Spring Boot JDBC：加載DataSource過程的源碼分析及yml中DataSource的配置

Spring Boot實現了自動加載DataSource及相關配置。當然，使用時加上@EnableAutoConfiguration注解是必須的。下面就是對這一部分的源碼分析。

（1）Spring Boot啟動后會調用org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration。下面是部分源碼。

@Configuration
@ConditionalOnClass({ DataSource.class, EmbeddedDatabaseType.class })
@EnableConfigurationProperties(DataSourceProperties.class)
@Import({ DataSourcePoolMetadataProvidersConfiguration.class,
        DataSourceInitializationConfiguration.class })
public class DataSourceAutoConfiguration {

    @Configuration
    @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.Hikari.class, DataSourceConfiguration.Tomcat.class,
            DataSourceConfiguration.Dbcp2.class, DataSourceConfiguration.Generic.class,
            DataSourceJmxConfiguration.class })
    protected static class PooledDataSourceConfiguration {
    }
    ......
}

我們從中可以看出，DataSourceAutoConfiguration中有兩個嵌套類，一個是EmbeddedDatabaseConfiguration，另一個是PooledDataSourceConfiguration。

EmbeddedDatabaseConfiguration表示已經嵌入Spring Boot的DataSource，除了Maven中加入相應的Driver，可以不做其他額外配置就能使用。從EmbeddedDatabaseType類可以看出，Spring Boot的內嵌DataSource支持HSQL，H2，DERBY這三種DB。

PooledDataSourceConfiguration表示Spring Boot還支持一些實現Pool的DataSource。從org.springframework.boot.jdbc.DataSourceBuilder中可以看出，當前版本的Spring Boot（2.0）只支持com.zaxxer.hikari.HikariDataSource，org.apache.tomcat.jdbc.pool.DataSource，org.apache.commons.dbcp2.BasicDataSource。其中，性能更加優秀的HikariDataSource是Spring Boot的默認選擇（DataSourceBuilder中DATA_SOURCE_TYPE_NAMES[0] = com.zaxxer.hikari.HikariDataSource）。所以，當application.yml文件中做如下配置時，Spring Boot默認使用HikariDataSource數據庫連接池。

spring:
  datasource:
    url: jdbc:mysql://localhost:3306/sas
    username: root
    password: ****
    driver-class-name: com.mysql.jdbc.Driver
    #type: com.zaxxer.hikari.HikariDataSource

 

（2）我們以HikariDataSource舉例，接下來調用PooledDataSourceConfiguration中org.springframework.boot.autoconfigure.jdbc.DataSourceConfiguration抽象類的Hikari嵌套類（DataSourceConfiguration抽象類的一個實現類）。

abstract class DataSourceConfiguration {

    @SuppressWarnings("unchecked")
    protected <T> T createDataSource(DataSourceProperties properties,
            Class<? extends DataSource> type) {
        return (T) properties.initializeDataSourceBuilder().type(type).build();
    }

    /* Omit Tomcat Pool DataSource configuration.*/
    /**
     * Hikari DataSource configuration.
     */
    @ConditionalOnClass(HikariDataSource.class)
    @ConditionalOnProperty(name = "spring.datasource.type", havingValue = "com.zaxxer.hikari.HikariDataSource", matchIfMissing = true)
    static class Hikari extends DataSourceConfiguration {

        @Bean
        @ConfigurationProperties(prefix = "spring.datasource.hikari") 19         public HikariDataSource dataSource(DataSourceProperties properties) { 20             HikariDataSource dataSource = createDataSource(properties,
                    HikariDataSource.class);
            if (StringUtils.hasText(properties.getName())) {
                dataSource.setPoolName(properties.getName());
            }
            return dataSource;
        }
    }
    /* Omit DBCP DataSource configuration.*/
}

 我們從黃色部分可以看出，當application.yml文件中配置spring.datasource.type = com.zaxxer.hikari.HikariDataSource時，會使用HikariDataSource作為數據庫連接池（當然上面也分析了，它是默認選擇）。我們從綠色部分可以看出它的配置信息主要從兩個類中讀取，一個是org.springframework.boot.autoconfigure.jdbc.DataSourceProperties，另一個則是本類HikariDataSource的父類com.zaxxer.hikari.HikariConfig。

