Mr. Cappuccino的第57杯咖啡——简单手写Mybatis大致原理

大致原理

底层基于JDK动态代理技术实现

项目结构

项目代码

pom.xml

<?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><groupId>com</groupId><artifactId>mybatis-jdk-proxy</artifactId><version>1.0-SNAPSHOT</version><build><plugins><plugin><groupId>org.apache.maven.plugins</groupId><artifactId>maven-compiler-plugin</artifactId><configuration><source>8</source><target>8</target></configuration></plugin></plugins></build><dependencies><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>8.0.18</version></dependency></dependencies></project>

config.properties

driverClass=com.mysql.cj.jdbc.Driver
url=jdbc:mysql://127.0.0.1:3306/db_mybatis?serverTimezone=UTC
user=root
password=admin

UserEntity.java

package com.mybatis.entity;/*** @author honey* @date 2023-07-26 15:29:38*/
public class UserEntity {private Integer id;private String name;@Overridepublic String toString() {return "UserEntity{" +"id=" + id +", name='" + name + '\'' +'}';}
}

UserMapper.java

package com.mybatis.mapper;import com.mybatis.proxy.Insert;/*** @author honey* @date 2023-07-26 21:04:23*/
public interface UserMapper {/*** 新增用户** @return int*/@Insert("INSERT INTO `tb_user` (`id`, `name`) VALUES (null, 'Faker');")int insertUser();
}

Insert.java

package com.mybatis.proxy;import java.lang.annotation.*;/*** @author honey* @date 2023-07-27 20:48:38*/
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface Insert {String value();
}

JdbcUtils.java

package com.mybatis.proxy;import java.io.InputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.Properties;/*** @author honey* @date 2023-07-27 20:57:08*/
public class JdbcUtils {private JdbcUtils() {}private static String url;private static String user;private static String password;static {try {InputStream resourceAsStream = JdbcUtils.class.getClassLoader().getResourceAsStream("config.properties");Properties properties = new Properties();properties.load(resourceAsStream);String driverClass = properties.getProperty("driverClass");url = properties.getProperty("url");user = properties.getProperty("user");password = properties.getProperty("password");Class.forName(driverClass);} catch (Exception e) {e.printStackTrace();}}public static Connection getConnection() {try {return DriverManager.getConnection(url, user, password);} catch (Exception e) {e.printStackTrace();return null;}}public static void closeConnection(ResultSet resultSet, Statement statement, Connection connection) {try {if (resultSet != null) {resultSet.close();}if (statement != null) {statement.close();}if (connection != null) {connection.close();}} catch (Exception e) {e.printStackTrace();}}public static void closeConnection(Statement statement, Connection connection) {closeConnection(null, statement, connection);}
}

MapperProxy.java

package com.mybatis.proxy;import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.sql.Connection;
import java.sql.PreparedStatement;/*** @author honey* @date 2023-07-27 20:17:23*/
public class MapperProxy implements InvocationHandler {private final Class<?> mapperClass;public MapperProxy(Class<?> mapperClass) {this.mapperClass = mapperClass;}@Overridepublic Object invoke(Object proxy, Method method, Object[] args) throws Throwable {// 使用Java反射技术获取该方法上的注解Insert declaredAnnotation = method.getDeclaredAnnotation(Insert.class);String insertSql = declaredAnnotation.value();// 执行sql语句Connection connection = JdbcUtils.getConnection();PreparedStatement preparedStatement = connection.prepareStatement(insertSql);return preparedStatement.executeUpdate();}public <T> T getProxy() {return (T) Proxy.newProxyInstance(mapperClass.getClassLoader(), new Class[]{mapperClass}, this);}
}

SqlSession.java

package com.mybatis.proxy;/*** @author honey* @date 2023-07-27 21:10:30*/
public class SqlSession {public static <T> T getMapper(Class<T> type) {return new MapperProxy(type).getProxy();}
}

MybatisTest.java

package com.mybatis.test;import com.mybatis.mapper.UserMapper;
import com.mybatis.proxy.SqlSession;/*** @author honey* @date 2023-07-26 15:26:48*/
public class MybatisTest {public static void main(String[] args) {System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", "true");UserMapper userMapper = SqlSession.getMapper(UserMapper.class);int result = userMapper.insertUser();System.out.println(result);}
}

代码测试

运行MybatisTest类

SqlSession.java

MapperProxy.java

MybatisTest.java

MapperProxy.java

MybatisTest.java

运行结果