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 </span>= "secondDatasource"<span style="color: #000000;">)</br>




@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 {



</span><span style="color: #0000ff;">private</span> <span style="color: #0000ff;">static</span> <span style="color: #0000ff;">final</span> Log logger =<span style="color: #000000;"> LogFactory</br>

        .getLog(DataSourceAutoConfiguration.</span><span style="color: #0000ff;">class</span><span style="color: #000000;">);</br>







    @Bean


    @ConditionalOnMissingBean


    public DataSourceInitializer dataSourceInitializer(DataSourceProperties properties,


            ApplicationContext applicationContext) {


        return new DataSourceInitializer(properties, applicationContext);


    }



</span><span style="color: #008000;">/**</span><span style="color: #008000;"></br>

 * Determines if the {</span><span style="color: #808080;">@code</span><span style="color: #008000;"> dataSource} being used by Spring was created from</br>

 * {</span><span style="color: #808080;">@link</span><span style="color: #008000;"> EmbeddedDataSourceConfiguration}.</br>

 * </span><span style="color: #808080;">@param</span><span style="color: #008000;"> beanFactory the bean factory</br>

 * </span><span style="color: #808080;">@return</span><span style="color: #008000;"> true if the data source was auto-configured.</br>

 </span><span style="color: #008000;">*/</span></br>

<span style="color: #0000ff;">public</span> <span style="color: #0000ff;">static</span> <span style="color: #0000ff;">boolean</span><span style="color: #000000;"> containsAutoConfiguredDataSource(</br>

        ConfigurableListableBeanFactory beanFactory) {</br>

    </span><span style="color: #0000ff;">try</span><span style="color: #000000;"> {</br>

        BeanDefinition beanDefinition </span>= beanFactory.getBeanDefinition("dataSource"<span style="color: #000000;">);</br>

        </span><span style="color: #0000ff;">return</span> EmbeddedDataSourceConfiguration.<span style="color: #0000ff;">class</span><span style="color: #000000;">.getName()</br>

                .equals(beanDefinition.getFactoryBeanName());</br>

    }</br>

    </span><span style="color: #0000ff;">catch</span><span style="color: #000000;"> (NoSuchBeanDefinitionException ex) {</br>

        </span><span style="color: #0000ff;">return</span> <span style="color: #0000ff;">false</span><span style="color: #000000;">;</br>

    }</br>

}</br></br>

@Conditional(EmbeddedDatabaseCondition.</span><span style="color: #0000ff;">class</span><span style="color: #000000;">)</br>

@ConditionalOnMissingBean({ DataSource.</span><span style="color: #0000ff;">class</span>, XADataSource.<span style="color: #0000ff;">class</span><span style="color: #000000;"> })</br>

@Import(EmbeddedDataSourceConfiguration.</span><span style="color: #0000ff;">class</span><span style="color: #000000;">)</br>

</span><span style="color: #0000ff;">protected</span> <span style="color: #0000ff;">static</span> <span style="color: #0000ff;">class</span><span style="color: #000000;"> EmbeddedDatabaseConfiguration {</br></br>

}</br>

@Configuration</br>

@Conditional(PooledDataSourceCondition.</span><span style="color: #0000ff;">class</span><span style="color: #000000;">)</br>

@ConditionalOnMissingBean({ DataSource.</span><span style="color: #0000ff;">class</span>, XADataSource.<span style="color: #0000ff;">class</span><span style="color: #000000;"> })</br>

@Import({ DataSourceConfiguration.Tomcat.</span><span style="color: #0000ff;">class</span>, DataSourceConfiguration.Hikari.<span style="color: #0000ff;">class</span><span style="color: #000000;">,</br>

        DataSourceConfiguration.Dbcp2.</span><span style="color: #0000ff;">class</span>, DataSourceConfiguration.Generic.<span style="color: #0000ff;">class</span><span style="color: #000000;"> })</br>

</span><span style="color: #0000ff;">protected</span> <span style="color: #0000ff;">static</span> <span style="color: #0000ff;">class</span><span style="color: #000000;"> PooledDataSourceConfiguration {</br></br>

}</br>

@Configuration</br>

@ConditionalOnProperty(prefix </span>= "spring.datasource", name = "jmx-enabled"<span style="color: #000000;">)</br>

@ConditionalOnClass(name </span>= "org.apache.tomcat.jdbc.pool.DataSourceProxy"<span style="color: #000000;">)</br>

@Conditional(DataSourceAutoConfiguration.DataSourceAvailableCondition.</span><span style="color: #0000ff;">class</span><span style="color: #000000;">)</br>

@ConditionalOnMissingBean(name </span>= "dataSourceMBean"<span style="color: #000000;">)</br>

</span><span style="color: #0000ff;">protected</span> <span style="color: #0000ff;">static</span> <span style="color: #0000ff;">class</span><span style="color: #000000;"> TomcatDataSourceJmxConfiguration {</br>







        @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;


        }



}</br>

</span><span style="color: #008000;">/**</span><span style="color: #008000;"></br>

