slf4j + log4j原理實現及源碼分析
#0 系列目錄#html
- 2種日誌接口框架，4種日誌實現框架
- jdk-logging、log4j、logback日誌介紹及原理
- jcl與jul、log4j一、log4j二、logback的集成原理
- slf4j與jul、log4j一、log4j二、logback的集成原理
- slf4j、jcl、jul、log4j一、log4j二、logback大總結
- slf4j + log4j原理實現及源碼分析
- Apache Log4j
- Log4j架構分析與實戰
- Log4J配置文件詳解
- Apache Commons Logging
- Commons Logging 架構分析
- JDK Logging
- JDK Logging 深刻分析
- Logback
- 從Log4j遷移到LogBack的理由
- Logback 深刻分析
- Apache Log4j2
- Log4j2架構分析與實戰
- Log4j2配置文件詳解
#1 Slf4j# ##1.1 介紹## SLF4J，即簡單日誌門面（Simple Logging Facade for Java）。從設計模式的角度考慮，它是用來在log和代碼層之間起到門面的做用。對用戶來講只要使用slf4j提供的接口，便可隱藏日誌的具體實現。這與jdbc和類似。使用jdbc也就避免了不一樣的具體數據庫。使用了slf4j能夠對客戶端應用解耦。由於當咱們在代碼實現中引入log日誌的時候，用的是接口，因此能夠實時的更具狀況來調換具體的日誌實現類。這就是slf4j的做用。java
SLF4J所提供的核心API是一些接口以及一個LoggerFactory的工廠類。SLF4J提供了統一的記錄日誌的接口，只要按照其提供的方法記錄便可，最終日誌的格式、記錄級別、輸出方式等經過具體日誌系統的配置來實現，所以能夠在應用中靈活切換日誌系統。數據庫
配置SLF4J是很是簡單的一件事，只要將與你打算使用的日誌系統對應的jar包加入到項目中，SLF4J就會自動選擇使用你加入的日誌系統。apache
##1.2 簡單使用##設計模式
/**
* Slf4j 日誌門面接口 Test
* @author taomk
* @version 1.0
* @since 15-10-15 下午3:39
*/
public class Slf4jFacadeTest {
private static Logger logger = LoggerFactory.getLogger(Slf4jFacadeTest.class);
public static void main(String[] args){
if(logger.isDebugEnabled()){
logger.debug("slf4j-log4j debug message");
}
if(logger.isInfoEnabled()){
logger.debug("slf4j-log4j info message");
}
if(logger.isTraceEnabled()){
logger.debug("slf4j-log4j trace message");
}
}
}
上述Logger接口、LoggerFactory類都是slf4j本身定義的。那麼，SLF4J是怎麼實現日誌綁定的？api
##1.3 日誌綁定##性能優化
- 在應用中，經過LoggerFactory類的靜態getLogger()獲取logger，代碼以下：
private static Logger logger = LoggerFactory.getLogger(Slf4jFacadeTest.class);
- LoggerFactory.getLogger(Slf4jFacadeTest.class)方法的源碼以下：LoggerFactory.java
public static Logger getLogger(String name) {
ILoggerFactory iLoggerFactory = getILoggerFactory();
return iLoggerFactory.getLogger(name);
}
上述獲取Log的過程大體分紅2個階段：服務器
- 獲取ILoggerFactory的過程 (從字面上理解就是生產Logger的工廠)；
- 根據ILoggerFactory獲取Logger的過程；
下面來詳細說明：架構
- 1 獲取ILoggerFactory的過程，
又能夠分紅3個過程： - 1.1 從類路徑中尋找
org/slf4j/impl/StaticLoggerBinder.class類：LoggerFactory.java
private static String STATIC_LOGGER_BINDER_PATH = "org/slf4j/impl/StaticLoggerBinder.class";
private static Set<URL> findPossibleStaticLoggerBinderPathSet() {
// use Set instead of list in order to deal with bug #138
// LinkedHashSet appropriate here because it preserves insertion order during iteration
Set<URL> staticLoggerBinderPathSet = new LinkedHashSet<URL>();
try {
ClassLoader loggerFactoryClassLoader = LoggerFactory.class.getClassLoader();
Enumeration<URL> paths;
if (loggerFactoryClassLoader == null) {
paths = ClassLoader.getSystemResources(STATIC_LOGGER_BINDER_PATH);
} else {
paths = loggerFactoryClassLoader.getResources(STATIC_LOGGER_BINDER_PATH);
}
while (paths.hasMoreElements()) {
URL path = (URL) paths.nextElement();
staticLoggerBinderPathSet.add(path);
}
