使用数据库是开发应用的基本基础，那么，使用Spring Boot如何连接数据库呢？
前提，需要知道如何建一个Spring Boot项目，可参照：//www.greatytc.com/p/d6e6c84cd190
作者：莫问以
链接：//www.greatytc.com/p/414ef5b49a69
来源：简书
著作权归作者所有。商业转载请联系作者获得授权，非商业转载请注明出处。
一、准备工作：
1、建一个简单的数据库，名为springboot_db，在其下建一个表，名为t_author，脚本如下：
CREATE DATABASE/*!32312 IF NOT EXISTS*/`springboot_db`/*!40100 DEFAULT CHARACTER SET utf8 */;USE`springboot_db`;DROP TABLE IF EXISTS`t_author`;CREATE TABLE`t_author`(`id`bigint(20)unsigned NOT NULL AUTO_INCREMENT COMMENT'用户ID',`real_name`varchar(32)NOT NULL COMMENT'用户名称',`nick_name`varchar(32)NOT NULL COMMENT'用户匿名',PRIMARY KEY(`id`))ENGINE=InnoDB AUTO_INCREMENT=1DEFAULT CHARSET=utf8;
2、添加配置文件，可用使用yaml配置，即application.yml（与application.properties配置文件，没什么太大的区别）连接池的配置如下：
spring: datasource: url: jdbc:mysql://127.0.0.1:3306/springboot_db?useUnicode=true&characterEncoding=UTF-8&useSSL=false driverClassName: com.mysql.jdbc.Driver username: root password: root type: com.alibaba.druid.pool.DruidDataSource
3、需要建立与数据库对应的POJO类，代码如下：
publicclassAuthor{privateLong id;privateString realName;privateString nickName;// SET和GET方法略}
二、方式一：与JdbcTemplate集成
通过JdbcTemplate来访问数据库，Spring boot提供了如下的starter来支撑：
<dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-jdbc</artifactId></dependency>
再引入Junit测试Starter:
<dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-test</artifactId><scope>test</scope></dependency>
DAO接口：
packagecom.guxf.dao;importjava.util.List;importcom.guxf.domain.Author;publicinterfaceAuthorDao{intadd(Authorauthor);intupdate(Authorauthor);intdelete(Longid);AuthorfindAuthor(Longid);List<Author>findAuthorList();}
实现Dao接口代码（此处只写Add，其他方法略）：
packagecom.guxf.impl;importjava.util.HashMap;importjava.util.List;importjava.util.Map;importorg.springframework.beans.factory.annotation.Autowired;importorg.springframework.jdbc.core.namedparam.NamedParameterJdbcTemplate;importorg.springframework.stereotype.Repository;importcom.guxf.dao.AuthorDao;importcom.guxf.domain.Author;@RepositorypublicclassAuthorDaoJdbcTemplateImplimplementsAuthorDao{@AutowiredprivateNamedParameterJdbcTemplatejdbcTemplate;@Overridepublicintadd(Authorauthor){Stringsql="insert into t_author(id,real_name,nick_name) "+"values(:id,:realName,:nickName)";Map<String,Object>param=newHashMap<>();param.put("id",author.getId());param.put("realName",author.getRealName());param.put("nickName",author.getNickName());return(int)jdbcTemplate.update(sql,param);}@Overridepublicintupdate(Authorauthor){return0;}@Overridepublicintdelete(Longid){return0;}@OverridepublicAuthorfindAuthor(Longid){returnnull;}@OverridepublicList<Author>findAuthorList(){returnnull;}}
通过JUnit来测试上面的代码(需根据自己的实际Application名稍作修改)：
packagecom.guxf.boot;importorg.junit.Test;importorg.junit.runner.RunWith;importorg.springframework.beans.factory.annotation.Autowired;importorg.springframework.boot.test.context.SpringBootTest;importorg.springframework.test.context.junit4.SpringJUnit4ClassRunner;importcom.guxf.BootApplication;importcom.guxf.dao.AuthorDao;importcom.guxf.domain.Author;@RunWith(SpringJUnit4ClassRunner.class)@SpringBootTest(classes=BootApplication.class)publicclassAuthorDaoTest{@AutowiredprivateAuthorDao authorDao;@TestpublicvoidtestInsert(){Author author=newAuthor();author.setId(1L);author.setRealName("莫言");author.setNickName("疯子");authorDao.add(author);System.out.println("插入成功！");}}
插入成功：
成功.png
PS:需要注意的是，Application类所在的包必须是其他包的父包，@SpringBootApplication这个注解继承了@ComponentScan，其默认情况下只会扫描Application类所在的包及子包，结构图：
目录结构图.png
Application代码示例：
packagecom.guxf;importorg.springframework.boot.SpringApplication;importorg.springframework.boot.autoconfigure.SpringBootApplication;@SpringBootApplicationpublicclassBootApplication{publicstaticvoidmain(String[]args){SpringApplication.run(BootApplication.class,args);}}
三、方式二：与JPA集成
引入Starter:
<!-- 引入JPA --><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-data-jpa</artifactId></dependency>
对POJO类增加Entity的注解，并指定表名（如果不指定，默认的表名为author），然后指定ID的及其生成策略，这些都是JPA的知识，与Spring boot无关，代码：
packagecom.guxf.domain;importjavax.persistence.Entity;importjavax.persistence.GeneratedValue;importjavax.persistence.Id;@Entity(name="t_author")publicclassAuthor{@Id@GeneratedValueprivateLong id;privateString realName;privateString nickName;// SET和GET方法略}
需要继承JpaRepository这个类，这里我们实现了两个查询方法，第一个是符合JPA命名规范的查询，JPA会自动帮我们完成查询语句的生成，另一种方式是我们自己实现JPQL（JPA支持的一种类SQL的查询）：
