Logback是由log4j创始人设计的另一个开源日志组件，性能比log4j要好。
官方网站：https://logback.qos.ch/index.html
Logback主要分为三个模块：
logback-core：其它两个模块的基础模块logback-classic：它是log4j的一个改良版本，同时它完整实现了slf4j APIlogback-access：访问模块与Servlet容器集成提供通过Http来访问日志的功能 后续的日志代码都是通过SLF4J日志门面搭建日志系统，所以在代码是没有区别，主要是通过修改配置文件和pom.xml依赖
入门案例 第一步：创建maven项目，添加依赖项目中无需单独引入slf4j，因为logback-classic依赖包里引用了slf4j
第二步：测试代码4.0.0 com.example logging-test 0.0.1-SNAPSHOT 8 8 junit junit 4.12 ch.qos.logback logback-classic 1.2.10 org.apache.maven.plugins maven-compiler-plugin 3.8.1 ${maven.compiler.source} ${maven.compiler.target} UTF-8
package com.example.test;
import org.junit.Test;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class TestLogback {
private static final Logger logger = LoggerFactory.getLogger(TestLogback.class);
@Test
public void testLogback() {
logger.error("error");
logger.warn("warn");
logger.info("info");
logger.debug("debug");
logger.trace("trace");
}
}
源码解读
1、我们从日志工厂的常见看起，这里是slf4j的实现
private static final Logger logger = LoggerFactory.getLogger(TestLogback.class);
核心方法只有一句
public static Logger getLogger(Class clazz) {
Logger logger = getLogger(clazz.getName());
....省略
return logger;
}
看一下getLogger方法，这里是先获取日志工厂，在从工厂中提取日志对象，我们不考虑日志对象，主要看看日志工厂的环境怎么初始化的
public static Logger getLogger(String name) {
ILoggerFactory iLoggerFactory = getILoggerFactory();
return iLoggerFactory.getLogger(name);
}
进入getILoggerFactory方法看：
public static ILoggerFactory getILoggerFactory() {
if (INITIALIZATION_STATE == 0) {
Class var0 = LoggerFactory.class;
synchronized(LoggerFactory.class) {
if (INITIALIZATION_STATE == 0) {
INITIALIZATION_STATE = 1;
//重要方法
performInitialization();
}
}
}
...省略
}
进入performInitialization方法
private static final void performInitialization() {
//一看bind就知道slf4j绑定logback的重要方法
bind();
if (INITIALIZATION_STATE == 3) {
versionSanityCheck();
}
}
进入bind方法：
private final static void bind() {
try {
Set staticLoggerBinderPathSet = null;
// skip check under android, see also
// http://jira.qos.ch/browse/SLF4J-328
if (!isAndroid()) {
staticLoggerBinderPathSet = findPossibleStaticLoggerBinderPathSet();
reportMultipleBindingAmbiguity(staticLoggerBinderPathSet);
}
// the next line does the binding
//这一行做绑定操作，重要
StaticLoggerBinder.getSingleton();
....省略
}
进入getSingleton方法，此时已经进入桥接包的StaticLoggerBinder类了，log4j桥接包和jul桥接包中都有这个StaticLoggerBinder类：
public static StaticLoggerBinder getSingleton() {
return SINGLETON;
}
我们翻下可以看到它有个静态代码块：
static {
SINGLETON.init();
}
进入init方法
void init() {
try {
try {
//感觉autoConfig是重要方法
(new ContextInitializer(this.defaultLoggerContext)).autoConfig();
...省略
}
进入autoConfig方法
public void autoConfig() throws JoranException {
StatusListenerConfigHelper.installIfAsked(this.loggerContext);
//生成URL通过默认配置文件
URL url = this.findURLOfDefaultConfigurationFile(true);
if (url != null) {
this.configureByResource(url);
} else {
//spi机制获取配置类
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 {
//当没有配置文件时，默认的配置
BasicConfigurator basicConfigurator = new BasicConfigurator();
basicConfigurator.setContext(this.loggerContext);
basicConfigurator.configure(this.loggerContext);
}
}
}
我们可以看下findConfigFileURLFromSystemProperties方法：
public URL findURLOfDefaultConfigurationFile(boolean updateStatus) {
ClassLoader myClassLoader = Loader.getClassLoaderOfObject(this);
URL url = findConfigFileURLFromSystemProperties(myClassLoader, updateStatus);
if (url != null) {
return url;
}
url = getResource(TEST_AUTOCONFIG_FILE, myClassLoader, updateStatus);
if (url != null) {
return url;
}
return getResource(AUTOCONFIG_FILE, myClassLoader, updateStatus);
}
我们发现，它读取配置文件有优先级，先读取classpath下是否有logback-test.xml，没有则读取classpath下是否有logback.xml
debug发现Configurator c = EnvUtil.loadFromServiceLoader(Configurator.class);返回为null。
然后进入到BasicConfigurator，然后发现basicConfigurator.configure(loggerContext);比较重要
public void configure(LoggerContext lc) {
addInfo("Setting up default configuration.");
ConsoleAppender ca = new ConsoleAppender();
ca.setContext(lc);
ca.setName("console");
LayoutWrappingEncoder encoder = new LayoutWrappingEncoder();
encoder.setContext(lc);
// same as
// PatternLayout layout = new PatternLayout();
// layout.setPattern("%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n");
TTLLLayout layout = new TTLLLayout();
layout.setContext(lc);
layout.start();
encoder.setLayout(layout);
ca.setEncoder(encoder);
ca.start();
Logger rootLogger = lc.getLogger(Logger.ROOT_LOGGER_NAME);
rootLogger.addAppender(ca);
}
结果一看，rootLogger指向appender，appender指向encoder，encoder指向layout，比log4j多了encoder，但大致一样
我们在看TTLLLayout类
package ch.qos.logback.classic.layout; import ch.qos.logback.classic.pattern.ThrowableProxyConverter; import ch.qos.logback.classic.spi.ILoggingEvent; import ch.qos.logback.classic.spi.IThrowableProxy; import ch.qos.logback.core.CoreConstants; import ch.qos.logback.core.Layoutbase; import ch.qos.logback.core.util.CachingDateFormatter; public class TTLLLayout extends Layoutbase{ CachingDateFormatter cachingDateFormatter = new CachingDateFormatter("HH:mm:ss.SSS"); ThrowableProxyConverter tpc = new ThrowableProxyConverter(); @Override public void start() { tpc.start(); super.start(); } @Override public String doLayout(ILoggingEvent event) { if (!isStarted()) { return CoreConstants.EMPTY_STRING; } StringBuilder sb = new StringBuilder(); long timestamp = event.getTimeStamp(); sb.append(cachingDateFormatter.format(timestamp)); sb.append(" ["); sb.append(event.getThreadName()); sb.append("] "); sb.append(event.getLevel().toString()); sb.append(" "); sb.append(event.getLoggerName()); sb.append(" - "); sb.append(event.getFormattedMessage()); sb.append(CoreConstants.LINE_SEPARATOR); IThrowableProxy tp = event.getThrowableProxy(); if (tp != null) { String stackTrace = tpc.convert(event); sb.append(stackTrace); } return sb.toString(); } }
发现doLayout做的操作跟打印的出来格式一模一样的
