Spring Boot 自定义 Starter

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前言

Spring Boot 最大的特性可以说就是开箱即用,内部提供的默认自动配置功能,让我们可以在 "零配置" 的情况下,就能够很方便地集成第三方框架。

这一切都要归功于启动器 starter, 比如说,想搭建一个 Spring Boot Web 项目,我们只需要添加 spring-boot-starter-web依赖即可,可以在不做一行配置的情况下,启动一个 Tomcat 应用。

下面是我们常用的 starter 启动器:

  • 单元测试: spring-boot-starter-web;
  • 数据库持久层框架 JPA:spring-boot-starter-data-jpa
  • 安全框架:spring-boot-starter-security;
  • Redis 缓存:spring-boot-starter-data-redis
  • ....

用起来是爽了,但是也有人抱怨不如以前的 SSM 框架那样透明化,虽然配置是烦了点,但是我至少知道我开启了哪些功能,如今用了 Spring Boot 后,出了问题,压根不知道问题根源在哪里,蛋疼!

所以说,了解启动器 starter 默认地自动化配置是如何工作的,还是非常有必要的!本文以手写一个自定义的入门级 starter, 带你了解其工作原理。

实践

需求描述

假设我们有这样一个需求:需要自定义一个女盆友 starter, 她带有一个问候的功能,要如何来实现呢?

新建 maven 项目

为其取名为:girl-friend-spring-boot-starter.

Spring 官方对 starter 的命名是有规范的,只有官方提供的 starter, 才能命名为 spring-boot-starter-{name}, 比如 spring-boot-starter-web; 而对于非官方的,需以 {name}-spring-boot-starter 的格式命名。

添加 spring-boot-autoconfigure 依赖

pom.xml 文件内容如下:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.2.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>site.exception</groupId>
    <artifactId>girl-friend-spring-boot-starter</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <!-- 自动化配置依赖,自定义 starter 核心依赖包 -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-autoconfigure</artifactId>
        </dependency>
    </dependencies>

</project>

新增功能类

新增下面三个类:

  • GirlFriendServiceProperties(配置类);

  • GirlFriendService (女盆友接口);

  • GirlFriendServiceImpl(女盆友接口实现);

上源码:

GirlFriendServiceProperties.java:

package site.exception;

import org.springframework.boot.context.properties.ConfigurationProperties;

/**
 * @author www.excpetion.site(exception 教程网)
 * @date 2019/1/30
 * @time 11:22
 * @discription
 **/
@ConfigurationProperties(prefix = "spring.girlfriend")
public class GirlFriendServiceProperties {

    /** 默认输出 */
    private String message = "Hi, good morning !";

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }
}

@ConfigurationProperties注解能够自动获取 application.properties 配置文件中前缀为 spring.girlfriend 节点下 message属性的内容,这里我们给了它一个默认值: Hi, good morning !

GirlFriendService.java:

package site.exception;

/**
 * @author www.excpetion.site(exception 教程网)
 * @date 2019/1/30
 * @time 11:07
 * @discription
 **/
public interface GirlFriendService {
    /**
     * 打招呼
     * @return
     */
    void say();
}

GirlFriendServiceImpl.java:

package site.exception;

import org.springframework.beans.factory.annotation.Autowired;

/**
 * @author www.excpetion.site(exception 教程网)
 * @date 2019/1/30
 * @time 11:07
 * @discription
 **/
public class GirlFriendServiceImpl implements GirlFriendService {

    @Autowired
    private GirlFriendServiceProperties girlFriendServiceProperties;

    /**
     * 打招呼
     *
     */
    @Override
    public void say() {
        String message = girlFriendServiceProperties.getMessage();
        System.out.println("Girl Friend: " + message);
    }
}

GirlFriendServiceImpl 实现了 GirlFriendService 接口的 say() 方法,它会获取 GirlFriendServiceProperties 配置类 message 内容,并打印到控制台。

新增自动配置类(重点)

创建类 GirlFriendAutoConfiguration.java 来实现自动配置化功能:

package site.exception;

import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

/**
 * @author www.excpetion.site(exception 教程网)
 * @date 2019/1/30
 * @time 11:11
 * @discription
 **/
@Configuration
@ConditionalOnClass(GirlFriendService.class)
@EnableConfigurationProperties(GirlFriendServiceProperties.class)
public class GirlFriendAutoConfiguration {

    @Bean
    @ConditionalOnMissingBean
    public GirlFriendService girlFriendService() {
        return new GirlFriendServiceImpl();
    }
}

接下来,对上面相关注解说明一下:

