1.DataSource配置

1.1 默认配置application.xml

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

需要在pom.xml加入依赖(我使用了mybatis+mysql)

      <dependency><groupId>org.mybatis</groupId><artifactId>mybatis</artifactId><version>${mybatis.version}</version></dependency><dependency><groupId>org.mybatis</groupId><artifactId>mybatis-spring</artifactId><version>${mybatis-spring.version}</version></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId></dependency>　　　

　　　<dependency>
　　　　<groupId>com.zaxxer</groupId>
　　　　<artifactId>HikariCP</artifactId>
　　　　<exclusions>
　　　　　　<exclusion>
　　　　　　　　<artifactId>tools</artifactId>
　　　　　　　　<groupId>com.sun</groupId>
　　　　　　</exclusion>
　　　　</exclusions>
　　</dependency>

2.自定义DataSource

1.1 application.xml配置文件

spring:application:name: data-multidatasourcedatasource:type: com.zaxxer.hikari.HikariDataSourceurl: jdbc:mysql://localhost:3306/testusername: sapassword: ****second-datasource:driver-class-name: org.hsqldb.jdbc.JDBCDriverurl: jdbc:hsqldb:mem:db2username: sapassword:****

1.2 自定义DataSource配置

@Configurationpublic classSencondDataSourceConfiguration {@Bean@ConfigurationProperties(prefix= "spring.datasource")publicDataSource newDataSource() {returnDataSourceBuilder.create().build();}@Bean(name= "secondDatasource")@ConfigurationProperties(prefix= "spring.second-datasource")publicDataSource secondDataSource() {returnDataSourceBuilder.create().build();}
}

3.工作原理

spring boot的auto-configuration最具魔力的地方是@EnableAutoConfiguration注解

通常注解application应用使用@SpringBootApplication或者如下自定义的方式：

@Configuration@EnableAutoConfiguration@ComponentScanpublic classApplication{}

@EnableAutoConfiguration注解开启了spring ApplicationContext的自动配置功能，

它通过扫描classpath下的组件，满足不同Conditions的bean注册到容器中。

spring boot提供了不同的AutoConfiguration实现类，这些类都在spring-boot-autoconfigure-{version}.jar中，用来注册各种各样的组件。

通常，当AutoConfiguration实现类打上@Configuration标签，可以作为spring配置类，当AutoConfiguration实现类打上@EnableConfigurationProperties标签，可以绑定自定义属性或者更多Conditional bean注册方法。

