1. starter简介

:::tips SpringBoot 最强大的功能就是把我们常用的场景抽取成了一个个starter（场景启动器），我们通过引入springboot 为我提供的这些场景启动器，我们再进行少量的配置就能使用相应的功能。即使是这样,springboot也不能囊括我们所有的使用场景，往往我们需要自定义starter，来简化我们对springboot的使用。
:::

2. 如何自定义

2.1 Spring-boot自动装配规范 :::tips springboot的出现就是为了简化spring开发,提供开箱即用的手脚架功能.基于springboot自动装配原理手撸一个starterstarter
命名规范:

官方命名格式:spring-boot-starter-模块名
自定义命名规范:模块名-spring-boot-starter :::

步骤
创建项目:mck-spring-boot-starter
引入pom依赖

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-configuration-processor</artifactId>
  <optional>true</optional>
</dependency>
<dependency>
  <groupId>org.projectlombok</groupId>
  <artifactId>lombok</artifactId>
  <optional>true</optional>
</dependency>

引入打包工具

<build>
<plugins>
  <plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <configuration>
      <encoding>${project.build.sourceEncoding}</encoding>
      <source>${java.version}</source>
      <target>${java.version}</target>
      <showWarnings>true</showWarnings>
    </configuration>
  </plugin>
</plugins>
</build>

编写MckProperties

package com.itmck.mckspringbootstarter.config;
import lombok.Data;
import org.springframework.boot.context.properties.ConfigurationProperties;
/**
 * 太阳当空照,花儿对我笑
 * <p>
 * Create by M ChangKe 2021/8/7 21:51
 **/
@Data
@ConfigurationProperties(prefix = "mck")
public class MckProperties {
    private String nm;
}

DesAopConfig

package com.itmck.mckspringbootstarter.config;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.Configuration;
@Configuration
@EnableConfigurationProperties(MckProperties.class)
@ConditionalOnProperty(
        prefix = "mck",
        name = "nm",
        havingValue = "true"
)
public class DesAopConfig {
    @Autowired
    MckProperties mckProperties;
    public String handler() {
        return mckProperties.getNm();
    }
}

创建resources\META-INF\spring.factories

:::info org.springframework.boot.autoconfigure.EnableAutoConfiguration=com.itmck.mckspringbootstarter.config.DesAopConfig :::

打包

:::info mvn clean install :::

使用starter步骤:

引入依赖

<dependency>
<groupId>com.itmck</groupId>
<artifactId>mck-spring-boot-starter</artifactId>
<version>0.0.1-SNAPSHOT</version>
</dependency>

application.yml

mck:
  nm: true

java中引入如下:

@Slf4j
@Component
public class Publisher {
  @Resource
  DesAopConfig desAopConfig;
  public void send() {
      log.info("desAopConfig nm:{}",desAopConfig.handler());
  }
}

运行结果如下

3.源码简述

:::tips 通过上面springboot自动装配的源码发现

AutoConfigurationImportSelector implements DeferredImportSelector
DeferredImportSelector extends ImportSelector :::

因为springboot通过一系列操作最终还是找到factories进行读取配置.但是从上面源码我们还可以直接通过使用 @Import 设置对应的类也是一样的所以还可以直接:
@Import({DesAopConfig.class}) 或者@Import({MyImportSelector.class})

注意,通过自定义类实现ImportSelector 重写 selectImports 方法可以注入多个

MyImportSelector ```java package com.itmck.mckspringbootstarter.init;

import com.itmck.mckspringbootstarter.config.DesAopConfig; import org.springframework.context.annotation.ImportSelector; import org.springframework.core.type.AnnotationMetadata;

/**

太阳当空照,花儿对我笑
Create by M ChangKe 2021/8/7 19:26 **/ public class MyImportSelector implements ImportSelector {

@Override public String[] selectImports(AnnotationMetadata annotationMetadata) {
```
 return new String[]{DesAopConfig.class.getName()};
```
} } ```

自定义注解

package com.itmck.mckspringbootstarter.config;
import com.itmck.mckspringbootstarter.init.MyImportSelector;
import org.springframework.context.annotation.Import;
import java.lang.annotation.*;
/**
 * 太阳当空照,花儿对我笑
 * <p>
 * Create by M ChangKe 2021/8/7 22:01
 **/
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import({MyImportSelector.class})
public @interface Mck {
}

启动类上开启注解 @Mck ```java @Mck @SpringBootApplication public class SpringbootMqApplication {

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

}

```

运行同上
4.DeferredImportSelector 与 ImportSelector 区别
:::tips 延迟加载,分组,springboot通过实现延迟加载目的:如果类路径下存在用户自定义优先加载用户自定义. :::

Java 实战入门

如何自定义Spring-boot-starter?

1. starter简介

2. 如何自定义

3.源码简述

4.DeferredImportSelector 与 ImportSelector 区别