插件介绍

通用 Mapper 是一个可以实现任意 MyBatis 通用方法的框架,项目提供了常规的增删改查操作以及 Example 相关的单表操作。通用 Mapper 是为了解决 MyBatis 使用中 90% 的基本操作,PageHelper则提供通用的分页查询功能,使用它们可以很方便的进行开发,可以节省开发人员大量的时间。

通用Mapper的GIT地址: https://gitee.com/free/Mapper

分页插件的GIT地址: https://github.com/pagehelper/Mybatis-PageHelper

项目结构

 

导入依赖

 <!-- 通用Mapper插件 
  文档地址:https://gitee.com/free/Mapper/wikis/Home --> 
 <dependency> 
     <groupId>tk.mybatis</groupId> 
     <artifactId>mapper-spring-boot-starter</artifactId> 
     <version>2.1.5</version> 
 </dependency> 
 <!-- 分页插件 
  文档地址:https://github.com/pagehelper/Mybatis-PageHelper/blob/master/wikis/zh/HowToUse.md --> 
 <dependency> 
     <groupId>com.github.pagehelper</groupId> 
     <artifactId>pagehelper-spring-boot-starter</artifactId> 
     <version>1.2.10</version> 
 </dependency> 
 <!-- MYSQL包 --> 
 <dependency> 
     <groupId>mysql</groupId> 
     <artifactId>mysql-connector-java</artifactId> 
 </dependency> 
 <!-- 默认就内嵌了Tomcat 容器,如需要更换容器也极其简单--> 
 <dependency> 
     <groupId>org.springframework.boot</groupId> 
     <artifactId>spring-boot-starter-web</artifactId> 
 </dependency>

属性配置

在 application.properties 文件中分别添加上数据库、Mybatis、通用Mapper、PageHelper的属性配置

spring.datasource.url=jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=UTF-8&zeroDateTimeBehavior=convertToNull&allowMultiQueries=true&useSSL=false 
spring.datasource.username=root 
spring.datasource.password=123456 
# 如果想看到mybatis日志需要做如下配置 
logging.level.com.carry=DEBUG 
######### Mybatis 自身配置 ########## 
mybatis.mapper-locations=classpath:com/carry/mapper/*Mapper.xml 
mybatis.type-aliases-package=com.carry.entity 
# 驼峰命名规范 如:数据库字段是  order_id 那么 实体字段就要写成 orderId 
mybatis.configuration.map-underscore-to-camel-case=true
######### 通用Mapper ########## # 主键自增回写方法,默认值MYSQL,详细说明请看文档 mapper.identity=MYSQL mapper.mappers=tk.mybatis.mapper.common.Mapper # 设置 insert 和 update 中,是否判断字符串类型!='' mapper.not-empty=true # 枚举按简单类型处理 mapper.enum-as-simple-type=true ######### 分页插件 ########## pagehelper.helper-dialect=mysql pagehelper.params=count=countSql pagehelper.reasonable=false pagehelper.support-methods-arguments=true

通用Mapper:

  • mapper.enum-as-simple-type: 枚举按简单类型处理,如果有枚举字段则需要加上该配置才会做映射
  • mapper.not-empty: 设置以后,会去判断 insert 和 update 中符串类型!=''

分页插件:

  • pagehelper.reasonable: 分页合理化参数,默认值为false。当该参数设置为 true 时,pageNum<=0 时会查询第一页, pageNum>pages(超过总数时),会查询最后一页。默认false 时,直接根据参数进行查询
  • support-methods-arguments: 支持通过 Mapper 接口参数来传递分页参数,默认值false,分页插件会从查询方法的参数值中,自动根据上面 params 配置的字段中取值,查找到合适的值时就会自动分页

注意事项:

由于 mybatis.mapper-locations=classpath:com/carry/mapper/*.xml配置的在java package中,而Spring Boot默认只打入java package -> *.java,所以我们需要给pom.xml文件添加如下内容

 <build> 
     <resources> 
         <resource> 
             <directory>src/main/resources</directory> 
         </resource> 
         <resource> 
             <directory>src/main/java</directory> 
             <includes> 
                 <include>**/*.xml</include> 
             </includes> 
             <filtering>true</filtering> 
         </resource> 
     </resources> 
     <plugins> 
         <plugin> 
             <groupId>org.springframework.boot</groupId> 
             <artifactId>spring-boot-maven-plugin</artifactId> 
         </plugin> 
     </plugins> 
 </build>

具体编码

1、表结构

创建一张 user

CREATE TABLE `user` ( 
  `id` int(8) NOT NULL AUTO_INCREMENT COMMENT '主键自增', 
  `username` varchar(50) NOT NULL COMMENT '用户名', 
  `password` varchar(50) NOT NULL COMMENT '密码', 
  PRIMARY KEY (`id`) 
) ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='用户表'; 

