一、简介
对于数据访问层，无论是SQL还是NOSQL， Spring Boot默认采用整合Spring Data的方式进行统一处理，添加大量自动配置，屏蔽了很多设置。
引入各种xxxTemplate， xxxRepository来简化我们对数据访问层的操作。对我们来说只需要进行简单的设置即可。我们将在数据访问章节测试使用SQL相关、NOSQL在缓存、消息、检索等章节测试。
相关的 starter：
二、整合JDBC
1、添加依赖信息
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-jdbc</artifactId>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.11</version>
<scope>runtime</scope>
</dependency>
2、配置数据库信息
spring:
datasource:
username: root
password: '123456'
driver-class-name: com.mysql.cj.jdbc.Driver
# driver-class-name: com.mysql.jdbc.Driver
url: jdbc:mysql://192.168.1.6:3306/jdbc
如果没有更新驱动的，使用 com.mysql.jdbc.Driver。
如果在 Maven 中更新了 mysql 驱动，使用 com.mysql.cj.jdbc.Driver 驱动。
3、测试
@RunWith(SpringRunner.class)
@SpringBootTest
public class SpringBoot06DataJdbcApplicationTests {
@Autowired
private DataSource dataSource;
@Test
public void contextLoads() throws SQLException {
System.out.println(dataSource.getClass());
Connection connection = dataSource.getConnection();
System.out.println("connection = " + connection);
}
}
4、效果
（1）默认是用org.apache.tomcat.jdbc.pool.DataSource作为数据源；
（2）数据源的相关配置都在DataSourceProperties里面；
三、自动配置原理
jdbc 自动配置相关类所在包：
org.springframework.boot.autoconfigure.jdbc
1、数据源的自动配置
参考 DataSourceConfiguration，根据配置创建数据源，默认使用 Tomcat 连接池；
可以使用 spring.datasource.type 指定自定义的数据源类型；
2、SpringBoot 默认支持的数据源
org.apache.tomcat.jdbc.pool.DataSource
com.zaxxer.hikari.HikariDataSource
org.apache.commons.dbcp.BasicDataSource
org.apache.commons.dbcp2.BasicDataSource
3、自定义数据源类型
/**
* Generic DataSource configuration.
*/
@ConditionalOnMissingBean(DataSource.class)
@ConditionalOnProperty(name = "spring.datasource.type")
static class Generic {
@Bean
public DataSource dataSource(DataSourceProperties properties) {
//使用DataSourceBuilder创建数据源，利用反射创建响应type的数据源，并且绑定相关属性
return properties.initializeDataSourceBuilder().build();
}
}
public DataSourceBuilder initializeDataSourceBuilder() {
return DataSourceBuilder.create(getClassLoader()).type(getType())
.driverClassName(determineDriverClassName()).url(determineUrl())
.username(determineUsername()).password(determinePassword());
}
public DataSource build() {
Class<? extends DataSource> type = getType();
DataSource result = BeanUtils.instantiate(type);
maybeGetDriverClassName();
bind(result);
return result;
}
private void bind(DataSource result) {
MutablePropertyValues properties = new MutablePropertyValues(this.properties);
new RelaxedDataBinder(result).withAlias("url", "jdbcUrl")
.withAlias("username", "user").bind(properties);
}
4、DataSourceInitializer
在 DataSourceAutoConfiguration 类中会导入一个 DataSourceInitializer 组件：
DataSourceInitializer 组件：
/**
* Bean to handle {@link DataSource} initialization by running {@literal schema-*.sql} on
* {@link PostConstruct} and {@literal data-*.sql} SQL scripts on a
* {@link DataSourceInitializedEvent}.
