SpringBoot + MyBatis 查询语句（根据条件查询）

1.新建数据库和表内容

全部根据 tt 中的数据进行查询

2.创建工程目录结构（springboot创建好后）

pom.xml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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.4.5</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.kejian</groupId>
    <artifactId>demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>demo</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>1.8</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <!--mybatis.jar-->
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>2.2.0</version>
        </dependency>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.5.6</version>
        </dependency>

        <dependency>
            <!--mySql的驱动-->
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <!--druid连接池-->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid</artifactId>
            <version>1.2.3</version>
        </dependency>
        <dependency>
            <groupId>commons-lang</groupId>
            <artifactId>commons-lang</artifactId>
            <version>2.3</version>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.20</version>
        </dependency>
    </dependencies>

    <build><resources>
        <resource>
            <directory>src/main/java</directory>
            <includes>
                <include>**/*.yml</include>
                <include>**/*.properties</include>
                <include>**/*.xml</include>
            </includes>
            <filtering>false</filtering>
        </resource>
        <resource>
            <directory>src/main/resources</directory>
            <includes>
                <include>**/*.yml</include>
                <include>**/*.properties</include>
                <include>**/*.xml</include>
            </includes>
            <filtering>false</filtering>
        </resource>
    </resources>
    </build>

</project>

application.yml（修改全局变量）

#自定义端口号
server:
  port: 8081

#连接数据库（我的是数据库名是kejain）
spring:
  datasource:
    url: jdbc:mysql://localhost:3306/kejian?useUnicode=true&characterEncoding=UTF-8&allowMultiQueries=true&serverTimezone=UTC
    #?后增加编码格式
    username: root #数据库用户名
    password: root #数据库密码
    driver-class-name: com.mysql.cj.jdbc.Driver

#扫描相关文件
mybatis:
  mapper-locations: classpath:/mapper/*.xml
  config-location: classpath:mybatis-config.xml

在resources目录下新建mybatis-config.xml（按需求添加，可以不要）

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <settings>
        <!--     使用jdbc的getGeneratedKeys获得数据库自增主键值-->
        <setting name="useGeneratedKeys" value="true"/>

        <!--           使用列标签替换列别名，默认true-->
        <setting name="useColumnLabel" value="true"/>

        <!--        开启驼峰命名create_time->createTime-->
        <setting name="mapUnderscoreToCamelCase" value="true"/>
    </settings>
</configuration>

至此基础配置OK，在目录下添加类

3.entity层下添加实体类

entity包也有叫 pojo, damain，都是一个意思

新建 Poem.java（添加实体类，和数据库对应）

@Data
public class Poem {
    private Integer id;
    private String tt;
    private String title;
    private String A;
    private String B;
    private String C;
    private String D;
    private String letter;

    public Integer getId() {
        return id;
    }

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

    public String getTt() {
        return tt;
    }

    public void setTt(String tt) {
        this.tt = tt;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public String getA() {
        return A;
    }

    public void setA(String a) {
        A = a;
    }

    public String getB() {
        return B;
    }

    public void setB(String b) {
        B = b;
    }

    public String getC() {
        return C;
    }

    public void setC(String c) {
        C = c;
    }

    public String getD() {
        return D;
    }

    public void setD(String d) {
        D = d;
    }

    public String getLetter() {
        return letter;
    }

    public void setLetter(String letter) {
        this.letter = letter;
    }

    @Override
    public String toString() {
        return "Poem{" +
                "id=" + id +
                ", time='" + tt + '\'' +
                ", title='" + title + '\'' +
                ", A='" + A + '\'' +
                ", B='" + B + '\'' +
                ", C='" + C + '\'' +
                ", D='" + D + '\'' +
                ", letter='" + letter + '\'' +
                '}';
    }
}

4.添加 mapper 操纵数据库

dao 层名为持久层，也可叫 mapper 层

dao 层下新建PoemMapper.java

@Mapper
public interface PoemMapper {
    //因为需要返回多个，设为List
    List<Poem> findSome(@Param("tt")String time);
}

resources 下新建 mapper 文件夹，存放dao 层 mapper 的映射文件

<?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">
<!--namespace是命名空间，对应dao层mapper文件-->
<mapper namespace="com.example.first_demo3.dao.PoemMapper">
    <!--id名对应dao层mapper的函数-->
    <select id="findSome" resultType="com.example.first_demo3.entity.Poem">
        select id,title,A,B,C,D,letter from poem where tt = #{tt}
    </select>
</mapper>

5.添加业务逻辑

service层为业务逻辑层，处理算法并返回数据给界面层

service下新建 PoemService.java 选择接口类

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public interface PoemService {
    List<Poem> findSome(String time);
}

service下新建impl文件夹，管理映射
impl下新建PoemServiceImpl.java

@Service
public class PoemServiceImpl implements PoemService {
    @Autowired
    private PoemMapper poemMapper;

    @Override
    public List<Poem> findSome(String tt) {
        return poemMapper.findSome(tt);
    }
}

6.终于可以写接口了

controller 层又名界面层，调用 service

controller 下新建PoemController.java

@RestControllerpublic class PoemController {    
    @Autowired    
    private PoemService poemService;        
    //查找后返回部分数据    
    @PostMapping("/get/{tt}")    
    public List<Poem>getSome(@PathVariable String tt){        return poemService.findSome(tt);
   }
}

7.PostMan测试接口

其他的雷同，在 /get/ 输入对应的 tt 值就可调用

最终的目录

/*
**    The author disclaims copyright to this source code.
**    In place of a legal notice, here is a blessing:
**
**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
*/

散人阿畅

springboot查询

SpringBoot + MyBatis 查询语句（根据条件查询）

1.新建数据库和表内容

2.创建工程目录结构（springboot创建好后）

3.entity层下添加实体类

4.添加 mapper 操纵数据库

5.添加业务逻辑

6.终于可以写接口了

7.PostMan测试接口

SpringBoot + MyBatis 查询语句 （根据条件查询）

1.新建数据库和表内容

2.创建工程目录结构（springboot创建好后）

3.entity层下添加实体类

4.添加 mapper 操纵数据库

5.添加业务逻辑

6.终于可以写接口了

7.PostMan测试接口

SpringBoot + MyBatis 查询语句（根据条件查询）