JAVA语言之MyBatis源码解读-职坐标

JAVA语言之MyBatis源码解读

小标 2019-03-27 来源：阅读 614 评论 0

摘要：本文主要向大家介绍了JAVA语言之MyBatis源码解读，通过具体的内容向大家展示，希望对大家学习JAVA语言有所帮助。

本文主要向大家介绍了JAVA语言之MyBatis源码解读，通过具体的内容向大家展示，希望对大家学习JAVA语言有所帮助。

JAVA语言之MyBatis源码解读

之前我们通过图片讲解了Mybatis底层原理，今天我们就从源码入手去解读下Mybatis这个持久化框架是如何执行SQL的这个完整过程。

老样子，我们在看源码之前先写下demo，参考官方文档进行编写即可。
mysql5.7\mybatis1.3.9\springboot项目

mybatisdemo

User表的model类

package com.ckmike.mybatisdemo.model;

import java.util.Date;

/**
 * User 简要描述
 * <p> TODO:描述该类职责 </p>
 *
 * @author ckmike
 * @version 1.0
 * @date 18-12-16 下午3:14
 * @copyright ckmike
 **/
public class User {

    private int id;
    private String name;
    private int age;
    private String address;
    private Date ctime;

    public User() {  }

    public User(int id, String name, int age, String address, Date ctime) {
        this.id = id;
        this.name = name;
        this.age = age;
        this.address = address;
        this.ctime = ctime;
    }

    public void setId(int id) {
        this.id = id;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public void setCtime(Date ctime) {
        this.ctime = ctime;
    }

    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public int getAge() {
        return age;
    }

    public String getAddress() {
        return address;
    }

    public Date getCtime() {
        return ctime;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age +
                ", address='" + address + '\'' +
                ", ctime=" + ctime +
                '}';
    }
}

UserMapper接口

package com.ckmike.mybatisdemo.mapper;

import com.ckmike.mybatisdemo.model.User;
import org.apache.ibatis.annotations.Mapper;

import java.util.List;

/**
 * @ClassName UserMapper
 * @Description TODO:描述该接口职责
 * @Author ckmike
 * @Date 18-12-16 下午3:18
 * @Version 1.0
 * @Copyright ckmike
 **/
@Mapper
public interface UserMapper {

    List<User> getUser();
}

UserMapper.xml接口映射SQL文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "//mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="com.ckmike.mybatisdemo.mapper.UserMapper">

    <select id="getUser" resultType="com.ckmike.mybatisdemo.model.User">
        SELECT * FROM user;
    </select>
</mapper>

mybatis-config.xml配置文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "//mybatis.org/dtd/mybatis-3-config.dtd">

<configuration>

    <settings>
        <setting name="cacheEnabled" value="true"/>
        <setting name="lazyLoadingEnabled" value="false"/>
        <setting name="logImpl" value="STDOUT_LOGGING"/>
    </settings>

    <typeAliases>
        <typeAlias type="com.ckmike.mybatisdemo.model.User" alias="User"/>
    </typeAliases>

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC" /> <!-- 声明使用那种事务管理机制 JDBC/MANAGED -->
            <!-- 配置数据库连接信息 -->
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver" />
                <property name="url" value="jdbc:mysql://127.0.0.1:3306/ckmike?serverTimezone=UTC&amp;useUnicode=true&amp;characterEncoding=utf8&amp;characterSetResults=utf8&amp;useSSL=false&amp;verifyServerCertificate=false&amp;autoReconnct=true&amp;autoReconnectForPools=true&amp;allowMultiQueries=true" />
                <property name="username" value="root" />
                <property name="password" value="******" />
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper resource="mybatis/UserMapper.xml"/>
    </mappers>

</configuration>

这里开启了mybatis日志执行输出。

接下来就是看测试代码：

package com.ckmike.mybatisdemo;

import com.ckmike.mybatisdemo.mapper.UserMapper;
import com.ckmike.mybatisdemo.model.User;
import com.ckmike.mybatisdemo.service.UserService;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringRunner;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

@RunWith(SpringRunner.class)
@SpringBootTest
public class MybatisDemoApplicationTests {

