[大数据]Mybatis底层源码解析以及Sql语句的构建

mybatis-config.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <properties resource="jdbc.properties"></properties>
    <settings>
        <setting name="logImpl" value="LOG4J"/>
    </settings>
    <!-- 为包下面的类 指定别名 name 包名   包下面类 默认别名就是类名   -->
    <typeAliases>
        <package name="com.wxz.domain"></package>
    </typeAliases>
    <plugins>
        <plugin interceptor="com.github.pagehelper.PageInterceptor"></plugin>
    </plugins>

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="${driver}"/>
                <property name="url" value="${url}"/>
                <property name="username" value="${username}"/>
                <property name="password" value="${password}"/>
            </dataSource>
        </environment>
    </environments>

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

UserMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
  PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.wxz.mapper.UserMapper">
  <select id="selectOne" resultType="com.wxz.domain.User" >
    select id as id,name as name , address as address ,age as age from user where id = 4
  </select>
  <select id="selectAll" resultType="com.wxz.domain.User" >
    select id as id,name as name , address as address ,age as age from user
</select>
</mapper>

UserMapper

package com.wxz.mapper;

import com.wxz.domain.User;

import java.util.List;

public interface UserMapper {

    public User selectOne();


    public List<User> selectAll();

}

测试类

package com.wxz;

import com.wxz.domain.User;
import com.wxz.mapper.UserMapper;
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 java.io.IOException;
import java.io.InputStream;

/**
 * TODO
 *
 * @author wxz
 * @date 2022/1/9 16:35
 */
public class Test {
    public static void main(String[] args) {
        InputStream inputStream = null;
        try {
            inputStream = Resources.getResourceAsStream("mybatis-config.xml");
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
            SqlSession sqlSession = sqlSessionFactory.openSession();
            User user = sqlSession.selectOne("com.wxz.mapper.UserMapper.selectOne");
//          UserMapper userDao = sqlSession.getMapper(UserMapper.class);
//          User user = userDao.selectOne();
            System.out.println(user);
        } catch (IOException e) {
            e.printStackTrace();
        }

    }
}

第一步,解析mybatis-config.xml文件

XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);

?找到mybatis-config.xml中的根节点configuration

?解析配置文件中所有的节点

?找到mappers节点中resource再去解析UserMapper.xml文件

?开始解析UserMapper.xml文件中的mapper节点

?namespace==boundType,并且将namespace放进configration类loadedResources中

将接口放入

将接口(namespace)放进configration 类mapperRegistry中? knownMappers

Map<Class<?>, MapperProxyFactory<?>> knownMappers = new HashMap();

?

为接口创建代理类,(com.wxz.mapper.UserMapper)放入map容器中,使用接口的class对象作为key(UserMapper.class),value值为 MapperProxyFactory<?>

查询的时候,UserMapper.class作为参数,如果namespace和接口的全路径不一致,则抛出绑定异常

?

??Map<Method, MapperMethodInvoker> methodCache = new ConcurrentHashMap()

在MapperProxyFactory<?>中又创建一个map,将方法名称作为key,value值为MapperMethodInvoker,包含sql的标签,包含sql命令的类型,id值

<select id="selectOne" resultType="com.wxz.domain.User" >
    select id as id,name as name , address as address ,age as age from user where id = 4
  </select>

总之,将接口的代理类放入mapperRegistry中,

?同时将namespace+id? 作为key,valueMappedStatement?放入mappedStatements中

Map<String, MappedStatement> mappedStatements;

?第二步:将xml信息转化为Configuration类对象

?第三步:将Configuration类对象作为参数传入,创建一个SqlSessionFactory对象

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

?第四步:实际上 new DefaultSqlSessionFactory(config)

?第五步:根据sqlSessionFactory获取sqlSession

SqlSession sqlSession = sqlSessionFactory.openSession();

?第六步:具体的数据库操作

第一种:使用(namespace+id)作为key,去mappedStatements中查询

 public <T> T selectOne(String statement, Object parameter) {
        List<T> list = this.selectList(statement, parameter);
        if (list.size() == 1) {
            return list.get(0);
        } else if (list.size() > 1) {
            throw new TooManyResultsException("Expected one result (or null) to be returned by selectOne(), but found: " + list.size());
        } else {
            return null;
        }
    }

statement就是namespace+id 在前面就将namespace+id 作为key放入map中,value是mappedStatent根据key查询mappedStatent

第七步:根据statement找到对应的MappedStatement MappedStatement ms = this.configuration.getMappedStatement(statement);

第八步:调用executor去查询,从MappedStatement获取到sql语句

var6 = this.executor.query(ms, this.wrapCollection(parameter), rowBounds, handler);?
BoundSql boundSql = ms.getBoundSql(parameterObject);

第九步:查询缓存,从缓存中获取,若缓存没有,则查询数据库,再放入缓存中

?第十步:根据结果映射关系将查询的结果转化为具体的指定的类 ,此处将查询到的结果转化为User对象

第二种:使用代理(UserMapper.class)作为key,去mapperRegistry中查询

?

?上面已经说明了代理的实现,mybatis源码分析到此结束

根据接口创建代理类(com.wxz.mapper.UserMapper)放入容器中,使用接口的class对象作为key(UserMapper.class),value值为 MapperProxyFactory<?>

private final Map<Class<?>, MapperProxyFactory<?>> knownMappers = new HashMap();

Mabatis中?sql语句的构建

?

public String parse(String text) {
        if (text != null && !text.isEmpty()) {
            int start = text.indexOf(this.openToken);
            if (start == -1) {
                return text;
            } else {
                char[] src = text.toCharArray();
                int offset = 0;
                StringBuilder builder = new StringBuilder();
                StringBuilder expression = null;

                do {
                    if (start > 0 && src[start - 1] == '\\') {
                        builder.append(src, offset, start - offset - 1).append(this.openToken);
                        offset = start + this.openToken.length();
                    } else {
                        if (expression == null) {
                            expression = new StringBuilder();
                        } else {
                            expression.setLength(0);
                        }

                        builder.append(src, offset, start - offset);
                        offset = start + this.openToken.length();

                        int end;
                        for(end = text.indexOf(this.closeToken, offset); end > -1; end = text.indexOf(this.closeToken, offset)) {
                            if (end <= offset || src[end - 1] != '\\') {
                                expression.append(src, offset, end - offset);
                                break;
                            }

                            expression.append(src, offset, end - offset - 1).append(this.closeToken);
                            offset = end + this.closeToken.length();
                        }

                        if (end == -1) {
                            builder.append(src, start, src.length - start);
                            offset = src.length;
                        } else {
                            builder.append(this.handler.handleToken(expression.toString()));
                            offset = end + this.closeToken.length();
                        }
                    }

                    start = text.indexOf(this.openToken, offset);
                } while(start > -1);

                if (offset < src.length) {
                    builder.append(src, offset, src.length - offset);
                }

                return builder.toString();
            }
        } else {
            return "";
        }
    }