logback的使用和原理 - IT评测·应用市场-qidao123.com技术社区

<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter</artifactId>
</dependency>
</dependencies>

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package org.example;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import java.util.Date;
import java.util.UUID;
public class LogPathOnLinuxApp
{
private static final Logger logger = LoggerFactory.getLogger(LogPathOnLinuxApp.class);
public static void main(String[] args) {
logger.info(new Date().toString() + "生成了 UUID: " + UUID.randomUUID());
}
}

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// 1.1 使用时传入的class对象，调用的是这个方法
public static Logger getLogger(Class<?> clazz) {
// 1.2 调用上面的方法，传入一个String类型的class的名字，返回一个Logger对象，这个就是最终返回的Logger对象，ctrl+鼠标左键，点进去
Logger logger = getLogger(clazz.getName());
if (DETECT_LOGGER_NAME_MISMATCH) {
Class<?> autoComputedCallingClass = Util.getCallingClass();
if (autoComputedCallingClass != null && nonMatchingClasses(clazz, autoComputedCallingClass)) {
Util.report(String.format("Detected logger name mismatch. Given name: "%s"; computed name: "%s".", logger.getName(), autoComputedCallingClass.getName()));
Util.report("See http://www.slf4j.org/codes.html#loggerNameMismatch for an explanation");
}
}
// 最终返回给调用者的logger
return logger;
}
// 1.2
public static Logger getLogger(String name) {
// 1.3 调用getILoggerFactory方法，返回一个ILoggerFactory对象，点进去
ILoggerFactory iLoggerFactory = getILoggerFactory();
// 最终返回iLoggerFactory.getLogger(name)的Logger对象
return iLoggerFactory.getLogger(name);
}
// 这是类中的静态变量，在类加载的时候初始化
static final int UNINITIALIZED = 0; // 未初始化
static final int ONGOING_INITIALIZATION = 1; // 正在初始化
static final int FAILED_INITIALIZATION = 2; // 初始化失败
static final int SUCCESSFUL_INITIALIZATION = 3; // 初始化成功
static final int NOP_FALLBACK_INITIALIZATION = 4; // 无回退初始化
static volatile int INITIALIZATION_STATE = 0; // 初始化状态
// 1.3
public static ILoggerFactory getILoggerFactory() {
// 如果未初始化，就进行初始化操作
if (INITIALIZATION_STATE == 0) {
Class var0 = LoggerFactory.class;
// 对LoggerFactory类加锁
synchronized(LoggerFactory.class) {
// 如果未初始化，将状态设置为正在初始化，执行performInitialization()
if (INITIALIZATION_STATE == 0) {
INITIALIZATION_STATE = 1;
// 执行初始化
performInitialization();
}
}
}
// 判断初始化状态
switch (INITIALIZATION_STATE) {
case 1:
return SUBST_FACTORY;
case 2:
throw new IllegalStateException("org.slf4j.LoggerFactory in failed state. Original exception was thrown EARLIER. See also http://www.slf4j.org/codes.html#unsuccessfulInit");
// 如果初始化成功，返回 StaticLoggerBinder.getSingleton().getLoggerFactory();
case 3:
// 1.4 看这个方法 getLoggerFactory
return StaticLoggerBinder.getSingleton().getLoggerFactory();
case 4:
return NOP_FALLBACK_FACTORY;
default:
throw new IllegalStateException("Unreachable code");
}
}

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private static StaticLoggerBinder SINGLETON = new StaticLoggerBinder();
private LoggerContext defaultLoggerContext = new LoggerContext();
static {
SINGLETON.init();
}
void init() {
try {
try {
// 自动配置，autoConfig 点进去
(new ContextInitializer(this.defaultLoggerContext)).autoConfig();
} catch (JoranException var2) {
Util.report("Failed to auto configure default logger context", var2);
}
if (!StatusUtil.contextHasStatusListener(this.defaultLoggerContext)) {
StatusPrinter.printInCaseOfErrorsOrWarnings(this.defaultLoggerContext);
}
this.contextSelectorBinder.init(this.defaultLoggerContext, KEY);
this.initialized = true;
} catch (Exception var3) {
Util.report("Failed to instantiate [" + LoggerContext.class.getName() + "]", var3);
}
}

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// 此处的静态常量，表示的是logback的配置文件名
public static final String AUTOCONFIG_FILE = "logback.xml";
public static final String TEST_AUTOCONFIG_FILE = "logback-test.xml";
public static final String CONFIG_FILE_PROPERTY = "logback.configurationFile";
final LoggerContext loggerContext;
//
public void autoConfig() throws JoranException {
StatusListenerConfigHelper.installIfAsked(this.loggerContext);
// 没有任何配置文件时url为null
URL url = this.findURLOfDefaultConfigurationFile(true);
if (url != null) {
// 读取自定义的配置文件，logback.xml文件配置生效
this.configureByResource(url);
} else {
Configurator c = (Configurator)EnvUtil.loadFromServiceLoader(Configurator.class);
if (c != null) {
try {
c.setContext(this.loggerContext);
c.configure(this.loggerContext);
} catch (Exception var4) {
throw new LogbackException(String.format("Failed to initialize Configurator: %s using ServiceLoader", c != null ? c.getClass().getCanonicalName() : "null"), var4);
}
} else {
// 这一段代码保证了，没有任何配置文件时，也可以进行基础的自动配置，进行日志输出
BasicConfigurator basicConfigurator = new BasicConfigurator();
basicConfigurator.setContext(this.loggerContext);
basicConfigurator.configure(this.loggerContext);
}
}
}

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<configuration>
<contextListener />
<appender name="dailyRollingFileAppender" >
<File>${LOG_PATH}/${PROJECT_NAME}/logs/LogsPathTest.log</File>
<rollingPolicy >
<FileNamePattern>${LOG_PATH}/${PROJECT_NAME}/logs/LogsPathTest.%d{yyyy-MM-dd}.%i.log.gz</FileNamePattern>
<MaxHistory>15</MaxHistory>
<MaxFileSize>2MB</MaxFileSize>
</rollingPolicy>
<encoder>
<Pattern>%date{yyyy-MM-dd HH:mm:ss}\t%level\t%logger{96}\t%msg%n</Pattern>
</encoder>
<filter >
<level>INFO</level>
</filter>
</appender>
<appender name="STDOUT" >
<encoder>
<Pattern>%date{yyyy-MM-dd HH:mm:ss}\t%level\t%logger{96}\t%msg%n</Pattern>
</encoder>
<filter >
<level>INFO</level>
</filter>
</appender>
<root level="INFO">
<appender-ref ref="dailyRollingFileAppender"/>
<appender-ref ref="STDOUT"/>
</root>
</configuration>

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