Markfred Chen

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创建自定义Spring Boot Starter

发表于 更新于 分类于 ，
Java架构师实用工具。带你看看Spring Boot Starter怎么玩的。

摘要

在大家使用Spring Boot进行开发的过程中，应该可以接触到Spring Boot提供的很多Starter。比如

  • spring-boot-starter-web
  • spring-boot-starter-jdbc
  • …

Spring Boot AutoConfiguration原理

Auto Configuration类

在Spring Boot启动的过程中，会去找classpath:META-INF/spring.factories文件，来决定加载哪些AutoConfiguration类。
让我们看一下spring-boot-autoconfigure项目中的spring.factories文件。下面列出部分AutoConfiguration类。

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# Auto Configure
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\
org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\
org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration,\
org.springframework.boot.autoconfigure.batch.BatchAutoConfiguration,\
org.springframework.boot.autoconfigure.cache.CacheAutoConfiguration,\
org.springframework.boot.autoconfigure.cassandra.CassandraAutoConfiguration,\
org.springframework.boot.autoconfigure.cloud.CloudAutoConfiguration,\
org.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.redis.RedisAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration,\
...

Spring Boot会尝试去运行所有org.springframework.boot.autoconfigure.EnableAutoConfiguration列出的AutoConfiguration类。此处大家可以会有疑问，很多我在项目里没有用到。对应组件是不是也会被初始化？答案是不会。我们用RedisAutoConfiguration为例来看一下背后发生了什么。

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@Configuration
@ConditionalOnClass(RedisOperations.class)
@EnableConfigurationProperties(RedisProperties.class)
@Import({ LettuceConnectionConfiguration.class, JedisConnectionConfiguration.class })
public class RedisAutoConfiguration {

	@Bean
	@ConditionalOnMissingBean(name = "redisTemplate")
	public RedisTemplate<Object, Object> redisTemplate(
			RedisConnectionFactory redisConnectionFactory) throws UnknownHostException {
		RedisTemplate<Object, Object> template = new RedisTemplate<>();
		template.setConnectionFactory(redisConnectionFactory);
		return template;
	}

	@Bean
	@ConditionalOnMissingBean
	public StringRedisTemplate stringRedisTemplate(
			RedisConnectionFactory redisConnectionFactory) throws UnknownHostException {
		StringRedisTemplate template = new StringRedisTemplate();
		template.setConnectionFactory(redisConnectionFactory);
		return template;
	}

}
  • Line 1: @Configuration定义Configuration组件
  • Line 2: @ConditionalOnClass(RedisOperations.class) 在classpath中如果有RedisOperation类，则会运行此AutoConfiguration。反之则不会运行。
  • Line 8: @ConditionalOnMissingBean(name = "redisTemplate") 如果在Spring容器中没有名为redisTemplate的Bean被注册，则执行redisTemplate()方法。反之则不会执行。

注：Spring Boot提供了一系列@Condition选择，同时还可以实现自定义Condition。参考Spring Boot - Condition Annotations

AutoConfiguration Hints

AutoConfiguration Hints功能主要便于开发人员在做配置时，IDE可以提示auto complete。如下截图：
auto-complete
Auto Complete信息包括：

  • 配置名称
  • 配置描述
  • 配置默认值

具体信息在additional-spring-configuration-metadata.json中定义

创建自定义Starter

  1. 需要封装的Service类
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    public class FooService {
        private final String fooMessage;
        private final String barMessage;

        public FooService(String fooMessage, String barMessage) {
            this.fooMessage = fooMessage;
            this.barMessage = barMessage;
        }

        public String getFooMessage() {
            return this.fooMessage;
        }

        public String getBarMessage() {
            return this.barMessage;
        }
    }
  2. AutoConfiguration类
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    package io.markfredchen.custom.starter.config;

    import ...;

    @Configuration
    @PropertySource("classpath:config/foo.properties")
    public class FooAutoConfiguration {
        @Value("${foo.fooMessage}")
        private String fooMessage;
        @Value("${foo.barMessage}")
        private String barMessage;

        @Bean
        @ConditionalOnMissingBean
        public FooService fooService() {
            return new FooService(fooMessage, barMessage);
        }
    }

  3. spring.factories
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    org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
    io.markfredchen.custom.starter.config.FooAutoConfiguration
  4. 默认配置
    创建 resources/config/foo.properties
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    foo.fooMessage=Foo!
    foo.barMessage=Bar!

使用自定义Starter

  1. 创建新项目
  2. SpringBootApplication
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    @SpringBootApplication
    public class FooApplication {
        public static void main(String[] args) {
            SpringApplication.run(FooApplication.class, args);
        }

        @Bean
        public CommandLineRunner runner(final FooService fooService) {
            return args -> {
                System.out.println(fooService.getFooMessage());
                System.out.println(fooService.getBarMessage());
            };
        }
    }
  3. pom.xml添加以下依赖
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    <dependencies>
        <dependency>
            <groupId>io.markfredchen</groupId>
            <artifactId>foo-spring-boot-starter</artifactId>
            <version>1.0-SNAPSHOT</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
            <version>2.0.5.RELEASE</version>
        </dependency>
    </dependencies>
  4. 运行结果
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    2018-10-11 11:28:55.457  INFO 23978 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/webjars/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
    2018-10-11 11:28:55.457  INFO 23978 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
    2018-10-11 11:28:55.548  INFO 23978 --- [           main] o.s.j.e.a.AnnotationMBeanExporter        : Registering beans for JMX exposure on startup
    2018-10-11 11:28:55.586  INFO 23978 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
    2018-10-11 11:28:55.590  INFO 23978 --- [           main] i.m.c.s.foo.application.FooApplication   : Started FooApplication in 1.725 seconds (JVM running for 2.44)
    Foo!
    Bar!
  5. 覆盖默认配置
    创建resources/application.properties
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    foo.barMessage=Updated Bar!
  6. 运行结果
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    2018-10-11 11:28:55.457  INFO 23978 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/webjars/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
    2018-10-11 11:28:55.457  INFO 23978 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
    2018-10-11 11:28:55.548  INFO 23978 --- [           main] o.s.j.e.a.AnnotationMBeanExporter        : Registering beans for JMX exposure on startup
    2018-10-11 11:28:55.586  INFO 23978 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
    2018-10-11 11:28:55.590  INFO 23978 --- [           main] i.m.c.s.foo.application.FooApplication   : Started FooApplication in 1.725 seconds (JVM running for 2.44)
    Foo!
    Updated Bar!
  7. AutoConfiguration Hints
    创建resources/META-INF/additional-spring-configuration-metadata.json
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    {
      "properties": [
        {
          "name": "foo.fooMessage",
          "type": "java.lang.String",
          "description": "Foo Message.",
          "defaultValue": "Foo!"
        },
        {
          "name": "foo.barMessage",
          "type": "java.lang.String",
          "description": "Bar Message.",
          "defaultValue": "Bar!"
        }
      ]
    }
    效果
    auto complete

参考

总结

本文介绍了spring boot starter机制以及如何创建自定义的starter。starter的目标是对现在有项目进行有效封装，减少开发人员的重复工作。
完整源代码访问GitHub