} catch (IOException ioe) {
Util.report("Error getting resources from path", ioe);
}
return staticLoggerBinderPathSet;
}
若是找到多個，則輸出 Class path contains multiple SLF4J bindings，表示有多個日誌實現與slf4j進行了綁定。下面看下當出現多個StaticLoggerBinder的時候的輸出日誌（簡化了一些內容）：LoggerFactory.javaapp
SLF4J: Class path contains multiple SLF4J bindings. SLF4J: Found binding in [slf4j-log4j12-1.7.12.jar!/org/slf4j/impl/StaticLoggerBinder.class] SLF4J: Found binding in [logback-classic-1.1.3.jar!/org/slf4j/impl/StaticLoggerBinder.class] SLF4J: Found binding in [slf4j-jdk14-1.7.12.jar!/org/slf4j/impl/StaticLoggerBinder.class] SLF4J: See http://www.slf4j.org/codes.html#multiple_bindings for an explanation. SLF4J: Actual binding is of type [org.slf4j.impl.Log4jLoggerFactory]
- 1.2
「隨機選取"一個StaticLoggerBinder.class來建立一個單例：
private final static void bind() {
try {
Set<URL> staticLoggerBinderPathSet = findPossibleStaticLoggerBinderPathSet();
// 打印搜索到的全部StaticLoggerBinder日誌
reportMultipleBindingAmbiguity(staticLoggerBinderPathSet);
// the next line does the binding 隨機選取綁定
StaticLoggerBinder.getSingleton();
INITIALIZATION_STATE = SUCCESSFUL_INITIALIZATION;
// 打印最終實際綁定StaticLoggerBinder日誌
reportActualBinding(staticLoggerBinderPathSet);
fixSubstitutedLoggers();
} catch (NoClassDefFoundError ncde) {
String msg = ncde.getMessage();
if (messageContainsOrgSlf4jImplStaticLoggerBinder(msg)) {
INITIALIZATION_STATE = NOP_FALLBACK_INITIALIZATION;
Util.report("Failed to load class \"org.slf4j.impl.StaticLoggerBinder\".");
Util.report("Defaulting to no-operation (NOP) logger implementation");
Util.report("See " + NO_STATICLOGGERBINDER_URL + " for further details.");
} else {
failedBinding(ncde);
throw ncde;
}
} catch (java.lang.NoSuchMethodError nsme) {
String msg = nsme.getMessage();
if (msg != null && msg.indexOf("org.slf4j.impl.StaticLoggerBinder.getSingleton()") != -1) {
INITIALIZATION_STATE = FAILED_INITIALIZATION;
Util.report("slf4j-api 1.6.x (or later) is incompatible with this binding.");
Util.report("Your binding is version 1.5.5 or earlier.");
Util.report("Upgrade your binding to version 1.6.x.");
}
throw nsme;
} catch (Exception e) {
failedBinding(e);
throw new IllegalStateException("Unexpected initialization failure", e);
}
}
- 1.3 根據上述建立的StaticLoggerBinder單例，
返回一個ILoggerFactory實例：LoggerFactory.java
public static ILoggerFactory getILoggerFactory() {
if (INITIALIZATION_STATE == UNINITIALIZED) {
INITIALIZATION_STATE = ONGOING_INITIALIZATION;
performInitialization();
}
switch (INITIALIZATION_STATE) {
case SUCCESSFUL_INITIALIZATION:
// 返回綁定
return StaticLoggerBinder.getSingleton().getLoggerFactory();
case NOP_FALLBACK_INITIALIZATION:
return NOP_FALLBACK_FACTORY;
case FAILED_INITIALIZATION:
throw new IllegalStateException(UNSUCCESSFUL_INIT_MSG);
case ONGOING_INITIALIZATION:
// support re-entrant behavior.
