实现MyBatis核心机制环境搭建

1.核心框架示意图

2.模块搭建

1.创建maven项目

2.引入依赖

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><parent><groupId>com.sunxiansheng</groupId><artifactId>core_mechanisms</artifactId><version>1.0-SNAPSHOT</version></parent><artifactId>sun-mybatis</artifactId><properties><maven.compiler.source>8</maven.compiler.source><maven.compiler.target>8</maven.compiler.target><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding></properties><dependencies><!-- 解析xml --><dependency><groupId>dom4j</groupId><artifactId>dom4j</artifactId><version>1.6.1</version></dependency><!-- mysql --><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>8.0.22</version></dependency><!-- lombok --><dependency><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId><version>1.18.30</version></dependency><!-- junit --><dependency><groupId>junit</groupId><artifactId>junit</artifactId><version>4.13.2</version></dependency></dependencies></project>

3.连接数据库

4.数据库表设计

CREATE DATABASE `sun_mybatis`;
USE `sun_mybatis`;CREATE TABLE `monster`
(`id`       INT          NOT NULL AUTO_INCREMENT,`age`      INT          NOT NULL,`birthday` DATE DEFAULT NULL,`email`    VARCHAR(255) NOT NULL,`gender`   TINYINT      NOT NULL,`name`     VARCHAR(255) NOT NULL,`salary`   DOUBLE       NOT NULL,PRIMARY KEY (`id`)
) CHARSET = utf8;INSERT INTO `monster` (`age`, `birthday`, `email`, `gender`, `name`, `salary`)
VALUES (25, '1998-01-15', 'example@example.com', 1, 'John Doe', 50000.00);

3.设计图

读取配置文件，得到数据库连接

1.目录

2.sun-config.xml 配置文件

<?xml version="1.0" encoding="utf-8" ?>
<!-- 配置数据库连接信息 -->
<database><!-- 驱动 --><property name="driverClassName" value="com.mysql.cj.jdbc.Driver"/><!-- 连接地址 --><property name="url" value="jdbc:mysql://bj--grp-.sql.tencentcdb.com:24169/sun_mybatis?useSSL=false&amp;useUnicode=true&amp;characterEncoding=UTF-8"/>    <!-- 用户名 --><!-- 用户名 --><property name="username" value=""/><!-- 密码 --><property name="password" value=""/>
</database>

3.SunConfiguration.java 读取配置文件获取数据库连接

package com.sunxiansheng.mybatis.sqlsession;import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;import java.io.InputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.List;/*** Description: 读取xml配置文件** @Author sun* @Create 2024/8/8 16:25* @Version 1.0*/
public class SunConfiguration {private static final Logger log = LoggerFactory.getLogger(SunConfiguration.class);private static ClassLoader loader = ClassLoader.getSystemClassLoader();/*** 读取xml文件** @param resource 这个必须是类路径下的文件路径，不用带第一个斜杠，sun-config.xml就可以* @return*/public Connection build(String resource) {InputStream resourceAsStream = loader.getResourceAsStream(resource);// 使用dom4j解析配置文件SAXReader saxReader = new SAXReader();try {// 获取文档Document document = saxReader.read(resourceAsStream);// 根元素Element rootElement = document.getRootElement();// 根元素下的所有property元素List<Element> property = rootElement.elements("property");// 初始化连接信息String driverClassName = null;String url = null;String username = null;String password = null;// 遍历property元素获取连接信息for (Element element : property) {String name = element.attributeValue("name");String value = element.attributeValue("value");switch (name) {case "driverClassName":driverClassName = value;log.info("加载驱动类:{}", value);break;case "url":url = value;log.info("加载url:{}", value);break;case "username":username = value;log.info("加载用户名:{}", value);break;case "password":password = value;log.info("加载密码:{}", value);break;default:throw new RuntimeException("未知的property属性名");}}// 类加载驱动类Class.forName(driverClassName);return DriverManager.getConnection(url, username, password);} catch (DocumentException | ClassNotFoundException | SQLException e) {log.error("解析xml配置文件失败", e);throw new RuntimeException(e);}}}

4.SunConfigurationTest.java 测试

package com.sunxiansheng.mybatis.sqlsession;import org.junit.Test;import java.sql.Connection;/*** Description: 读取xml配置文件** @Author sun* @Create 2024/8/8 16:25* @Version 1.0*/
public class SunConfigurationTest {@Testpublic void build() {SunConfiguration sunConfiguration = new SunConfiguration();Connection build = sunConfiguration.build("sun-config.xml");System.out.println("build = " + build);}}

