本文參照Http編碼的配置原始碼，自己實現一個starter。

    1.新建maven工程。

    在pom.xml中修改，新增autoconfigure依賴：

<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>com.springboot</groupId>
  <artifactId>springboot_starter</artifactId>
  <version>1.0-SNAPSHOT</version>
  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>2.5</version>
        <configuration>
          <source>1.8</source>
          <target>1.8</target>
        </configuration>
      </plugin>
    </plugins>
  </build>
  <packaging>jar</packaging>

  <name>springboot_starter</name>
  <url>http://maven.apache.org</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>

  <dependencies>

    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-autoconfigure</artifactId>
      <version>1.5.8.RELEASE</version>
    </dependency>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-configuration-processor</artifactId>
      <version>1.5.8.RELEASE</version>
      <optional>true</optional>
    </dependency>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>
  </dependencies>
</project>
 

    2.屬性配置類，程式碼如下：

package com.springboot;

import org.springframework.boot.context.properties.ConfigurationProperties;

import javax.naming.Name;

/**
 * Created by leijun on 2018/4/3.
 */
@ConfigurationProperties(prefix = "user")
public class UserInfoProperties {

    private static final String UNAME = "springboot";

    private String uName = UNAME;

    public String getUName() {
        return uName;
    }

    public void setUName(String uName) {
        this.uName = uName;
    }
}
 

    3.判斷依據類，程式碼如下：

package com.springboot;

/**
 * Created by leijun on 2018/4/3.
 */
public class UserInfo {

    private String uName;

    public String getUserInfo(){
        return "My name is " + getUName();
    }

    public String getUName() {
        return uName;
    }

    public void setUName(String uName) {
        this.uName = uName;
    }
}
 

    4.自動配置類，程式碼如下：

package com.springboot;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

/**
 * Created by leijun on 2018/4/3.
 */
@Configuration
@EnableConfigurationProperties(UserInfoProperties.class)
@ConditionalOnClass(UserInfo.class)
@ConditionalOnProperty(prefix = "user",value = "enabled",matchIfMissing = true)
public class UserInfoAutoConfiguration {

    @Autowired
    private UserInfoProperties userInfoProperties;

    @Bean
    @ConditionalOnMissingBean(UserInfo.class)
    public UserInfo userInfo(){
        UserInfo userInfo = new UserInfo();
        userInfo.setUName(userInfoProperties.getUName());
        return userInfo;
    }
}

    5.註冊配置。自動配置類需要註冊才可以實現自動配置。在resources下建立META-INF/spring.factories，spring.factories中內容如下：

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
com.springboot.UserInfoAutoConfiguration

    其中如果想要多個自動配置類，用”,“隔開，”\“作用是換行仍能讀到屬性值。

    至此，整個starter編寫完成，下面來使用這個starter。

    建立新springboot的專案。

    在pom.xml中新增剛才編寫的springboot_starter的依賴：

<dependency>
   <groupId>com.springboot</groupId>
   <artifactId>springboot_starter</artifactId>
   <version>1.0-SNAPSHOT</version>
</dependency>

    測試類程式碼如下：

package com.springboot;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

/**
 * Created by leijun on 2018/4/3.
 */
@RestController
@SpringBootApplication
public class App {

    @Autowired
    private UserInfo userInfo;

    @GetMapping("/")
    public String getUserInfo(){
        return userInfo.getUserInfo();
    }

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

    測試類中UserInfo在新專案中並沒有配置Bean，但是可以注入，這就是通過自動配置完成的。執行程式，在瀏覽器輸入localhost:8080，效果如下：

    在application.properties中配置uName的屬性值：

user.uName=leijun

    在瀏覽器再次測試：

    在application.properties中新增debug屬性，檢視自動配置報告：

debug=true

    可以看到我們自定義的配置顯示在控制檯：