  • @Configuration: 标注类为一个配置类,让 spring 去扫描它;
  • @ConditionalOnClass:条件注解,只有在 classpath 路径下存在指定 class 文件时,才会实例化 Bean;
  • @EnableConfigurationProperties:使指定配置类生效;
  • @Bean: 创建一个实例类注入到 Spring Ioc 容器中;
  • @ConditionalOnMissingBean:条件注解,意思是,仅当 Ioc 容器不存在指定类型的 Bean 时,才会创建 Bean。

新增 spring.factories 文件

resources 目录下创建名为 META-INF 的目录,并新建文件 spring.factories,内容如下:

# 指定刚刚创建的 GirlFriendAutoConfiguration 的全路径名
org.springframework.boot.autoconfigure.EnableAutoConfiguration=site.exception.GirlFriendAutoConfiguration

Spring Boot 会在启动时,自动会去查找指定文件 /META-INF/spring.factories,若有,就会根据配置的类的全路径去自动化配置。

完成这一步后,一个入门级的 spring-boot-starter 已经开发完成了,看下整体的目录结构:

打包 jar

接下来,就是将 girl-friend-spring-boot-starter 打成 jar 包,放到本地的 maven 仓库中去,在项目根路径下执行 maven 命令: mvn clean install.

C:\dev\idea_workspace_personal\spring-boot-tutorial\girl-friend-spring-boot-starter>mvn clean install
[INFO] Scanning for projects...
[INFO]
[INFO] -----------< site.exception:girl-friend-spring-boot-starter >-----------
[INFO] Building girl-friend-spring-boot-starter 1.0-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
[INFO]
[INFO] --- maven-clean-plugin:3.1.0:clean (default-clean) @ girl-friend-spring-boot-starter ---
[INFO] Deleting C:\dev\idea_workspace_personal\spring-boot-tutorial\girl-friend-spring-boot-starter\target
[INFO]
[INFO] --- maven-resources-plugin:3.1.0:resources (default-resources) @ girl-friend-spring-boot-starter ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] Copying 0 resource
[INFO] Copying 1 resource
[INFO]
[INFO] --- maven-compiler-plugin:3.8.0:compile (default-compile) @ girl-friend-spring-boot-starter ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 4 source files to C:\dev\idea_workspace_personal\spring-boot-tutorial\girl-friend-spring-boot-starter\target\classes
[INFO]
[INFO] --- maven-resources-plugin:3.1.0:testResources (default-testResources) @ girl-friend-spring-boot-starter ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] skip non existing resourceDirectory C:\dev\idea_workspace_personal\spring-boot-tutorial\girl-friend-spring-boot-starter\src\test\resources
[INFO]
[INFO] --- maven-compiler-plugin:3.8.0:testCompile (default-testCompile) @ girl-friend-spring-boot-starter ---
[INFO] Nothing to compile - all classes are up to date
[INFO]
[INFO] --- maven-surefire-plugin:2.22.1:test (default-test) @ girl-friend-spring-boot-starter ---
[INFO] No tests to run.
[INFO]
[INFO] --- maven-jar-plugin:3.1.1:jar (default-jar) @ girl-friend-spring-boot-starter ---
[INFO] Building jar: C:\dev\idea_workspace_personal\spring-boot-tutorial\girl-friend-spring-boot-starter\target\girl-friend-spring-boot-starter-1.0-SNAPSHOT.jar
[INFO]
[INFO] --- maven-install-plugin:2.5.2:install (default-install) @ girl-friend-spring-boot-starter ---
[INFO] Installing C:\dev\idea_workspace_personal\spring-boot-tutorial\girl-friend-spring-boot-starter\target\girl-friend-spring-boot-starter-1.0-SNAPSHOT.jar to C:\User
s\allen\.m2\repository\site\exception\girl-friend-spring-boot-starter\1.0-SNAPSHOT\girl-friend-spring-boot-starter-1.0-SNAPSHOT.jar
[INFO] Installing C:\dev\idea_workspace_personal\spring-boot-tutorial\girl-friend-spring-boot-starter\pom.xml to C:\Users\allen\.m2\repository\site\exception\girl-frien
d-spring-boot-starter\1.0-SNAPSHOT\girl-friend-spring-boot-starter-1.0-SNAPSHOT.pom
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  6.247 s
[INFO] Finished at: 2019-01-30T15:31:03+08:00
[INFO] ------------------------------------------------------------------------

新建一个 Spring Boot Web 项目,引用自定 starter

新创建一个 Spring Boot Web 项目,在 pom.xml 文件中加入自定义的 starter 依赖:

<!-- Girl Friend starter -->
<dependency>
    <groupId>site.exception</groupId>
    <artifactId>girl-friend-spring-boot-starter</artifactId>
    <version>1.0-SNAPSHOT</version>
</dependency>

