Log4j容器初始化探究
Log4j第一步就是初始化Logger容器Repository,这一章我们来探究Logger容器，从别从独立应用以及servlet容器下启动初始化两方面探究。
1 独立应用
静态初始化，java语言保证静态初始化只被执行一次，静态初始化源码在LogManager中。
时序图:
初始化流程:
第一步: LogManager获取配置文件的URL
第二步: OptionConverter获取Configurator实现类(配置类)
第三步: Configurator读取配置文件内容,配置Logger容器(默认配置Hierarchy)
1.1 LoggManager探究
LogManager获取配置文件的URL
源码:
//只在内部使用，将来版本将变为protected级别。
static public final String DEFAULT_CONFIGURATION_FILE = "log4j.properties";
static final String DEFAULT_XML_CONFIGURATION_FILE = "log4j.xml";
//将来版本变为private级别
public String DEFAULT_CONFIGURATION_KEY="log4j.configuration";
//将来版本将变为private级别。用来指定在定义配置类
static final public String CONFIGURATOR_CLASS_KEY="log4j.configuratorClass";
//将来版本将变为private级别。如果不为空并且不为`false`则直接跳过初始化阶段
public static final String DEFAULT_INIT_OVERRIDE_KEY = "log4j.defaultInitOverride";
static private Object guard = null;
//Logger容器选择器
static private RepositorySelector repositorySelector;
static {
//初始化Logger容器为Hierarchy。根节点是RootLogger,默认级别是DEBUG
Hierarchy h = new Hierarchy(new RootLogger((Level) Level.DEBUG));
//初始化Logger容器选择器，以Hierarchy为Logger容器
repositorySelector = new DefaultRepositorySelector(h);
//获取系统属性log4j.defaultInitOverride
String override =OptionConverter.getSystemProperty(DEFAULT_INIT_OVERRIDE_KEY,null);
//如果没有设置log4j.defaultInitOverride,或者log4j.defaultInitOverride为false,进入初始化流程,否则跳过初始化
if(override == null || "false".equalsIgnoreCase(override)) {
//读取系统属性log4j.configuration
String configurationOptionStr = OptionConverter.getSystemProperty(DEFAULT_CONFIGURATION_KEY, null);
//读取系统属性log4j.configuratorClass
String configuratorClassName = OptionConverter.getSystemProperty(CONFIGURATOR_CLASS_KEY, null);
URL url = null;
//如果不存在log4j.configuration
if(configurationOptionStr == null) {
//第一步先检查是否有log4j.xml
url = Loader.getResource(DEFAULT_XML_CONFIGURATION_FILE);
//如果没有检查是否有log4j.properties
if(url == null) {
url = Loader.getResource(DEFAULT_CONFIGURATION_FILE);
}
} else {
try {
url = new URL(configurationOptionStr);
} catch (MalformedURLException ex) {
url = Loader.getResource(configurationOptionStr);
}
}
if(url != null) {
LogLog.debug("Using URL ["+url+"] for automatic log4j configuration.");
try {
//如果存在url,则利用URL配置Logger容器
OptionConverter.selectAndConfigure(url, configuratorClassName,LogManager.getLoggerRepository());
} catch (NoClassDefFoundError e) {
LogLog.warn("Error during default initialization", e);
}
} else {
LogLog.debug("Could not find resource: ["+configurationOptionStr+"].");
}
} else {
LogLog.debug("Default initialization of overridden by " + DEFAULT_INIT_OVERRIDE_KEY + "property.");
}
}
源码流程解析:
1.初始化Logger容器Hierarchy,设置根节点为RootLogger
2.初始LoggerRepositorySelector(容器选择器)为默认的DefaultRepositorySelector,容器为Hierarchy
3.读取系统属性log4j.defaultInitOverride,如果没有设置或者为false进行初始化,否则跳过初始化
4.读取系统属性log4j.configuration(log4j文件路径配置),如果存在对应的文件,则得到URL.如果没有对应的文件,首先检查是否存在log4j.xml文件,如果存在,得到Log4j配置文件URL,如果不存在log4j.xml,继续检查是否存在log4j.properties文件,如果存在该文件,得到log4j配置文件的URL,否则提示没有发现配置文件。
5.读取系统属性log4j.configuratorClass(自定义Configurator配置类全路径,一般不自定义)
6.调用OptionConverter.selectAndConfigure(url, configuratorClassName,LogManager.getLoggerRepository()),初始化logger容器
1.2 OptionConverter探究