packagecom.guxf.service;importjava.util.List;importjava.util.Optional;importorg.springframework.data.jpa.repository.JpaRepository;importorg.springframework.data.jpa.repository.Query;importorg.springframework.data.repository.query.Param;importcom.guxf.domain.Author;publicinterfaceAuthorRepository extends JpaRepository<Author,Long>{publicOptional<Author>findById(Long userId);@Query("select au from com.guxf.domain.Author au where nick_name=:nickName")publicList<Author>queryByNickName(@Param("nickName")String nickName);}
测试代码：
package com.guxf.boot;importstaticorg.junit.Assert.*;importjava.util.List;importorg.junit.Test;importorg.junit.runner.RunWith;importorg.springframework.beans.factory.annotation.Autowired;importorg.springframework.boot.test.context.SpringBootTest;importorg.springframework.test.context.junit4.SpringJUnit4ClassRunner;importcom.guxf.BootApplication;importcom.guxf.domain.Author;importcom.guxf.service.AuthorRepository;@RunWith(SpringJUnit4ClassRunner.class)@SpringBootTest(classes=BootApplication.class)publicclassAuthorDaoTestJPA{@AutowiredprivateAuthorRepositoryauthorRepository;@TestpublicvoidtestQuery(){List<Author>authorList=authorRepository.queryByNickName("疯子");assertTrue(authorList.size()>0);System.out.println("成功！");}}
四、方式三：与MyBatis集成
引入starter：
<!-- 引入Mybatis --><dependency><groupId>org.mybatis.spring.boot</groupId><artifactId>mybatis-spring-boot-starter</artifactId><version>1.1.1</version></dependency>
MyBatis一般可以通过XML或者注解的方式来指定操作数据库的SQL，首先，我们需要配置mapper的目录。我们在application.yml中进行配置：
spring: datasource: url: jdbc:mysql://127.0.0.1:3306/springboot_db?useUnicode=true&characterEncoding=UTF-8&useSSL=false driverClassName: com.mysql.jdbc.Driver username: root password: root type: com.alibaba.druid.pool.DruidDataSourcemybatis: #config-locations: mybatis/mybatis-config.xml mapper-locations: com/guxf/mapper/*.xml type-aliases-package: com.guxf.mapper.AuthorMapper
编写mapper对应的接口：
packagecom.guxf.mapper;importorg.apache.ibatis.annotations.Mapper;importcom.baomidou.mybatisplus.mapper.BaseMapper;importcom.guxf.domain.Author;@MapperpublicinterfaceAuthorMapperextendsBaseMapper<Author>{publicLonginsertAuthor(Authorauthor);publicvoidupdateAuthor(Authorauthor);publicAuthorqueryById(Longid);}
配置Mapper的XML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" ><mappernamespace="com.guxf.mapper.AuthorMapper"><!-- 此处需要注意的是，由于我们数据库定义的id存储类型为intbig,但是我们的Entity中Id是Long --><!-- 前面的两种方式插入没问题，此处报了数据库类型异常 --><!-- 所以数据库的ID类型改为了Varchar --><resultMapid="authorMap"type="com.guxf.domain.Author"><idcolumn="id"property="id"jdbcType="VARCHAR"/><resultcolumn="real_name"property="realName"jdbcType="VARCHAR"/><resultcolumn="nick_name"property="nickName"jdbcType="VARCHAR"/></resultMap><sqlid="base_column">id,real_name,nick_name</sql><insertid="insertAuthor"parameterType="com.guxf.domain.Author">INSERT INTO t_author(<includerefid="base_column"/>) VALUE (#{id},#{realName},#{nickName})</insert><updateid="updateAuthor"parameterType="com.guxf.domain.Author">UPDATE t_author<set><iftest="realName != null">real_name = #{realName},</if><iftest="nickName != null">nick_name = #{nickName},</if></set>WHERE id = #{id}</update><selectid="queryById"parameterType="Long"resultMap="authorMap">SELECT id,<includerefid="base_column"></include>FROM t_author WHERE id = #{id}</select></mapper>
测试类代码：
packagecom.guxf;importstaticorg.junit.Assert.*;importorg.junit.Test;importorg.junit.runner.RunWith;importorg.springframework.beans.factory.annotation.Autowired;importorg.springframework.boot.test.context.SpringBootTest;importorg.springframework.test.context.junit4.SpringJUnit4ClassRunner;importcom.guxf.BootApplication;importcom.guxf.domain.Author;importcom.guxf.mapper.AuthorMapper;@RunWith(SpringJUnit4ClassRunner.class)@SpringBootTest(classes=BootApplication.class)publicclassAuthorDaoTestMybatis{@AutowiredprivateAuthorMappermapper;@TestpublicvoidtestInsert(){Authorauthor=newAuthor();author.setId(4L);author.setRealName("唐钰");author.setNickName("小宝");mapper.insertAuthor(author);System.out.println("成功!");}@TestpublicvoidtestMybatisQuery(){Authorauthor=mapper.queryById(1L);assertNotNull(author);System.out.println(author);}@TestpublicvoidtestUpdate(){Authorauthor=mapper.queryById(2L);author.setNickName("月儿");author.setRealName("林月如");mapper.updateAuthor(author);}}
我们看测试结果：
测试结果.png
配置扫描，需要根据自己项目结构实际修改，下面贴上我的项目结构图：
结构.png
作者：莫问以
链接：//www.greatytc.com/p/414ef5b49a69
来源：简书
著作权归作者所有。商业转载请联系作者获得授权，非商业转载请注明出处。
