SSM框架之Mybatis

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0. ssm框架大纲

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1. Mybatis

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2. 第一个Mybatis程序mybatis-01

  • 搭建环境
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CREATE DATABASE `mybatis`;

USE `mybatis`;

CREATE TABLE `user` (
`id` INT(20) NOT NULL PRIMARY KEY,
`name` VARCHAR(30) DEFAULT NULL,
`pwd` VARCHAR(30) DEFAULT NULL
) ENGINE=INNODB DEFAULT CHARSET=utf8;


INSERT INTO `user` (`id`,`name`,`pwd`) VALUES
(1, '狂神', '123456'),
(2, '李四', '123456'),
(3, '张三', '123890')

  • 新建项目(创建子模块)

    • 配置mybatis的核心配置文件
    • 编写mybatis工具类

  • 编写实体类

    • 实体类
    • Dao接口
    • 接口实现类

  • 测试

    • junit测试
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# 错误1
org.apache.ibatis.binding.BindingException: Type interface com.xiaofan.dao.UserDao is not known to the MapperRegistry.

# 解决方案
<mappers>
	<mapper resource="com/xiaofan/dao/UserMapper.xml"/>
</mappers>

# 错误2
Cause: org.apache.ibatis.builder.BuilderException: Error parsing SQL Mapper Configuration. Cause: java.io.IOException: Could not find resource com/xiaofan/dao/UserMapper.xml

# 解决方案
    <build>
        <resources>
            <resource>
                <directory>src/main/resources</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                    <include>**/*.tld</include>
                </includes>
                <filtering>true</filtering>
            </resource>
            <resource>
                <directory>src/main/java</directory>
                <includes>
                    <include>**/*.properties</include>
                    <include>**/*.xml</include>
                    <include>**/*.tld</include>
                </includes>
                <filtering>true</filtering>
            </resource>
        </resources>
    </build>

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  • 传递Map的情况
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int addUser1(Map<String, Object> map);
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<!-- map只要和键值保持一致即可 -->
<insert id="addUser1" parameterType="map">
    insert into mybatis.user (id, name, pwd) values(#{userId}, #{userName}, #{password})
</insert>
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@Test
public void testAddUser1() {
    SqlSession sqlSession = MybatisUtils.getSqlSession();

    UserMapper mapper = sqlSession.getMapper(UserMapper.class);
    Map<String, Object> map = new HashMap<String, Object>();
    map.put("userId", 5);
    map.put("userName", "胡一刀");
    map.put("password", "123456");

    mapper.addUser1(map);
    // 增删改必须提交事务
    sqlSession.commit();
    sqlSession.close();
}

  • 模糊查询

    • Java代码执行的时候，传递通配符%%

    • 在拼接sql中拼接通配符！

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    List<User> getUserLike(String value);
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    <select id="getUserLike" resultType="com.xiaofan.pojo.User">
        select * from mybatis.user where name like #{value}
    </select>
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    @Test
    public void testGetUserLike() {

        SqlSession sqlSession = null;

        try {
            sqlSession = MybatisUtils.getSqlSession();

            UserMapper mapper = sqlSession.getMapper(UserMapper.class);
            List<User> userList = mapper.getUserLike("%胡%");

            for (User user : userList) {
                System.out.println(user);
            }

        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (sqlSession != null) {
                sqlSession.close();
            }
        }
    }

3. mybatis配置解析mybatis-02

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import org.apache.ibatis.type.Alias;

@Alias(value = "hello")
public class User {

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4. 结果集映射（解决属性名和字段名不一致的情况）mybatis-03

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<?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.xiaofan.dao.UserMapper">

    <resultMap id="UserMap" type="User">
        <!--column: 数据库中的字段 property: 实体字段-->
        <!--数据库字段和实体字段一样的就不用做处理-->
        <!--<result column="id" property="id" />
        <result column="name" property="name" />-->
        <result column="pwd" property="password" />
    </resultMap>
    
    <select id="getUserById" resultMap="UserMap">
        select * from mybatis.user where id = #{id}
    </select>

</mapper>

5. 日志mybatis-04

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  • STDOUT_LOGGING标准日志

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  • LOG4J

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# 将等级为DEBUG的日志信息输出到console和file这两个目的地，console和file的定义在下面的代码
log4j.rootLogger=DEBUG,console,file