OptionConverter获取Configurator实现类(配置类)
源码:
//利用给定URL配置Logger容器
static public void selectAndConfigure(URL url, String clazz, LoggerRepository hierarchy) {
Configurator configurator = null;
String filename = url.getFile();
//优先检查使用xml文件,并查看是否有自定义的configurator
if(clazz == null && filename != null && filename.endsWith(".xml")) {
clazz = "org.apache.log4j.xml.DOMConfigurator";
}
if(clazz != null) {
LogLog.debug("Preferred configurator class: " + clazz);
configurator = (Configurator) instantiateByClassName(clazz, Configurator.class, null);
if(configurator == null) {
LogLog.error("Could not instantiate configurator ["+clazz+"].");
return;
}
} else {
configurator = new PropertyConfigurator();
}
configurator.doConfigure(url, hierarchy);
}
源码流程解析:
1.如果没有自定义配置类Configurator并且文件的后缀名是xml.配置类设置为org.apache.log4j.xml.DOMConfigurator
2.如果自定义了配置类,根据配置类的全限定名,发射得到配置类实例
3.上面两种情况都没有匹配成功,默认是PropertyConfigurator配置类
4.调用configurator.doConfigure(url,hierarchy),根据配置文件URL,配置logger容器Hierarchy(已经静态化构造了简单的容器,RootLogger是根节点)
1.3 Configurator探究(以ProptertyConfigurator为例)
Configurator读取配置文件内容,配置Logger容器
1.3.1 doConfigure(URL,LoggerRepository)
源码:
//从URL中读取配置文件,配置Logger容器Hierarchy
publicvoid doConfigure(java.net.URL configURL, LoggerRepository hierarchy) {
Properties props = new Properties();
LogLog.debug("Reading configuration from URL " + configURL);
InputStream istream = null;
URLConnection uConn = null;
try {
uConn = configURL.openConnection();
uConn.setUseCaches(false);
istream = uConn.getInputStream();
props.load(istream);
} catch (Exception e) {
if (e instanceof InterruptedIOException || e instanceof InterruptedException) {
Thread.currentThread().interrupt();
}
LogLog.error("Could not read configuration file from URL [" + configURL + "].", e);
LogLog.error("Ignoring configuration file [" + configURL +"].");
return;
} finally {
if (istream != null) {
try {
istream.close();
} catch(InterruptedIOException ignore) {
Thread.currentThread().interrupt();
} catch(IOException ignore) {
} catch(RuntimeException ignore) {
}
}
}
doConfigure(props, hierarchy);
}
源码流程解析:
1.文件URL读取文件内容,赋值给Properties
2.调用doConfigure(properties,hierarchy)配置logger容器
1.3.2 doConfigure(Properties , LoggerRepository)
源码:
public void doConfigure(Properties properties, LoggerRepository hierarchy) {
repository = hierarchy;
String value = properties.getProperty(LogLog.DEBUG_KEY);
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));
}
// if log4j.reset=true then
// reset hierarchy
String reset = properties.getProperty(RESET_KEY);
if (reset != null && OptionConverter.toBoolean(reset, false)) {
hierarchy.resetConfiguration();
}
String thresholdStr = OptionConverter.findAndSubst(THRESHOLD_PREFIX, properties);
if(thresholdStr != null) {
hierarchy.setThreshold(OptionConverter.toLevel(thresholdStr, (Level) Level.ALL));
LogLog.debug("Hierarchy threshold set to ["+hierarchy.getThreshold()+"].");
}
configureRootCategory(properties, hierarchy);
configureLoggerFactory(properties);
parseCatsAndRenderers(properties, hierarchy);
LogLog.debug("Finished configuring.");
// We don't want to hold references to appenders preventing their
// garbage collection.
