Mybatis源码解析之日志模块

一、整体架构

Mybatis整体可以分为三层，此篇主要来解析一下提供基础支撑的日志模块ython 机器学习入门之pandas的使用

二、需求分析 

日志模块的需求:

1、Mybatis没有提供日志的实现类，需要接入第三方日志组件,但是第三方组件都有各自的Log级别，且各不相同

2、Mybatis需要统一提供trace、debug 、warn 、error四个级别。

3、自动扫描实现，并且第三方日志插件加载优先级如下：

slf4j->commonsLogging->log4J2->log4J->JdkLog

4、日志使用需要优雅嵌入主体功能中

三、源码分析

附类图：

来看源码如何实现

package org.apache.ibatis.logging;

import java.lang.reflect.Constructor;


public final class LogFactory {

  
  public static final String MARKER = "MYBATIS";

  private static Constructor logConstructor;

  static {
    tryImplementation(LogFactory::useSlf4jLogging);
    tryImplementation(LogFactory::useCommonsLogging);
    tryImplementation(LogFactory::useLog4J2Logging);
    tryImplementation(LogFactory::useLog4JLogging);
    tryImplementation(LogFactory::useJdkLogging);
    tryImplementation(LogFactory::useNoLogging);
  }

  private LogFactory() {
    // disable construction
  }

  public static Log getLog(Class clazz) {
    return getLog(clazz.getName());
  }

  public static Log getLog(String logger) {
    try {
      return logConstructor.newInstance(logger);
    } catch (Throwable t) {
      throw new LogException("Error creating logger for logger " + logger + ".  Cause: " + t, t);
    }
  }

  public static synchronized void useCustomLogging(Class clazz) {
    setImplementation(clazz);
  }

  public static synchronized void useSlf4jLogging() {
    setImplementation(org.apache.ibatis.logging.slf4j.Slf4jImpl.class);
  }

  public static synchronized void useCommonsLogging() {
    setImplementation(org.apache.ibatis.logging.commons.JakartaCommonsLoggingImpl.class);
  }

  public static synchronized void useLog4JLogging() {
    setImplementation(org.apache.ibatis.logging.log4j.Log4jImpl.class);
  }

  public static synchronized void useLog4J2Logging() {
    setImplementation(org.apache.ibatis.logging.log4j2.Log4j2Impl.class);
  }

  public static synchronized void useJdkLogging() {
    setImplementation(org.apache.ibatis.logging.jdk14.Jdk14LoggingImpl.class);
  }

  public static synchronized void useStdOutLogging() {
    setImplementation(org.apache.ibatis.logging.stdout.StdOutImpl.class);
  }

  public static synchronized void useNoLogging() {
    setImplementation(org.apache.ibatis.logging.nologging.NoLoggingImpl.class);
  }

  private static void tryImplementation(Runnable runnable) {
    if (logConstructor == null) {
      try {
        runnable.run();
      } catch (Throwable t) {
        // ignore
      }
    }
  }

  private static void setImplementation(Class implClass) {
    try {
      Constructor 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);
    }
  }

}

从LogFactory看出，这里使用到了适配器模式,将多个三方组建兼容适配成我们要的标准。

package org.apache.ibatis.logging;


public interface Log {

  boolean isDebugEnabled();

  boolean isTraceEnabled();

  void error(String s, Throwable e);

  void error(String s);

  void debug(String s);

  void trace(String s);

  void warn(String s);

}

这里Log定义标准，Jdk14LoggingImpl 就是适配器之一，实现Log

package org.apache.ibatis.logging.jdk14;

import java.util.logging.Level;
import java.util.logging.Logger;

import org.apache.ibatis.logging.Log;


public class Jdk14LoggingImpl implements Log {

  private final Logger log;

  public Jdk14LoggingImpl(String clazz) {
    log = Logger.getLogger(clazz);
  }

  @Override
  public boolean isDebugEnabled() {
    return log.isLoggable(Level.FINE);
  }