 * {</span><span style="color: #808080;">@link</span><span style="color: #008000;"> AnyNestedCondition} that checks that either {</span><span style="color: #808080;">@code</span><span style="color: #008000;"> spring.datasource.type}</br>

 * is set or {</span><span style="color: #808080;">@link</span><span style="color: #008000;"> PooledDataSourceAvailableCondition} applies.</br>

 </span><span style="color: #008000;">*/</span></br>

<span style="color: #0000ff;">static</span> <span style="color: #0000ff;">class</span> PooledDataSourceCondition <span style="color: #0000ff;">extends</span><span style="color: #000000;"> AnyNestedCondition {









PooledDataSourceCondition() {



super(ConfigurationPhase.PARSE_CONFIGURATION);



}



    @ConditionalOnProperty(prefix </span>= "spring.datasource", name = "type"<span style="color: #000000;">)</br>

    </span><span style="color: #0000ff;">static</span> <span style="color: #0000ff;">class</span><span style="color: #000000;"> ExplicitType {</br></br>

    }</br></br>

    @Conditional(PooledDataSourceAvailableCondition.</span><span style="color: #0000ff;">class</span><span style="color: #000000;">)</br>

    </span><span style="color: #0000ff;">static</span> <span style="color: #0000ff;">class</span><span style="color: #000000;"> PooledDataSourceAvailable {</br></br>

    }</br></br>

}</br></br></br>

</span><span style="color: #008000;">/**</span><span style="color: #008000;"></br>

 * {</span><span style="color: #808080;">@link</span><span style="color: #008000;"> Condition} to test if a supported connection pool is available.</br>

 </span><span style="color: #008000;">*/</span></br>

<span style="color: #0000ff;">static</span> <span style="color: #0000ff;">class</span> PooledDataSourceAvailableCondition <span style="color: #0000ff;">extends</span><span style="color: #000000;"> SpringBootCondition {</br></br>

    @Override</br>

    </span><span style="color: #0000ff;">public</span><span style="color: #000000;"> ConditionOutcome getMatchOutcome(ConditionContext context,</br>

            AnnotatedTypeMetadata metadata) {</br>

        ConditionMessage.Builder message </span>=<span style="color: #000000;"> ConditionMessage</br>

                .forCondition(</span>"PooledDataSource"<span style="color: #000000;">);</br>

        </span><span style="color: #0000ff;">if</span> (getDataSourceClassLoader(context) != <span style="color: #0000ff;">null</span><span style="color: #000000;">) {</br>

            </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> ConditionOutcome</br>

                    .match(message.foundExactly(</span>"supported DataSource"<span style="color: #000000;">));</br>

        }</br>

        </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> ConditionOutcome</br>

                .noMatch(message.didNotFind(</span>"supported DataSource"<span style="color: #000000;">).atAll());</br>

    }</br>

    </span><span style="color: #008000;">/**</span><span style="color: #008000;"></br>

     * Returns the class loader for the {</span><span style="color: #808080;">@link</span><span style="color: #008000;"> DataSource} class. Used to ensure that</br>

     * the driver class can actually be loaded by the data source.</br>

     * </span><span style="color: #808080;">@param</span><span style="color: #008000;"> context the condition context</br>

     * </span><span style="color: #808080;">@return</span><span style="color: #008000;"> the class loader</br>

     </span><span style="color: #008000;">*/</span></br>

    <span style="color: #0000ff;">private</span><span style="color: #000000;"> ClassLoader getDataSourceClassLoader(ConditionContext context) {</br>

        Class</span>&lt;?&gt; dataSourceClass = <span style="color: #0000ff;">new</span><span style="color: #000000;"> DataSourceBuilder(context.getClassLoader())

                .findType();</br>

        </span><span style="color: #0000ff;">return</span> (dataSourceClass == <span style="color: #0000ff;">null</span> ? <span style="color: #0000ff;">null</span><span style="color: #000000;"> : dataSourceClass.getClassLoader());</br>

    }</br></br>

}</br>

</span><span style="color: #008000;">/**</span><span style="color: #008000;"></br>

 * {</span><span style="color: #808080;">@link</span><span style="color: #008000;"> Condition} to detect when an embedded {</span><span style="color: #808080;">@link</span><span style="color: #008000;"> DataSource} type can be used.</br>

 * If a pooled {</span><span style="color: #808080;">@link</span><span style="color: #008000;"> DataSource} is available, it will always be preferred to an</br>

 * {</span><span style="color: #808080;">@code</span><span style="color: #008000;"> EmbeddedDatabase}.</br>

 </span><span style="color: #008000;">*/</span></br>

<span style="color: #0000ff;">static</span> <span style="color: #0000ff;">class</span> EmbeddedDatabaseCondition <span style="color: #0000ff;">extends</span><span style="color: #000000;"> SpringBootCondition {</br></br>

