5.集成持久层框架MyBatis

1.MyBatis简介 MyBatis是一款优秀的数据持久层框架，它支持定制化SQL、存储过程以及高级映射。其避免了JDBC一系列繁杂的操作过程，改用简单的XML或注解来配置和映射原生信息，将接口和Java的POJO类映射成数据库中的记录。

2.引入依赖 新建一个SpringBoot工程，并在pom.xml文件中添加集成MyBatis所需要的dependency。

<dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-jdbc</artifactId> </dependency> <dependency> <groupId>org.mybatis.spring.boot</groupId> <artifactId>mybatis-spring-boot-starter</artifactId> <version>1.1.1</version> </dependency> <dependency> <groupId>org.projectlombok</groupId> <artifactId>lombok</artifactId> <version>1.18.2</version> <scope>provided</scope> </dependency>

3.添加配置 在application.properties文件中添加如下配置信息。

############################################################ # # MySQL配置 # ############################################################ ### 连接信息 spring.datasource.url = jdbc:mysql://localhost:3306/mydb ### 用户名 spring.datasource.username = root ### 密码 spring.datasource.password = admin123 ### 驱动 spring.datasource.driver-class-name = com.mysql.cj.jdbc.Driver ############################################################ # # MyBatis配置 # ############################################################ ### po类存放目录 mybatis.type-aliases-package = com.leichuangkj.mybatis.dao.po ### mapper(.xml)资源文件存放路径 mybatis.mapper-locations = classpath:mybatis/mapper/*.xml

4.开发服务端通用返回对象 在项目目录“/src/main/java/com/leichuangkj/mybatis”下新建common目录，并在common目录下新建ResponseCode枚举类和ServerResponse类，具体代码如下。

public enum ResponseCode { //1.定义枚举值 ERROR(0,"ERROR"), SUCCESS(1,"SUCCESS"); //2.定义枚举属性 private final int code; private final String desc; //3.定义构造函数 ResponseCode(int code, String desc){ this.code = code; this.desc = desc; } //4.定义get方法 public int getCode(){ return code; } public String getDesc(){ return desc; } } @JsonSerialize(include = JsonSerialize.Inclusion.NON_NULL) //保证序列化json的时候,如果是null的对象,key也会消失 public class ServerResponse<T> implements Serializable { //1.定义属性 private int status; private String message; private T data; //2.定义构造函数 private ServerResponse(int status) { this.status = status; } private ServerResponse(int status, T data) { this.status = status; this.data = data; } private ServerResponse(int status, String message, T data) { this.status = status; this.message = message; this.data = data; } private ServerResponse(int status, String message) { this.status = status; this.message = message; } //3.getter方法 public int getStatus() { return status; } public T getData() { return data; } public String getMessage() { return message; } @JsonIgnore //使之不在json序列化结果当中 //4.判断这个响应是不是一个正确的响应 public boolean isSuccess() { return this.status == ResponseCode.SUCCESS.getCode(); } //5.定义返回对象的方法 public static <T> ServerResponse<T> createBySuccess() { return new ServerResponse<T>(ResponseCode.SUCCESS.getCode()); } public static <T> ServerResponse<T> createBySuccessMessage(String message) { return new ServerResponse<T>(ResponseCode.SUCCESS.getCode(), message); } public static <T> ServerResponse<T> createBySuccess(T data) { return new ServerResponse<T>(ResponseCode.SUCCESS.getCode(), data); } public static <T> ServerResponse<T> createBySuccess(String message, T data) { return new ServerResponse<T>(ResponseCode.SUCCESS.getCode(), message, data); } public static <T> ServerResponse<T> createByError() { return new ServerResponse<T>(ResponseCode.ERROR.getCode(), ResponseCode.ERROR.getDesc()); } public static <T> ServerResponse<T> createByErrorMessage(String errorMessage) { return new ServerResponse<T>(ResponseCode.ERROR.getCode(), errorMessage); } public static <T> ServerResponse<T> createByErrorCodeMessage(int errorCode, String errorMessage) { return new ServerResponse<T>(errorCode, errorMessage); } public static <T> ServerResponse<T> createByErrorCodeMessageData(int errorCode, String errorMessage,T data) { return new ServerResponse<T>(errorCode, errorMessage,data); } }

5.dao层开发 首先在项目目录“/src/main/java/com/leichuangkj/mybatis”下新建“/dao/po”目录，并在po目录下新建User实体类，具体代码如下。

@Data @NoArgsConstructor @AllArgsConstructor @ToString public class User { private Integer id; private String name; private String email; }

然后在dao目录下新建mapper目录，并在mapper目录下新建UserMapper接口，具体代码如下。

@Repository public interface UserMapper { User findByName(String id); }

最后在resource目录下新建“mybatis/mapper”目录，并在mapper目录下新建UserMapper.xml文件，具体代码如下。

<?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.leichuangkj.mybatis.dao.mapper.UserMapper" > <resultMap id="BaseResultMap" type="com.leichuangkj.mybatis.dao.po.User"> <constructor> <idArg column="id" javaType="java.lang.Integer" jdbcType="INTEGER" /> <arg column="name" javaType="java.lang.String" jdbcType="VARCHAR" /> <arg column="email" javaType="java.lang.String" jdbcType="VARCHAR" /> </constructor> </resultMap> <select id="findByName" parameterType="java.lang.String" resultMap="BaseResultMap"> select id, name, email from user where name = #{name,jdbcType=VARCHAR} </select> </mapper>

6.service层开发 在项目目录“/src/main/java/com/leichuangkj/mybatis”下新建service目录，并在service目录下新建IUser接口，具体代码如下。

public interface IUser { ServerResponse findByName(String name); }

然后在service目录下新建impl目录，并在impl目录下新建UserImpl实现类，具体代码如下。

@Service public class UserImpl implements IUser { @Autowired UserMapper userMapper; @Override public ServerResponse findByName(String name) { User user = userMapper.findByName(name); if(user == null){ return ServerResponse.createByErrorMessage("没有查询到用户"); } return ServerResponse.createBySuccess(user); } }

7.controller层开发 在项目目录“/src/main/java/com/leichuangkj/mybatis”下新建controller目录，并在controller目录下新建UserController类，具体代码如下。

@Controller @RequestMapping("/user") public class UserController { @Autowired UserImpl userImpl; @RequestMapping(value = "/findByName",method = RequestMethod.POST) @ResponseBody public ServerResponse findByName(@RequestBody User user){ return userImpl.findByName(user.getName()); } }

8.启动项目 在启动类MyBatisApplication上添加注解“@MapperScan(basePackages = “com.leichuangkj.mybatis.dao.mapper”)”，然后启动项目。

@MapperScan(basePackages = "com.leichuangkj.mybatis.dao.mapper") @SpringBootApplication public class MyBatisApplication { public static void main(String[] args) { SpringApplication.run(MyBatisApplication.class, args); } }

9.测试 启动项目，然后在postman中请求“http://localhost:8080/user/findByName”，可以查询到相应的信息，测试结果如下图所示。

10.工程目录结构