【SpringBoot】启动器（starter）并自定义启动器

SpringBoot启动器

参考： https://docs.spring.io/spring-boot/docs/current/reference/htmlsingle/#using-boot-starter

Springboot的Stater的概念其实很像操作系统中的bootloader，在应用或者系统启动的时候需要把设备驱动、内存环境等都装配好。对于Springboot就是把依赖项和配置项进行装配啦。

启动器的特点就是你不需要每次都把依赖和配置相关代码拷贝到你的工程里，可以通过include所需starter来实现。

启动器的官方命名

SpringBoot的命名模板：

spring-boot-starter-*

对于第三方的starter应该不以spring-boot作为前缀，或者可以在spring-boot前面添加如：

thirdpartyproject-spring-boot-starter

SpringBoot提供的启动器

Spring Boot application starters

Name	Description
spring-boot-starter	Core starter, including auto-configuration support, logging and YAML 核心启动器，包括了自动配置和日志、和yaml
spring-boot-starter-activemq	Starter for JMS messaging using Apache ActiveMQ
spring-boot-starter-amqp	Starter for using Spring AMQP and Rabbit MQ
spring-boot-starter-aop	Starter for aspect-oriented programming with Spring AOP and AspectJ
spring-boot-starter-artemis	Starter for JMS（Java Message Service） messaging using Apache Artemis
spring-boot-starter-batch	Starter for using Spring Batch
spring-boot-starter-cache	Starter for using Spring Framework’s caching support
spring-boot-starter-data-cassandra	Starter for using Cassandra distributed database and Spring Data Cassandra （Cassandra是一种分布式NoSQL数据库系统）
spring-boot-starter-data-cassandra-reactive	Starter for using Cassandra distributed database and Spring Data Cassandra Reactive
spring-boot-starter-data-couchbase	Starter for using Couchbase document-oriented database and Spring Data Couchbase
spring-boot-starter-data-couchbase-reactive	Starter for using Couchbase document-oriented database and Spring Data Couchbase Reactive
spring-boot-starter-data-elasticsearch	Starter for using Elasticsearch search and analytics engine and Spring Data Elasticsearch
spring-boot-starter-data-jdbc	Starter for using Spring Data JDBC
spring-boot-starter-data-jpa	Starter for using Spring Data JPA with Hibernate
spring-boot-starter-data-ldap	Starter for using Spring Data LDAP
spring-boot-starter-data-mongodb	Starter for using MongoDB document-oriented database and Spring Data MongoDB
spring-boot-starter-data-mongodb-reactive	Starter for using MongoDB document-oriented database and Spring Data MongoDB Reactive
spring-boot-starter-data-neo4j	Starter for using Neo4j graph database and Spring Data Neo4j
spring-boot-starter-data-r2dbc	Starter for using Spring Data R2DBC
spring-boot-starter-data-redis	Starter for using Redis key-value data store with Spring Data Redis and the Lettuce client
spring-boot-starter-data-redis-reactive	Starter for using Redis key-value data store with Spring Data Redis reactive and the Lettuce client
spring-boot-starter-data-rest	Starter for exposing Spring Data repositories over REST using Spring Data REST
spring-boot-starter-data-solr	Starter for using the Apache Solr search platform with Spring Data Solr. Deprecated since 2.3.9
spring-boot-starter-freemarker	Starter for building MVC web applications using FreeMarker views
spring-boot-starter-groovy-templates	Starter for building MVC web applications using Groovy Templates views
spring-boot-starter-hateoas	Starter for building hypermedia-based RESTful web application with Spring MVC and Spring HATEOAS
spring-boot-starter-integration	Starter for using Spring Integration
spring-boot-starter-jdbc	Starter for using JDBC with the HikariCP connection pool
spring-boot-starter-jersey	Starter for building RESTful web applications using JAX-RS and Jersey. An alternative to spring-boot-starter-web
spring-boot-starter-jooq	Starter for using jOOQ to access SQL databases. An alternative to spring-boot-starter-data-jpa or spring-boot-starter-jdbc
spring-boot-starter-json	Starter for reading and writing json
spring-boot-starter-jta-atomikos	Starter for JTA transactions using Atomikos
spring-boot-starter-jta-bitronix	Starter for JTA transactions using Bitronix. Deprecated since 2.3.0
spring-boot-starter-mail	Starter for using Java Mail and Spring Framework’s email sending support
spring-boot-starter-mustache	Starter for building web applications using Mustache views
spring-boot-starter-oauth2-client	Starter for using Spring Security’s OAuth2/OpenID Connect client features
spring-boot-starter-oauth2-resource-server	Starter for using Spring Security’s OAuth2 resource server features
spring-boot-starter-quartz	Starter for using the Quartz scheduler
spring-boot-starter-rsocket	Starter for building RSocket clients and servers
spring-boot-starter-security	Starter for using Spring Security
spring-boot-starter-test	Starter for testing Spring Boot applications with libraries including JUnit Jupiter, Hamcrest and Mockito
spring-boot-starter-thymeleaf	Starter for building MVC web applications using Thymeleaf views
spring-boot-starter-validation	Starter for using Java Bean Validation with Hibernate Validator
spring-boot-starter-web	Starter for building web, including RESTful, applications using Spring MVC. Uses Tomcat as the default embedded container(服务容器在这个启动器里被装配的)
spring-boot-starter-web-services	Starter for using Spring Web Services
spring-boot-starter-webflux	Starter for building WebFlux applications using Spring Framework’s Reactive Web support
spring-boot-starter-websocket	Starter for building WebSocket applications using Spring Framework’s WebSocket support

