本文主要是介绍06-数据访问(上)，对大家解决编程问题具有一定的参考价值，需要的程序猿们随着小编来一起学习吧！

1. 数据源的自动配置

1.1 导入 JDBC 场景

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-jdbc</artifactId>
</dependency>

查看依赖：

为什么导入 JDBC 场景，官方不导入驱动？因为官方不知道我们接下要操作什么数据库。

<properties>
    ...
    <mysql.version>5.1.49</mysql.version>
</properties>
<dependencies>
    <!-- 版本控制依赖的是 8.x.x，但本机上的数据库是 5.7.x，↑ ↓ 修改依赖版本的两种方式 -->
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <!-- <version>5.1.49</version> -->
    </dependency>
    ...
<dependencies>

1.2 相关自动配置

DataSourceAutoConfiguration（数据源的自动配置类）

@ConfigurationProperties(prefix = "spring.datasource")
public class DataSourceProperties implements ... { ... }

// ··········································································

@Configuration(proxyBeanMethods = false)
@ConditionalOnClass({ DataSource.class, EmbeddedDatabaseType.class })
@ConditionalOnMissingBean(type = "io.r2dbc.spi.ConnectionFactory") // 响应式编程
@EnableConfigurationProperties(DataSourceProperties.class)
@Import({
    DataSourcePoolMetadataProvidersConfiguration.class,
    DataSourceInitializationConfiguration.class
})
public class DataSourceAutoConfiguration {

  @Configuration(proxyBeanMethods = false)
  @Conditional(PooledDataSourceCondition.class)
  @ConditionalOnMissingBean({ DataSource.class, XADataSource.class })
  @Import({ DataSourceConfiguration.Hikari.class, DataSourceConfiguration.Tomcat.class,
            DataSourceConfiguration.Dbcp2.class, DataSourceConfiguration.OracleUcp.class,
            DataSourceConfiguration.Generic.class, DataSourceJmxConfiguration.class })
  protected static class PooledDataSourceConfiguration {}

  // ...

}

数据库连接池的配置，须在容器中没有 DataSource 的情况下才会自动配置；查看上面场景依赖可知，底层配置好的连接池是 Hikari。

修改数据源的配置信息：

spring:
  datasource:
    url: jdbc:mysql://localhost:3306/test
    username: root
    password: root
    driver-class-name: com.mysql.cj.jdbc.Driver
    # type: com.zaxxer.hikari.HikariDataSource

补充：

• DataSourceTransactionManagerAutoConfiguration（事务管理器的自动配置）
• XADataSourceAutoConfiguration（分布式事务相关的自动配置）

2. 使用 Druid 数据源

整合第三方技术的两种方式：① 自定义√；② starter

2.1 自定义方式

2.1.1 配置数据源

<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>druid</artifactId>
    <version>1.1.17</version>
</dependency>

虽然 data-jdbc 场景默认导入了 Hikari 数据源，但是可以看到 DataSourceConfiguration 类中的各种数据源配置上都有 @ConditionalOnMissingBean(DataSource.class) 这个条件，所以我们只需自己在配置类里配置一个 DruidDataSource，Hikari 就不会生效了。

@Configuration
public class DaoConfig {
    @Bean
    @ConfigurationProperties("spring.datasource")
    public DataSource dataSource() {
        DruidDataSource dataSource = new DruidDataSource();
        return dataSource;
    }
}

2.1.2 监控统计功能

打开Druid的监控统计功能&使用Druid的内置监控页面

（1）Druid 内置提供一个 StatFilter，用于统计监控信息。

StatFilter 的别名是 stat，这个别名映射配置信息保存在 druid-xxx.jar!/META-INF/druid-filter.properties 中。在 Spring 中使用别名配置方式如下：

<bean id="dataSource" class="com.alibaba.druid.pool.DruidDataSource" ...>
  ...
  <property name="filters" value="stat" />
</bean>

转换成 SpringBoot 的写法：① 在核心配置文件中配置 spring.datasource.filters=stat 以绑定到 DruidDataSource 上；② 配置数据源的时候直接 set 进去，如下所示。

