spring-boot日志相关梳理(-)

背景：日常开发使用的是spring-boot框架，日志配置方式基本都是各个仓库相互copy的配置，究其为何如此配置不知原因，大多数都是尝试操作。

问题list：

日志整体理解很难，阐述一下要求证的问题，明确一下学习的边界。

1.spring-boot-starter-logging里使用的是什么日志，是如何生效的。

2.spring-boot 项目里如何配置logging

3.常见的日志框架或者api之间的关系：spring-boot-starter-logging, java.util.logging, slf4j, org.apache.commons.logging，logback, log4j,log4j2,slf4j2 

4.lombok里的和日志相关的注解代表什么？和对应的日志框架是如何配置使用的。

5.以其中一个log框架为例，梳理其和spring-boot 和lombok的组合使用方式.

 

学习过程：

1. spring-boot-starter-logging.jar 基本解释

我们发现spring-boot-starter-logging.jar里只有 META-INF/MANIFEST.MF

Manifest-Version: 1.0
Implementation-Title: Spring Boot Logging Starter
Automatic-Module-Name: spring.boot.starter.logging
Implementation-Version: 2.1.3.RELEASE
Built-By: Spring
Created-By: Apache Maven 3.6.0
Build-Jdk: 1.8.0_202

以及对应的pom依赖：

<dependencies>
    <dependency>
      <groupId>ch.qos.logback</groupId>
      <artifactId>logback-classic</artifactId>
      <version>1.2.3</version>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>org.apache.logging.log4j</groupId>
      <artifactId>log4j-to-slf4j</artifactId>
      <version>2.11.2</version>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>org.slf4j</groupId>
      <artifactId>jul-to-slf4j</artifactId>
      <version>1.7.25</version>
      <scope>compile</scope>
    </dependency>
  </dependencies>

关于spring-boot-starter-*格式：https://juejin.im/post/5d9f41eae51d4578034d2db2

针对于spring-boot-starter-logging 总结起来就是：

（1）pom 文件里引入了相关依赖(具体的第三方实现)； 

  (2) MANIFEST.MF Automatic-Module-Name 指定了logging入口相关的在  spring-boot-autoconfigure.jar包org.springframework.boot.autoconfigure下对应的目录(logging)

 (3) spring-boot-autoconfigure/META-INF/spring.factories中声明了logging starter的入口类

org.springframework.boot.autoconfigure.logging.ConditionEvaluationReportLoggingListener

2.spring-boot-logging-starter 代码分析

类：org.springframework.boot.autoconfigure.logging.ConditionEvaluationReportLoggingListener

LogFactory，LogAdapter都是spring-jcl里内容

public class ConditionEvaluationReportLoggingListener implements ApplicationContextInitializer<ConfigurableApplicationContext> {
    private final Log logger = LogFactory.getLog(getClass());

    /** */
}


public abstract class LogFactory {

	/**	 */
	public static Log getLog(Class<?> clazz) {
		return getLog(clazz.getName());
	}

	/**	 */
	public static Log getLog(String name) {
		return LogAdapter.createLog(name);
	}

    /***/
}


final class LogAdapter {

	private static final String LOG4J_SPI = "org.apache.logging.log4j.spi.ExtendedLogger";

	private static final String LOG4J_SLF4J_PROVIDER = "org.apache.logging.slf4j.SLF4JProvider";

	private static final String SLF4J_SPI = "org.slf4j.spi.LocationAwareLogger";

	private static final String SLF4J_API = "org.slf4j.Logger";


	private static final LogApi logApi;

	static {
		if (isPresent(LOG4J_SPI)) {
			if (isPresent(LOG4J_SLF4J_PROVIDER) && isPresent(SLF4J_SPI)) {
				// log4j-to-slf4j bridge -> we'll rather go with the SLF4J SPI;
				// however, we still prefer Log4j over the plain SLF4J API since
				// the latter does not have location awareness support.
				logApi = LogApi.SLF4J_LAL;
			}
			else {
				// Use Log4j 2.x directly, including location awareness support
				logApi = LogApi.LOG4J;
			}
		}
		else if (isPresent(SLF4J_SPI)) {
			// Full SLF4J SPI including location awareness support
			logApi = LogApi.SLF4J_LAL;
		}
		else if (isPresent(SLF4J_API)) {
			// Minimal SLF4J API without location awareness support
			logApi = LogApi.SLF4J;
		}
		else {
			// java.util.logging as default
			logApi = LogApi.JUL;
		}
	}

public static Log createLog(String name) {
		switch (logApi) {
			case LOG4J:
				return Log4jAdapter.createLog(name);
			case SLF4J_LAL:
				return Slf4jAdapter.createLocationAwareLog(name);
			case SLF4J:
				return Slf4jAdapter.createLog(name);
			default:
				return JavaUtilAdapter.createLog(name);
		}
	}

  /**/

	}

到这一步基本搞懂了spring-boot-starter-logging是怎么处理日志的？

1. 日志的入口在autoconfigure

2.autoconfigure 里和日志相关的依赖

3.spring-jcl自己包了一层，支持slf4j 系列 ，log4j 系列，java原生日志记录

4.spring-boot-starter-logging 日志引入了相关的日志实现。

http://www.slf4j.org/images/legacy.png

这个图没理解，待看