registry.clear();
}
void configureRootCategory(Properties props, LoggerRepository hierarchy) {
String effectiveFrefix = ROOT_LOGGER_PREFIX;
String value = OptionConverter.findAndSubst(ROOT_LOGGER_PREFIX, props);
if(value == null) {
value = OptionConverter.findAndSubst(ROOT_CATEGORY_PREFIX, props);
effectiveFrefix = ROOT_CATEGORY_PREFIX;
}
if(value == null)
LogLog.debug("Could not find root logger information. Is this OK?");
else {
Logger root = hierarchy.getRootLogger();
synchronized(root) {
parseCategory(props, root, effectiveFrefix, INTERNAL_ROOT_NAME, value);
}
}
}
protected void configureLoggerFactory(Properties props) {
String factoryClassName = OptionConverter.findAndSubst(LOGGER_FACTORY_KEY,props);
if(factoryClassName != null) {
LogLog.debug("Setting category factory to ["+factoryClassName+"].");
loggerFactory = (LoggerFactory)OptionConverter.instantiateByClassName(factoryClassName,LoggerFactory.class,loggerFactory);
PropertySetter.setProperties(loggerFactory, props, FACTORY_PREFIX + ".");
}
}
protected void parseCatsAndRenderers(Properties props, LoggerRepository hierarchy) {
Enumeration enumeration = props.propertyNames();
while(enumeration.hasMoreElements()) {
String key = (String) enumeration.nextElement();
if(key.startsWith(CATEGORY_PREFIX) || key.startsWith(LOGGER_PREFIX)) {
String loggerName = null;
if(key.startsWith(CATEGORY_PREFIX)) {
loggerName = key.substring(CATEGORY_PREFIX.length());
} else if(key.startsWith(LOGGER_PREFIX)) {
loggerName = key.substring(LOGGER_PREFIX.length());
}
String value = OptionConverter.findAndSubst(key, props);
Logger logger = hierarchy.getLogger(loggerName, loggerFactory);
synchronized(logger) {
parseCategory(props, logger, key, loggerName, value);
parseAdditivityForLogger(props, logger, loggerName);
}
} else if(key.startsWith(RENDERER_PREFIX)) {
String renderedClass = key.substring(RENDERER_PREFIX.length());
String renderingClass = OptionConverter.findAndSubst(key, props);
if(hierarchy instanceof RendererSupport) {
RendererMap.addRenderer((RendererSupport) hierarchy, renderedClass, renderingClass);
}
} else if (key.equals(THROWABLE_RENDERER_PREFIX)) {
if (hierarchy instanceof ThrowableRendererSupport) {
ThrowableRenderer tr = (ThrowableRenderer) OptionConverter.instantiateByKey(props, THROWABLE_RENDERER_PREFIX, org.apache.log4j.spi.ThrowableRenderer.class, null);
if(tr == null) {
LogLog.error( "Could not instantiate throwableRenderer.");
} else {
PropertySetter setter = new PropertySetter(tr);
setter.setProperties(props, THROWABLE_RENDERER_PREFIX + ".");
((ThrowableRendererSupport) hierarchy).setThrowableRenderer(tr);
}
}
}
}
}
源码流程解析:
1.获取log4j.debug(log4j内部是否debug打印日志),如果为ture打印,false不打印。如果没有设置,尝试读取log4j.configdebug(已经废弃,用logdebug取代)
2.读取log4j.reset,如果设置为true,重置logger容器
3.读取log4j.threshold,设置logger容器总阀值,低于阀值将不打印日志。如果没有配置,默认设置为最低级别Level.ALL
4.调用configureRootCategory\(Properties, LoggerRepository\),配置RootLogger.RootLogger级别不能设置为空或者inherit.解析设置RootLogger的Appenders和Filters.
5.调用configureLoggerFactory(Properties props),配置Logger工厂类LoggerFactory.