# 配置CONSOLE输出到控制台
log4j.appender.console=org.apache.log4j.ConsoleAppender
log4j.appender.console.layout=org.apache.log4j.PatternLayout 
# 配置CONSOLE日志的输出格式  [frame] 2019-08-22 22:52:12,000  %r耗费毫秒数 %p日志的优先级 %t线程名 %C所属类名通常为全类名 %L代码中的行号 %x线程相关联的NDC %m日志 %n换行
log4j.appender.console.layout.ConversionPattern=[frame] %d{yyyy-MM-dd HH:mm:ss,SSS} - %-4r %-5p [%t] %C:%L %x - %m%n

# 输出到日志文件中
log4j.appender.file=org.apache.log4j.RollingFileAppender
# 保存编码格式
log4j.appender.file.Encoding=UTF-8
# 输出文件位置此为项目根目录下的logs文件夹中
log4j.appender.file.File=logs/root.log
# 后缀可以是KB,MB,GB达到该大小后创建新的日志文件
log4j.appender.file.MaxFileSize=10MB
# 设置滚定文件的最大值3 指可以产生root.log.1、root.log.2、root.log.3和root.log四个日志文件
log4j.appender.file.MaxBackupIndex=3  
# 配置logfile为自定义布局模式
log4j.appender.file.layout=org.apache.log4j.PatternLayout
log4j.appender.file.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %F %p %m%n

# 输出日志级别(设置mybatis的日志级别)
log4j.logger.org.mybatis=DEBUG

# 对不同的类输出不同的日志文件
# com.xiaofan.dao包下的日志单独输出到xiaofan.log
log4j.logger.com.xiaofan.dao=DEBUG,xiaofan
# 设置为false该日志信息就不会加入到rootLogger中了
log4j.additivity.com.xiaofan.dao=false
# 下面就和上面配置一样了
log4j.appender.xiaofan=org.apache.log4j.RollingFileAppender
log4j.appender.xiaofan.Encoding=UTF-8
log4j.appender.xiaofan.File=logs/xiaofan.log
log4j.appender.xiaofan.MaxFileSize=10MB
log4j.appender.xiaofan.MaxBackupIndex=3
log4j.appender.xiaofan.layout=org.apache.log4j.PatternLayout
log4j.appender.xiaofan.layout.ConversionPattern=%d{yyyy-MM-dd HH:mm:ss} %F %p %m%n

测试通过！

参考链接：https://www.cnblogs.com/zhangguangxiang/p/12007924.html

​ https://www.cnblogs.com/yidaxia/p/5820036.html

6. 分页 mybatis-04

7. Mybatis执行流程

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8. Lombok的使用(真正开发项目中不用)

  • idea 安装Lombok插件
  • 导包
  • 用法
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package com.xiaofan.pojo;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@AllArgsConstructor
@NoArgsConstructor
public class Student {
    private String id;
    private String name;
    private int age;
}

9 复杂查询环境搭建

注解和xml配合使用，对于简单的可以使用注解，复杂的使用xml

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CREATE TABLE `teacher` (
  `id` INT(10) NOT NULL PRIMARY KEY,
  `name` VARCHAR(30) DEFAULT NULL
) ENGINE=INNODB DEFAULT CHARSET=utf8;

INSERT INTO teacher (`id`, `name`) VALUES (1, '秦老师');

CREATE TABLE `student` (
  `id` INT(10) NOT NULL,
  `name` VARCHAR(30) DEFAULT NULL,
  `tid` INT(10) DEFAULT NULL,
   PRIMARY KEY(`id`),
   KEY `fktid` (`tid`),
   CONSTRAINT `fktid` FOREIGN KEY (`tid`) REFERENCES `teacher`(`id`)
) ENGINE=INNODB DEFAULT CHARSET=utf8;

INSERT INTO `student` (`id`, `name`, `tid`) VALUES(1, '小明', 1);
INSERT INTO `s`student`tudent` (`id`, `name`, `tid`) VALUES(2, '小红', 1);
INSERT INTO `student` (`id`, `name`, `tid`) VALUES(3, '小张', 1);
INSERT INTO `student` (`id`, `name`, `tid`) VALUES(4, '小李', 1);
INSERT INTO `student` (`id`, `name`, `tid`) VALUES(5, '小王', 1);

