MyBatis见解

2023-12-21 13:07:16

一，mybatis介绍

为什么要使用mybatis?
手动创建和释放连接
对结果的解析
sql语句硬编译在代码中
什么是mybatis?
mybatis前身是apache的ibatis，是封装了jdbc的持久层框架，使开发者只需关注sql即可

二，mybatis入门

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.by</groupId>
    <artifactId>01_mybatis_HelloWorld</artifactId>
    <version>1.0-SNAPSHOT</version>
    
    <properties>
        <!-- 项目源码及编译输出的编码 -->
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <!-- 项目编译JDK版本 -->
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
    </properties>
    
    <dependencies>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.4.5</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            // 如果jdk的版本不是8.0以上，需要修改
            //<version>版本号</version>
            <version>5.1.47</version>
        </dependency>
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
    </dependencies>
    <build>
        <!-- 如果不添加此节点src/main/java目录下的所有配置文件都会被漏掉。 -->
        <resources>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.xml</include>
                </includes>
            </resource>
        </resources>
    </build>
</project>

log4j.properties

# Global logging configuration
log4j.rootLogger=DEBUG, stdout
# Console output...
log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%5p [%t] - %m%n

pojo

public class User implements Serializable {
    private Integer id;
    private String username;
    private Date birthday;
    private String sex;
    private String address;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getUsername() {
        return username;
    }

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

    public Date getBirthday() {
        return birthday;
    }

    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }

    public String getSex() {
        return sex;
    }

    public void setSex(String sex) {
        this.sex = sex;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", username='" + username + '\'' +
                ", birthday=" + birthday +
                ", sex='" + sex + '\'' +
                ", address='" + address + '\'' +
                '}';
    }
}

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>
 <configuration>
            <!--使用dev环境-->
            <environments default="dev">
                <!--dev环境-->
                <environment id="dev">
                    <transactionManager type="JDBC"></transactionManager>
                    <!--使用连接池中的数据源-->
                    <dataSource type="POOLED">
                    //jdk版本8以上的
                    // <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                    // <property name="url" value="jdbc:mysql://localhost:3306/mybatis?useSSL=false&amp;serverTimezone=Asia/Shanghai"/>
                        <property name="driver" value="com.mysql.jdbc.Driver"/>
                        <property name="url" value="jdbc:mysql://127.0.0.1:3306/mybatis?characterEncoding=UTF-8"/>
                        <property name="username" value="root"/>
                        <property name="password" value="1111"/>
                    </dataSource>
                </environment>
            </environments>
            <!-- 扫描映射文件 -->
            <mappers>
                <mapper resource="com/by/dao/UserDao.xml"/>
            </mappers>
        </configuration>

mapper

public interface UserDao{
            List<User> findAll();
        }

mapper.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="com.by.dao.UserDao">
            <select id="findAll" resultType="com.by.pojo.User">
                select * from user
            </select>
        </mapper>

pom.xml

 <build>
            <!-- 如果不添加此节点src/main/java目录下的所有配置文件都会被漏掉。 -->
            <resources>
                <resource>
                    <directory>src/main/java</directory>
                    <includes>
                        <include>**/*.xml</include>
                    </includes>
                </resource>
            </resources>
        </build>

三，mybatis的运行原理

在这里插入图片描述

四，mybatis传递多个参数

序号传递多个参数

WHERE id=#{arg0} AND username=#{arg1}
WHERE id=#{param1} AND username=#{param2}

// 定义的方法
User getUser(Integer id, String username);


<select id="getUser" resultType="com.by.pojo.User">
        <!--select * from user where id=#{arg0} and username=#{arg1}--><!-- arg0 arg1-->
        select * from user where id=#{param1} and username=#{param2}<!-- param1 param2-->
    </select>

/**
     * 序号传递多个参数
     * @throws IOException
     */
    @Test
    public void testGetUse() throws IOException {
        //返回接口的代理类
        UserDao userDao = sqlSession.getMapper(UserDao.class);
        User user = userDao.getUser(43,"俞莲舟");
        System.out.println(user);
    }

注解传递多个参数—【推荐】

User getUser2(@Param(“id”) Integer id, @Param(“username”) String username);
select * from user where id=#{id} and username=#{username}

User getUser2(@Param("id")Integer id, @Param("username") String username);

<select id="getUser2" resultType="com.by.pojo.User">
        select * from user where id=#{id} and username=#{username}
    </select>
/**
     * 注释传递多个参数
     * @throws IOException
     */
    @Test
    public void testGetUse2() throws IOException {
        //返回接口的代理类
        UserDao userDao = sqlSession.getMapper(UserDao.class);
        User user = userDao.getUser2(43,"俞莲舟");
        System.out.println(user);
    }

pojo传递多个参数—【推荐】

User getUser3(User user);
select * from user where id=#{id} and username=#{username}

User getUser3(User user);

<select id="getUser3" parameterType="com.by.pojo.User" resultType="com.by.pojo.User">
        select * from user where id=#{id} and username=#{username}
    </select>