6.调用parseCatsAndRenderers(Properties, LoggerRepository),配置Logger以及Renderer
2 Web应用
最常用的就是与Spring集成,这里主要将和Spring集成以及启动流程.其实web应用初始化log4j流程就是,容器启动的时候,首先找到Log4j配置文件,然后调用log4j API进行log4j初始化配置(同上)
2.1 搭建web环境
第一步:加入依赖
<properties>
<spring.version>4.2.4.RELEASE</spring.version>
<log4j.version>1.2.17</log4j.version>
</properties>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.4</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>servlet-api</artifactId>
<version>2.5</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>jsp-api</artifactId>
<version>2.0</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-webmvc</artifactId>
<version>${spring.version}</version>
</dependency>
<!-- Log4j1 日志框架包 -->
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>${log4j.version}</version>
</dependency>
</dependencies>
第二步:在web.xml中加入Log4jConfigListener
<listener>
<listener-class>org.springframework.web.util.Log4jConfigListener</listener-class>
</listener>
第三步:在resources文件夹下加入log4j.xml或者log4j.properties
### 设置###
log4j.rootLogger = debug,stdout,D,E
log4j.threshold= debug
## log4j内部是否debug
log4j.debug= false
### 配置自己的log工厂类
log4j.loggerFactory=com.log.log4j.configure.MyLoggerFactory
### 输出信息到控制抬 ###
log4j.appender.stdout = org.apache.log4j.ConsoleAppender
log4j.appender.stdout.Target = System.out
log4j.appender.stdout.Threshold = warn
log4j.appender.stdout.layout = org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern = [%-5p] %d{yyyy-MM-dd HH:mm:ss,SSS} method:%l%n%m%n
### 输出DEBUG 级别以上的日志到=/data/applogs/log/logtopic/app.log ###
log4j.appender.D = org.apache.log4j.DailyRollingFileAppender
log4j.appender.D.File = /data/applogs/log/logtopic/app.log
log4j.appender.D.Append = true
log4j.appender.D.Threshold = DEBUG
log4j.appender.D.layout = org.apache.log4j.PatternLayout
log4j.appender.D.layout.ConversionPattern = %-d{yyyy-MM-dd HH:mm:ss} [ %t:%r ] - [ %p ] %m%n
### 输出ERROR 级别以上的日志到=/data/applogs/log/log4jLearning/error.log ###
log4j.appender.E = org.apache.log4j.DailyRollingFileAppender
log4j.appender.E.File =/data/applogs/log/logtopic/error.log
log4j.appender.E.Append = true
log4j.appender.E.Threshold = ERROR
log4j.appender.E.layout = org.apache.log4j.PatternLayout
log4j.appender.E.layout.ConversionPattern = %-d{yyyy-MM-dd HH:mm:ss} [ %t:%r ] - [ %p ] %m%n
第四步:编写ServletDemo并配置
ServletDemo代码:
public class Log4jServletDemo extends HttpServlet {
public static final Logger LOGGER = Logger.getLogger(Log4jServletDemo.class);
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
service(req, resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException{
service(req, resp);
}
@Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException{
LOGGER.debug("Log4jServletDemo Info Level");
LOGGER.info("Log4jServletDemo Info Level");
LOGGER.warn("Log4jServletDemo Info Level");
LOGGER.error("Log4jServletDemo Info Level");
req.getRequestDispatcher("/index.jsp").forward(req, resp);
}
}
web.xml中配置:
<servlet>
<servlet-name>servletDemo</servlet-name>
<servlet-class>com.log.log4j.web.Log4jServletDemo</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>servletDemo</servlet-name>
<url-pattern>/demo</url-pattern>
</servlet-mapping>
2.2 log4jweb初始化
初始化时序图:
初始化流程:
1.tomcat容器加载Log4jConfigListener
2.Log4jConfigListener把初始化Log4j的工作为委托给Log4jWebConfigurer
3.Log4jWebConfigurer获取配置文件路径。然后再委托给Log4jConfigurer
4.Log4jConfigurer调用Log4j框架的DomConfigurator.configure(url)或者PropertyConfigurator.configure(url)初始化配置Log4j,这样就走到了上面独立应用初始化Log4j的过程
2.3 源码探究
2.3.1 Log4jConfigListener
源码:
public class Log4jConfigListener implements ServletContextListener {
@Override
public void contextInitialized(ServletContextEvent event) {
Log4jWebConfigurer.initLogging(event.getServletContext());
}
@Override
public void contextDestroyed(ServletContextEvent event) {
Log4jWebConfigurer.shutdownLogging(event.getServletContext());
}
}
源码流程解析:
1.调用contextInitialized(ServletContextEvent)初始化Log4j
2.委托给Log4jWebConfigurer初始化Log4j
2.3.2 Log4jWebConfigurer
源码:
public static void initLogging(ServletContext servletContext) {
// 首先检查是否暴露系统属性,默认是暴露
if (exposeWebAppRoot(servletContext)) {
WebUtils.setWebAppRootSystemProperty(servletContext);
}
//得到自定义的log4j配置文件位置
String location = servletContext.getInitParameter(CONFIG_LOCATION_PARAM);
if (location != null) {
// 主要是获取log4j配置文件的真实路径
try {
// Resolve property placeholders before potentially resolving a real path.
