366 lines
11 KiB
Markdown
366 lines
11 KiB
Markdown
[id]:2018-09-01
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[type]:javaee
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[tag]:java,spring,mysql,mybatis,xml
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## 写在前面
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刚毕业的第一份工作是java开发，项目中需要用到mybatis，特此记录学习过程，这只是一个简单demo，mybatis用法很多不可能全部写出来，有更复杂的需求建议查看mybatis的官方中文文档，[点击跳转](http://www.mybatis.org/mybatis-3/zh/index.html)。下面时项目环境/版本。
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- 开发工具：IDEA
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- jdk版本：1.8
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- springboot版本：2.03
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其他依赖版本见下面pom.xml:
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```xml
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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<groupId>com.example</groupId>
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<artifactId>mybatis-test</artifactId>
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<version>0.0.1-SNAPSHOT</version>
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<packaging>jar</packaging>
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<name>mybatis-test</name>
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<description>Demo project for Spring Boot</description>
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<parent>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-starter-parent</artifactId>
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<version>2.0.3.RELEASE</version>
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<relativePath/> <!-- lookup parent from repository -->
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</parent>
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<properties>
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<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
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<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
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<java.version>1.8</java.version>
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</properties>
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<dependencies>
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<dependency>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-starter-web</artifactId>
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</dependency>
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<dependency>
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<groupId>mysql</groupId>
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<artifactId>mysql-connector-java</artifactId>
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<scope>runtime</scope>
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</dependency>
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<!--mybatis依赖 -->
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<dependency>
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<groupId>org.mybatis.spring.boot</groupId>
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<artifactId>mybatis-spring-boot-starter</artifactId>
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<version>1.3.2</version>
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</dependency>
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<!--alibaba连接池依赖-->
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<dependency>
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<groupId>com.alibaba</groupId>
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<artifactId>druid-spring-boot-starter</artifactId>
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<version>1.1.9</version>
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</dependency>
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<!--分页依赖-->
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<dependency>
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<groupId>com.github.pagehelper</groupId>
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<artifactId>pagehelper-spring-boot-starter</artifactId>
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<version>1.2.5</version>
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</dependency>
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<dependency>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-starter-test</artifactId>
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<scope>test</scope>
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</dependency>
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</dependencies>
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<build>
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<plugins>
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<plugin>
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<groupId>org.springframework.boot</groupId>
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<artifactId>spring-boot-maven-plugin</artifactId>
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</plugin>
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</plugins>
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</build>
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</project>
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```
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## 1.创建项目
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使用idea中的spring initializr生成maven项目，项目命令为mybatis-test，选择web，mysql，mybatis依赖，即可成功。（详细过程不赘述，如有需要学习springboot创建过程，可参考[这篇文章]()。
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然后依照上面的pom文件，补齐缺少的依赖。接着创建包entity，service和mybatis映射文件夹mapper，创建。为了方便配置将application.properties改成application.yml。由于我们时REST接口，故不需要static和templates目录。修改完毕后的项目结构如下：
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修改启动类，增加`@MapperScan("com.example.mybatistest.dao") `,以自动扫描dao目录，避免每个dao都手动加`@Mapper`注解。代码如下：
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```java
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@SpringBootApplication
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@MapperScan("com.example.mybatistest.dao")
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public class MybatisTestApplication {
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public static void main(String[] args) {
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SpringApplication.run(MybatisTestApplication.class, args);
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}
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}
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```
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修改application.yml,配置项目，代码如下：
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```yml
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mybatis:
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#对应实体类路径
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type-aliases-package: com.example.mybatistest.entity
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#对应mapper映射文件路径
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mapper-locations: classpath:mapper/*.xml
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#pagehelper物理分页配置
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pagehelper:
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helper-dialect: mysql
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reasonable: true
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support-methods-arguments: true
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params: count=countSql
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returnPageInfo: check
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server:
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port: 8081
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spring:
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datasource:
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name: mysqlTest
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type: com.alibaba.druid.pool.DruidDataSource
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#druid连接池相关配置
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druid:
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#监控拦截统计的filters
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filters: stat
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driver-class-name: com.mysql.jdbc.Driver
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url: jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=utf-8&useSSL=true
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username: root
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password: 123456
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#配置初始化大小，最小，最大
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initial-size: 1
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min-idle: 1
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max-active: 20
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#获取连接等待超时时间
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max-wait: 6000
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#间隔多久检测一次需要关闭的空闲连接
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time-between-eviction-runs-millis: 60000
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#一个连接在池中的最小生存时间
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min-evictable-idle-time-millis: 300000
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#打开PSCache，并指定每个连接上PSCache的大小。oracle设置为true，mysql设置为false。分库分表设置较多推荐设置
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pool-prepared-statements: false
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max-pool-prepared-statement-per-connection-size: 20
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http:
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encoding:
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charset: utf-8
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enabled: true
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```
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## 2.编写代码
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首先创建数据表，sql语句如下：
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```sql
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CREATE TABLE `user` (
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`id` int(11) NOT NULL AUTO_INCREMENT,
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`name` varchar(255) NOT NULL,
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`age` tinyint(4) NOT NULL DEFAULT '0',
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`password` varchar(255) NOT NULL DEFAULT '123456',
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PRIMARY KEY (`id`)
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) ENGINE=InnoDB AUTO_INCREMENT=0 DEFAULT CHARSET=utf8;
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```
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然后在entity包中创建实体类User.java
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```java
