spring全家桶学习-springboot默认使⽤hikaricp
根据springboot ⾃动装配的特性来分析为什么 springboot 默认使⽤ hikaricp 作为数据库连接池?
通过 SpringBootApplication 注解可以看到⼀个关键的注解就是 EnableAutoConfiguration;
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
spring boot选择题@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication {
.... 省略其他
}
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(AutoConfigurationImportSelector.class) // 核⼼点
public @interface EnableAutoConfiguration {
...
}
其通过使⽤ Import注解往当前容器引⼊AutoConfigurationImportSelector作为组件, 其通
过 org.springframework.boot.autoconfigure.AutoConfigurationImportSelector#selectImports ⽅法来加载 spring-boot-auto-configure jar中的 META-INF/spring.factories ⽂件中关于 EnableAutoConfiguration属性中的相关属性值，通过加载解析相关的 **AutoConfiguration类来实现⾃动装配的⽬的;
以 DataSourceAutoConfiguration 为例
@Configuration(proxyBeanMethods = false)
@ConditionalOnClass({ DataSource.class, EmbeddedDatabaseType.class })
@ConditionalOnMissingBean(type = "io.r2dbc.spi.ConnectionFactory")
@EnableConfigurationProperties(DataSourceProperties.class)
@Import({ DataSourcePoolMetadataProvidersConfiguration.class, DataSourceInitializationConfiguration.class })
public class DataSourceAutoConfiguration {
@Configuration(proxyBeanMethods = false)
@Conditional(EmbeddedDatabaseCondition.class)
@ConditionalOnMissingBean({ DataSource.class, XADataSource.class })
@Import(EmbeddedDataSourceConfiguration.class)
protected static class EmbeddedDatabaseConfiguration {
}
@Configuration(proxyBeanMethods = false) // 声明当前类作为配置类装载到spring 容器中
@Conditional(PooledDataSourceCondition.class) // 限制要求只有在满⾜当前注解中属性值(PooledDataSourceCondition)判断通过的情况下才允许初始化当前bean
@ConditionalOnMissingBean({ DataSource.class, XADataSource.class }) // 如果容器中不存在当前bean(DataSource / XADataSource)，则会执⾏当前注解标记的类或⽅法来实现bean的初始化
@Import({ DataSourceConfiguration.Hikari.class, DataSourceConfiguration.Tomcat.class,
DataSourceConfiguration.Dbcp2.class, DataSourceConfiguration.OracleUcp.class,
DataSourceConfiguration.Generic.class, DataSourceJmxConfiguration.class })// 关于Import的作⽤为给容器注⼊⼀个组件,⽀持通过数组配置多个类，表⽰将所有存在的bean引⼊当前配置
protected static class PooledDataSourceConfiguration { // 连接池相关配置
}
... 省略代码
}
在这⾥其核⼼主要使⽤以下注解
1. Conditional 条件判断限制bean的⽣成
2. ConditionalOnMissingBean 判断需要的bean是否存在，当bean在容器中不存在的情况下，会注解中配置的bean的类型进⾏初始化操作
3. Import 为当前容器引⼊对应的组件(bean)
关于 Import 中的 "DataSourceConfiguration.Hikari.class"
/**
* Hikari DataSource configuration.
