13.5. Starts

Starters是一个依赖描述符的集合，你可以将它包含进项目中，这样添加依赖就非常方便。你可以获取所有Spring及相关技术的一站式服务，而不需要翻阅示例代码，拷贝粘贴大量的依赖描述符。例如，如果你想使用Spring和JPA进行数据库访问，只需要在项目中包含 spring-boot-starter-data-jpa 依赖，然后你就可以开始了。该starters包含很多搭建，快速运行项目所需的依赖，并提供一致的，可管理传递性的依赖集。

第三方starters不应该以spring-boot 开头，因为它跟Spring Boot官方artifacts冲突。一个acme的第三方starter通常命名为acmespring-boot-starter

具体的依赖传递过程如下图所示： 首先，我们的项目继承了spring-boot-starter-parent，而spring-boot-starter-parent项目继承了spring-boot-dependencies，因此我们的项目可以使用这两个项目pom中的属性和依赖管理。

然后，spring-boot-starters是所有starter类型项目的父项目，该项目继承了spring-boot-parent，spring-boot-parent继承了spring-boot-dependencies，因此spring-boot-starters项目可以使用依赖管理。

接着，spring-boot-starters使用Maven 聚合的方式，聚合了诸如spring-boot-starter-xx的模块（module），这些项目中定义了具体需要用到的依赖（jar包），但本身没有代码只有一个pom.xml，在dependence里引入这些项目，就等于将它们pom定义里的依赖引入到当前我们的项目，从而又形成了依赖树

由上图可以看出，因为spring-boot-starter-xx项目都经过严密的测试，因此其相互依赖版本是一致且安全的，spring-boot-starter依赖spring-boot依赖spring-core，而spring-boot-starter自身又依赖spring-core，但由于spring-core版本相同，因此不存在冲突（没有两个不同版本的相同的依赖jar包），这就是spring-boot-starter-xx另一个好处了，可以放心使用

IDEA用户可以在maven插件中直接查看依赖树

使用Maven命令查看依赖树

# 查看依赖树
mvn dependency:tree -Dverbose

spring-boot-starter-xx的模块也不需要指定<version>，因为这个已经定义在它的父pomspring-boot-dependencies里了

最后，我们在自己的项目里<dependences>导入spring-boot-starter-xx，就是将它代表的功能模块需要的依赖带入项目中，而不需要挨个复制具体的jar包，且不需要指定具体<version>

所谓Maven的聚合就是通过一个父项目，将所有子项目以module的方式组合在该父项目的POM下（该父项目只有一个pomx.xml），子项目继承该父项目，同时子项目间可以互相依赖

Table Spring Boot application starters

具体见spring-boot-reference

Name	Description	Pom
spring-boot-starter	Core starter, including auto-configuration support, logging and YAML	Pom
spring-boot-starter-activemq	Starter for JMS messaging using Apache ActiveMQ	Pom
spring-boot-starter-amqp	Starter for using Spring AMQP and Rabbit MQ	Pom
spring-boot-starter-aop	Starter for aspect-oriented programming with Spring AOP and AspectJ	Pom
spring-boot-starter-artemis	Starter for JMS messaging using Apache Artemis	Pom
spring-boot-starter-batch	Starter for using Spring Batch	Pom
spring-boot-starter-cache	Starter for using Spring Framework’s caching support	Pom
spring-boot-starter-cloud-connectors	Starter for using Spring Cloud Connectors which simplifies connecting to services in cloud platforms like Cloud Foundry and Heroku	Pom
spring-boot-starter-data-cassandra	Starter for using Cassandra distributed database and Spring Data Cassandra	Pom
spring-boot-starter-data-couchbase	Starter for using Couchbase document-oriented database and Spring Data Couchbase	Pom
spring-boot-starter-data-elasticsearch	Starter for using Elasticsearch search and analytics engine and Spring Data Elasticsearch	Pom
spring-boot-starter-data-gemfire	Starter for using GemFire distributed data store and Spring Data GemFire	Pom
spring-boot-starter-data-jpa	Starter for using Spring Data JPA with Hibernate	Pom
spring-boot-starter-data-ldap	Starter for using Spring Data LDAP	Pom
spring-boot-starter-data-mongodb	Starter for using MongoDB document-oriented database and Spring Data MongoDB	Pom
spring-boot-starter-data-neo4j	Starter for using Neo4j graph database and Spring Data Neo4j	Pom
spring-boot-starter-data-redis	Starter for using Redis key-value data store with Spring Data Redis and the Jedis client	Pom
spring-boot-starter-data-rest	Starter for exposing Spring Data repositories over REST using Spring Data REST	Pom
spring-boot-starter-data-solr	Starter for using the Apache Solr search platform with Spring Data Solr	Pom
spring-boot-starter-freemarker	Starter for building MVC web applications using FreeMarker views	Pom
spring-boot-starter-groovy-templates	Starter for building MVC web applications using Groovy Templates views	Pom
spring-boot-starter-hateoas	Starter for building hypermedia-based RESTful web application with Spring MVC and Spring HATEOAS	Pom
spring-boot-starter-integration	Starter for using Spring Integration	Pom
spring-boot-starter-jdbc	Starter for using JDBC with the Tomcat JDBC connection pool	Pom
spring-boot-starter-jersey	Starter for building RESTful web applications using JAX-RS and Jersey. An alternative to spring-boot-starter-web	Pom
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	Pom
spring-boot-starter-jta-atomikos	Starter for JTA transactions using Atomikos	Pom
spring-boot-starter-jta-bitronix	Starter for JTA transactions using Bitronix	Pom
spring-boot-starter-jta-narayana	Spring Boot Narayana JTA Starter	Pom
spring-boot-starter-mail	Starter for using Java Mail and Spring Framework’s email sending support	Pom
spring-boot-starter-mobile	Starter for building web applications using Spring Mobile	Pom
spring-boot-starter-mustache	Starter for building MVC web applications using Mustache views	Pom
spring-boot-starter-security	Starter for using Spring Security	Pom
spring-boot-starter-social-facebook	Starter for using Spring Social Facebook	Pom
spring-boot-starter-social-linkedin	Stater for using Spring Social LinkedIn	Pom
spring-boot-starter-social-twitter	Starter for using Spring Social Twitter	Pom
spring-boot-starter-test	Starter for testing Spring Boot applications with libraries including JUnit, Hamcrest and Mockito	Pom
spring-boot-starter-thymeleaf	Starter for building MVC web applications using Thymeleaf views	Pom
spring-boot-starter-validation	Starter for using Java Bean Validation with Hibernate Validator	Pom
spring-boot-starter-web	Starter for building web, including RESTful, applications using Spring MVC. Uses Tomcat as the default embedded container	Pom
spring-boot-starter-web-services	Starter for using Spring Web Services	Pom
spring-boot-starter-websocket	Starter for building WebSocket applications using Spring Framework’s WebSocket support	Pom