  @Override
  public boolean isTraceEnabled() {
    return log.isLoggable(Level.FINER);
  }

  @Override
  public void error(String s, Throwable e) {
    log.log(Level.SEVERE, s, e);
  }

  @Override
  public void error(String s) {
    log.log(Level.SEVERE, s);
  }

  @Override
  public void debug(String s) {
    log.log(Level.FINE, s);
  }

  @Override
  public void trace(String s) {
    log.log(Level.FINER, s);
  }

  @Override
  public void warn(String s) {
    log.log(Level.WARNING, s);
  }

}

使用适配器模式符合单一、依赖倒转、开闭等设计原则，每个适配器负责自己的特性，高层接口不依赖底层实现，互不耦合，对修改关闭，对扩展开放。

  static {
    tryImplementation(LogFactory::useSlf4jLogging);
    tryImplementation(LogFactory::useCommonsLogging);
    tryImplementation(LogFactory::useLog4J2Logging);
    tryImplementation(LogFactory::useLog4JLogging);
    tryImplementation(LogFactory::useJdkLogging);
    tryImplementation(LogFactory::useNoLogging);
  }
   //这里实现了日志组件的优先级加载

  private static void tryImplementation(Runnable runnable) {
   //若有该组件，并获取到这个类构造器，则后面的组件不再加载
    if (logConstructor == null) {
      try {
        runnable.run();
      } catch (Throwable t) {
        // ignore
      }
    }
  }

以上解决1、2、3点需求，再看如何解决第四点需求，附类图

 这里很明显用到了代理模式，在各种场景进行日志增强。

ConnectionLogger:负责打印链接信息和sql语句并创建PreparedStatementLogger.

PreparedStatementLogger:负责打印参数信息，并创建ResultsetLogger

ResultSetLogger:负责打印数据结果信息

package org.apache.ibatis.logging.jdbc;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.Statement;

import org.apache.ibatis.logging.Log;
import org.apache.ibatis.reflection.ExceptionUtil;


public final class ConnectionLogger extends baseJdbcLogger implements InvocationHandler {

  private final Connection connection;

  private ConnectionLogger(Connection conn, Log statementLog, int queryStack) {
    super(statementLog, queryStack);
    this.connection = conn;
  }

  @Override
  public Object invoke(Object proxy, Method method, Object[] params)
      throws Throwable {
    try {
      //如果是从Object继承的方法直接忽略
      if (Object.class.equals(method.getDeclaringClass())) {
        return method.invoke(this, params);
      }
      //如果是调用prepareStatement、prepareCall、createStatement的方法，打印要执行的
      //sql语句并返回prepareStatement的代理对象，让prepareStatement也具备日志打印能力
      //打印参数
      if ("prepareStatement".equals(method.getName()) || 
 "prepareCall".equals(method.getName())) {
        if (isDebugEnabled()) {
          //打印sql语句
          debug(" Preparing: " + removeExtraWhitespace((String) params[0]), true);
        }
        PreparedStatement stmt = (PreparedStatement) method.invoke(connection, params);
        //创建代理对象
        stmt = PreparedStatementLogger.newInstance(stmt, statementLog, queryStack);
        return stmt;
      } else if ("createStatement".equals(method.getName())) {
        //创建代理对象
        Statement stmt = (Statement) method.invoke(connection, params);
        stmt = StatementLogger.newInstance(stmt, statementLog, queryStack);
        return stmt;
      } else {
        return method.invoke(connection, params);
      }
    } catch (Throwable t) {
      throw ExceptionUtil.unwrapThrowable(t);
    }
  }


public static Connection newInstance(Connection conn, Log statementLog, int queryStack) {
    InvocationHandler handler = new ConnectionLogger(conn, statementLog, queryStack);
    ClassLoader cl = Connection.class.getClassLoader();
    return (Connection) Proxy.newProxyInstance(cl, new Class[]{Connection.class}, 
    handler);
}

  
  public Connection getConnection() {
    return connection;
  }

}