9.1. 多对一mybatis-05

  • 按照嵌套查询进行处理（子查询）
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<select id="getStudent1" resultMap="StudentTeacher1">
    select * from mybatis.student;
</select>

<resultMap id="StudentTeacher1" type="Student">
    <result property="id" column="id"/>
    <result property="name" column="name"/>
    <!--复杂的属性需要单独处理 对象：association 集合：collection-->
    <association property="teacher" column="tid" javaType="Teacher" select="getTeacherById"/>
</resultMap>

<select id="getTeacherById" resultType="Teacher">
    select * from mybatis.teacher where id = #{id}
</select>
  • 按照结果嵌套处理（多表关联）
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<select id="getStudent2" resultMap="StudentTeacher2">
    select s.id sid, s.name sname, t.name tname from student s, teacher t where s.tid = t.id
</select>
<!-- 注意别名问题 -->
<resultMap id="StudentTeacher2" type="Student">
    <result property="id" column="sid"/>
    <!-- 学生的名字 -->
    <result property="name" column="sname"/>

    <association property="teacher" javaType="Teacher">
        <!-- 老师的名字-->
        <result property="name" column="tname"/>
    </association>
</resultMap>

9.2. 一对多mybatis-06

  • 按照嵌套查询进行处理（子查询）
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package com.xiaofan.dao;

import com.xiaofan.pojo.Teacher;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;

public interface TeacherMapper {

    @Select("select * from mybatis.teacher where id = #{id}")
    Teacher getTeacherById(@Param("id") int id);

    Teacher getTeacher1(@Param("tid") int id);
}

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<select id="getTeacher1" resultMap="TeacherStudent1">
    select * from mybatis.teacher where id = #{tid}
</select>

<resultMap id="TeacherStudent1" type="Teacher">
    <collection property="students" ofType="Student" javaType="ArrayList" select="getStudentByTeacherId" column="id"/>
</resultMap>

<select id="getStudentByTeacherId" resultType="Student">
    select * from mybatis.student where tid = #{tid}
</select>
  • 按照结果嵌套处理（多表关联）
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<select id="getTeacher2" resultMap="TeacherStudent">
    select s.id sid, s.name sname, t.id tid, t.name tname
    from student s, teacher t
    where s.tid = t.id and t.id = #{tid};
</select>

<resultMap id="TeacherStudent" type="Teacher">
    <result property="id" column="tid"/>
    <result property="name" column="tname"/>

    <collection property="students" ofType="Student">
        <result property="id" column="sid"/>
        <result property="name" column="sname" />
        <result property="tid" column="tid"/>
    </collection>
</resultMap>

10. 动态Sqlmybatis-07

动态SQL就是指根据不同的条件生成不同的SQL语句

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create table blog (
	id varchar(50) not null comment '博客id',
    title varchar(100) not null comment '博客标题',
    author varchar(30) not null comment '博客作者',
    create_time datetime not null comment '创建时间',
    views int(30) not null comment '浏览量'
) ENGINE=InnoDB DEFAULT charset=utf8;
  • if
  • choose (when, otherwise)
  • trim (where, set)
  • foreach
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package com.xiaofan.dao;

import com.xiaofan.pojo.Blog;

import java.util.List;
import java.util.Map;

public interface BlogMapper {

    int addBlog(Blog blog);

    List<Blog> queryBlogIF(Map map);

    List<Blog> queryBlogChoose(Map map);

    int updateBlog(Map map);

    List<Blog> queryBlogForeach(Map map);
}

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<?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.xiaofan.dao.BlogMapper">

    <insert id="addBlog" parameterType="blog">
        insert into mybatis.blog (id, title, author, create_time, views)
        values (#{id}, #{title}, #{author}, #{createTime}, #{views});
    </insert>

    <select id="queryBlogIF" parameterType="map" resultType="blog">
        select * from mybatis.blog
        <where>
            <if test="title != null">
                title = #{title}
            </if>
            <if test="author != null">
                and author = #{author}
            </if>
        </where>
    </select>

    <select id="queryBlogChoose" parameterType="map" resultType="blog">
        select * from mybatis.blog
        <where>
            <choose>
                <when test="title != null">
                    title = #{title}
                </when>
                <when test="author != null">
                    and author = #{author}
                </when>
                <otherwise>
                    and views = #{views}
                </otherwise>
            </choose>

