mybatis 日志加载

墨蓝 2022-05-20 03:07 155阅读 0赞

# mybatis 日志处理 #

为了避免歧义,这里附上分析的版本号

<table> 
 <tbody> 
  <tr> 
   <td>名称</td> 
   <td>版本</td> 
  </tr> 
  <tr> 
   <td>java</td> 
   <td>1.8.0_102</td> 
  </tr> 
  <tr> 
   <td>mybatis</td> 
   <td>3.4.6</td> 
  </tr> 
 </tbody> 
</table>

# 环境 #

## maven ##

<dependency>
                <groupId>org.mybatis</groupId>
                <artifactId>mybatis</artifactId>
                <version>3.4.6</version>
            </dependency>
    
            <dependency>
                <groupId>junit</groupId>
                <artifactId>junit</artifactId>
                <version>4.12</version>
            </dependency>

## 例子 ##

public class LogTest {
            public static void main(String[] args) {
                org.apache.ibatis.logging.Log log = org.apache.ibatis.logging.LogFactory.getLog(LogTest.class);
                log.debug("debug message");
            }
        }

控制台没有任何输出.

# 分析加载过程 #

首先分析 org.apache.ibatis.logging.LogFactory 类加载时调用的静态区域

static {
        tryImplementation(() -> {useSlf4jLogging();); tryImplementation(() -> {useCommonsLogging();); tryImplementation(() -> {useLog4J2Logging();); tryImplementation(() -> {useLog4JLogging();); tryImplementation(() -> {useJdkLogging();); tryImplementation(() -> {useNoLogging();); }

按照 slf4j -> commons -> log4j2 -> log4j -> jdklog -> nolog 去加载日志.

<table> 
 <tbody> 
  <tr> 
   <td>名称</td> 
   <td>类别</td> 
   <td>描述</td> 
  </tr> 
  <tr> 
   <td>slf4j</td> 
   <td>接口</td> 
   <td>可以自由配置: log4j,logback,log4j2 等日志实现</td> 
  </tr> 
  <tr> 
   <td>commons-logging</td> 
   <td>接口</td> 
   <td>可以自由配置: log4j,logback,log4j2 等日志实现</td> 
  </tr> 
  <tr> 
   <td>log4j2</td> 
   <td>实现</td> 
   <td>log4j的第二代进化版本</td> 
  </tr> 
  <tr> 
   <td>log4j</td> 
   <td>实现</td> 
   <td>log4j第一代</td> 
  </tr> 
  <tr> 
   <td>jdklog</td> 
   <td>接口</td> 
   <td>配置jdk自带的 控制台,文件 或自定义日志</td> 
  </tr> 
  <tr> 
   <td>nolog</td> 
   <td>实现</td> 
   <td>所有日志打印均不作任何操作</td> 
  </tr> 
 </tbody> 
</table>

由于目前没有配置任何和日志有关的信息,所以这里一定会加载到 jdklog

接下来逐步分析每个类型的加载过程

## slf4j ##

public static synchronized void useSlf4jLogging() {
            setImplementation(org.apache.ibatis.logging.slf4j.Slf4jImpl.class);
        }
    
    
      private static void setImplementation(Class<? extends Log> implClass) { 
          try {
            Constructor<? extends Log> candidate = implClass.getConstructor(String.class);
            Log log = candidate.newInstance(LogFactory.class.getName());
            if (log.isDebugEnabled()) {
              log.debug("Logging initialized using '" + implClass + "' adapter.");
            }
            logConstructor = candidate;
          } catch (Throwable t) {
            throw new LogException("Error setting Log implementation. Cause: " + t, t);
          }
        }

实际上就是创建 new Slf4jImpl(“org.apache.ibatis.logging.LogFactory”);

### 创建实现类 ###

源码中,是import 的 org.slf4j.Logger。 这里为了便于理解,直接加载类前面

public class Slf4jImpl implements org.apache.ibatis.logging.Log { 
    
      private org.apache.ibatis.logging.Log log;
    
      public Slf4jImpl(String clazz) {
        org.slf4j.Logger logger = org.slf4j.LoggerFactory.getLogger(clazz);
    
        if (logger instanceof org.slf4j.LocationAwareLogger) {
          try {
            // check for slf4j >= 1.6 method signature
            logger.getClass().getMethod("log", Marker.class, String.class, int.class, String.class, Object[].class, Throwable.class);
            log = new org.slf4j.Slf4jLocationAwareLoggerImpl((LocationAwareLogger) logger);
            return;
          } catch (SecurityException e) {
            // fail-back to Slf4jLoggerImpl
          } catch (NoSuchMethodException e) {
            // fail-back to Slf4jLoggerImpl
          }
        }
    