    </span><span style="color: #0000ff;">private</span> <span style="color: #0000ff;">final</span> SpringBootCondition pooledCondition = <span style="color: #0000ff;">new</span><span style="color: #000000;"> PooledDataSourceCondition();</br></br>

    @Override</br>

    </span><span style="color: #0000ff;">public</span><span style="color: #000000;"> ConditionOutcome getMatchOutcome(ConditionContext context,

            AnnotatedTypeMetadata metadata) {</br>

        ConditionMessage.Builder message </span>=<span style="color: #000000;"> ConditionMessage</br>

                .forCondition(</span>"EmbeddedDataSource"<span style="color: #000000;">);</br>

        </span><span style="color: #0000ff;">if</span> (anyMatches(context, metadata, <span style="color: #0000ff;">this</span><span style="color: #000000;">.pooledCondition)) {</br>

            </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> ConditionOutcome</br>

                    .noMatch(message.foundExactly(</span>"supported pooled data source"<span style="color: #000000;">));</br>

        }</br>

        EmbeddedDatabaseType type </span>=<span style="color: #000000;"> EmbeddedDatabaseConnection</br>

                .get(context.getClassLoader()).getType();</br>

        </span><span style="color: #0000ff;">if</span> (type == <span style="color: #0000ff;">null</span><span style="color: #000000;">) {</br>

            </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> ConditionOutcome</br>

                    .noMatch(message.didNotFind(</span>"embedded database"<span style="color: #000000;">).atAll());</br>

        }</br>

        </span><span style="color: #0000ff;">return</span> ConditionOutcome.match(message.found("embedded database"<span style="color: #000000;">).items(type));</br>

    }</br></br>

}</br></br>

</span><span style="color: #008000;">/**</span><span style="color: #008000;"></br>

 * {</span><span style="color: #808080;">@link</span><span style="color: #008000;"> Condition} to detect when a {</span><span style="color: #808080;">@link</span><span style="color: #008000;"> DataSource} is available (either because

 * the user provided one or because one will be auto-configured).</br>

 </span><span style="color: #008000;">*/</span><span style="color: #000000;"></br>

@Order(Ordered.LOWEST_PRECEDENCE </span>- 10<span style="color: #000000;">)</br>

</span><span style="color: #0000ff;">static</span> <span style="color: #0000ff;">class</span> DataSourceAvailableCondition <span style="color: #0000ff;">extends</span><span style="color: #000000;"> SpringBootCondition {</br></br>

    </span><span style="color: #0000ff;">private</span> <span style="color: #0000ff;">final</span> SpringBootCondition pooledCondition = <span style="color: #0000ff;">new</span><span style="color: #000000;"> PooledDataSourceCondition();</br></br>

    </span><span style="color: #0000ff;">private</span> <span style="color: #0000ff;">final</span> SpringBootCondition embeddedCondition = <span style="color: #0000ff;">new</span><span style="color: #000000;"> EmbeddedDatabaseCondition();</br></br>

    @Override</br>

    </span><span style="color: #0000ff;">public</span><span style="color: #000000;"> ConditionOutcome getMatchOutcome(ConditionContext context,</br>

            AnnotatedTypeMetadata metadata) {</br>

        ConditionMessage.Builder message </span>=<span style="color: #000000;"> ConditionMessage</br>

                .forCondition(</span>"DataSourceAvailable"<span style="color: #000000;">);</br>

        </span><span style="color: #0000ff;">if</span> (hasBean(context, DataSource.<span style="color: #0000ff;">class</span><span style="color: #000000;">)</br>

                </span>|| hasBean(context, XADataSource.<span style="color: #0000ff;">class</span><span style="color: #000000;">)) {</br>

            </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> ConditionOutcome</br>

                    .match(message.foundExactly(</span>"existing data source bean"<span style="color: #000000;">));</br>

        }</br>

        </span><span style="color: #0000ff;">if</span> (anyMatches(context, metadata, <span style="color: #0000ff;">this</span><span style="color: #000000;">.pooledCondition,</br>

                </span><span style="color: #0000ff;">this</span><span style="color: #000000;">.embeddedCondition)) {</br>

            </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> ConditionOutcome.match(message</br>

                    .foundExactly(</span>"existing auto-configured data source bean"<span style="color: #000000;">));</br>

        }</br>

        </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> ConditionOutcome</br>

                .noMatch(message.didNotFind(</span>"any existing data source bean"<span style="color: #000000;">).atAll());</br>

    }</br></br>

    </span><span style="color: #0000ff;">private</span> <span style="color: #0000ff;">boolean</span> hasBean(ConditionContext context, Class&lt;?&gt;<span style="color: #000000;"> type) {</br>

        </span><span style="color: #0000ff;">return</span><span style="color: #000000;"> BeanFactoryUtils.beanNamesForTypeIncludingAncestors(</br>

                context.getBeanFactory(), type, </span><span style="color: #0000ff;">true</span>, <span style="color: #0000ff;">false</span>).length &gt; 0<span style="color: #000000;">;</br>

    }</br></br>

}</br></br>




}

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

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