Applicaiton 启动类中,自动注入 GirlFriendService 实例,并调用 say() 方法:

package site.exception.springboothello;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import site.exception.GirlFriendService;

@SpringBootApplication
public class SpringBootHelloApplication implements CommandLineRunner {

	public static void main(String[] args) {
		SpringApplication.run(SpringBootHelloApplication.class, args);
	}

	@Autowired
	private GirlFriendService girlFriendService;

	@Override
	public void run(String... args) throws Exception {
		// 调用打招呼方法
		girlFriendService.say();
	}
}

启动项目,看看在零配置的情况下,它的输出:

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.1.2.RELEASE)

2019-01-30 15:40:48.308  INFO 25320 --- [  restartedMain] s.e.s.SpringBootHelloApplication         : Starting SpringBootHelloApplication on DESKTOP-RL6P6LA with PID 25320 (C:\dev\idea_workspace_personal\spring-boot-tutorial\spring-boot-hello\target\classes started by allen in C:\dev\idea_workspace_personal\spring-boot-tutorial)
2019-01-30 15:40:48.314  INFO 25320 --- [  restartedMain] s.e.s.SpringBootHelloApplication         : No active profile set, falling back to default profiles: default
2019-01-30 15:40:48.457  INFO 25320 --- [  restartedMain] .e.DevToolsPropertyDefaultsPostProcessor : Devtools property defaults active! Set 'spring.devtools.add-properties' to 'false' to disable
2019-01-30 15:40:48.458  INFO 25320 --- [  restartedMain] .e.DevToolsPropertyDefaultsPostProcessor : For additional web related logging consider setting the 'logging.level.web' property to 'DEBUG'
2019-01-30 15:40:51.299  INFO 25320 --- [  restartedMain] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2019-01-30 15:40:51.372  INFO 25320 --- [  restartedMain] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2019-01-30 15:40:51.373  INFO 25320 --- [  restartedMain] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.14]
2019-01-30 15:40:51.387  INFO 25320 --- [  restartedMain] o.a.catalina.core.AprLifecycleListener   : The APR based Apache Tomcat Native library which allows optimal performance in production environments was not found on the java.library.path: [C:\dev\java\jdk1.8\bin;C:\WINDOWS\Sun\Java\bin;C:\WINDOWS\system32;C:\WINDOWS;C:\dev\java\jdk1.8\bin;C:\dev\java\jdk1.8\jre\bin;C:\Program Files (x86)\Common Files\Oracle\Java\javapath;C:\WINDOWS\system32;C:\WINDOWS;C:\WINDOWS\System32\Wbem;C:\WINDOWS\System32\WindowsPowerShell\v1.0\;C:\WINDOWS\System32\OpenSSH\;C:\Program Files (x86)\pycSafefile\x64;C:\dev\java\apache-maven-3.6.0\bin;D:\dev\redis\;C:\dev\git\cmd;C:\Users\allen\AppData\Local\Microsoft\WindowsApps;;C:\Program Files\Docker Toolbox;.]
2019-01-30 15:40:51.628  INFO 25320 --- [  restartedMain] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2019-01-30 15:40:51.629  INFO 25320 --- [  restartedMain] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 3171 ms
2019-01-30 15:40:51.921  INFO 25320 --- [  restartedMain] o.s.s.concurrent.ThreadPoolTaskExecutor  : Initializing ExecutorService 'applicationTaskExecutor'
2019-01-30 15:40:52.142  INFO 25320 --- [  restartedMain] o.s.b.d.a.OptionalLiveReloadServer       : LiveReload server is running on port 35729
2019-01-30 15:40:52.204  INFO 25320 --- [  restartedMain] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2019-01-30 15:40:52.207  INFO 25320 --- [  restartedMain] s.e.s.SpringBootHelloApplication         : Started SpringBootHelloApplication in 4.56 seconds (JVM running for 6.523)
Girl Friend: Hi, good morning !

可以看到,在没做任何配置的情况下,输出的是默认打招呼信息:Hi, good morning !,接下来,我们手动配置一下新的打招呼内容,看看是否能自动获取到。

application.properties 文件中配置如下:

spring.girlfriend.message=I LOVE YOU

重启项目,验证一下,是否输出的还是默认信息:

正确打印我们自己配置的:I LOVE YOU

GitHub 源码地址

https://github.com/weiwosuoai/spring-boot-tutorial

总结

此文中,我们学习了如何自定义入门级 spring-boot-starter,这仅仅是个开始,能做的远不止于此,这里也只是抛砖引玉而已,希望您阅读愉快!