(二)Mybatis总结之经过Dao层与数据交互

Mybatis概述

定义: Mybatis是一个支持普通sql查询，存储过程和高级映射的优秀持久层框架。java

Mybatis是（半自动的）跟数据库打交道的orm（object relationship mapping 对象关系映射）框架.
MyBatis 是一个优秀的基于 Java 的持久层框架，它内部封装了 JDBC（Java数据库链接），使开发者只需关注 SQL 语句自己，而不用再花费精力去处理诸如注册驱动、建立 Connection、配置 Statement 等繁杂过程。

对框架的粗浅理解

框架做用:解耦,即下降耦合度，减小开发时间(偷懒)的东西,可是并不表明框架的运行速度很高。如下两个原则是框架的重要思想。mysql

重构原则：事不过三，三则重构（有三个地方代码重复）sql

“高内聚低耦合”作法：
- 写且只写一次
- 一个类只作一种事
- 一个方法只作一件事

Mybatis的特色

Sql语句写在XML文件中，实现了代码与Sql分离，下降耦合度
半自动的mybatis更利于开发人员设计Sql语句
简单易学
支持动态Sql

Mybatis配置和初步使用

Mybatis经过dao层与数据交互

1.pom.xml导入相应依赖数据库

<!-- mybatis核心包 -->
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.3.0</version>
        </dependency>
        <!-- mysql驱动包 -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.40</version>
        </dependency>

Maven要按照大佬博客说的配置,接下来file-->settings-->Maven-->Maven home directory设置为Maven安装包路径 而后user settings file 设置为安装包路径\conf\settings.xml,不然导依赖失败apache

2.mybatis核心配置mybatis-config.xmlsession

<?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="mysql.properties"/>
    
    <settings>
        <!--全局性设置懒加载。若是设为‘false’，则全部相关联的都会被初始化加载,默认值为false-->
        <setting name="lazyLoadingEnabled" value="true"/>
        <!--当设置为‘true’的时候，懒加载的对象可能被任何懒属性所有加载。不然，每一个属性都按需加载。默认值为true-->
        <setting name="aggressiveLazyLoading" value="false"/>
    </settings>
    <typeAliases>
        <!-- 其实就是将bean的替换成一个短的名字-->
        <typeAlias type="com.qf.pojo.User" alias="User"/>
    </typeAliases>
    <!--对事务的管理和链接池的配置-->
    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"></transactionManager>
            <dataSource type="POOLED"><!--POOLED：使用Mybatis自带的数据库链接池来管理数据库链接-->
                <property name="driver" value="${jdbc.driver}"/>
                <property name="url" value="${jdbc.url}"/>
                <property name="username" value="${jdbc.username}"/>
                <property name="password" value="${jdbc.password}"/>
            </dataSource>
        </environment>
    </environments>
    <!--mapping文件路径配置-->
    <mappers>
        <mapper resource="mapper/UserMapper.xml"/>
    </mappers>

</configuration>

3.配置mysql.propertiesmybatis

jdbc.driver=com.mysql.jdbc.Driver
jdbc.url=jdbc:mysql://127.0.0.1:3306/demo1?useUnicode=true&characterEncoding=utf8&characterSetResults=utf8
jdbc.username=root
jdbc.password=123456

其中?useUnicode=true&characterEncoding=utf8&characterSetResults=utf8是为了防止乱码而加的app

4.配置映射文件，如下有增删改查sql语句框架

<?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.qf.mybatisdemo.pojo.User">
 
    <!--部分查询->
    <select id="getUserByName" resultType="com.qf.mybatisdemo.pojo.User" parameterType="java.lang.String">
        SELECT * FROM USER where username = #{username}
    </select>
   
    <insert id="addUser" parameterType="com.qf.mybatisdemo.pojo.User" >
        insert into USER(username,age) values(#{username},#{age})
    </insert>

    <update id="updateUserAge" parameterType="com.qf.mybatisdemo.pojo.User">
        update user set age=#{age} where username=#{username}
    </update>

    <delete id="deleUser" parameterType="com.qf.mybatisdemo.pojo.User">
        delete from user where username=#{username} and age=#{age}
    </delete>
</mapper>

5.建立与数据库表的字段对应的实体类ide

package com.qf.mybatisdemo.pojo;

public class User {
    String username;
    int age;

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "User{" +
                "username='" + username + '\'' +
                ", age=" + age +
                '}';
    }
}

6.建立会话（dao层与数据库交互数据的介质）接口

package com.qf.mybatisdemo.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.Reader;

public class BaseDao {
    public SqlSession getSqlSession() {
        String fileName = "mybatis-config.xml";
        Reader reader = null;
        try {
            reader = Resources.getResourceAsReader(fileName);
        } catch (IOException e) {
            e.printStackTrace();
        }
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
        SqlSession sqlSession = sqlSessionFactory.openSession();
        return sqlSession;
    }
}

7.增删改查接口

package com.qf.mybatisdemo.dao;

import com.qf.mybatisdemo.pojo.User;
import org.apache.ibatis.session.SqlSession;

import java.util.List;

public class UserDao extends BaseDao{
    User user;

    /**
     * 根据名字查询
     */
    public User getUserByName(String userName) {
        SqlSession sqlSession = this.getSqlSession();
        user = sqlSession.selectOne("getUserByName",userName);
        return user;
    }


    /**
     * 增
     */
    public int addUser(User user) {
        int count = 0;
        SqlSession sqlSession = this.getSqlSession();
        count = sqlSession.insert("addUser",user);
        sqlSession.commit();
        return count;
    }

    /**
     * 改
     */
    public int updateUserAge(User user) {
        int count= 0;
        SqlSession sqlSession = this.getSqlSession();
        count = sqlSession.update("updateUserAge",user);
        sqlSession.commit();
        return count;
    }

    /**
     * 删除
     */
    public int deleUser(User user) {
        int count= 0;
        SqlSession sqlSession = this.getSqlSession();
        count = sqlSession.update("deleUser",user);
        sqlSession.commit();
        return count;
    }
}

8.测试类

package com.qf.mybatisdemo;

import com.qf.mybatisdemo.dao.UserDao;
import com.qf.mybatisdemo.pojo.User;
import org.junit.Test;

import javax.jws.soap.SOAPBinding;


public class TestMybatis {
    UserDao userDao;
    /**
     * 根据名字查询
     */
    @Test
    public void getUserByName () {
        User user;
        user = userDao.getUserByName("张三");
        System.out.println(user);
    }


    public static void main(String[] args) {
            UserDao userDao = new UserDao();

        /**
         * 增
         */
//            User user = new User();
//            int count = 0;
//            user.setAge(18);
//            user.setUsername("小风");
//            count = userDao.addUser(user);
//            System.out.println(count);

        /**
         * 改
         */
//        User user = new User();
//        int count = 0;
//        user.setAge(20);
//        user.setUsername("小风");
//        count = userDao.updateUserAge(user);
//        System.out.println("新的"+count);



        /**
         * 删
         */
        User user = new User();
        int count = 0;
        user.setAge(20);
        user.setUsername("小风");
        count = userDao.deleUser(user);
        System.out.println(count);
    }
}