2、实体类

 package com.carry.entity; 
  
 import java.io.Serializable; 
  
 import javax.persistence.GeneratedValue; 
 import javax.persistence.GenerationType; 
 import javax.persistence.Id; 
 import javax.persistence.Table; 
  
 @Table(name = "user") 
 public class User implements Serializable { 
  
     private static final long serialVersionUID = -8057591359892731452L; 
  
     @Id 
     @GeneratedValue(strategy = GenerationType.IDENTITY) 
     private Long id; 
     private String username; 
     private String password; 
     public Long getId() { 
         return id; 
     } 
     public void setId(Long id) { 
         this.id = id; 
     } 
     public String getUsername() { 
         return username; 
     } 
     public void setUsername(String username) { 
         this.username = username; 
     } 
     public String getPassword() { 
         return password; 
     } 
     public void setPassword(String password) { 
         this.password = password; 
     } 
      
      
     public User() {} 
     public User(String username, String password) { 
         super(); 
         this.username = username; 
         this.password = password; 
     } 
 }

3、持久层

package com.carry.mapper; 
 
import com.carry.entity.User; 
import tk.mybatis.mapper.common.Mapper; 

public interface UserMapper extends Mapper<User> { 

  /**
* 根据用户名统计(假设它是一个很复杂的SQL)
*
@param username 用户名
*
@return 统计结果
*/
  int countByUsername(String username);
}

4、映射文件UserMapper.xml

 <?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.carry.mapper.UserMapper"> 
  
   <select id="countByUsername" resultType="java.lang.Integer"> 
       SELECT count(1) FROM user WHERE username = #{username} 
   </select> 
 </mapper>

5、启动类

import org.springframework.boot.SpringApplication; 
import org.springframework.boot.autoconfigure.SpringBootApplication; 
import tk.mybatis.spring.annotation.MapperScan; 
 
@SpringBootApplication 
@MapperScan(basePackages = "com.carry.mapper") 
public class SpringbootMapperPagehelperApplication {  
 
  public static void main(String[] args) {             
    SpringApplication.run(SpringbootMapperPagehelperApplication.class, args);   } }

 

测试

完成数据访问层接口后,编写一个junit测试类来检验代码的正确性。

 package com.carry; 
  
 import org.junit.Test; 
 import org.junit.runner.RunWith; 
 import org.slf4j.Logger; 
 import org.slf4j.LoggerFactory; 
 import org.springframework.beans.factory.annotation.Autowired; 
 import org.springframework.boot.test.context.SpringBootTest; 
 import org.springframework.test.context.junit4.SpringRunner; 
  
 import com.carry.entity.User; 
 import com.carry.mapper.UserMapper; 
 import com.github.pagehelper.PageHelper; 
 import com.github.pagehelper.PageInfo; 
  
 @RunWith(SpringRunner.class) 
 @SpringBootTest 
 public class SpringbootMapperPagehelperApplicationTests { 
  
     private final Logger logger = LoggerFactory.getLogger(this.getClass()); 
  
     @Autowired 
     private UserMapper userMapper; 
  
     @Test 
     public void test() { 
         try { 
             final User user1 = new User("u1", "p1"); 
             final User user2 = new User("u1", "p2"); 
             final User user3 = new User("u3", "p3"); 
             userMapper.insertSelective(user1); 
             logger.info("[user1回写主键] - [{}]", user1.getId()); 
             userMapper.insertSelective(user2); 
             logger.info("[user2回写主键] - [{}]", user2.getId()); 
             userMapper.insertSelective(user3); 
             logger.info("[user3回写主键] - [{}]", user3.getId()); 
             final int count = userMapper.countByUsername("u1"); 
             logger.info("[调用自己写的SQL] - [{}]", count); 
  
             // TODO 模拟分页 
             for (int i = 0; i < 20; i++) { 
                 userMapper.insertSelective(new User("u" + i, "p" + i)); 
             } 
             // TODO 分页 + 排序 this.userMapper.selectAll() 这一句就是我们需要写的查询,有了这两款插件无缝切换各种数据库 
             final PageInfo<User> pageInfo = PageHelper.startPage(1, 10).setOrderBy("id desc") 
                     .doSelectPageInfo(() -> this.userMapper.selectAll()); 
             logger.info("[lambda写法] - [分页信息] - [{}]", pageInfo.toString()); 
  
             PageHelper.startPage(1, 10).setOrderBy("id desc"); 
             final PageInfo<User> userPageInfo = new PageInfo<>(this.userMapper.selectAll()); 
             logger.info("[普通写法] - [{}]", userPageInfo); 
         } catch (Exception e) { 
             logger.error(e.getMessage()); 
         } 
     } 
  
 }

 

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