@Bean
@ConfigurationProperties("spring.datasource")
public DataSource dataSource() throws SQLException {
    DruidDataSource dataSource = new DruidDataSource();
    dataSource.setFilters("stat");
    return dataSource;
}

（2）Druid 内置提供了一个 StatViewServlet 用于展示 Druid 的统计信息。

这个 StatViewServlet 的用途包括：① 提供监控信息展示的 html 页面；② 提供监控信息的 JSON API。

根据配置中的 url-pattern 来访问内置监控页面，如果是下面的配置，内置监控页面的首页是 /druid/index.html。

<servlet>
  <servlet-name>DruidStatView</servlet-name>
  <servlet-class>com.alibaba.druid.support.http.StatViewServlet</servlet-class>
</servlet>
<servlet-mapping>
  <servlet-name>DruidStatView</servlet-name>
  <url-pattern>/druid/*</url-pattern>
</servlet-mapping>

转换成 SpringBoot 的写法：

@Bean
public ServletRegistrationBean statViewServlet() {
    StatViewServlet servlet = new StatViewServlet();
    ServletRegistrationBean<StatViewServlet> bean = new ServletRegistrationBean<>(servlet, "/druid/*");
    return bean;
}

如果不想该页面直接被访问，可以配置监控页面访问密码（loginUsername&loginPassword），还可以配置 allow 和 deny（访问 IP）。

（3）WebStatFilter 用于采集 web-jdbc 关联监控的数据（详见上面的超链接）。

2.2 starter 方式

https://github.com/alibaba/druid/tree/master/druid-spring-boot-starter

2.2.1 导入 starter

注掉 druid 的依赖，引入 druid-starter 的依赖：

<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>druid-spring-boot-starter</artifactId>
    <version>1.1.17</version>
</dependency>

2.2.2 自动配置类

@Configuration
@ConditionalOnClass(DruidDataSource.class)
// before! 不然就先创建 Hikari 了！
@AutoConfigureBefore(DataSourceAutoConfiguration.class)
@EnableConfigurationProperties({DruidStatProperties.class, DataSourceProperties.class})
@Import({DruidSpringAopConfiguration.class, DruidStatViewServletConfiguration.class,
         DruidWebStatFilterConfiguration.class, DruidFilterConfiguration.class})
public class DruidDataSourceAutoConfigure {
    @Bean(initMethod = "init")
    @ConditionalOnMissingBean
    public DataSource dataSource() {
        LOGGER.info("Init DruidDataSource");
        return new DruidDataSourceWrapper();
    }
}

2.2.3 配置类

（1）DruidStatProperties

@ConfigurationProperties("spring.datasource.druid")
public class DruidStatProperties {
    private String[] aopPatterns;
    private StatViewServlet statViewServlet = new StatViewServlet();
    private WebStatFilter webStatFilter = new WebStatFilter();

    public static class StatViewServlet {
        /**
         * Enable StatViewServlet, default false.
         */
        private boolean enabled;
        private String urlPattern;
        private String allow;
        private String deny;
        private String loginUsername;
        private String loginPassword;
        private String resetEnable;
    }

    public static class WebStatFilter {
        /**
         * Enable WebStatFilter, default false.
         */
        private boolean enabled;
        private String urlPattern;
        private String exclusions;
        private String sessionStatMaxCount;
        private String sessionStatEnable;
        private String principalSessionName;
        private String principalCookieName;
        private String profileEnable;
    }
}

（2）DruidSpringAopConfiguration

@ConditionalOnProperty("spring.datasource.druid.aop-patterns")
public class DruidSpringAopConfiguration { ... }

（3）DruidStatViewServletConfiguration

@ConditionalOnWebApplication
@ConditionalOnProperty(name = "spring.datasource.druid.stat-view-servlet.enabled", havingValue = "true")
public class DruidStatViewServletConfiguration { ... }

（4）DruidWebStatFilterConfiguration

@ConditionalOnWebApplication
@ConditionalOnProperty(name = "spring.datasource.druid.web-stat-filter.enabled", havingValue = "true")
public class DruidWebStatFilterConfiguration { ... }

