作者 | 温安适
来源 | https://my.oschina.net/floor/blog/4435699
只要你用Springboot，一定会用到各种spring-boot-starter。其实写一个spring-boot-starter
，仅需4步。下面我们就写一个starter，它将实现，在日志中打印方法执行时间。
在使用spring-boot-starter，会发现，有的项目名称是 XX-spring-boot-starter，有的是
spring-boot-starter-XX，这个项目的名称有什么讲究呢？
从springboot官方文档摘录如下：
“
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.
从这段话可以看出spring-boot-starter命名的潜规则。
命名潜规则
spring-boot-starter-XX是springboot官方的starter
XX-spring-boot-starter是第三方扩展的starter
打印方法执行时间的功能，需要用到aop，咱们的项目就叫做
aspectlog-spring-boot-starter吧。
项目的pom文件如下：
<?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>
<groupId>org.example</groupId>
<artifactId>aspectlog-spring-boot-starter</artifactId>
<version>1.0.2</version>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.1.15.RELEASE</version>
</parent>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-autoconfigure</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-aop</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-configuration-processor</artifactId>
<optional>true</optional>
</dependency>
</dependencies>
</project>
关于spring-boot-configuration-processor的说明，引自springBoot官方文档：
“
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
简单说就是：写starter时，在pom中配置spring-boot-autoconfigure-processor，在编译时会自动收集配置类的条件，写到一个META-INF/spring-autoconfigure-metadata.properties中。
各种condition
类型注解说明Class Conditions类条件注解@ConditionalOnClass当前classpath下有指定类才加载@ConditionalOnMissingClass当前classpath下无指定类才加载
Bean ConditionsBean条件注解@ConditionalOnBean当期容器内有指定bean才加载@ConditionalOnMissingBean当期容器内无指定bean才加载
Property Conditions环境变量条件注解（含配置文件）@ConditionalOnPropertyprefix 前缀name 名称havingValue 用于匹配配置项值matchIfMissing 没找指定配置项时的默认值ResourceConditions 资源条件注解@ConditionalOnResource有指定资源才加载Web Application Conditionsweb条件注解@ConditionalOnWebApplication是web才加载@ConditionalOnNotWebApplication不是web才加载
SpEL Expression Conditions@ConditionalOnExpression符合SpEL 表达式才加载
本次我们就选用@ConditionalOnProperty。即配置文件中有aspectLog.enable=true，才加载我们的配置类。
下面开始写自动配置类
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: 用于控制定时任务的开启与关闭
* 对应切面
* creat_user: wenl
* creat_time: 2018/11/10 18:45
**/
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface AspectLog {
}
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;
}
}
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 {
//执行方法名称
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() {
//保证事务等切面先执行
return Integer.MAX_VALUE;
}
}
配置类简要说明：
@ConditionalOnProperty(prefix = "aspectLog", name = "enable",havingValue = "true", matchIfMissing = true)
当配置文件有aspectLog.enable=true时开启，如果配置文件没有设置aspectLog.enable也开启。
META-INF/spring.factories是spring的工厂机制，在这个文件中定义的类，都会被自动加载。多个配置使用逗号分割，换行用
如果有兴趣可以查看这2篇blog：
2.@Enable驱动原理(设置连接)
3.@EnableAutoConfiguration处理逻辑(设置连接)
org.springframework.boot.autoconfigure.EnableAutoConfiguration=
com.shanyuan.autoconfiguration.aspectlog.AspectLogAutoConfiguration
这是我们最终的目录结构
在IDEA中，进行mvn intall
打包完成后，在其他项目中的pom中引入进行测试
参考资料
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