*/
@Configuration(proxyBeanMethods = false) // 表⽰当前也为配置类
@ConditionalOnClass(HikariDataSource.class)// 条件判断要求 HikariDataSource 类必须存在于当前classPath下，由于spring-boot-stater-jdbc jar中默认引⼊了 HikariCP jar，且HikariCPDataSource类在当前jar中存在 @ConditionalOnMissingBean(DataSource.class) // 判断如果当前 Datasource bean 在spring 容器中不存在，则通过当前配置类执⾏bean初始化操作
@ConditionalOnProperty(name = "pe", havingValue = "com.zaxxer.hikari.HikariDataSource",
matchIfMissing = true) // 判断属性是否存在，通过设置matchIfMissing = true 表⽰即使在当前属性条件不满⾜的情况下也会执⾏后续的操作
static class Hikari {
@Bean // 通过⽅法⽣成当前类作为springbean
@ConfigurationProperties(prefix = "spring.datasource.hikari") // 解析配置⽂件中指定前缀的属性值，并注⼊到当前参数中
HikariDataSource dataSource(DataSourceProperties properties) {
HikariDataSource dataSource = createDataSource(properties, HikariDataSource.class);//创建 HikariDataSource实例并返回，其会被加载到spring 容器中作为spring bean 存在if (StringUtils.Name())) {
dataSource.Name());
}
return dataSource;
}
}
回答开篇的问题，为什么SpringBoot 2.0 中在不配置任何属性情况下能⾃动获取到Hikaricp作为默认数据库连接池?
由于HikariDataSource 当前类属于 com.zaxxer.HikariCP jar, 从springboot 2.0 开始 spring-boot-starter-jdbc 默认引⼊了HikariCP jar(参考以下xml⽂件);
因此在不额外引⼊其他相关数据库连接池依赖jar 的情况下，会默认使⽤ hikaricp作为默认数据库连接池;
需要注意的⼀点在于，在spring-boot 2.0中如果需要使⽤其他的⽀持⾃动装配的数据库连接池，最好排除(exclude) HikariCP jar;
由于⾃动装配的优先级最低，且⼀般要求只有在容器中不存在指定bean的情况下才会进⾏⾃动配置;
如果通过⾃定义配置类来设置相关的DataSource Bean，则⾃动装配实际并不会被执⾏；但还是建议在SpringBootApplication注解的 exclude 属性中排除掉相关的
*AutoConfiguration类
<?xml version="1.0" encoding="UTF-8"?>
<project xsi:schemaLocation="/POM/4.0.0 /xsd/maven-4.0.0.xsd" xmlns="/POM/4.0.0"
xmlns:xsi="/2001/XMLSchema-instance">
<!-- This module was also published with a richer model, Gradle metadata, -->
<!-- which should be used instead. Do not delete the following line which -->
<!-- is to indicate to Gradle or any Gradle module metadata file consumer -->
<!-- that they should prefer consuming it instead. -->
<!-- do_not_remove: published-with-gradle-metadata -->
<modelVersion>4.0.0</modelVersion>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-jdbc</artifactId>
<version>2.4.1</version>
<name>spring-boot-starter-jdbc</name>
<description>Starter for using JDBC with the HikariCP connection pool</description>
<url>spring.io/projects/spring-boot</url>
<organization>
<name>Pivotal Software, Inc.</name>
<url>spring.io</url>
</organization>
<licenses>
<license>
<name>Apache License, Version 2.0</name>
<url>/licenses/LICENSE-2.0</url>
</license>
</licenses>
<developers>
<developer>
<name>Pivotal</name>
<email>info@pivotal.io</email>
<organization>Pivotal Software, Inc.</organization>
<organizationUrl>www.spring.io</organizationUrl>
</developer>
</developers>
<scm>
<connection>scm:git:git://github/spring-projects/spring-boot.git</connection>
<developerConnection>scm:git:ssh://git@github/spring-projects/spring-boot.git</developerConnection>
<url>github/spring-projects/spring-boot</url>
</scm>
<issueManagement>
<system>GitHub</system>
<url>github/spring-projects/spring-boot/issues</url>
</issueManagement>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter</artifactId>
<version>2.4.1</version>
<scope>compile</scope>
</dependency>
<dependency>
<groupId>com.zaxxer</groupId>
<artifactId>HikariCP</artifactId>
<version>3.4.5</version>
<scope>compile</scope>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-jdbc</artifactId>
<version>5.3.2</version>
<scope>compile</scope>
</dependency>
</dependencies>
</project>
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