// See also http://bugzilla.slf4j.org/show_bug.cgi?id=106
return TEMP_FACTORY;
}
throw new IllegalStateException("Unreachable code");
}
因此slf4j與其餘實際的日誌框架的集成jar包中，都會含有這樣的一個org/slf4j/impl/StaticLoggerBinder.class類文件，而且提供一個ILoggerFactory的實現。
- 2 根據ILoggerFactory獲取Logger的過程：
這就要看具體的ILoggerFactory類型了，下面與Log4j集成來詳細說明。
#2 Log4j介紹# Apache的一個開放源代碼項目，經過使用Log4j，咱們能夠控制日誌信息輸送的目的地是控制檯、文件、GUI組件、甚至是套接口服務器、NT的事件記錄器、UNIX Syslog守護進程等；用戶也能夠控制每一條日誌的輸出格式；經過定義每一條日誌信息的級別，用戶可以更加細緻地控制日誌的生成過程。這些能夠經過一個配置文件來靈活地進行配置，而不須要修改程序代碼。具體詳細介紹，參見Log4j架構分析與實戰。
#3 Slf4j與Log4j集成# ##3.1 Maven依賴##
<!-- slf4j -->
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>1.7.12</version>
</dependency>
<!-- slf4j-log4j -->
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-log4j12</artifactId>
<version>1.7.12</version>
</dependency>
<!-- log4j -->
<dependency>
<groupId>log4j</groupId>
<artifactId>log4j</artifactId>
<version>1.2.17</version>
</dependency>
##3.2 使用案例##
- 第一步：編寫log4j.properties配置文件,放到類路徑下
log4j.rootLogger = debug, console
log4j.appender.console = org.apache.log4j.ConsoleAppender
log4j.appender.console.layout = org.apache.log4j.PatternLayout
log4j.appender.console.layout.ConversionPattern = %-d{yyyy-MM-dd HH:mm:ss} %m%n
配置文件的詳細內容參見Log4J配置文件詳解。
- 第二步：代碼中以下使用
private static Logger logger=LoggerFactory.getLogger(Log4jSlf4JTest.class);
public static void main(String[] args){
if(logger.isDebugEnabled()){
logger.debug("slf4j-log4j debug message");
}
if(logger.isInfoEnabled()){
logger.info("slf4j-log4j info message");
}
if(logger.isTraceEnabled()){
logger.trace("slf4j-log4j trace message");
}
}
- 補充說明：
- 1 配置文件一樣能夠隨意放置，如log4j1原生方式加載配置文件的方式log4j1原生開發
- 2 注意二者方式的不一樣：
slf4j: Logger logger=LoggerFactory.getLogger(Log4jSlf4JTest.class); log4j: Logger logger=Logger.getLogger(Log4jTest.class);
slf4j的Logger是slf4j定義的接口，而log4j的Logger是類。LoggerFactory是slf4j本身的類。
##3.3 原理分析## 先來看下slf4j-log4j12包中的內容：
- 的確是有
org/slf4j/impl/StaticLoggerBinder.class類。 - 該StaticLoggerBinder返回的ILoggerFactory類型將會是
Log4jLoggerFactory。 - Log4jLoggerAdapter就是實現了slf4j定義的Logger接口。
來看下具體過程：
- 1 獲取對應的ILoggerFactory：從上面的slf4j的原理中咱們知道：ILoggerFactory是由StaticLoggerBinder來建立出來的，因此能夠簡單分紅2個過程：