@ConfigurationProperties(prefix = "spring.datasource")
public class DataSourceProperties implements BeanClassLoaderAware, InitializingBean {}

@ConfigurationProperties(prefix = "spring.datasource.hikari")
public HikariDataSource dataSource(DataSourceProperties properties) {}

我們從@ConfigurationProperties配置及兩個具體的類所包含的的域可以得出配置HikariDataSource信息。下面是例子。

spring:
  datasource:
    name: #Name of the datasource. Default to "testdb" when using an embedded database.
    driverClassName: #Fully qualified name of the JDBC driver. Auto-detected based on the URL by default.
    url: #DBC URL of the database.
    type: #Fully qualified name of the connection pool implementation to use. By default, it is auto-detected from the classpath.
    username: #Login username of the database.
    password: #Login password of the database.
    ## For more details please see DataSourceProperties.
    hikari:
      connectionTimeout:
      validationTimeout:
      maxPoolSize:
      minIdle:
      dataSourceProperties:
      ## For more details please see HikariConfig.

 

（3）當讀完配置后，則會通過HikariDataSource.getConnection()方法創建HikariPool對象。HikariPool及其父類PoolBase做了許多復雜的工作，包括創建Pool，創建Connection，讀取Config，驗證等等。調用HikariDataSource.getConnection()方法最終得到了這個Connection對象。這個過程中主要做了以下幾步：

① 創建HikariPool對象。

② 調用HikariPool對象的父類對象PoolBase的構造器，讀取HikariConfig配置信息配置PoolBase的屬性。

③ 調用PoolBase的構造器的initializeDataSource方法，利用com.zaxxer.hikari.util.DriverDataSource創建DataSource對象（這里主要指JDBC URL方式）。DriverDataSource中會把所有的DataSource信息封裝到driverProperties屬性中，這是為了適配java.sql.Driver的connect(String url, java.util.Properties info)方法。

public final class DriverDataSource implements DataSource {

    private final String jdbcUrl;
    private final Properties driverProperties;
    private Driver driver;

    public DriverDataSource(String jdbcUrl, String driverClassName, Properties properties, String username, String password) {
        this.jdbcUrl = jdbcUrl;
        this.driverProperties = new Properties();
        Iterator e = properties.entrySet().iterator();

        while(e.hasNext()) {
            Entry driverClass = (Entry)e.next();
            this.driverProperties.setProperty(driverClass.getKey().toString(), driverClass.getValue().toString());
        }

        if(username != null) {
            this.driverProperties.put("user", this.driverProperties.getProperty("user", username));
        }

        if(password != null) {
            this.driverProperties.put("password", this.driverProperties.getProperty("password", password));
        }
    ......
    }

   @Override
   public Connection getConnection() throws SQLException
   {
      return driver.connect(jdbcUrl, driverProperties);
   }
}

④ 調用HikariPool對象的構造器，同樣也是配置一堆線程池信息。

⑤ 返回HikariPool.getConnection()。這個過程中，做了包含PoolBase.newPoolEntry()及PoolBase.newConnection()的許多復雜方法。從PoolBase.newConnection()可以看出，最終還是調用的步驟③的getConnection()方法獲取到了這個Connection對象。

   private Connection newConnection() throws Exception
   {
      final long start = currentTime();

      Connection connection = null;
      try {
         String username = config.getUsername();
         String password = config.getPassword();

         connection = (username == null) ? dataSource.getConnection() : dataSource.getConnection(username, password);
         if (connection == null) {
            throw new SQLTransientConnectionException("DataSource returned null unexpectedly");
         }

         setupConnection(connection);
         lastConnectionFailure.set(null);
         return connection;
      }
      catch (Exception e) {
         if (connection != null) {
            quietlyCloseConnection(connection, "(Failed to create/setup connection)");
         }
         else if (getLastConnectionFailure() == null) {
            LOGGER.debug("{} - Failed to create/setup connection: {}", poolName, e.getMessage());
         }

         lastConnectionFailure.set(e);
         throw e;
      }
      finally {
         // tracker will be null during failFast check
         if (metricsTracker != null) {
            metricsTracker.recordConnectionCreated(elapsedMillis(start));
         }
      }
   }