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

<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>4.0.0modelVersion>

    <groupId>comgroupId>
    <artifactId>mybatis-jdk-proxyartifactId>
    <version>1.0-SNAPSHOTversion>
    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.pluginsgroupId>
                <artifactId>maven-compiler-pluginartifactId>
                <configuration>
                    <source>8source>
                    <target>8target>
                configuration>
            plugin>
        plugins>
    build>

    <dependencies>
        <dependency>
            <groupId>mysqlgroupId>
            <artifactId>mysql-connector-javaartifactId>
            <version>8.0.18version>
        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;

    @Override
    public 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;
    }

    @Override
    public 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