- 1.1 第一個過程：slf4j尋找綁定類StaticLoggerBinder：使用ClassLoader來加載
「org/slf4j/impl/StaticLoggerBinder.class"這樣的類的url，而後就找到了slf4j-log4j12包中的StaticLoggerBinder。 - 1.2 第二個過程：建立出StaticLoggerBinder實例，
並建立出ILoggerFactory，源碼以下：
StaticLoggerBinder.getSingleton().getLoggerFactory();
以slf4j-log4j12中的StaticLoggerBinder爲例，建立出的ILoggerFactory爲Log4jLoggerFactory。
- 2 根據ILoggerFactory獲取Logger的過程，來看下Log4jLoggerFactory是如何返回一個slf4j定義的Logger接口的實例的，源碼以下：
org.apache.log4j.Logger log4jLogger;
if (name.equalsIgnoreCase(Logger.ROOT_LOGGER_NAME))
log4jLogger = LogManager.getRootLogger();
else
log4jLogger = LogManager.getLogger(name);
Logger newInstance = new Log4jLoggerAdapter(log4jLogger);
- 2.1 咱們能夠看到是經過log4j1的原生方式，即便用log4j1的LogManager來獲取，
引起log4j1的加載配置文件，而後初始化，最後返回一個org.apache.log4j.Logger log4jLogger，參見log4j1原生開發。 - 2.2 將上述的org.apache.log4j.Logger
log4jLogger封裝成Log4jLoggerAdapter，而Log4jLoggerAdapter是實現了slf4j的接口，因此咱們使用的slf4j的Logger接口實例（這裏即Log4jLoggerAdapter）都會委託給內部的org.apache.log4j.Logger實例。
#4 Slf4j與Log4j源碼分析# ##4.1 Slf4j初始化##
- 初始化時機：下面這行代碼，會在
當前類類加載時或者顯示得執行調用LoggerFactory.getLogger()方法時，觸發Slf4j初始化，並綁定具體日誌：Slf4jFacadeTest.java
private static Logger logger = LoggerFactory.getLogger(Slf4jFacadeTest.class);
- 初始化步驟：
- 源碼1：LoggerFactory.java
public static Logger getLogger(String name) {
// 1. 初始化LoggerFactory，綁定具體日誌，得到具體日誌的LoggerFactory。
ILoggerFactory iLoggerFactory = getILoggerFactory();
// 2. 根據具體日誌的LoggerFactory，觸發具體日誌的初始化並得到具體日誌的Logger對象；
return iLoggerFactory.getLogger(name);
}
- 源碼2：LoggerFactory.java
public static ILoggerFactory getILoggerFactory() {
// 1. 是否已經初始化了，不然進行初始化
if (INITIALIZATION_STATE == UNINITIALIZED) {
INITIALIZATION_STATE = ONGOING_INITIALIZATION;
performInitialization();
}
switch (INITIALIZATION_STATE) {
case SUCCESSFUL_INITIALIZATION:
// 2. 成功初始化，則直接得到具體日誌的LoggerFactory
return StaticLoggerBinder.getSingleton().getLoggerFactory();
case NOP_FALLBACK_INITIALIZATION:
return NOP_FALLBACK_FACTORY;
case FAILED_INITIALIZATION:
throw new IllegalStateException(UNSUCCESSFUL_INIT_MSG);
case ONGOING_INITIALIZATION:
// support re-entrant behavior.
