mybatis读数据库

前言

本文介绍如何在java中使用mybatis，本文使用maven项目。

准备数据库

create table `Blog`(
    `id` INT(11) NOT NULL AUTO_INCREMENT,
    `name` CHAR(20) DEFAULT '' COMMENT '名字',
    PRIMARY KEY(`id`)
)COMMENT="博客";
INSERT INTO Blog (id,name) VALUES (101,'nick');
INSERT INTO Blog (name) VALUES ('nickqiu');

编码

• 新建maven项目org.nick.mybatistest，加入依赖

<?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>

    <groupId>org.nick</groupId>
    <artifactId>mybatis-demo</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.4.6</version>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.16.20</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.46</version>
        </dependency>
        <dependency>
            <groupId>com.google.code.gson</groupId>
            <artifactId>gson</artifactId>
            <version>2.8.4</version>
        </dependency>
    </dependencies>
</project>

• mybatis 配置 mybatisdemo/src/main/resources/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>
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://localhost:3306/test"/>
                <property name="username" value="root"/>
                <property name="password" value="123456"/>
                <!--<property name="url" value="${url}"/>-->
                <!--<property name="username" value="${username}"/>-->
                <!--<property name="password" value="${password}"/>-->
            </dataSource>
        </environment>
    </environments>
    <mappers>
        <mapper resource="sqlmapping/BlogMapper.xml"/>
    </mappers>
</configuration>

• 类配置文件mybatisdemo/src/main/resources/sqlmapping/BlogMapper.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="org.nick.mybatistest.BlogMapper">
    <select id="selectBlog" resultType="org.nick.mybatistest.entity.Blog">
    select * from Blog where id = #{id}
  </select>
</mapper>

• 实体类mybatisdemo/src/main/java/org/nick/mybatistest/entity/Blog.java

package org.nick.mybatistest.entity;
import lombok.Data;
@Data
public class Blog {
    private int id;
    private String name;
}

• 数据库链接类mybatisdemo/src/main/java/org/nick/mybatistest/dao/DbConnect.java

package org.nick.mybatistest.dao;

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;
/**
 * 链接数据库
 */
public class DbConnect {
    private static SqlSessionFactory sqlSessionFactory = null;
    private static String resource = "mybatis-config.xml";

    private static synchronized void get(){
        if(sqlSessionFactory == null){
            InputStream inputStream = null;
            try {
                inputStream = Resources.getResourceAsStream(resource);
                sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
            } catch (
            IOException e) {
                e.printStackTrace();
            }
        }
    }

    public static SqlSession  getSqlSection(){
        get();
        SqlSession session = sqlSessionFactory.openSession();
        return  session;
    }

}

• 测试类

package org.nick.mybatistest;

import com.google.gson.Gson;
import org.apache.ibatis.session.SqlSession;
import org.nick.mybatistest.dao.DbConnect;
import org.nick.mybatistest.entity.Blog;

public class Application {

    public static void main(String[] args) {

        SqlSession session = DbConnect.getSqlSection();
        try {
            Blog blog = (Blog) session.selectOne("org.nick.mybatistest.BlogMapper.selectBlog", 101);
            System.out.println("blog:"+new Gson().toJson(blog));
        } finally {
            session.close();
        }
    }
}

执行效果

image.png

改造使用接口

• 添加接口mapper类

package org.nick.mybatistest.dao;

import org.apache.ibatis.annotations.Select;
import org.nick.mybatistest.entity.Blog;

public interface BlogMapper1 {
    @Select("SELECT * FROM blog WHERE id = #{id}")
    Blog selectBlog(int id);
}

• 修改DB链接类的get方法，java代码中添加mapper

 package org.nick.mybatistest.dao;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.Configuration;
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;


/**
 * 链接数据库
 */
public class DbConnect {
    private static SqlSessionFactory sqlSessionFactory = null;
    private static String resource = "mybatis-config.xml";

    private static synchronized void get(){
        if(sqlSessionFactory == null){
            InputStream inputStream = null;
            try {
                inputStream = Resources.getResourceAsStream(resource);
                sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
                Configuration configuration = sqlSessionFactory.getConfiguration();
                configuration.addMapper(BlogMapper1.class);
            } catch (
            IOException e) {
                e.printStackTrace();
            }
        }
    }

    public static SqlSession  getSqlSection(){
        get();
        SqlSession session = sqlSessionFactory.openSession();
        return  session;
    }

}

• 新的测试类

package org.nick.mybatistest;

import com.google.gson.Gson;
import org.apache.ibatis.session.SqlSession;
import org.nick.mybatistest.dao.BlogMapper1;
import org.nick.mybatistest.dao.DbConnect;
import org.nick.mybatistest.entity.Blog;

public class Application1 {
    public static void main(String[] args) {

        SqlSession session = DbConnect.getSqlSection();
        try {
            BlogMapper1 mapper = session.getMapper(BlogMapper1.class);
            Blog blog = mapper.selectBlog(101);
            System.out.println("blog:"+new Gson().toJson(blog));
        } finally {
            session.close();
        }
    }
}