        // Logger is not LocationAwareLogger or slf4j version < 1.6
        log = new org.slf4j.Slf4jLoggerImpl(logger);
      }
      // 省略其他无关的方法
    }

使用适配器模式, 实现 org.apache.ibatis.logging.Log 接口,内部调用 org.slf4j.LoggerFactory.getLogger 的方法

这里分两种情况  
1. 找到 LoggerFactory 和 Logger 类, 创建代理对象 log = = new org.slf4j.Slf4jLoggerImpl(logger);  
2. 未找到 LoggerFactory 和 Logger 类, 抛出 java.lang.NoClassDefFoundError: org/slf4j/LoggerFactory, 然后被最顶层的 tryImplementation 捕获后忽略

这里说找到 LoggerFactory 和 Logger 类, 而不是说引入slf4j的jar包,

表示我们可以自己建立这两个类, 来替代实现. (不推荐, 引入jar包就行)

后面的内容都相同,直接附上不同的代理类和代理对象

## commons-logging ##

*  代理类: org.apache.ibatis.logging.commons.JakartaCommonsLoggingImpl.class
 *  代理对象: org.apache.commons.logging.Log

## log4j ##

*  代理类: org.apache.ibatis.logging.log4j.Log4jImpl.class
 *  代理对象: org.apache.log4j.Logger

## log4j2 ##

*  代理类: org.apache.ibatis.logging.commons.JakartaCommonsLoggingImpl.class
 *  代理对象: org.apache.logging.log4j.Logger

## jdk ##

*  代理类: org.apache.ibatis.logging.jdk14.Jdk14LoggingImpl.class
 *  代理对象: java.util.logging.Logger

## 加载流程图 ##

![mybatis日志流程图][mybatis]

# 使用 #

## log4j ##

### 添加maven配置 ###

### 添加 log4j.properties ###

log4j.rootLogger=TRACE, stdout
    
    log4j.appender.stdout=org.apache.log4j.ConsoleAppender
    log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
    log4j.appender.stdout.layout.ConversionPattern=%d{ABSOLUTE} %5p %t %c{
       2}:%L - %m%n

控制台输出:

11:49:19,636 DEBUG main logging.LogFactory:135 - Logging initialized using 'class org.apache.ibatis.logging.log4j.Log4jImpl' adapter.
    11:49:19,638 DEBUG main aya.LogTest:6 - debug message

## slf4j+log4j12 ##

### maven ###

<dependency>
                <groupId>org.apache.logging.log4j</groupId>
                <artifactId>log4j-slf4j-impl</artifactId>
                <version>2.11.0</version>
            </dependency>

log4j-slf4j-impl 2.11.0 会自动引入 slf4j 1.8.0-alpha2 和log4j 2.11.0 的依赖

### log4j2.xml ###

<?xml version="1.0" encoding="UTF-8"?>
    <Configuration status="DEBUG">
        <Appenders>
            <Console name="Console" target="SYSTEM_OUT">
                <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n"/>
            </Console>
        </Appenders>
        <Loggers>
            <Root level="DEBUG">
                <AppenderRef ref="Console"/>
            </Root>
        </Loggers>
    </Configuration>

运行程序,控制台输出:

12:19:01.191 [main] DEBUG com.aya.LogTest - debug message

# 总结 #

1.  自动查找顺序: slf4j -> commons -> log4j2 -> log4j -> jdklog -> nolog

可以在settings 设置 logImpl 指定以下的其中一种，未指定时自动查找  
1. SLF4J  
2. LOG4J  
3. LOG4J2  
4. JDK\_LOGGING  
5. COMMONS\_LOGGING  
6. STDOUT\_LOGGING  
7. NO\_LOGGING

# 资料 #

[http://www.mybatis.org/mybatis-3/zh/configuration.html\#settings][http_www.mybatis.org_mybatis-3_zh_configuration.html_settings]

[mybatis]: http://cdn.blog.shangwantong.com/mybatis/log/mybatis-log.png
[http_www.mybatis.org_mybatis-3_zh_configuration.html_settings]: http://www.mybatis.org/mybatis-3/zh/configuration.html#settings