        </where>
    </select>

    <update id="updateBlog" parameterType="map">
        update mybatis.blog
        <set>
            <if test="title != null">
                title = #{title},
            </if>
            <if test="author != null">
                author = #{author}
            </if>
        </set>
        where id = #{id}
    </update>

    <!-- select * from mybatis.blog where 1=1 and (id=1 or id=2 or id=3) -->
    <select id="queryBlogForeach" parameterType="map" resultType="blog">
        select * from mybatis.blog
        <where>
            <foreach collection="ids" item="id" open="and (" close=")" separator="or">
                id = #{id}
            </foreach>
        </where>
    </select>
</mapper>
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package com.xiaofan.dao;

import com.xiaofan.pojo.Blog;
import com.xiaofan.utils.IDUtils;
import com.xiaofan.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.junit.Test;

import java.util.*;

public class MyTest {

    @Test
    public void testAddBlog() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);

        Blog blog = new Blog(IDUtils.getId(), "Mybatis如此简单", "狂神说", new Date(), 9999);
        mapper.addBlog(blog);

        blog.setId(IDUtils.getId());
        blog.setTitle("Java如此简单");
        mapper.addBlog(blog);

        blog.setId(IDUtils.getId());
        blog.setTitle("Spring如此简单");
        mapper.addBlog(blog);

        blog.setId(IDUtils.getId());
        blog.setTitle("微服务如此简单");
        mapper.addBlog(blog);
        sqlSession.close();
    }

    @Test
    public void queryBlogIF() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);

        Map<String, Object> map = new HashMap();
        map.put("title", "Mybatis如此简单");
        map.put("author", "狂神说");
        mapper.queryBlogIF(map);
        sqlSession.close();
    }

    @Test
    public void queryBlogChoose() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);

        Map<String, Object> map = new HashMap();
        map.put("title", "Mybatis如此简单");
        map.put("author", "狂神说");
        map.put("views", 1000);
        mapper.queryBlogChoose(map);
        sqlSession.close();
    }

    @Test
    public void updateBlog() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);

        Map<String, Object> map = new HashMap();
        map.put("title", "Mybatis如此简单2");
//        map.put("author", "狂神说");
        map.put("id", "0d15b0c288514e39a8f757030a5708a9");
        mapper.updateBlog(map);
        sqlSession.close();
    }

    @Test
    public void queryBlogForeach() {
        SqlSession sqlSession = MybatisUtils.getSqlSession();
        BlogMapper mapper = sqlSession.getMapper(BlogMapper.class);

        Map<String, Object> map = new HashMap();
        List<Integer> ids = new ArrayList<Integer>();
        ids.add(1);
        ids.add(2);
        ids.add(3);

        map.put("ids", ids);

        List<Blog> blogs = mapper.queryBlogForeach(map);
        for (Blog blog : blogs) {
            System.out.println(blog);
        }
        sqlSession.close();
    }

}

11. SQL片段

有的时候，我们可能会将一些功能的部分抽取出来，方便复用！

  1. 使用sql标签抽取公共部分
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<sql id="if-title_author">
    <if test="title != null">
        title = #{title}
    </if>
    <if test="author != null">
        and author = #{author}
    </if>
</sql>
  1. 在需要使用的地方使用include标签应用即可
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<select id="queryBlogIF" parameterType="map" resultType="com.xiaofan.pojo.Blog">
    select * from mybatis.blog
    <where>
        <include refid="if-title_author"/>
    </where>
</select>

注意事项：

  1. 最好基于单标来定义sql片段
  2. 不要存在where标签

12. 缓存mybatis-08

  • 一级缓存（默认开启）

    • 开启日志

    • 测试在一个Session中查询两次相同的记录

    • 查看日志输出

    • 缓存失效的情况

      • 查询不同的东西
      • 增删改查操作，可能会改变原来的数据，所以必定会刷新缓存！
      • 查询不同的Mapper.xml
      • 手动清除缓存

  • 二级缓存

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    • 开启全局缓存
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    <setting name="cacheEnabled" value="true"/>
    • 在当前Mapper中使用缓存
    1
    2
    <!-- 开启二级缓存 -->
    <cache />

    注意事项：实体需要序列化哦！

    在这里插入图片描述

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