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public class User {
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private int id;
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private String name;
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private int age;
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private String password;
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public User(int id, String name, int age, String password) {
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this.id = id;
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this.name = name;
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this.age = age;
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this.password = password;
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}
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public User(){}
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//getter setter自行添加
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}
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```
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在dao包下创建UserDao.java
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```java
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public interface UserDao {
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//插入用户
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int insert(User user);
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//根据id查询
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User selectById(String id);
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//查询所有
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List<User> selectAll();
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}
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```
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在mapper文件夹下创建UserMapper.xml,具体的xml编写方法查看文首的官方文档。
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```xml
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<?xml version="1.0" encoding="utf-8" ?>
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<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
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<mapper namespace="com.example.mybatistest.dao.UserDao">
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<sql id="BASE_TABLE">
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user
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</sql>
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<sql id="BASE_COLUMN">
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id,name,age,password
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</sql>
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<insert id="insert" parameterType="com.example.mybatistest.entity.User" useGeneratedKeys="true" keyProperty="id">
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INSERT INTO <include refid="BASE_TABLE"/>
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<trim prefix="(" suffix=")" suffixOverrides=",">
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name,password,
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<if test="age!=null">
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age
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</if>
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</trim>
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<trim prefix=" VALUE(" suffix=")" suffixOverrides=",">
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#{name,jdbcType=VARCHAR},#{password},
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<if test="age!=null">
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#{age}
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</if>
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</trim>
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</insert>
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<select id="selectById" resultType="com.example.mybatistest.entity.User">
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select
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<include refid="BASE_COLUMN"/>
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from
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<include refid="BASE_TABLE"/>
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where id=#{id}
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</select>
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<select id="selectAll" resultType="com.example.mybatistest.entity.User">
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select
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<include refid="BASE_COLUMN"/>
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from
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<include refid="BASE_TABLE"/>
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</select>
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</mapper>
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```
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至此使用mybatis的代码编写完了，之后要用时调用dao接口中的方法即可。
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## 3.测试
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我们通过编写service，controller然后使用postman进行测试。
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首先编写UserService.java,代码如下：
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```java
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@Component
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public class UserService {
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@Autowired
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private UserDao userDao;
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public User getByUserId(String id){
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return userDao.selectById(id);
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}
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//获取全部用户
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public List<User> getAll(){
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return userDao.selectAll();
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}
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//测试分页
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public PageInfo<User> getAll(int pageNum,int pageSize){
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PageHelper.startPage(pageNum,pageSize);
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List<User> users = userDao.selectAll();
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System.out.println(users.size());
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PageInfo<User> result = new PageInfo<>(users);
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return result;
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}
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public int insert(User user){
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return userDao.insert(user);
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}
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}
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```
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编写UserController.java
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```java
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@RestController
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public class UserController {
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@Autowired
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private UserService userService;
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@GetMapping("/user/{userId}")
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public User getUser(@PathVariable String userId){
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return userService.getByUserId(userId);
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}
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@GetMapping("/user")
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public List<User> getAll(){
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return userService.getAll();
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}
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@GetMapping("/user/page/{pageNum}")
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public Object getPage(@PathVariable int pageNum,
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@RequestParam(name = "pageSize",required = false,defaultValue = "10") int pageSize){
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return userService.getAll(pageNum,pageSize);
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}
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@PostMapping("/user")
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public Object addOne(User user){
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userService.insert(user);
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return user;
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}
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}
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```
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启动项目，通过postman进行请求测试，测试结果如下：
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- 插入数据：
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- 查询数据
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- 分页查询
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## 4.注解编写sql
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上面使用的是xml方式编写sql代码，其实mybatis也支持在注解中编写sql，这样可以避免编写复杂的xml查询文件，但同时也将sql语句耦合到了代码中，也不易实现复杂查询，因此多用于简单sql语句的编写。
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要使用注解首先将applicaton.yml配置文件中的`mapper-locations: classpath:mapper/*.xml`注释掉。然后在UserDao.java中加入sql注解，代码如下：
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```java
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public interface UserDao {
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//插入用户
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@Insert("insert into user(name,age,password) value(#{name},#{age},#{password})")
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@Options(useGeneratedKeys=true,keyColumn="id",keyProperty="id")
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int insert(User user);
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//根据id查询
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@Select("select * from user where id=#{id}")
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User selectById(String id);
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//查询所有
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@Select("select * from user")
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List<User> selectAll();
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}
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```
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然后重新启动项目测试，测试结果跟上面完全一样。
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```
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如果对你有帮助记得点赞、收藏哦！
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``` |