使用SunExecutor来执行SQL

1.目录

2.Monster.java

package com.sunxiansheng.mybatis.entity;import lombok.Data;import java.io.Serializable;
import java.util.Date;@Data
public class Monster implements Serializable {private Integer id;private Integer age;private Date birthday;private String email;private Byte gender;private String name;private Double salary;private static final long serialVersionUID = 1L;
}

3.Executor.java

package com.sunxiansheng.mybatis.sqlsession;/*** Description: 执行器接口** @Author sun* @Create 2024/8/9 12:37* @Version 1.0*/
public interface Executor {public <T> T query(String sql, Object parameter);}

4.SunExecutor.java 具体的执行器

package com.sunxiansheng.mybatis.sqlsession;import com.sunxiansheng.mybatis.entity.Monster;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;/*** Description: 执行器** @Author sun* @Create 2024/8/9 12:39* @Version 1.0*/
public class SunExecutor implements Executor{public static final SunConfiguration configuration = new SunConfiguration();private static final Logger log = LoggerFactory.getLogger(SunExecutor.class);@Overridepublic <T> T query(String sql, Object parameter) {// 获取DB连接Connection connection = configuration.build("sun-config.xml");log.info("获取连接:{}", connection);ResultSet resultSet = null;PreparedStatement preparedStatement = null;// 实体类Monster monster = new Monster();try {// sql预处理preparedStatement = connection.prepareStatement(sql);// 填参数preparedStatement.setString(1, parameter.toString());// 执行查询resultSet = preparedStatement.executeQuery();// 将结果封装到实体类中（写死了）while (resultSet.next()) {monster.setId(resultSet.getInt("id"));monster.setAge(resultSet.getInt("age"));monster.setBirthday(resultSet.getDate("birthday"));monster.setEmail(resultSet.getString("email"));monster.setGender(resultSet.getByte("gender"));monster.setName(resultSet.getString("name"));monster.setSalary(resultSet.getDouble("salary"));}log.info("查询结果:{}", monster);} catch (Exception e) {throw new RuntimeException(e);} finally {// 关闭资源try {if (resultSet != null) {resultSet.close();}if (preparedStatement != null) {preparedStatement.close();}if (connection != null) {connection.close();}} catch (Exception e) {throw new RuntimeException(e);}}// 这里的T是由类型推断来指定的，也就是使用什么类型接受，就返回什么类型return (T) monster;}}

5.SunConfigurationTest.java 测试

@Test
public void executor() {SunExecutor sunExecutor = new SunExecutor();// 这里是使用的类型推断自动转换类型Monster monster = sunExecutor.query("select * from monster where id = ?", 1);
}

将SqlSession封装到执行器

1.目录

2.SunSqlSession.java

package com.sunxiansheng.mybatis.sqlsession;/*** Description: SqlSession** @Author sun* @Create 2024/8/9 13:08* @Version 1.0*/
public class SunSqlSession {// 执行器（操作db）private Executor executor = new SunExecutor();// 配置（用于获取连接）private SunConfiguration configuration = new SunConfiguration();public <T> T selectOne(String statement, Object parameter) {return executor.query(statement, parameter);}
}

3.测试

@Test
public void selectOne() {SunSqlSession sunSqlSession = new SunSqlSession();Monster monster = sunSqlSession.selectOne("select * from monster where id = ?", 1);System.out.println("monster = " + monster);
}

开发MapperBean和Function

1.目录

2.MonsterMapper.java

package com.sunxiansheng.mapper;import com.sunxiansheng.entity.Monster;/*** Description: MonsterMapper** @Author sun* @Create 2024/8/9 13:21* @Version 1.0*/
public interface MonsterMapper {public Monster getMonsterById(Integer id);}

3.MonsterMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<mapper namespace="com.sunxiansheng.mapper.MonsterMapper"><select id="getMonsterById" resultType="com.sunxiansheng.entity.Monster">select * from monster where id = ?</select>
</mapper>

4.Function.java 记录对应的mapper.xml的方法信息

package com.sunxiansheng.mybatis.config;import lombok.Data;/*** Description: 记录对应的mapper.xml的方法信息** @Author sun* @Create 2024/8/9 13:31* @Version 1.0*/
@Data
public class Function {/*** sql类型*/private String sqlType;/*** 方法名*/private String funcName;/*** SQL语句*/private String sql;/*** 返回类型*/private Object resultType;}

5.MapperBean.java 将mapper接口信息进行封装

package com.sunxiansheng.mybatis.config;import java.util.List;/*** Description: 将mapper接口信息进行封装** @Author sun* @Create 2024/8/9 13:35* @Version 1.0*/
public class MapperBean {/*** 接口全路径*/private String interfaceName;/*** 方法列表*/private List<Function> functions;}

