裝載至：https://www.cnblogs.com/storml/p/8611388.html
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。
1 @Configuration
2 @ConditionalOnClass({ DataSource.class, EmbeddedDatabaseType.class })
3 @EnableConfigurationProperties(DataSourceProperties.class)
4 @Import({ DataSourcePoolMetadataProvidersConfiguration.class,
5 DataSourceInitializationConfiguration.class })
6 public class DataSourceAutoConfiguration {
7
8 @Configuration
9 @Conditional(EmbeddedDatabaseCondition.class)
10 @ConditionalOnMissingBean({ DataSource.class, XADataSource.class })
11 @Import(EmbeddedDataSourceConfiguration.class)
12 protected static class EmbeddedDatabaseConfiguration {
13 }
14
15 @Configuration
16 @Conditional(PooledDataSourceCondition.class)
17 @ConditionalOnMissingBean({ DataSource.class, XADataSource.class })
18 @Import({ DataSourceConfiguration.Hikari.class, DataSourceConfiguration.Tomcat.class,
19 DataSourceConfiguration.Dbcp2.class, DataSourceConfiguration.Generic.class,
20 DataSourceJmxConfiguration.class })
21 protected static class PooledDataSourceConfiguration {
22 }
23 ......
24 }
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）。
1 abstract class DataSourceConfiguration {
2
3 @SuppressWarnings("unchecked")
4 protected <T> T createDataSource(DataSourceProperties properties,
5 Class<? extends DataSource> type) {
6 return (T) properties.initializeDataSourceBuilder().type(type).build();
7 }
8
9 /* Omit Tomcat Pool DataSource configuration.*/
10 /**
11 * Hikari DataSource configuration.
12 */
13 @ConditionalOnClass(HikariDataSource.class)
14 @ConditionalOnProperty(name = "spring.datasource.type", havingValue = "com.zaxxer.hikari.HikariDataSource", matchIfMissing = true)
15 static class Hikari extends DataSourceConfiguration {
16
17 @Bean
18 @ConfigurationProperties(prefix = "spring.datasource.hikari")
19 public HikariDataSource dataSource(DataSourceProperties properties) {
20 HikariDataSource dataSource = createDataSource(properties,
21 HikariDataSource.class);
22 if (StringUtils.hasText(properties.getName())) {
23 dataSource.setPoolName(properties.getName());
24 }
25 return dataSource;
26 }
27 }
28 /* Omit DBCP DataSource configuration.*/
29 }
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。
1 public final class DriverDataSource implements DataSource {
2
3 private final String jdbcUrl;
4 private final Properties driverProperties;
5 private Driver driver;
6
7 public DriverDataSource(String jdbcUrl, String driverClassName, Properties properties, String username, String password) {
8 this.jdbcUrl = jdbcUrl;
9 this.driverProperties = new Properties();
10 Iterator e = properties.entrySet().iterator();
11
12 while(e.hasNext()) {
13 Entry driverClass = (Entry)e.next();
14 this.driverProperties.setProperty(driverClass.getKey().toString(), driverClass.getValue().toString());
15 }
16
17 if(username != null) {
18 this.driverProperties.put("user", this.driverProperties.getProperty("user", username));
19 }
20
21 if(password != null) {
22 this.driverProperties.put("password", this.driverProperties.getProperty("password", password));
23 }
24 ......
25 }
26
27 @Override
28 public Connection getConnection() throws SQLException
29 {
30 return driver.connect(jdbcUrl, driverProperties);
31 }
32 }
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。
1 private Connection newConnection() throws Exception
2 {
3 final long start = currentTime();
4
5 Connection connection = null;
6 try {
7 String username = config.getUsername();
8 String password = config.getPassword();
9
10 connection = (username == null) ? dataSource.getConnection() : dataSource.getConnection(username, password);
11 if (connection == null) {
12 throw new SQLTransientConnectionException("DataSource returned null unexpectedly");
13 }
14
15 setupConnection(connection);
16 lastConnectionFailure.set(null);
17 return connection;
18 }
19 catch (Exception e) {
20 if (connection != null) {
21 quietlyCloseConnection(connection, "(Failed to create/setup connection)");
22 }
23 else if (getLastConnectionFailure() == null) {
24 LOGGER.debug("{} - Failed to create/setup connection: {}", poolName, e.getMessage());
25 }
26
27 lastConnectionFailure.set(e);
28 throw e;
29 }
30 finally {
31 // tracker will be null during failFast check
32 if (metricsTracker != null) {
33 metricsTracker.recordConnectionCreated(elapsedMillis(start));
34 }
35 }
36 }