引言

只要你用 Spring boot，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。

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：

"1.0"?encoding="UTF-8"?>
"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">
????4.0.0

????org.example
????aspectlog-spring-boot-starter
????1.0.2
????
????????org.springframework.boot
????????spring-boot-starter-parent
????????2.1.15.RELEASE
????
????
????
????????
????????????org.springframework.boot
????????????spring-boot-autoconfigure
????????
????????
????????????org.springframework.boot
????????????spring-boot-starter-aop
????????
????????
????????????org.springframework.boot
????????????spring-boot-configuration-processor
????????????true
????????
????

關(guān)于spring-boot-configuration-processor的說(shuō)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:

??org.springframework.boot
??spring-boot-autoconfigure-processor
??true

簡(jiǎn)單說(shuō)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。

不熟悉 Spring Boot 基礎(chǔ)的可以看下這個(gè)倉(cāng)庫(kù)：https://github.com/javastacks/spring-boot-best-practice

第二步寫自動(dòng)配置邏輯

各種condition

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。

不熟悉 Spring Boot 基礎(chǔ)的可以看下這個(gè)倉(cāng)庫(kù)：https://github.com/javastacks/spring-boot-best-practice

下面開(kāi)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(kāi)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(shuō)明：

@ConditionalOnProperty(prefix?=?"aspectLog",?name?=?"enable",havingValue?=?"true",?matchIfMissing?=?true)

當(dāng)配置文件有aspectLog.enable=true時(shí)開(kāi)啟，如果配置文件沒(méi)有設(shè)置aspectLog.enable也開(kāi)啟。基礎(chǔ)知識(shí)不熟悉的可以關(guān)注公眾號(hào)Java技術(shù)棧回復(fù)boot獲取一份完整教程。

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\

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