（5）DruidFilterConfiguration

public class DruidFilterConfiguration {

    @Bean
    @ConfigurationProperties(XXX)
    @ConditionalOnProperty(prefix = XXX, name = "enabled")
    @ConditionalOnMissingBean
    public XXX xXX() {
        return new XXX();
    }

    private static final String FILTER_STAT_PREFIX = "spring.datasource.druid.filter.stat";
    private static final String FILTER_CONFIG_PREFIX = "spring.datasource.druid.filter.config";
    private static final String FILTER_ENCODING_PREFIX = "spring.datasource.druid.filter.encoding";
    private static final String FILTER_SLF4J_PREFIX = "spring.datasource.druid.filter.slf4j";
    private static final String FILTER_LOG4J_PREFIX = "spring.datasource.druid.filter.log4j";
    private static final String FILTER_LOG4J2_PREFIX = "spring.datasource.druid.filter.log4j2";
    private static final String FILTER_COMMONS_LOG_PREFIX = "spring.datasource.druid.filter.commons-log";
    private static final String FILTER_WALL_PREFIX = "spring.datasource.druid.filter.wall";
    private static final String FILTER_WALL_CONFIG_PREFIX = FILTER_WALL_PREFIX + ".config";
}

2.2.4 配置示例

spring:
  datasource:
    url: jdbc:mysql://localhost:3306/test
    username: root
    password: root
    driver-class-name: com.mysql.jdbc.Driver

    druid:
      aop-patterns: cn.edu.nuist.admin.*  # 监控 SpringBean
      filters: stat,wall                  # 底层开启功能: stat(sql监控)、wall(防火墙)

      stat-view-servlet:                  # 配置监控页功能
        enabled: true
        login-username: admin
        login-password: admin
        resetEnable: false

      web-stat-filter:                    # 监控 web
        enabled: true
        urlPattern: /*
        exclusions: '*.js,*.gif,*.jpg,*.png,*.css,*.ico,/druid/*'


      filter:
        stat:                             # 对上面 filters 中开启的 StatFilter 的详细配置
          slow-sql-millis: 1000
          logSlowSql: true
          enabled: true
        wall:                             # 配置 WallFilter
          enabled: true
          config:
            drop-table-allow: false

3. 整合 MyBatis

https://github.com/mybatis/spring-boot-starter

3.1 导入依赖&自动配置

<dependency>
    <groupId>org.mybatis.spring.boot</groupId>
    <artifactId>mybatis-spring-boot-starter</artifactId>
    <version>2.1.4</version>
</dependency>

@ConfigurationProperties(prefix = MybatisProperties.MYBATIS_PREFIX)
public class MybatisProperties {

    public static final String MYBATIS_PREFIX = "mybatis";

    // ...

}

// ·································································

@org.springframework.context.annotation.Configuration
@ConditionalOnClass({ SqlSessionFactory.class, SqlSessionFactoryBean.class })
@ConditionalOnSingleCandidate(DataSource.class)
@EnableConfigurationProperties(MybatisProperties.class)
@AutoConfigureAfter({
    DataSourceAutoConfiguration.class, MybatisLanguageDriverAutoConfiguration.class
})
public class MybatisAutoConfiguration implements InitializingBean {

  private static final Logger logger;
  private final MybatisProperties properties;
  private final Interceptor[] interceptors;
  private final TypeHandler[] typeHandlers;
  private final LanguageDriver[] languageDrivers;
  private final ResourceLoader resourceLoader;
  private final DatabaseIdProvider databaseIdProvider;
  private final List<ConfigurationCustomizer> configurationCustomizers;

  @Bean
  @ConditionalOnMissingBean
  public SqlSessionFactory sqlSessionFactory(DataSource dataSource) throws Exception { ... }

  @Bean
  @ConditionalOnMissingBean
  public SqlSessionTemplate sqlSessionTemplate(SqlSessionFactory sqlSessionFactory) {
    ExecutorType executorType = this.properties.getExecutorType();
    if (executorType != null) {
      return new SqlSessionTemplate(sqlSessionFactory, executorType);
    } else {
      return new SqlSessionTemplate(sqlSessionFactory);
    }
  }

  // ...

