java的spring boot学习

[better2021]

配置文件

SpringBoot使用的一个全局配置文件，配置文件名是固定的：

• application.properties
• application.yml

在application.properties 文件中写 server.port=8081，表示应用启动端口为8081

pom.xml 是java的依赖包配置文件，所有的依赖包都在这里配置，配置之后springBoot会自动下载所有的依赖包，相当于js中的package.json文件

[better2021]

连接数据库

application.yml文件中配置

spring:
datasource:
username: root
password: 709463253
url: jdbc:mysql://localhost:3306/node?useUnicode=true&characterEncoding=utf8&serverTimezone=GMT
driver-class-name: com.mysql.cj.jdbc.Driver

[better2021]

mytains的使用

• 排序

  example.setOrderByClause("age DESC");

  • 条件查询

  //条件查询使用的是属性名
  example.createCriteria().andEqualTo("name", "张三");

  • 大小对比

  example.createCriteria().andGreaterThan("id",3);

• 新增数据并加入id

  Text text = new Text(null, "啦啦啦");
  if (mTestMapper.insertUseGeneratedKeys(text) <= 0) {
  throw new Exception(block.getId() + " 创建失败");
  }
  // id 被写入
  log.info(text.id)

• 结果顺序 按 in() 中的ID排序

  <select id="queryTestList" resultMap="TestResult">
  select * from test
  <where>
    id in
    <foreach item="item" index="index" collection="ids" open="(" close=")" separator=",">
      #{item}
    </foreach>
    order by field
    <foreach item="item" index="index" collection="ids" open="(id," close=")" separator=",">
      #{item}
    </foreach>
  </where>
  </select>

  List<Test> queryTestList(@Param("ids") List<String> ids);

  对应 mysql语句

  select * FROM test where id in (1,3,2,5)  order by field (id,1,3,2,5);

• find_in_set 的使用

  <select id="queryTest" resultMap="TestResult">
  select * from test
  <where>
    <if test="myIds != null">
      FIND_IN_SET(#{myIds,jdbcType=VARCHAR},test_ids)
    </if>
  </where>
  </select>

  List<TestResult> queryTest(@Param("myIds") String myIds);

  select * from app_models where FIND_IN_SET('3',type_ids)

• 批量更新多个不同值的字段

  <update id="updateBatch"  parameterType="java.util.List">  
    <foreach collection="list" item="item" index="index" open="" close="" separator=";">
        update course
        <set>
            name=${item.name}
        </set>
        where id = ${item.id}
    </foreach>      
  </update>

• 对比的基本使用

  Example example = new Example(Test.class);
  Example.Criteria criteria = example.createCriteria();
  criteria.andBetween("data",begin,end)
  criteria.andEqualTo("lv", lv);
  example.setOrderByClause("sort ASC");
  List<TestList> taskLists = mTestListMapper.selectByExample(example);

• 常见问题

  • 一些坑

  // 实体类对比时
  POJo 对象 不要使用 int 要使用 Integer

  • 为什么MyBatis返回null对象的集合？

  mybatis.configuration.return-instance-for-empty-row=true

• 比较复杂的例子

  <mapper namespace="org.imooc.dao.BusinessDao">
  <resultMap type="Business" id="BusinessResultMap">
      <id column="id" property="id" />
      <result column="img_file_name" property="imgFileName" />
      <result column="title" property="title" />
      <result column="subtitle" property="subtitle" />
      <result column="price" property="price" />
      <result column="distance" property="distance" />
      <result column="number" property="number" />
      <result column="desc" property="desc" />
      <result column="city" property="city" />
      <result column="category" property="category" />
      <result column="star_total_num" property="starTotalNum" />
      <result column="comment_total_num" property="commentTotalNum" />
      <association property="cityDic" javaType="Dic">
          <result column="city_name" property="name"/>
      </association>
      <association property="categoryDic" javaType="Dic">
          <result column="category_name" property="name"/>
      </association>
  </resultMap>
  
  <insert id="insert">
      insert into business(img_file_name,title,subtitle,price,distance,number,`desc`,city,category,star_total_num,comment_total_num)
      values(#{imgFileName},#{title},#{subtitle},#{price},#{distance},#{number},#{desc},#{city},#{category},#{starTotalNum},#{commentTotalNum})
  </insert>
  
  <select id="selectById" resultType="Business">
      select
      id,img_file_name,title,subtitle,price,distance,number,`desc`,city,category,star_total_num,comment_total_num
      from business where id=#{_parameter}
  </select>
  
  <select id="selectByPage" resultMap="BusinessResultMap">
      select b.id,b.img_file_name,b.title,b.subtitle,b.price
      ,b.distance,b.number,b.`desc`,b.city,b.category,b.star_total_num,b.comment_total_num
      ,d_city.name city_name,d_category.name category_name
      from
      business b
      left join dic d_city on b.city=d_city.code and
      d_city.type='${@org.imooc.constant.DicTypeConst@CITY}'
      left join dic d_category on
      b.category=d_category.code and d_category.type='${@org.imooc.constant.DicTypeConst@CATEGORY}'
      <where>
          <if test="title != null and title != ''">
              and b.title like '%' #{title} '%'
          </if>
          <if test="subtitle != null and subtitle != ''">
              and b.subtitle like '%' #{subtitle} '%'
          </if>
          <if test="desc != null and desc != ''">
              and b.`desc` like '%' #{desc} '%'
          </if>
          <if test="city != null and city != ''">
              and b.city = #{city}
          </if>
          <if test="category != null and category != ''">
              and b.category = #{category}
          </if>
      </where>
      order by id
  </select>
  
  <select id="selectLikeByPage" resultType="Business">
      select id,img_file_name,title,subtitle,price,distance,number,`desc`,city,category,star_total_num,comment_total_num
      from business
      <where>
          <if test="title != null and title != ''
           and subtitle != null and subtitle != ''
           and desc != null and desc != ''">
              and
              (title like '%' #{title} '%' or subtitle like '%' #{subtitle} '%' or `desc` like '%' #{desc} '%')
          </if>
          <if test="city != null and city != ''">
              and city = #{city}
          </if>
          <if test="category != null and category != ''">
              and category = #{category}
          </if>
      </where>
      order by id
  </select>
  
  <update id="updateNumber">
      update business b,(select business_id,count(*) cou from orders group by business_id) c
      set b.number=b.number + c.cou where b.id=c.business_id
  </update>
  
  <update id="updateStar">
      update business b,
  
      (select o.business_id,sum(c.star) star_num,count(*) comment_num from comment c,orders o where c.orders_id=o.id and c.create_time &lt;= #{endTime}
      <if test="startTime != null">
          and c.create_time &gt; #{startTime}
      </if>
      group by o.business_id)t
  
      set b.star_total_num = b.star_total_num + t.star_num,b.comment_total_num = b.comment_total_num + t.comment_num
      where b.id=t.business_id
  </update>
  </mapper>

• 输出日志

  格式：logging.level.Mapper类的包=debug