读取xml文件解析MapperBean

1.目录

2.Function.java 加链式调用注解

3.MapperBean.java 加Data注解

4. SunConfiguration.java 增加解析MapperBean的方法

/*** 读取mapper.xml文件，构建MapperBean* @param path* @return*/
public MapperBean readMapper(String path) {// 要返回的结果MapperBean mapperBean = new MapperBean();// 使用类加载器读取配置文件ClassLoader loader = ClassLoader.getSystemClassLoader();InputStream resourceAsStream = loader.getResourceAsStream(path);// 解析xml文件SAXReader saxReader = new SAXReader();try {// 获取文档Document document = saxReader.read(resourceAsStream);// 获取根元素Element rootElement = document.getRootElement();// 获取根元素的属性：namespaceString namespace = rootElement.attributeValue("namespace");// 获取子元素List<Element> elements = rootElement.elements();// 遍历子元素List<Function> functions = elements.stream().map(element -> {Function function = new Function();// 获取sql类型String sqlType = element.getName();// 获取方法名String funcName = element.attributeValue("id");// 获取返回类型String resultType = element.attributeValue("resultType");// 获取sql语句String sql = element.getTextTrim();// 封装到Function对象中function.setSqlType(sqlType).setFuncName(funcName).setResultType(resultType).setSql(sql);return function;}).collect(Collectors.toList());// 构建MapperBeanmapperBean.setInterfaceName(namespace);mapperBean.setFunctions(functions);} catch (DocumentException e) {throw new RuntimeException(e);}// 输出mapperBean的日志log.info("mapperBean:{}", mapperBean);return mapperBean;
}

5.SunConfigurationTest.java 测试

    @Testpublic void readMapper() {SunConfiguration sunConfiguration = new SunConfiguration();sunConfiguration.readMapper("MonsterMapper.xml");}

动态代理Mapper方法

1.目录

2.MapperProxyFactory.java 代理工厂，可以获取接口的代理对象

package com.sunxiansheng.mybatis.sqlsession;import java.lang.reflect.Proxy;/*** Description: 代理工厂** @Author sun* @Create 2024/8/9 14:14* @Version 1.0*/
public class MapperProxyFactory {public static <T> T getMapperProxy(Class<T> clazz, SunSqlSession sunSqlSession, SunConfiguration sunConfiguration) {return (T) Proxy.newProxyInstance(clazz.getClassLoader(), new Class[]{clazz}, new SunMapperProxy(sunSqlSession, clazz, sunConfiguration));}}

3.SunMapperProxy.java 代理逻辑

package com.sunxiansheng.mybatis.sqlsession;import com.sunxiansheng.mybatis.config.Function;
import com.sunxiansheng.mybatis.config.MapperBean;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.util.List;/*** Description: 代理Mapper接口** @Author sun* @Create 2024/8/9 14:08* @Version 1.0*/
public class SunMapperProxy implements InvocationHandler {private static final Logger log = LoggerFactory.getLogger(SunMapperProxy.class);/*** 用于连接数据库和执行sql*/private SunSqlSession sunSqlSession;/*** mapper文件名*/private String mapperFile;/*** 配置类（可以根据mapper文件名来获取MapperBean）*/private SunConfiguration sunConfiguration;public SunMapperProxy(SunSqlSession sunSqlSession, Class<?> mapperFile, SunConfiguration sunConfiguration) {this.sunSqlSession = sunSqlSession;this.mapperFile = mapperFile.getSimpleName() + ".xml";this.sunConfiguration = sunConfiguration;}@Overridepublic Object invoke(Object proxy, Method method, Object[] args) throws Throwable {// 获取方法名String methodName = method.getName();// 获取MapperBeanMapperBean readMapper = sunConfiguration.readMapper(mapperFile);// 获取Function列表，过滤出需要执行的FunctionList<Function> functions = readMapper.getFunctions();Function targetFunction = null;for (Function function : functions) {if (methodName.equals(function.getFuncName())) {targetFunction = function;break;}}// 获取Function的信息String sqlType = targetFunction.getSqlType();String sql = targetFunction.getSql();// 将sql的第一个问号使用参数替换，使用字符串处理// 根据sqlType执行sqlif (sqlType.equals("select")) {Object selected = sunSqlSession.selectOne(sql, args[0]);log.info("invoke查询结果：{}", selected);return selected;}return null;}
}

4.测试

@Test
public void getResult() {MonsterMapper mapperProxy = MapperProxyFactory.getMapperProxy(MonsterMapper.class, new SunSqlSession(), new SunConfiguration());Monster monsterById = mapperProxy.getMonsterById(1);
}