仅需四步，写一个springboot starter

Z时代
2024-01-10
分类：技术分享

这个系列分为5篇

1. @Component，@Service等注解是如何被解析的

2. @Enable驱动原理

3. @EnableAutoConfiguration处理逻辑

4. spring，springBoot事件

5.仅需四步，写一个springboot starter

引言

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。

第一步创建maven项目

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:
<dependency>
<groupId> org.springframework.boot </groupId>
<artifactId> spring-boot-autoconfigure-processor </artifactId>
<optional> true </optional>
</dependency>

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。

第二步写自动配置逻辑

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 Conditions Bean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）	@ConditionalOnProperty	prefix 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
Resource Conditions 资源条件注解	@ConditionalOnResource	有指定资源才加载
Web Application Conditions web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

2.1.定义AspectLog注解，该注解用于标注需要打印执行时间的方法。

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 {}

2.2定义配置文件对应类

package com.shanyuan.autoconfiguration.aspectlog;
import org.springframework.boot.context.properties.ConfigurationProperties;
@ConfigurationProperties("aspectLog")
public class AspectLogProperties {
private boolean enable;
public boolean isEnable() {
returnenable;
}
public void setEnable(boolean enable) {
this.enable = enable;
}}

2.3定义自动配置类

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;
}}