* 通过在 {@link PostConstruct} 上运行 {@literal schema-.sql} 和在 {@link DataSourceInitializedEvent} 上运行 {@literal data-.sql} SQL 脚本来处理 {@link DataSource} 初始化的 Bean。
*/
class DataSourceInitializer implements ApplicationListener<DataSourceInitializedEvent> {}
作用：
（1）runSchemaScripts()：运行建表语句
@PostConstruct
public void init() {
if (!this.properties.isInitialize()) {
logger.debug("Initialization disabled (not running DDL scripts)");
return;
}
if (this.applicationContext.getBeanNamesForType(DataSource.class, false,
false).length > 0) {
this.dataSource = this.applicationContext.getBean(DataSource.class);
}
if (this.dataSource == null) {
logger.debug("No DataSource found so not initializing");
return;
}
runSchemaScripts();
}
private void runSchemaScripts() {
List<Resource> scripts = getScripts("spring.datasource.schema",
this.properties.getSchema(), "schema");
if (!scripts.isEmpty()) {
String username = this.properties.getSchemaUsername();
String password = this.properties.getSchemaPassword();
runScripts(scripts, username, password);
try {
this.applicationContext
.publishEvent(new DataSourceInitializedEvent(this.dataSource));
// The listener might not be registered yet, so don't rely on it.
if (!this.initialized) {
runDataScripts();
this.initialized = true;
}
}
catch (IllegalStateException ex) {
logger.warn("Could not send event to complete DataSource initialization ("
+ ex.getMessage() + ")");
}
}
}
private List<Resource> getScripts(String propertyName, List<String> resources,
String fallback) {
if (resources != null) {
return getResources(propertyName, resources, true);
}
String platform = this.properties.getPlatform();
List<String> fallbackResources = new ArrayList<String>();
fallbackResources.add("classpath*:" + fallback + "-" + platform + ".sql");
fallbackResources.add("classpath*:" + fallback + ".sql");
return getResources(propertyName, fallbackResources, false);
}
（2）runDataScripts()：运行插入数据的 SQL 语句
@Override
public void onApplicationEvent(DataSourceInitializedEvent event) {
if (!this.properties.isInitialize()) {
logger.debug("Initialization disabled (not running data scripts)");
return;
}
// NOTE the event can happen more than once and
// the event datasource is not used here
if (!this.initialized) {
runDataScripts();
this.initialized = true;
}
}
private void runDataScripts() {
List<Resource> scripts = getScripts("spring.datasource.data",
this.properties.getData(), "data");
String username = this.properties.getDataUsername();
String password = this.properties.getDataPassword();
runScripts(scripts, username, password);
}
private List<Resource> getScripts(String propertyName, List<String> resources,
String fallback) {
if (resources != null) {
return getResources(propertyName, resources, true);
}
String platform = this.properties.getPlatform();
List<String> fallbackResources = new ArrayList<String>();
fallbackResources.add("classpath*:" + fallback + "-" + platform + ".sql");
fallbackResources.add("classpath*:" + fallback + ".sql");
return getResources(propertyName, fallbackResources, false);
}
如果指定了 resources 资源路径，就加载，如果没有就加载 类路径下面的文件。
默认只需要将文件命名为：
schema-*.sql 、data-*.sql
默认规则（类路径下面）：schema.sql，schema-all.sql
也可以在配置文件中指定位置
spring:
schema:
- classpath:department.sql
data:
- classpath: abc.sql
指定位置
spring:
datasource:
username: root
password: '123456'
driver-class-name: com.mysql.cj.jdbc.Driver
url: jdbc:mysql://192.168.1.6:3306/jdbc
schema:
- classpath:department.sql
data:
- classpath:abc.sql
5、操作数据库：自动配置了 JdbcTemplate 操作数据库
JdbcTemplateAutoConfiguration 类自动注入了 JdbcTemplate：
@Configuration
@ConditionalOnClass({ DataSource.class, JdbcTemplate.class })
@ConditionalOnSingleCandidate(DataSource.class)
@AutoConfigureAfter(DataSourceAutoConfiguration.class)
public class JdbcTemplateAutoConfiguration {
private final DataSource dataSource;
public JdbcTemplateAutoConfiguration(DataSource dataSource) {
this.dataSource = dataSource;
}
@Bean
@Primary
@ConditionalOnMissingBean(JdbcOperations.class)
public JdbcTemplate jdbcTemplate() {
return new JdbcTemplate(this.dataSource);
}
@Bean
@Primary
@ConditionalOnMissingBean(NamedParameterJdbcOperations.class)
public NamedParameterJdbcTemplate namedParameterJdbcTemplate() {
return new NamedParameterJdbcTemplate(this.dataSource);
}
}