    @Autowired
    private UserService userService;

    @Test
    public void contextLoads() {
        // 1. 通过服务调用，获取users
        List<User> userList = this.userService.getUser();
        System.out.println(userList.get(0).toString());

        try {
            InputStream is = Resources.getResourceAsStream("mybatis-config.xml");
            // 2.通过执行sql获取
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);

            SqlSession session = sqlSessionFactory.openSession();

            String sql = "com.ckmike.mybatisdemo.mapper.UserMapper.getUser";
            List<User> list = session.selectList(sql);

            System.out.println(list.get(0).toString());

            // 3.通过获取Mapper
            UserMapper userMapper = session.getMapper(UserMapper.class);
            List<User> users = userMapper.getUser();
            System.out.println(users.get(0).toString());

            session.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

}

分析：
上面我们总共用来三种方式去调用mybatis执行sql语句，返回结果。
1.通过SpringBoot初始化项目，注入UserService调用UserMapper接口代理实例返回mybatis执行结果。
2.通过mybatis配置文件，构建一个SqlSessionFactory，开启一个SqlSession，通过执行UserMapper接口映射的方法返回结果。
3.通过SqlSession获取到UserMapper接口的代理实例，直接调用接口执行SQL返回结果。

其实上面1和3是同一种方式。只是前者通过application配置初始化了SqlSessionFactory,后续跟3是一致的。

那么我们就通过2和3两种方式开始解读这个mybatis源码，看看底层代码的设计实现是怎么样。

SqlSessionFactoryBuilder

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package org.apache.ibatis.session;

import java.io.IOException;
import java.io.InputStream;
import java.io.Reader;
import java.util.Properties;
import org.apache.ibatis.builder.xml.XMLConfigBuilder;
import org.apache.ibatis.exceptions.ExceptionFactory;
import org.apache.ibatis.executor.ErrorContext;
import org.apache.ibatis.session.defaults.DefaultSqlSessionFactory;

public class SqlSessionFactoryBuilder {
    public SqlSessionFactoryBuilder() {
    }

    public SqlSessionFactory build(Reader reader) {
        return this.build((Reader)reader, (String)null, (Properties)null);
    }

    public SqlSessionFactory build(Reader reader, String environment) {
        return this.build((Reader)reader, environment, (Properties)null);
    }

    public SqlSessionFactory build(Reader reader, Properties properties) {
        return this.build((Reader)reader, (String)null, properties);
    }

    public SqlSessionFactory build(Reader reader, String environment, Properties properties) {
        SqlSessionFactory var5;
        try {
            XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties);
            var5 = this.build(parser.parse());
        } catch (Exception var14) {
            throw ExceptionFactory.wrapException("Error building SqlSession.", var14);
        } finally {
            ErrorContext.instance().reset();

            try {
                reader.close();
            } catch (IOException var13) {
                ;
            }

        }

        return var5;
    }

    public SqlSessionFactory build(InputStream inputStream) {
        return this.build((InputStream)inputStream, (String)null, (Properties)null);
    }

    public SqlSessionFactory build(InputStream inputStream, String environment) {
        return this.build((InputStream)inputStream, environment, (Properties)null);
    }

    public SqlSessionFactory build(InputStream inputStream, Properties properties) {
        return this.build((InputStream)inputStream, (String)null, properties);
    }

    public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
        SqlSessionFactory var5;
        try {
            XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
            var5 = this.build(parser.parse());
        } catch (Exception var14) {
            throw ExceptionFactory.wrapException("Error building SqlSession.", var14);
        } finally {
            ErrorContext.instance().reset();

            try {
                inputStream.close();
            } catch (IOException var13) {
                ;
            }

        }

        return var5;
    }

    public SqlSessionFactory build(Configuration config) {
        return new DefaultSqlSessionFactory(config);
    }
}

