实现一个Spring Boot Starter入门

功能实现

Spring Boot Starter可以将需要的功能整合起来，方便使用。这个例子是一个非常简单的Starter实现，关键在于走通流程。首先单独创建一个maven项目，命名为greeter-spring-boot-starter。在项目中创建一个配置定义类GreeterProperties，主要定义一个配置前缀和对应的属性，一个starter核心类GreeterAutoConfiguration，通过这个实现基于starter方式的加载，如下：

@Configuration
@ConditionalOnClass(Greeter.class)
@ConditionalOnProperty(prefix = "appblog.greeter",value = "enable",matchIfMissing = true)
@EnableConfigurationProperties(GreeterProperties.class)
public class GreeterAutoConfiguration {

    @Bean
    @ConditionalOnMissingBean
    public Greeter greeter() {
        return new Greeter();
    }
}

最后一个业务类Greeter，一个根据当前时间打招呼的逻辑，如下：

package cn.appblog.autoconfigure;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.Calendar;

@Service
public class Greeter {

    @Autowired
    private GreeterProperties greeterProperties;

    private String sayMorning() {
        return greeterProperties.getMorningMsg();
    }

    private String sayAfternoon() {
        return greeterProperties.getAfternoonMsg();
    }

    private String sayEvening() {
        return greeterProperties.getEveningMsg();
    }

    /**
     * 外部调用方法
     * @return
     */
    public String sayHello() {
        String msg;
        int h = Calendar.getInstance().get(Calendar.HOUR_OF_DAY);
        if (h < 8) {
            msg = sayMorning();
        } else if (h >= 12 && h <= 16) {
            msg = sayAfternoon();
        } else {
            msg = sayEvening();
        }

        return "[" + greeterProperties.getUserName() + "] " + msg;
    }
}

配置定义的类GreeterProperties

package cn.appblog.autoconfigure;

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

@ConfigurationProperties(prefix = "appblog.greeter")
public class GreeterProperties {
    private String userName;
    private String morningMsg;
    private String afternoonMsg;
    private String eveningMsg;
    private String nightMsg;

    public String getUserName() {
        return userName;
    }

    public void setUserName(String userName) {
        this.userName = userName;
    }

    public String getMorningMsg() {
        return morningMsg;
    }

    public void setMorningMsg(String morningMsg) {
        this.morningMsg = morningMsg;
    }

    public String getEveningMsg() {
        return eveningMsg;
    }

    public void setEveningMsg(String eveningMsg) {
        this.eveningMsg = eveningMsg;
    }

    public String getNightMsg() {
        return nightMsg;
    }

    public void setNightMsg(String nightMsg) {
        this.nightMsg = nightMsg;
    }

    public String getAfternoonMsg() {
        return afternoonMsg;
    }

    public void setAfternoonMsg(String afternoonMsg) {
        this.afternoonMsg = afternoonMsg;
    }
}

另外在resource里需要定义META-INFO信息。建立META-INFO文件夹，将以下信息写入spring.factories文件，spring Boot就是通过这个文件加载Starter的。

org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
  cn.appblog.autoconfigure.GreeterAutoConfiguration

以上项目pom.xml文件依赖配置，只需要spring-boot-autoconfigure即可：

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-autoconfigure</artifactId>
    <version>2.1.2.RELEASE</version>
</dependency>

完成后mvn install，部署到本地仓库，就可以使用了。如果是生产或者企业开发环境，使用mvn deploy部署到远程仓库。

具体使用方式

在上面的步骤完成添加到本地仓库后，就可以在另外的项目中添加starter依赖，注意默认的版本号。pom.xml配置如下：

<dependency>
    <groupId>cn.appblog</groupId>
    <artifactId>greeter-spring-boot-starter</artifactId>
    <version>1.0-SNAPSHOT</version>
</dependency>

配置信息写入application.properties里，就可以调用具体的Greeter逻辑方法。

appblog.greeter.userName=netscape
appblog.greeter.morningMsg=中午好
appblog.greeter.afternoonMsg=下午好
appblog.greeter.eveningMsg=晚上好