  /**
   * This will just scan the same base package as Spring Boot does. If you want more power,
   * you can explicitly use {@link org.mybatis.spring.annotation.MapperScan} but this will
   * get typed mappers working correctly.
   */
  public static class AutoConfiguredMapperScannerRegistrar
              implements BeanFactoryAware, ImportBeanDefinitionRegistrar {

    private BeanFactory beanFactory;

    @Override
    public void registerBeanDefinitions(
        AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) { ... }
  }

  /**
   * If mapper registering configuration or mapper scanning configuration not present,
   * this configuration allow to scan mappers based on the same component-scanning path
   * as Spring Boot itself.
   */
  @org.springframework.context.annotation.Configuration
  @Import(AutoConfiguredMapperScannerRegistrar.class)
  @ConditionalOnMissingBean({ MapperFactoryBean.class, MapperScannerConfigurer.class })
  public static class MapperScannerRegistrarNotFoundConfiguration ...

}

3.2 简单整合示例

http://mybatis.org/spring-boot-starter/mybatis-spring-boot-autoconfigure/

CityMapper

@Mapper // 若觉得在每个 Mapper 接口上写注解麻烦，可以直接在启动类上增加 @MapperScan
public interface CityMapper {

  City getCityById(Long id);

  @Insert("INSERT INTO city(`name`,`state`,`country`) VALUES (#{name},#{state},#{country})")
  @Options(useGeneratedKeys = true, keyProperty = "id")
  boolean insertCity(City city);
}

CityMapper.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="cn.edu.nuist.mapper.CityMapper">
  <select id="getCityById">
    SELECT * FROM city WHERE id = #{id}
  </select>
</mapper>

application.yml

# mybatis.configuration(推荐) 和 mybatis.config-location 不能同时存在，全局配置要不然就
# 放全局配置文件中，要不就用 mybatis.configuration.xxx的方式挨个配好，不能混用。
mybatis:
  mapper-locations: classpath:mybatis.mapper/*.xml
  configuration:
    map-underscore-to-camel-case: true

4. 整合 MyBatisPlus

https://baomidou.com/guide/quick-start.html

4.1 导入依赖

<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-boot-starter</artifactId>
    <version>3.4.1</version>
</dependency>

只需要引入一个 MP，mybatis-starter 和 jdbc-starter 就都不用再引了。

4.2 整合测试

（1）实体类 UserPlus

@Data
@TableName("user") // 默认找 `user_plus` 表
public class UserPlus {
    private Long id;
    private String name;
    private Integer age;
    private String email;
    @TableField(exist = false)
    private String future;
}

（2）映射文件

因为 MybatisPlusProperties 已经有 String[] mapperLocations = new String[]{"classpath*:/mapper/**/*.xml"} 的默认配置，所以在 application.yml 中就没弄任何关于 mybatis / mybatis-plus 开头的配置，就把 *Mapper.xml 的外层目录由 resource/mybatis/mapper 改为 resource/mapper，简单整合嘛这不~

（3）映射文件绑定的接口（没加 @Mapper 注解，直接在主启动类上加 @MapperScan("cn.edu.nuist.mapper") 一次搞定）

public interface UserPlusMapper extends BaseMapper<UserPlus> {}

（4）Service 接口

public interface UserPlusService extends IService<UserPlus> {}

（5）Service 实现

@Service
public class UserPlusServiceImpl
        extends ServiceImpl<UserPlusMapper, UserPlus> implements UserPlusService {}

（6）分页插件

@Bean
public MybatisPlusInterceptor mybatisPlusInterceptor() {
    MybatisPlusInterceptor interceptor = new MybatisPlusInterceptor();
    interceptor.addInnerInterceptor(new PaginationInnerInterceptor(DbType.H2));
    return interceptor;
}

（7）Controller

@GetMapping("/user/delete/{id}")
public String delUser(@RequestParam(value = "pn", defaultValue = "1") Integer pn,
                        @PathVariable("id") Long id, RedirectAttributes ra ) {
    userPlusService.removeById(id);
    ra.addAttribute("pn", pn);
    return "redirect:/dynamic_table";
}

@GetMapping("/user/table")
public String users(@RequestParam(value="pn", defaultValue="1") Integer pn, Model model) {
    Page<UserPlus> page = new Page<>(pn, 3);
    userPlusService.page(page, null);
    model.addAttribute("users", page);
    return "table/dynamic_table";
}

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