只需4步，自己搞個(gè) Spring Boot Starter ！
引言
只要你用Springboot，一定會(huì)用到各種spring-boot-starter。其實(shí)寫一個(gè)spring-boot-starter，僅需4步。下面我們就寫一個(gè)starter，它將實(shí)現(xiàn)，在日志中打印方法執(zhí)行時(shí)間。
第一步 創(chuàng)建maven項(xiàng)目
在使用spring-boot-starter，會(huì)發(fā)現(xiàn)，有的項(xiàng)目名稱是 XX-spring-boot-starter，有的是
spring-boot-starter-XX，這個(gè)項(xiàng)目的名稱有什么講究呢？
從springboot官方文檔摘錄如下：
Do not start your module names with spring-boot, even if you use a different Maven groupId. We may offer official support for the thing you auto-configure in the future.
As a rule of thumb, you should name a combined module after the starter.
從這段話可以看出spring-boot-starter命名的潛規(guī)則。
命名潛規(guī)則
spring-boot-starter-XX是springboot官方的starter
XX-spring-boot-starter是第三方擴(kuò)展的starter
打印方法執(zhí)行時(shí)間的功能，需要用到aop，咱們的項(xiàng)目就叫做
aspectlog-spring-boot-starter吧。
項(xiàng)目的pom文件如下：
<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>4.0.0modelVersion>
????<groupId>org.examplegroupId>
????<artifactId>aspectlog-spring-boot-starterartifactId>
????<version>1.0.2version>
????<parent>
????????<groupId>org.springframework.bootgroupId>
????????<artifactId>spring-boot-starter-parentartifactId>
????????<version>2.1.15.RELEASEversion>
????parent>
????<dependencies>
????????<dependency>
????????????<groupId>org.springframework.bootgroupId>
????????????<artifactId>spring-boot-autoconfigureartifactId>
????????dependency>
????????<dependency>
????????????<groupId>org.springframework.bootgroupId>
????????????<artifactId>spring-boot-starter-aopartifactId>
????????dependency>
????????<dependency>
????????????<groupId>org.springframework.bootgroupId>
????????????<artifactId>spring-boot-configuration-processorartifactId>
????????????<optional>trueoptional>
????????dependency>
????dependencies>
project>
關(guān)于spring-boot-configuration-processor的說明，引自springBoot官方文檔：
Spring Boot uses an annotation processor to collect the conditions on auto-configurations in a metadata file ( META-INF/spring-autoconfigure-metadata.properties ). If that file is present, it is used to eagerly filter auto-configurations that do not match, which will improve startup time. It is recommended to add the following dependency in a module that contains auto-configurations:
<dependency>
????<groupId>org.springframework.bootgroupId>
????<artifactId>spring-boot-autoconfigure-processorartifactId>
????<optional>trueoptional>
dependency>
簡(jiǎn)單說就是?寫starter時(shí)，在pom中配置spring-boot-autoconfigure-processor， 在編譯時(shí)會(huì)自動(dòng)收集配置類的條件，寫到一個(gè)META-INF/spring-autoconfigure-metadata.properties中
第二步寫自動(dòng)配置邏輯
各種condition
| 類型 | 注解 | 說明 |
|---|---|---|
| Class Conditions類條件注解 | @ConditionalOnClass | 當(dāng)前classpath下有指定類才加載 |
| @ConditionalOnMissingClass | 當(dāng)前classpath下無指定類才加載 | |
| Bean ConditionsBean條件注解 | @ConditionalOnBean | 當(dāng)期容器內(nèi)有指定bean才加載 |
| @ConditionalOnMissingBean | 當(dāng)期容器內(nèi)無指定bean才加載 | |
| Property Conditions環(huán)境變量條件注解（含配置文件） | @ConditionalOnProperty | prefix 前綴name 名稱havingValue 用于匹配配置項(xiàng)值matchIfMissing 沒找指定配置項(xiàng)時(shí)的默認(rèn)值 |
| ResourceConditions 資源條件注解 | @ConditionalOnResource | 有指定資源才加載 |
| Web Application Conditionsweb條件注解 | @ConditionalOnWebApplication | 是web才加載 |
| @ConditionalOnNotWebApplication | 不是web才加載 | |
| SpEL Expression Conditions | @ConditionalOnExpression | 符合SpEL 表達(dá)式才加載 |
本次我們就選用@ConditionalOnProperty。即配置文件中有aspectLog.enable=true，才加載我們的配置類。下面開始寫自動(dòng)配置類
2.1.定義AspectLog注解，該注解用于標(biāo)注需要打印執(zhí)行時(shí)間的方法。
