Spring boot 数据源配置。

配置文件 ：

　　spring boot  配置文件 有两种形式 ，一种是properties文件、一种是yml文件。案列使用properties文件。

数据源的默认配置 ：

　　spring boot 约定优先于配置 ，所以数据源也有默认的配置，所有的默认配置文件基本都已xxxautoConfiguration.java 的形式放在spring-boot-configure.jar中，配置在“/META-INF/spring.factories”文件中 。数据源的默认配置类为：org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration ，在配置文件中导入了四中配置，黄色标记部分，如下

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

    }
        ...
}

而从DataSourceBuilder类代码看 ，知道 ，会去遍历加载，这个四个数据源，如果加载成功了，就返回，后面的不再加载。

public final class DataSourceBuilder<T extends DataSource> {

    private static final String[] DATA_SOURCE_TYPE_NAMES = new String[] { "com.zaxxer.hikari.HikariDataSource",
            "org.apache.tomcat.jdbc.pool.DataSource", "org.apache.commons.dbcp2.BasicDataSource" };
    ...
    @SuppressWarnings("unchecked")
    public static Class<? extends DataSource> findType(ClassLoader classLoader) {
        for (String name : DATA_SOURCE_TYPE_NAMES) {
            try {
                              //加载成功便会返回。
                return (Class<? extends DataSource>) ClassUtils.forName(name, classLoader);
            }
            catch (Exception ex) {
                // Swallow and continue
            }
        }
        return null;
    }
    ...

} 

看看我们Pom文件导入的数据源jar包，点击后跟踪到最后一个pom文件 ，看到只导入了HikariCP数据源。

　　　　<dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-jdbc</artifactId>
        </dependency>

      <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-jdbc</artifactId>
        <version>2.1.6.RELEASE</version>
      </dependency>

<?xml version="1.0" encoding="UTF-8"?>
<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <modelVersion>4.0.0</modelVersion>
  <parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starters</artifactId>
    <version>2.1.6.RELEASE</version>
  </parent>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-jdbc</artifactId>
  <version>2.1.6.RELEASE</version>
  <name>Spring Boot JDBC Starter</name>
  <description>Starter for using JDBC with the HikariCP connection pool</description>
  <url>https://projects.spring.io/spring-boot/#/spring-boot-parent/spring-boot-starters/spring-boot-starter-jdbc</url>
  <organization>
    <name>Pivotal Software, Inc.</name>
    <url>https://spring.io</url>
  </organization>
  <licenses>
    <license>
      <name>Apache License, Version 2.0</name>
      <url>https://www.apache.org/licenses/LICENSE-2.0</url>
    </license>
  </licenses>
  <developers>
    <developer>
      <name>Pivotal</name>
      <email>info@pivotal.io</email>
      <organization>Pivotal Software, Inc.</organization>
      <organizationUrl>https://www.spring.io</organizationUrl>
    </developer>
  </developers>
  <scm>
    <connection>scm:git:git://github.com/spring-projects/spring-boot.git/spring-boot-starters/spring-boot-starter-jdbc</connection>
    <developerConnection>scm:git:ssh://git@github.com/spring-projects/spring-boot.git/spring-boot-starters/spring-boot-starter-jdbc</developerConnection>
    <url>https://github.com/spring-projects/spring-boot/spring-boot-starters/spring-boot-starter-jdbc</url>
  </scm>
  <issueManagement>
    <system>Github</system>
    <url>https://github.com/spring-projects/spring-boot/issues</url>
  </issueManagement>
  <dependencies>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter</artifactId>
      <version>2.1.6.RELEASE</version>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>com.zaxxer</groupId>
      <artifactId>HikariCP</artifactId>
      <version>3.2.0</version>
      <scope>compile</scope>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-jdbc</artifactId>
      <version>5.1.8.RELEASE</version>
      <scope>compile</scope>
    </dependency>
  </dependencies>
</project>

根据代码分析，默认数据源配置就是 HikariCP ，注意，如果，不另外导入jar包，而配置另外的数据源 如：spring.datasource.type = org.apache.tomcat.jdbc.pool.DataSource，则会报错。

配置自定义数据源：

　　1.导入Druid maven 坐标

　　

<!-- https://mvnrepository.com/artifact/com.alibaba/druid -->
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid</artifactId>
            <version>1.1.16</version>
        </dependency>

　　1.以配置druid 数据源为例 ，驱动为mysql 。写入配置文件 ：

　　

spring.datasource.name = root
spring.datasource.password = 123456
spring.datasource.url = jdbc:mysql://192.168.1.103:3306/jdbc
spring.datasource.driverClassName = com.mysql.jdbc.Driver
spring.datasource.type = com.alibaba.druid.pool.DruidDataSource

　　3.指定配置type后还不够，数据源已切换过来 ，一下DruidConfig为配置别的属性，不写别的属性配置不进去。

@Configuration
public class DruidConfig {

    @ConfigurationProperties(prefix = "spring.datasource")
    @Bean
    public DataSource druid(){
       return  new DruidDataSource();
    }

    //配置Druid的监控
    //1、配置一个管理后台的Servlet
    @Bean
    public ServletRegistrationBean statViewServlet(){
        ServletRegistrationBean bean = new ServletRegistrationBean(new StatViewServlet(), "/druid/*");
        Map<String,String> initParams = new HashMap<>();

        initParams.put("loginUsername","admin");
        initParams.put("loginPassword","123456");
        initParams.put("allow","");//默认就是允许所有访问
        initParams.put("deny","192.168.15.21");

        bean.setInitParameters(initParams);
        return bean;
    }


    //2、配置一个web监控的filter
    @Bean
    public FilterRegistrationBean webStatFilter(){
        FilterRegistrationBean bean = new FilterRegistrationBean();
        bean.setFilter(new WebStatFilter());

        Map<String,String> initParams = new HashMap<>();
        initParams.put("exclusions","*.js,*.css,/druid/*");

        bean.setInitParameters(initParams);

        bean.setUrlPatterns(Arrays.asList("/*"));

        return  bean;
    }
}

4.测试：