/**
     * 对象传递多个参数
     * @throws IOException
     */
    @Test
    public void testGetUse3() throws IOException {
        //返回接口的代理类
        UserDao userDao = sqlSession.getMapper(UserDao.class);
        User user1 = new User();
        user1.setId(43);
        user1.setUsername("俞莲舟");
        User user = userDao.getUser3(user1);
        System.out.println(user);
    }

map传递多个参数

User getUser3(Map user);
select * from user where id=#{id} and username=#{username}

User getUser4(Map<String,Object> map);

<select id="getUser4" parameterType="java.util.Map" resultType="com.by.pojo.User">
        select * from user where id=#{id} and username=#{username}
    </select>

/**
     * 集合传递多个参数
     * @throws IOException
     */
    @Test
    public void testGetUse4() throws IOException {
        //返回接口的代理类
        UserDao userDao = sqlSession.getMapper(UserDao.class);
        Map<String,Object> map = new HashMap<>();
        map.put("id",43);
        map.put("username","俞莲舟");
        User user = userDao.getUser4(map);
        System.out.println(user);
    }

五，${}和#{}的区别
sql注入底层 jdbc类型转换单个简单类型的参数
$ 不防止 Statement 不转换 value
# 防止 preparedStatement 转换任意
结论：除模糊匹配外，杜绝使用${}

模糊查询

 /**
     * 模糊查询
     * @throws IOException
     */
    @Test
    public void testGetUserByUsername() throws IOException {
        //返回接口的代理类
        UserDao userDao = sqlSession.getMapper(UserDao.class);
        List<User> list = userDao.getUserByUsername("张");
        for (User user:list){
            System.out.println(user);
        }
    }

List<User> getUserByUsername(String username);

<select id="getUserByUsername" parameterType="java.lang.String" resultType="com.by.pojo.User">
        select * from user where username like '%${value}%'
    </select>

sql注入

 /**
     * sql注入
     * @throws IOException
     */
    @Test
    public void testLogin() throws IOException {
        //返回接口的代理类
        UserDao userDao = sqlSession.getMapper(UserDao.class);
        User userInfo = new User();
        userInfo.setUsername("张三丰'#");
        userInfo.setPassword("222");
        User user = userDao.login(userInfo);
        System.out.println(user);
    }

User login(User userInfo);

<select id="login" parameterType="com.by.pojo.User" resultType="com.by.pojo.User">
        select * from user where username='${username}' and password='${password}'
    </select>

六，mybatis的主键回填

<delete id="deleteUserById" parameterType="java.lang.Integer">
        delete from user where id = #{id}
    </delete>

void deleteUserById(Integer id);

/**
     * 删除sql
     * 返回值是Rolling
     * 需要删除调用sqlSession.commit()
     * @throws IOException
     */
    @Test
    public void testDeleteUserById() throws IOException {
        //返回接口的代理类
        UserDao userDao = sqlSession.getMapper(UserDao.class);
        userDao.deleteUserById(42);
        //提交
        sqlSession.commit();
    }

 void updateUserById(User user);

<update id="updateUserById" parameterType="com.by.pojo.User">
        update user set username=#{username}, password=#{password}, birthday=#{birthday}, sex=#{sex}, address=#{address} where id=#{id}
    </update>

/**
     * 修改指定内容
     * @throws IOException
     */
    @Test
    public void testUpdateUserById() throws IOException {
        //返回接口的代理类
        UserDao userDao = sqlSession.getMapper(UserDao.class);
        User user = new User();
        user.setUsername("郭襄");
        user.setPassword("222");
        user.setBirthday(new Date());
        user.setAddress("峨眉山");
        user.setSex("女");
        user.setId(42);
        userDao.updateUserById(user);
        sqlSession.commit();
    }

/**
     * 新增内容
     * @throws IOException
     */
    @Test
    public void testAddUser() throws IOException {
        //返回接口的代理类
        UserDao userDao = sqlSession.getMapper(UserDao.class);
        User user = new User();
        user.setUsername("杨过");
        user.setPassword("222");
        user.setBirthday(new Date());
        user.setAddress("峨眉山");
        user.setSex("男");
        userDao.AddUser(user);
        System.out.println("返回自增id:"+user.getId());

        //提交
        sqlSession.commit();
    }

void AddUser(User user);

 <!--
        useGeneratedKeys="true"：使用自增id
        keyProperty="id"：回填到实体类的哪个属性
    -->
    <insert id="AddUser" useGeneratedKeys="true" keyProperty="id" parameterType="com.by.pojo.User">
        <!--
                    逐渐回填(返回自增id)：插入记录后返回自增的id到参数
                    keyProperty="id"：回填到实体类的哪个属性
                    order="AFTER"：先执行插入，再主键回填
                    resultType="java.lang.Integer"：主键的类型
                <selectKey keyProperty="id" order="AFTER" resultType="java.lang.Integer">
                    SELECT LAST_INSERT_ID()
                </selectKey>-->
                INSERT INTO user(username,password,birthday,sex,address) VALUE(#{username},#{password},#{birthday},#{sex},#{address})
            </insert>

方式一:

<insert id="" useGeneratedKeys="true" keyProperty="id" parameterType="">

方式二:

        <selectKey keyProperty="id" order="AFTER" resultType="java.lang.Integer">
            SELECT LAST_INSERT_ID()
        </selectKey>

文章来源:https://blog.csdn.net/y666__/article/details/135093121
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