上面这个SqlSessionFactoryBuilder类非常的简单，就是构建SqlSessionFactory的工具类。可以通过Configuration类初始化一个SqlSessionFactory，也可以通过文件流的形式加载XML配置文件初始化SqlSessionFactory，不管Configuration也好、文件流也好，都是通过XML文件去构造Configuration或者文件流，核心就是Mybatis-config配置构造SqlSessionFactory.最终都是得到一个DefaultSqlSessionFactory（实现了SqlSessionFactory接口）。

DefaultSqlSessionFactory


package org.apache.ibatis.session.defaults;

import java.sql.Connection;
import java.sql.SQLException;
import org.apache.ibatis.exceptions.ExceptionFactory;
import org.apache.ibatis.executor.ErrorContext;
import org.apache.ibatis.executor.Executor;
import org.apache.ibatis.mapping.Environment;
import org.apache.ibatis.session.Configuration;
import org.apache.ibatis.session.ExecutorType;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.TransactionIsolationLevel;
import org.apache.ibatis.transaction.Transaction;
import org.apache.ibatis.transaction.TransactionFactory;
import org.apache.ibatis.transaction.managed.ManagedTransactionFactory;

public class DefaultSqlSessionFactory implements SqlSessionFactory {
    private final Configuration configuration;

    public DefaultSqlSessionFactory(Configuration configuration) {
        this.configuration = configuration;
    }

    public SqlSession openSession() {
        return this.openSessionFromDataSource(this.configuration.getDefaultExecutorType(), (TransactionIsolationLevel)null, false);
    }

    public SqlSession openSession(boolean autoCommit) {
        return this.openSessionFromDataSource(this.configuration.getDefaultExecutorType(), (TransactionIsolationLevel)null, autoCommit);
    }

    public SqlSession openSession(ExecutorType execType) {
        return this.openSessionFromDataSource(execType, (TransactionIsolationLevel)null, false);
    }

    public SqlSession openSession(TransactionIsolationLevel level) {
        return this.openSessionFromDataSource(this.configuration.getDefaultExecutorType(), level, false);
    }

    public SqlSession openSession(ExecutorType execType, TransactionIsolationLevel level) {
        return this.openSessionFromDataSource(execType, level, false);
    }

    public SqlSession openSession(ExecutorType execType, boolean autoCommit) {
        return this.openSessionFromDataSource(execType, (TransactionIsolationLevel)null, autoCommit);
    }

    public SqlSession openSession(Connection connection) {
        return this.openSessionFromConnection(this.configuration.getDefaultExecutorType(), connection);
    }

    public SqlSession openSession(ExecutorType execType, Connection connection) {
        return this.openSessionFromConnection(execType, connection);
    }

    public Configuration getConfiguration() {
        return this.configuration;
    }

    private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
        Transaction tx = null;

        DefaultSqlSession var8;
        try {
            Environment environment = this.configuration.getEnvironment();
            TransactionFactory transactionFactory = this.getTransactionFactoryFromEnvironment(environment);
            tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
            Executor executor = this.configuration.newExecutor(tx, execType);
            var8 = new DefaultSqlSession(this.configuration, executor, autoCommit);
        } catch (Exception var12) {
            this.closeTransaction(tx);
            throw ExceptionFactory.wrapException("Error opening session.  Cause: " + var12, var12);
        } finally {
            ErrorContext.instance().reset();
        }

        return var8;
    }

    private SqlSession openSessionFromConnection(ExecutorType execType, Connection connection) {
        DefaultSqlSession var8;
        try {
            boolean autoCommit;
            try {
                autoCommit = connection.getAutoCommit();
            } catch (SQLException var13) {
                autoCommit = true;
            }

            Environment environment = this.configuration.getEnvironment();
            TransactionFactory transactionFactory = this.getTransactionFactoryFromEnvironment(environment);
            Transaction tx = transactionFactory.newTransaction(connection);
            Executor executor = this.configuration.newExecutor(tx, execType);
            var8 = new DefaultSqlSession(this.configuration, executor, autoCommit);
        } catch (Exception var14) {
            throw ExceptionFactory.wrapException("Error opening session.  Cause: " + var14, var14);
        } finally {
            ErrorContext.instance().reset();
        }

        return var8;
    }

    private TransactionFactory getTransactionFactoryFromEnvironment(Environment environment) {
        return