location = ServletContextPropertyUtils.resolvePlaceholders(location, servletContext);
// 判断是否是资源路径,以classpath:" or "file:"开头
if (!ResourceUtils.isUrl(location)) {
// 获取配置文件的真实路径
location = WebUtils.getRealPath(servletContext, location); }
// Write log message to server log.
servletContext.log("Initializing log4j from [" + location + "]");
// 读取 log4jRefreshInterval 属性
String intervalString = servletContext.getInitParameter(REFRESH_INTERVAL_PARAM);
if (StringUtils.hasText(intervalString)) {
try {
long refreshInterval = Long.parseLong(intervalString);
//配置log4j并启动一个监控线程
org.springframework.util.Log4jConfigurer.initLogging(location, refreshInterval);
} catch (NumberFormatException ex) {
throw new IllegalArgumentException("Invalid 'log4jRefreshInterval' parameter: " + ex.getMessage()); }
} else {
//配置log4j
org.springframework.util.Log4jConfigurer.initLogging(location);
}
} catch (FileNotFoundException ex) {
throw new IllegalArgumentException("Invalid 'log4jConfigLocation' parameter: " + ex.getMessage());
}
}
}
//设置WebAppRoot属性
public static void setWebAppRootSystemProperty(ServletContext servletContext) throws IllegalStateException {
Assert.notNull(servletContext, "ServletContext must not be null");
String root = servletContext.getRealPath("/");
if (root == null) {
throw new IllegalStateException( "Cannot set web app root system property when WAR file is not expanded");
}
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 && !StringUtils.pathEquals(oldValue, root)) {
throw new IllegalStateException( "Web app root system property already set to different value: '" + key + "' = [" + oldValue + "] instead of [" + root + "] - " + "Choose unique values for the 'webAppRootKey' context-param in your web.xml files!");
}
System.setProperty(key, root);
servletContext.log("Set web app root system property: '" + key + "' = [" + root + "]");
}
源码流程解析
1.exposeWebAppRoot判断是否暴露WebAppRoot,默认是暴露.可以自定义,如下配置
<context-param>
<param-name>log4jExposeWebAppRoot</param-name>
<param-value>true</param-value>
</context-param>
2.如果暴露,将设置系统属性为 webapp.root = servletContext.getRealPath("/")(项目部署根路径),也可以自定义webAppRootKey,如下
<context-param>
<param-name>webAppRootKey</param-name>
<param-value>logtopic.root</param-value>
</context-param>
这样就会设置系统属性 logtopic.root = servletContext.getRealPath("/"),再配置文件中就可以用${logtopic.root}代替部署根路径
3.String location = servletContext.getInitParameter(CONFIG_LOCATION_PARAM)获取Log4j自定义配置路径,如果不为空解析得到真实路径location = WebUtils.getRealPath(servletContext, location)如下配置
<context-param>
<param-name>log4jConfigLocation</param-name>
<param-value>classpath:log4j.properties</param-value>
</context-param>
配置有两种情况
- `classpath`开头,找到项目类路径,最后用ClassLoader加载,所以不要用"/"开头
<context-param>
<param-name>log4jConfigLocation</param-name>
<param-value>classpath:log4j.properties</param-value>
</context-param>
-
file开头,配置文件具体位置
<context-param>
<param-name>log4jConfigLocation</param-name>
<param-value>file:///Users/lh/Desktop/log4j.properties</param-value>
</context-param>
4.读取log4jRefreshInterval属性,表示每隔一段时间,会重新读取配置文件,重新配置Log4j,自动检测更新。会单独启动一个线程来监控定时监控,单位是(ms).配置如下:
<context-param>
<param-name>log4jRefreshInterval</param-name>
<param-value>2000</param-value>
</context-param>
5.最后调用log4j自身的API进行配置
if (resolvedLocation.toLowerCase().endsWith(XML_FILE_EXTENSION)) {
DOMConfigurator.configure(url);
}else {
PropertyConfigurator.configure(url);
}