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-multidatasource
datasource:
type: com.zaxxer.hikari.HikariDataSource
url: jdbc:mysql://localhost:3306/test
username: sa
password: ****
second-datasource:
driver-class-name: org.hsqldb.jdbc.JDBCDriver
url: jdbc:hsqldb:mem:db2
username: sa
password:****
1.2 自定义DataSource配置
@Configuration public class SencondDataSourceConfiguration { @Bean @ConfigurationProperties(prefix = "spring.datasource") public DataSource newDataSource() { return DataSourceBuilder.create().build(); } @Bean(name = "secondDatasource") @ConfigurationProperties(prefix = "spring.second-datasource") public DataSource secondDataSource() { return DataSourceBuilder.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 @ComponentScan public class Application { }
@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：
/** * {@link EnableAutoConfiguration Auto-configuration} for {@link DataSource}. * * @author Dave Syer * @author Phillip Webb * @author Stephane Nicoll * @author Kazuki Shimizu */ @Configuration @ConditionalOnClass({ DataSource.class, EmbeddedDatabaseType.class }) @EnableConfigurationProperties(DataSourceProperties.class) @Import({ Registrar.class, DataSourcePoolMetadataProvidersConfiguration.class }) public class DataSourceAutoConfiguration { private static final Log logger = LogFactory .getLog(DataSourceAutoConfiguration.class); @Bean @ConditionalOnMissingBean public DataSourceInitializer dataSourceInitializer(DataSourceProperties properties, ApplicationContext applicationContext) { return new DataSourceInitializer(properties, applicationContext); } /** * Determines if the {@code dataSource} being used by Spring was created from * {@link EmbeddedDataSourceConfiguration}. * @param beanFactory the bean factory * @return true if the data source was auto-configured. */ public static boolean containsAutoConfiguredDataSource( 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 class EmbeddedDatabaseConfiguration { } @Configuration @Conditional(PooledDataSourceCondition.class) @ConditionalOnMissingBean({ DataSource.class, XADataSource.class }) @Import({ DataSourceConfiguration.Tomcat.class, DataSourceConfiguration.Hikari.class, DataSourceConfiguration.Dbcp2.class, DataSourceConfiguration.Generic.class }) protected static class PooledDataSourceConfiguration { } @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 class TomcatDataSourceJmxConfiguration { @Bean public Object dataSourceMBean(DataSource dataSource) { if (dataSource instanceof DataSourceProxy) { try { return ((DataSourceProxy) dataSource).createPool().getJmxPool(); } catch (SQLException ex) { logger.warn("Cannot expose DataSource to JMX (could not connect)"); } } return null; } } /** * {@link AnyNestedCondition} that checks that either {@code spring.datasource.type} * is set or {@link PooledDataSourceAvailableCondition} applies. */ static class PooledDataSourceCondition extends AnyNestedCondition { PooledDataSourceCondition() { super(ConfigurationPhase.PARSE_CONFIGURATION); } @ConditionalOnProperty(prefix = "spring.datasource", name = "type") static class ExplicitType { } @Conditional(PooledDataSourceAvailableCondition.class) static class PooledDataSourceAvailable { } } /** * {@link Condition} to test if a supported connection pool is available. */ static class PooledDataSourceAvailableCondition extends SpringBootCondition { @Override public ConditionOutcome getMatchOutcome(ConditionContext context, AnnotatedTypeMetadata metadata) { ConditionMessage.Builder message = ConditionMessage .forCondition("PooledDataSource"); if (getDataSourceClassLoader(context) != null) { return ConditionOutcome .match(message.foundExactly("supported DataSource")); } return ConditionOutcome .noMatch(message.didNotFind("supported DataSource").atAll()); } /** * Returns the class loader for the {@link DataSource} class. Used to ensure that * the driver class can actually be loaded by the data source. * @param context the condition context * @return the class loader */ private ClassLoader getDataSourceClassLoader(ConditionContext context) { Class<?> dataSourceClass = new DataSourceBuilder(context.getClassLoader()) .findType(); return (dataSourceClass == null ? null : dataSourceClass.getClassLoader()); } } /** * {@link Condition} to detect when an embedded {@link DataSource} type can be used. * If a pooled {@link DataSource} is available, it will always be preferred to an * {@code EmbeddedDatabase}. */ static class EmbeddedDatabaseCondition extends SpringBootCondition { private final SpringBootCondition pooledCondition = new PooledDataSourceCondition(); @Override public ConditionOutcome getMatchOutcome(ConditionContext context, AnnotatedTypeMetadata metadata) { ConditionMessage.Builder message = ConditionMessage .forCondition("EmbeddedDataSource"); if (anyMatches(context, metadata, this.pooledCondition)) { return ConditionOutcome .noMatch(message.foundExactly("supported pooled data source")); } EmbeddedDatabaseType type = EmbeddedDatabaseConnection .get(context.getClassLoader()).getType(); if (type == null) { return ConditionOutcome .noMatch(message.didNotFind("embedded database").atAll()); } return ConditionOutcome.match(message.found("embedded database").items(type)); } } /** * {@link Condition} to detect when a {@link DataSource} is available (either because * the user provided one or because one will be auto-configured). */ @Order(Ordered.LOWEST_PRECEDENCE - 10) static class DataSourceAvailableCondition extends SpringBootCondition { private final SpringBootCondition pooledCondition = new PooledDataSourceCondition(); private final SpringBootCondition embeddedCondition = new EmbeddedDatabaseCondition(); @Override public ConditionOutcome getMatchOutcome(ConditionContext context, AnnotatedTypeMetadata metadata) { ConditionMessage.Builder message = ConditionMessage .forCondition("DataSourceAvailable"); if (hasBean(context, DataSource.class) || hasBean(context, XADataSource.class)) { return ConditionOutcome .match(message.foundExactly("existing data source bean")); } if (anyMatches(context, metadata, this.pooledCondition, this.embeddedCondition)) { return ConditionOutcome.match(message .foundExactly("existing auto-configured data source bean")); } return ConditionOutcome .noMatch(message.didNotFind("any existing data source bean").atAll()); } private boolean hasBean(ConditionContext context, Class<?> type) { return BeanFactoryUtils.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 implements BeanClassLoaderAware, EnvironmentAware, InitializingBean { public static final String PREFIX = "spring.datasource"; ... ... private String driverClassName; private String url; private String username; private String 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