// See also http://bugzilla.slf4j.org/show_bug.cgi?id=106
return TEMP_FACTORY;
}
throw new IllegalStateException("Unreachable code");
}
- 源碼3：LoggerFactory.java
private final static void performInitialization() {
// 1. 綁定具體的日誌實現
bind();
if (INITIALIZATION_STATE == SUCCESSFUL_INITIALIZATION) {
versionSanityCheck();
}
}
- 源碼4：LoggerFactory.java
private final static void bind() {
try {
// 1. 掃描查找「org/slf4j/impl/StaticLoggerBinder.class」
Set<URL> staticLoggerBinderPathSet = findPossibleStaticLoggerBinderPathSet();
// 2. 打印找到多個「org/slf4j/impl/StaticLoggerBinder.class」的日誌
reportMultipleBindingAmbiguity(staticLoggerBinderPathSet);
// the next line does the binding 隨機選擇綁定，類加載器隨機選擇。
StaticLoggerBinder.getSingleton();
INITIALIZATION_STATE = SUCCESSFUL_INITIALIZATION;
// 3. 打印綁定具體org/slf4j/impl/StaticLoggerBinder.class的日誌
reportActualBinding(staticLoggerBinderPathSet);
fixSubstitutedLoggers();
} catch (NoClassDefFoundError ncde) {
String msg = ncde.getMessage();
if (messageContainsOrgSlf4jImplStaticLoggerBinder(msg)) {
INITIALIZATION_STATE = NOP_FALLBACK_INITIALIZATION;
Util.report("Failed to load class \"org.slf4j.impl.StaticLoggerBinder\".");
Util.report("Defaulting to no-operation (NOP) logger implementation");
Util.report("See " + NO_STATICLOGGERBINDER_URL + " for further details.");
} else {
failedBinding(ncde);
throw ncde;
}
} catch (java.lang.NoSuchMethodError nsme) {
String msg = nsme.getMessage();
if (msg != null && msg.indexOf("org.slf4j.impl.StaticLoggerBinder.getSingleton()") != -1) {
INITIALIZATION_STATE = FAILED_INITIALIZATION;
Util.report("slf4j-api 1.6.x (or later) is incompatible with this binding.");
Util.report("Your binding is version 1.5.5 or earlier.");
Util.report("Upgrade your binding to version 1.6.x.");
}
throw nsme;
} catch (Exception e) {
failedBinding(e);
throw new IllegalStateException("Unexpected initialization failure", e);
}
}
- 源碼5：LoggerFactory.java
private static Set<URL> findPossibleStaticLoggerBinderPathSet() {
// use Set instead of list in order to deal with bug #138
// LinkedHashSet appropriate here because it preserves insertion order during iteration
Set<URL> staticLoggerBinderPathSet = new LinkedHashSet<URL>();
try {
ClassLoader loggerFactoryClassLoader = LoggerFactory.class.getClassLoader();
Enumeration<URL> paths;
if (loggerFactoryClassLoader == null) {
// 1. 掃包查找「org/slf4j/impl/StaticLoggerBinder.class」
paths = ClassLoader.getSystemResources(STATIC_LOGGER_BINDER_PATH);
} else {
paths = loggerFactoryClassLoader.getResources(STATIC_LOGGER_BINDER_PATH);
}
while (paths.hasMoreElements()) {
URL path = (URL) paths.nextElement();
staticLoggerBinderPathSet.add(path);
}
} catch (IOException ioe) {
Util.report("Error getting resources from path", ioe);
}
return staticLoggerBinderPathSet;
}
- 源碼6：slf4j-log4j-1.6.2.jar中StaticLoggerBinder.java
private static final StaticLoggerBinder SINGLETON = new StaticLoggerBinder();
public static final StaticLoggerBinder getSingleton() {
// 1. 返回StaticLoggerBinder實例
return SINGLETON;
}
private StaticLoggerBinder() {
// 2. StaticLoggerBinder初始化
loggerFactory = new Log4jLoggerFactory();
try {
Level level = Level.TRACE;
}cache (NoSuchFieldError nsfe) {
Util.report("This version of SLF4J requires log4j version 1.2.12 or later. See also http://www.slf4j.org/codes.html#log4j_version");
}
}
以上就是Slf4j初始化過程的源代碼，其初始化過程就是綁定具體日誌實現；
##4.2 Log4j初始化## 這裏只在源碼層級作分析，不想看源碼，可直接參考具體詳細流程，請參見Log4j初始化分析。
-
初始化時機：前一小節Slf4j已提到，
在iLoggerFactory.getLogger(name)時觸發Log4j初始化。iLoggerFactory具體類型爲：Log4jLoggerFactory。 -
初始化步驟：
- 源碼1：Log4jLoggerFactory.java
public Logger getLogger(String name) {
Logger slf4jLogger = null;
// protect against concurrent access of loggerMap
synchronized (this) {
slf4jLogger = (Logger) loggerMap.get(name);
if (slf4jLogger == null) {
// 1. 獲取Logej具體的Logger對象。
org.apache.log4j.Logger log4jLogger;
if(name.equalsIgnoreCase(Logger.ROOT_LOGGER_NAME)) {
log4jLogger = LogManager.getRootLogger();
} else {
log4jLogger = LogManager.getLogger(name);
}
slf4jLogger = new Log4jLoggerAdapter(log4jLogger);
loggerMap.put(name, slf4jLogger);
}
}
return slf4jLogger;
}
- 源碼2：LogManager.java靜態代碼塊初始化Log4j
static {
// By default we use a DefaultRepositorySelector which always returns 'h'.