package?com.shanyuan.autoconfiguration.aspectlog;
import?java.lang.annotation.ElementType;
import?java.lang.annotation.Retention;
import?java.lang.annotation.RetentionPolicy;
import?java.lang.annotation.Target;
/**
?*?class_name:?ScheduleManage
?*?describe:???用于控制定時(shí)任務(wù)的開啟與關(guān)閉
?*?對(duì)應(yīng)切面
?*?creat_user:?wenl
?*?creat_time:??2018/11/10?18:45
?**/
@Target(ElementType.METHOD)@?Retention(RetentionPolicy.RUNTIME)
public@?interface?AspectLog?{}
2.2定義配置文件對(duì)應(yīng)類
package?com.shanyuan.autoconfiguration.aspectlog;
import?org.springframework.boot.context.properties.ConfigurationProperties;@
ConfigurationProperties("aspectLog")
public?class?AspectLogProperties?{
????private?boolean?enable;
????public?boolean?isEnable()?{
????????return?enable;
????}
????public?void?setEnable(boolean?enable)?{
????????this.enable?=?enable;
????}
}
2.3定義自動(dòng)配置類
package?com.shanyuan.autoconfiguration.aspectlog;
import?org.aspectj.lang.ProceedingJoinPoint;
import?org.aspectj.lang.annotation.Around;
import?org.aspectj.lang.annotation.Aspect;
import?org.slf4j.Logger;
import?org.slf4j.LoggerFactory;
import?org.springframework.boot.autoconfigure.condition.*;
import?org.springframework.context.annotation.Configuration;
import?org.springframework.context.annotation.EnableAspectJAutoProxy;
import?org.springframework.core.PriorityOrdered;
@Aspect
@EnableAspectJAutoProxy(exposeProxy?=?true,?proxyTargetClass?=?true)
@Configuration
@ConditionalOnProperty(prefix?=?"aspectLog",?name?=?"enable",
?????????????????????havingValue?=?"true",?matchIfMissing?=?true)
public?class?AspectLogAutoConfiguration?implements?PriorityOrdered?{
????protected?Logger?logger?=?LoggerFactory.getLogger(getClass());
@Around("@annotation(com.shanyuan.autoconfiguration.aspectlog.AspectLog)?")
????public?Object?isOpen(ProceedingJoinPoint?thisJoinPoint)?
????????????????????????????????????????throws?Throwable?{
????????//執(zhí)行方法名稱?
????????String?taskName?=?thisJoinPoint.getSignature()
????????????.toString().substring(
????????????????thisJoinPoint.getSignature()
????????????????????.toString().indexOf("?"),?
????????????????????thisJoinPoint.getSignature().toString().indexOf("("));
????????taskName?=?taskName.trim();
????????long?time?=?System.currentTimeMillis();
????????Object?result?=?thisJoinPoint.proceed();
????????logger.info("method:{}?run?:{}?ms",?taskName,?
????????????????????????????(System.currentTimeMillis()?-?time));
????????return?result;
????}
????@Override
????public?int?getOrder()?{
????????//保證事務(wù)等切面先執(zhí)行
????????return?Integer.MAX_VALUE;
????}
}
配置類簡(jiǎn)要說明：
@ConditionalOnProperty(prefix = "aspectLog", name = "enable",havingValue = "true", matchIfMissing = true)
當(dāng)配置文件有aspectLog.enable=true時(shí)開啟，如果配置文件沒有設(shè)置aspectLog.enable也開啟。
第三步META-INF/spring.factories
META-INF/spring.factories是spring的工廠機(jī)制，在這個(gè)文件中定義的類，都會(huì)被自動(dòng)加載。多個(gè)配置使用逗號(hào)分割，換行用\
如果有興趣可以查看這2篇blog：
2、@Enable驅(qū)動(dòng)原理(設(shè)置連接)
3、@EnableAutoConfiguration處理邏輯(設(shè)置連接)
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
com.shanyuan.autoconfiguration.aspectlog.AspectLogAutoConfiguration
第四步打包測(cè)試
這是我們最終的目錄結(jié)構(gòu)
在IDEA中，進(jìn)行mvn intall
打包完成后，在其他項(xiàng)目中的pom中引入進(jìn)行測(cè)試
作者 | 溫安適
參考資料
https://docs.spring.io/spring-boot/docs/2.1.15.RELEASE/reference/html/boot-features-developing-auto-configuration.html#boot-features-custom-starter
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