Spring Boot technical starters

Name	Description
spring-boot-starter-jetty	Starter for using Jetty as the embedded servlet container. An alternative to spring-boot-starter-tomcat
spring-boot-starter-log4j2	Starter for using Log4j2 for logging. An alternative to spring-boot-starter-logging
spring-boot-starter-logging	Starter for logging using Logback. Default logging starter
spring-boot-starter-reactor-netty	Starter for using Reactor Netty as the embedded reactive HTTP server.
spring-boot-starter-tomcat	Starter for using Tomcat as the embedded servlet container. Default servlet container starter used by spring-boot-starter-web
spring-boot-starter-undertow	Starter for using Undertow as the embedded servlet container. An alternative to spring-boot-starter-tomcat

自定义启动器包括内容

1. 依赖环境的导入（pom.xml）
2. 配置信息的导入 (application.yml、application.properties、@ConfigurationProperties等)
3. 自动装配Bean和配置项等 （spring.factories、@Configuration）

创建自定义启动器

命名：

为了和Springboot提供的分开，你的启动器命名就不能以spring-boot为开头。

比如你要创建一个acmestarter，可以把启动器命名为acme-spring-boot-stater

配置项

当你的启动器需要配置相关信息，可以使用一个独特的命名空间为它们坐区分。你可以把这个命名空间作为所有配置项的前缀。

使用注解@ConfigurationProperties来装配配置项信息，并为其添加javadoc

@ConfigurationProperties("acme")
public class AcmeProperties {

    /**
     * Whether to check the location of acme resources.
     */
    private boolean checkLocation = true;

    /**
     * Timeout for establishing a connection to the acme server.
     */
    private Duration loginTimeout = Duration.ofSeconds(3);

    // getters & setters

}

最好能为你的配置项填上默认值，这样在导入你这个starter的时候就可以非必须地对其进行配置了。

自动装配类

上面的对配置项属性文件进行读取导入。现在需要一个装配类文件对这些配置项进行使用了,

其实也是对我们这个启动器需要用到的Bean装载的IOC容器里，还能用一些条件注解来

@COnfigutration
@EnableConfigurationProperties(AcmeProperties.class)
@ConditionalOnWebApplication
public class AcmeAutoConfiguration {
    AcmeProperties acmeProperties
    public AcmeAutoConfiguration(AcmeProperties acmeProperties){
        this.acmeProperties = acmeProperties;
    }
        @Bean
        @ConditionalOnMissingBean
        public EmbeddedAcmeService embeddedAcmeService() { ... }
}

创建完我们的自动装配类，我们还需要在创建META-INF/spring.factories，并在该文件告诉SpringBoot我们的自动装配类是啥。因为SpringBoot会检查你发布的jar包中是否存在该文件，需要在该文件的EnableAutoConfiguration项下声明您的自动装配类

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
com.lmafia.AcmeAutoConfiguration1,\
com.lmafia.AcmeAutoConfiguration2

关于条件注解

条件	描述
ConditionalOnBean	当且仅当指定的bean classes and/or bean names在当前容器中,才创建标记上该注解的类的实例
ConditionalOnMissingBean	当且仅当指定的bean classes and/or bean names不存在当前容器中,才创建标记上该注解的类的实例，有指定忽略ignored的参数存在，可以忽略Class、Type等
ConditionalOnClass	当且仅当指定的bean classes and/or bean names在当前容器中,才创建标记上该注解的类的实例
ConditionalOnMissingClass	当且仅当ClassPath存在指定的Class时，才创建标记上该注解的类的实例
ConditionalOnProperty	是否存在指定配置
ConditionalOnJava	指定JDK的版本
ConditionalOnExpression	表达式⽤${…}=false等来表示
ConditionalOnJndi JNDI	存在该项时创建
ConditionalOnResource	在classpath下存在指定的resource时创建