// 1. 初始化Logger倉庫，並添加一個RootLogger實例，默認日誌級別爲DEBUG。
Hierarchy h = new Hierarchy(new RootLogger((Level) Level.DEBUG));
repositorySelector = new DefaultRepositorySelector(h);
/** Search for the properties file log4j.properties in the CLASSPATH. */
String override =OptionConverter.getSystemProperty(DEFAULT_INIT_OVERRIDE_KEY, null);
// 2. 檢查系統屬性log4j.defaultInitOverride，若是該屬性被設置爲false，則執行初始化；不然（只要不是false，不管是什麼值，甚至沒有值，都是不然），跳過初始化。
// if there is no default init override, then get the resource
// specified by the user or the default config file.
if(override == null || "false".equalsIgnoreCase(override)) {
String configurationOptionStr = OptionConverter.getSystemProperty(
DEFAULT_CONFIGURATION_KEY,
null);
String configuratorClassName = OptionConverter.getSystemProperty(
CONFIGURATOR_CLASS_KEY,
null);
URL url = null;
// 3. 把系統屬性log4j.configuration的值賦給變量resource。若是該系統變量沒有被定義，則把resource賦值爲"log4j.properties"。注意：在apache的log4j文檔中建議使用定義log4j.configuration系統屬性的方法來設置默認的初始化文件是一個好方法。
// if the user has not specified the log4j.configuration
// property, we search first for the file "log4j.xml" and then
// "log4j.properties"
if(configurationOptionStr == null) {
url = Loader.getResource(DEFAULT_XML_CONFIGURATION_FILE);
if(url == null) {
url = Loader.getResource(DEFAULT_CONFIGURATION_FILE);
}
} else {
try {
// 4. 試圖把resource變量轉化成爲一個URL對象url。若是通常的轉化方法行不通，就調用org.apache.log4j.helpers.Loader.getResource(resource, Logger.class)方法來完成轉化。
url = new URL(configurationOptionStr);
} catch (MalformedURLException ex) {
// so, resource is not a URL:
// attempt to get the resource from the class path
url = Loader.getResource(configurationOptionStr);
}
}
// If we have a non-null url, then delegate the rest of the
// configuration to the OptionConverter.selectAndConfigure
// method.
