spring boot自动配置之jdbc（转）

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