName()), t);
ok = false;
}
}
查看Spring log4j监听器
public class Log4jConfigListener
implements ServletContextListener
{
public Log4jConfigListener()
{
}
public void contextInitialized(ServletContextEvent event)
{
//初始化log4J位置，通过event.getServletContext()获取
Log4jWebConfigurer.initLogging(event.getServletContext());
}
public void contextDestroyed(ServletContextEvent event)
{
Log4jWebConfigurer.shutdownLogging(event.getServletContext());
}
}
log4jWeb初始化Log4jWebConfigurer
public static void initLogging(ServletContext servletContext)
{
if(exposeWebAppRoot(servletContext))
WebUtils.setWebAppRootSystemProperty(servletContext);
String location = servletContext.getInitParameter("log4jConfigLocation");
if(location != null)
try
{
location = ServletContextPropertyUtils.resolvePlaceholders(location, servletContext);
if(!ResourceUtils.isUrl(location))
location = WebUtils.getRealPath(servletContext, location);
servletContext.log((new StringBuilder()).append("Initializing log4j from [").append(location).append("]").toString());
String intervalString = servletContext.getInitParameter("log4jRefreshInterval");
if(StringUtils.hasText(intervalString))
try
{
long refreshInterval = Long.parseLong(intervalString);
//初始化log4j配置
Log4jConfigurer.initLogging(location, refreshInterval);
}
catch(NumberFormatException ex)
{
throw new IllegalArgumentException((new StringBuilder()).append("Invalid 'log4jRefreshInterval' parameter: ").append(ex.getMessage()).toString());
}
else
Log4jConfigurer.initLogging(location);
}
catch(FileNotFoundException ex)
{
throw new IllegalArgumentException((new StringBuilder()).append("Invalid 'log4jConfigLocation' parameter: ").append(ex.getMessage()).toString());
}
}
log4j属性变量配置Log4jConfigurer
public static void initLogging(String location, long refreshInterval)
throws FileNotFoundException
{
String resolvedLocation = SystemPropertyUtils.resolvePlaceholders(location);
File file = ResourceUtils.getFile(resolvedLocation);
if(!file.exists())
throw new FileNotFoundException((new StringBuilder()).append("Log4j config file [").append(resolvedLocation).append("] not found").toString());
//xml文件
if(resolvedLocation.toLowerCase().endsWith(".xml"))
DOMConfigurator.configureAndWatch(file.getAbsolutePath(), refreshInterval);
else
//properties文件
PropertyConfigurator.configureAndWatch(file.getAbsolutePath(), refreshInterval);
}
PropertyConfigurator，属性文件读取
public void doConfigure(Properties properties, LoggerRepository hierarchy)
{
repository = hierarchy;
String value = properties.getProperty("log4j.debug");
if(value == null)
{
value = properties.getProperty("log4j.configDebug");
if(value != null)
LogLog.warn("[log4j.configDebug] is deprecated. Use [log4j.debug] instead.");
}
if(value != null)
LogLog.setInternalDebugging(OptionConverter.toBoolean(value, true));
String reset = properties.getProperty("log4j.reset");
if(reset != null && OptionConverter.toBoolean(reset, false))
hierarchy.resetConfiguration();
String thresholdStr = OptionConverter.findAndSubst("log4j.threshold", properties);
if(thresholdStr != null)
{
hierarchy.setThreshold(OptionConverter.toLevel(thresholdStr, Level.ALL));
LogLog.debug("Hierarchy threshold set to [" + hierarchy.getThreshold() + "].");
}
//关键是下面三个函数配置LogFactory属性
configureRootCategory(properties, hierarchy);
configureLoggerFactory(properties);
parseCatsAndRenderers(properties, hierarchy);
LogLog.debug("Finished configuring.");
registry.clear();
}
至此LogFactory初始化完毕。
Logger实例的获取
public static Logger getLogger(Class clazz)
{
//根据类名获取logger实例
Logger logger = getLogger(clazz.getName());
if(DETECT_LOGGER_NAME_MISMATCH)
{
Class autoComputedCallingClass = Util.getCallingClass();
if(nonMatchingClasses(clazz, autoComputedCallingClass))
{
Util.report(String.format("Detected logger name mismatch. Given name: \"%s\"; computed name: \"%s\".", new Object[] {
logger.getName(), autoComputedCallingClass.getName()
}));
Util.report("See http://www.slf4j.org/codes.html#loggerNameMismatch for an explanation");
}
}
return logger;
}
public static Logger getLogger(String name)
{
//从具体的log工场实现中，获取log
//slf4j只是提供了一个工场类接口，具体的工场实现类在相关日志Jar包中
ILoggerFactory iLoggerFactory = getILoggerFactory();
return iLoggerFactory.getLogger(name);
}
写的有点匆忙,请见谅！