if(url != null) {
LogLog.debug("Using URL ["+url+"] for automatic log4j configuration.");
try {
// 5. 若是url以".xml"結尾，則調用方法DOMConfigurator.configure(url)來完成初始化；不然，則調用方法PropertyConfigurator.configure(url)來完成初始化。若是url指定的資源不能被得到，則跳出初始化過程。
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.");
}
}
- 源碼3：OptionConverter.java
public static void selectAndConfigure(URL url, String clazz, LoggerRepository hierarchy) {
Configurator configurator = null;
String filename = url.getFile();
// 1. 若是url以".xml"結尾，則調用方法DOMConfigurator.configure(url)來完成初始化；不然，則調用方法PropertyConfigurator.configure(url)來完成初始化。若是url指定的資源不能被得到，則跳出初始化過程。
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);
}
##4.3 Log4j輸出日誌## 這裏只在源碼層級作分析，不想看源碼，可直接參考具體詳細流程，請參見Log4j輸出日誌。
- 預處理： 當調用Log4j的方法（如：debug(String, Throwable)、info(String, Throwable)）輸出日誌時，首先對日誌信息進行預處理。
- 源碼1：Category.java（
Logger繼承自Category.java）
public void info(Object message) {
// 1. 根據全局日誌等級threshold進行判斷，若是日誌等級低於threshold，不輸出日誌。
if(repository.isDisabled(Level.INFO_INT))
return;
// 2. 根據當前logger配置的日誌等級level進行判斷，若是日誌等級低於當前logger配置的日誌等級，不輸出日誌。
if(Level.INFO.isGreaterOrEqual(this.getEffectiveLevel()))
// 3. 將日誌信息封裝成LoggingEvent對象。
forcedLog(FQCN, Level.INFO, message, null);
}
- 源碼2：Category.java
protected void forcedLog(String fqcn, Priority level, Object message, Throwable t) {
// 1. 將LoggingEvent對象分發給全部的Appender。
callAppenders(new LoggingEvent(fqcn, this, level, message, t));
}
public void callAppenders(LoggingEvent event) {
int writes = 0;
for(Category c = this; c != null; c=c.parent) {
// Protected against simultaneous call to addAppender, removeAppender,...
synchronized(c) {
if(c.aai != null) {
// 2. 將LoggingEvent對象分發給全部的Appender。
writes += c.aai.appendLoopOnAppenders(event);
}
if(!c.additive) {
break;
}
}
}
if(writes == 0) {
repository.emitNoAppenderWarning(this);
}
}
public int appendLoopOnAppenders(LoggingEvent event) {
int size = 0;
Appender appender;
if(appenderList != null) {
size = appenderList.size();
for(int i = 0; i < size; i++) {
appender = (Appender) appenderList.elementAt(i);
appender.doAppend(event);
}
}
return size;
}
- 輸出日誌前還有兩道工序須要處理：
Filter處理和日誌信息格式化。
- 源碼1：
public synchronized void doAppend(LoggingEvent event) {
if (closed) {
LogLog.error("Attempted to append to closed appender named ["
+ name + "].");
return;
}
if (!isAsSevereAsThreshold(event.getLevel())) {
return;
}
// Filter處理
Filter f = this.headFilter;
FILTER_LOOP: while (f != null) {
// 1. 有三種返回值 DENY、ACCEPT、NEUTRAL，DENY表示丟棄當前日誌信息，ACCEPT表示輸出當前日誌信息，NEUTRAL表示繼續下一個Filter。Filter只能在XML配置文件中使用，Properties文件中不支持。
switch (f.decide(event)) {
case Filter.DENY:
return;
case Filter.ACCEPT:
break FILTER_LOOP;
case Filter.NEUTRAL:
f = f.getNext();
}
}
this.append(event);
}
public void append(LoggingEvent event) {
// Reminder: the nesting of calls is:
//
// doAppend()
// - check threshold
// - filter
// - append();
// - checkEntryConditions();
// - subAppend();
if(!checkEntryConditions()) {
return;
}
subAppend(event);
}
protected void subAppend(LoggingEvent event) {
// 2. 日誌信息格式化：對日誌進行格式化處理。
this.qw.write(this.layout.format(event));
if (layout.ignoresThrowable()) {
String[] s = event.getThrowableStrRep();
if (s != null) {
int len = s.length;
for (int i = 0; i < len; i++) {
this.qw.write(s[i]);
this.qw.write(Layout.LINE_SEP);
}
}
}
if (shouldFlush(event)) {
// 3. 將日誌信息輸出至目的地（文件、數據庫或網格）
this.qw.flush();
}
}
- 若想了解Log4j的日誌異步輸出實現，請參見Log4j性能優化。
每日一句
-
每一个你不满意的现在，都有一个你没有努力的曾经。
歡迎關注本站公眾號,獲取更多信息