下面就org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration来分析一下：

/*** {@linkEnableAutoConfiguration Auto-configuration} for {@linkDataSource}.**@authorDave Syer*@authorPhillip Webb*@authorStephane Nicoll*@authorKazuki Shimizu*/@Configuration
@ConditionalOnClass({ DataSource.class, EmbeddedDatabaseType.class})
@EnableConfigurationProperties(DataSourceProperties.class)
@Import({ Registrar.class, DataSourcePoolMetadataProvidersConfiguration.class})public classDataSourceAutoConfiguration {private static final Log logger =LogFactory.getLog(DataSourceAutoConfiguration.class);@Bean@ConditionalOnMissingBeanpublicDataSourceInitializer dataSourceInitializer(DataSourceProperties properties,ApplicationContext applicationContext) {return newDataSourceInitializer(properties, applicationContext);}/*** Determines if the {@codedataSource} being used by Spring was created from* {@linkEmbeddedDataSourceConfiguration}.*@parambeanFactory the bean factory*@returntrue if the data source was auto-configured.*/public static booleancontainsAutoConfiguredDataSource(ConfigurableListableBeanFactory beanFactory) {try{BeanDefinition beanDefinition= beanFactory.getBeanDefinition("dataSource");return EmbeddedDataSourceConfiguration.class.getName().equals(beanDefinition.getFactoryBeanName());}catch(NoSuchBeanDefinitionException ex) {return false;}}@Conditional(EmbeddedDatabaseCondition.class)@ConditionalOnMissingBean({ DataSource.class, XADataSource.class})@Import(EmbeddedDataSourceConfiguration.class)protected static classEmbeddedDatabaseConfiguration {}@Configuration@Conditional(PooledDataSourceCondition.class)@ConditionalOnMissingBean({ DataSource.class, XADataSource.class})@Import({ DataSourceConfiguration.Tomcat.class, DataSourceConfiguration.Hikari.class,DataSourceConfiguration.Dbcp2.class, DataSourceConfiguration.Generic.class})protected static classPooledDataSourceConfiguration {}@Configuration@ConditionalOnProperty(prefix= "spring.datasource", name = "jmx-enabled")@ConditionalOnClass(name= "org.apache.tomcat.jdbc.pool.DataSourceProxy")@Conditional(DataSourceAutoConfiguration.DataSourceAvailableCondition.class)@ConditionalOnMissingBean(name= "dataSourceMBean")protected static classTomcatDataSourceJmxConfiguration {@BeanpublicObject dataSourceMBean(DataSource dataSource) {if (dataSource instanceofDataSourceProxy) {try{return((DataSourceProxy) dataSource).createPool().getJmxPool();}catch(SQLException ex) {logger.warn("Cannot expose DataSource to JMX (could not connect)");}}return null;}}/*** {@linkAnyNestedCondition} that checks that either {@codespring.datasource.type}* is set or {@linkPooledDataSourceAvailableCondition} applies.*/static class PooledDataSourceCondition extendsAnyNestedCondition {PooledDataSourceCondition() {super(ConfigurationPhase.PARSE_CONFIGURATION);}@ConditionalOnProperty(prefix= "spring.datasource", name = "type")static classExplicitType {}@Conditional(PooledDataSourceAvailableCondition.class)static classPooledDataSourceAvailable {}}/*** {@linkCondition} to test if a supported connection pool is available.*/static class PooledDataSourceAvailableCondition extendsSpringBootCondition {@OverridepublicConditionOutcome getMatchOutcome(ConditionContext context,AnnotatedTypeMetadata metadata) {ConditionMessage.Builder message=ConditionMessage.forCondition("PooledDataSource");if (getDataSourceClassLoader(context) != null) {returnConditionOutcome.match(message.foundExactly("supported DataSource"));}returnConditionOutcome.noMatch(message.didNotFind("supported DataSource").atAll());}/*** Returns the class loader for the {@linkDataSource} class. Used to ensure that* the driver class can actually be loaded by the data source.*@paramcontext the condition context*@returnthe class loader*/privateClassLoader getDataSourceClassLoader(ConditionContext context) {Class<?> dataSourceClass = newDataSourceBuilder(context.getClassLoader()).findType();return (dataSourceClass == null ? null: dataSourceClass.getClassLoader());}}/*** {@linkCondition} to detect when an embedded {@linkDataSource} type can be used.* If a pooled {@linkDataSource} is available, it will always be preferred to an* {@codeEmbeddedDatabase}.*/static class EmbeddedDatabaseCondition extendsSpringBootCondition {private final SpringBootCondition pooledCondition = newPooledDataSourceCondition();@OverridepublicConditionOutcome getMatchOutcome(ConditionContext context,AnnotatedTypeMetadata metadata) {ConditionMessage.Builder message=ConditionMessage.forCondition("EmbeddedDataSource");if (anyMatches(context, metadata, this.pooledCondition)) {returnConditionOutcome.noMatch(message.foundExactly("supported pooled data source"));}EmbeddedDatabaseType type=EmbeddedDatabaseConnection.get(context.getClassLoader()).getType();if (type == null) {returnConditionOutcome.noMatch(message.didNotFind("embedded database").atAll());}return ConditionOutcome.match(message.found("embedded database").items(type));}}/*** {@linkCondition} to detect when a {@linkDataSource} is available (either because* the user provided one or because one will be auto-configured).*/@Order(Ordered.LOWEST_PRECEDENCE- 10)static class DataSourceAvailableCondition extendsSpringBootCondition {private final SpringBootCondition pooledCondition = newPooledDataSourceCondition();private final SpringBootCondition embeddedCondition = newEmbeddedDatabaseCondition();@OverridepublicConditionOutcome getMatchOutcome(ConditionContext context,AnnotatedTypeMetadata metadata) {ConditionMessage.Builder message=ConditionMessage.forCondition("DataSourceAvailable");if (hasBean(context, DataSource.class)|| hasBean(context, XADataSource.class)) {returnConditionOutcome.match(message.foundExactly("existing data source bean"));}if (anyMatches(context, metadata, this.pooledCondition,this.embeddedCondition)) {returnConditionOutcome.match(message.foundExactly("existing auto-configured data source bean"));}returnConditionOutcome.noMatch(message.didNotFind("any existing data source bean").atAll());}private boolean hasBean(ConditionContext context, Class<?>type) {returnBeanFactoryUtils.beanNamesForTypeIncludingAncestors(context.getBeanFactory(), type,true, false).length > 0;}}}

从上面看到，

1. DataSourceAutoConfiguration打上了@ConditionalOnClass({ DataSource.class, EmbeddedDatabaseType.class })标签，这意味着只有当DataSource.class和EmbeddedDatabaseType.class出现在classpath时，DataSourceAutoConfiguration内的自动配置bean才可能被注册。

2. DataSourceAutoConfiguration打上了@EnableConfigurationProperties(DataSourceProperties.class)标签，意味着application.properties中的属性和DataSourceProperties类自动绑定了。

@ConfigurationProperties(prefix =DataSourceProperties.PREFIX)public class DataSourceProperties implementsBeanClassLoaderAware, EnvironmentAware, InitializingBean {public static final String PREFIX = "spring.datasource";......privateString driverClassName;privateString url;privateString username;privateString password;...//setters and getters
}

上面的配置类中说明，在application.properties中以spring.datasource开头的属性将自动绑定到DataSourceProperties对象上。其他注解，如@ConditionalOnMissingBean, @ConditionalOnClass and @ConditionalOnProperty等，标识只要条件满足，bean definition将注册到ApplicationContext中。

参考文件：

【1】http://www.liaoxuefeng.com/article/001484212576147b1f07dc0ab9147a1a97662a0bd270c20000

【2】https://dzone.com/articles/how-springboot-autoconfiguration-magic-works