自定义Spring-Boot @Enable注解

Spring-Boot中有很多Enable开头的注解，通过添加注解来开启一项功能，如

其原理是什么？如何开发自己的Enable注解？

1.原理

以@EnableScheduling为例，查看其源码，发现添加了一个@Import注解

继续查看@Import注解源码，发现其是由Spring提供的，用来导入配置类的，在配置类中定义的Bean(@Bean)，可通过@Autowired注入到容器中，也就是可以被扫描到

2.自定义

了解了Enable注解的原理，我们就可以开发自己的Enable注解了，下面的例子实现了通过@Enable注解方式开启服务器负载监控的功能

2.1 定义定时任务类

package com.yc.dudu.common.monitor;

import com.alibaba.fastjson.JSONObject;

import com.sun.management.OperatingSystemMXBean;

import com.yc.dudu.common.constant.CommonConstants;

import com.yc.dudu.common.util.DateTimeUtil;

import com.yc.dudu.common.vo.ServerMonitorInfo;

import lombok.extern.slf4j.Slf4j;

import org.slf4j.Logger;

import org.slf4j.LoggerFactory;

import org.springframework.boot.CommandLineRunner;

import org.springframework.scheduling.annotation.EnableScheduling;

import org.springframework.scheduling.annotation.Scheduled;

import java.io.File;

import java.lang.management.ManagementFactory;

import java.net.InetAddress;

import java.net.UnknownHostException;

/**

 * 收集服务器负载信息

 *

 * @author zhya

 * @date 2018/9/20

 **/

@Slf4j

@EnableScheduling

public class ServerLoadMonitorRunner implements CommandLineRunner {

    /**

     * 自定义log，输出服务器负载信息到日志文件

     */

    private static final Logger monitorLog = LoggerFactory.getLogger("serverMonitorLog");

    /**

     * 系统信息

     */

    private static final OperatingSystemMXBean mem = (OperatingSystemMXBean) ManagementFactory.getOperatingSystemMXBean();

    /**

     * 收集服务器负载信息并输出到日志文件

     */

    @Scheduled(cron = "*/5 * * * * ?")

    public void collectServerSystemLoad() {

        try {

            // 输出json格式的信息到文件

            monitorLog.info(JSONObject.toJSONString(new ServerMonitorInfo(InetAddress.getLocalHost().getHostName(),

                    String.valueOf(mem.getFreePhysicalMemorySize() / CommonConstants.BYTES_TO_MB),

                    String.valueOf(mem.getSystemCpuLoad()),

                    String.valueOf(File.listRoots()[0].getFreeSpace() / CommonConstants.BYTES_TO_MB),

                    DateTimeUtil.getNowDateTimeStr())));

        } catch (UnknownHostException e) {

            log.error(e.getMessage());

        }

    }

    /**

     * Callback used to run the bean.

     *

     * @param args incoming main method arguments

     * @throws Exception on error

     */

    @Override

    public void run(String... args) throws Exception {

        try {

            collectServerSystemLoad();

        } catch (Exception e) {

            log.error(e.getMessage());

            // 不做处理，继续运行

        }

    }

}

2.2 定义配置类，其中声明定时任务Bean

package com.yc.dudu.common.monitor;

import org.apache.commons.lang3.StringUtils;

import org.springframework.beans.factory.annotation.Value;

import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;

import org.springframework.context.annotation.Bean;

import org.springframework.context.annotation.Configuration;

import javax.annotation.PostConstruct;

/**

 * 服务器负载监控自动配置类

 *

 * @author zhya

 * @date 2018/09/20

 **/

@Configuration

public class ServerLoadMonitorAutoConfig {

    /**

     * 是否开启监控配置参数

     */

    @Value("${monitor.server.enabled:}")

    private String enabledConfig;

    /**

     * 错误提醒

     */

    @PostConstruct

    protected void init() {

        if (StringUtils.isBlank(enabledConfig)) {

            System.err.println("~~~Please config the monitor.server.enabled property in application.yml file to enable server monitor function~~~");

        }

    }

    /**

     * 根据运行环境决定是否开启服务器负载信息监控

     *

     * @return

     */

    @Bean

    @ConditionalOnProperty(prefix = "monitor.server", name = "enabled", havingValue = "true")

    protected ServerLoadMonitorRunner startServerMonitor() {

        return new ServerLoadMonitorRunner();

    }

}

2.3 定义自己的Enable注解，Import 配置类

package com.yc.dudu.common.monitor;

import org.springframework.context.annotation.Import;

import java.lang.annotation.*;

/**

 * 服务器负载监控开启注解

 *

 * @author zhya

 * @date 2018/09/20

 **/

@Target(ElementType.TYPE)

@Retention(RetentionPolicy.RUNTIME)

@Import(ServerLoadMonitorAutoConfig.class)

@Documented

@Inherited

public @interface EnableServerLoadMonitor {

}

2.4 使用自定义的EnableServerLoadMonitor注解，配合着配置参数，就可以开启服务器负载监控功能了

package com.yc.dudu.gate.admin;

import com.yc.dudu.auth.client.EnableDuduAuthClient;

import com.yc.dudu.common.monitor.EnableServerLoadMonitor;

import org.slf4j.Logger;

import org.slf4j.LoggerFactory;

import org.springframework.boot.SpringApplication;

import org.springframework.boot.autoconfigure.SpringBootApplication;

import org.springframework.cloud.client.discovery.EnableDiscoveryClient;

import org.springframework.cloud.netflix.hystrix.EnableHystrix;

import org.springframework.cloud.openfeign.EnableFeignClients;

import org.springframework.context.annotation.Bean;

import zipkin2.Span;

import zipkin2.reporter.Reporter;

/**

 * admin网关启动类

 *

 * @author zhya

 * @date 2018/9/20

 **/

@EnableHystrix

@EnableServerLoadMonitor

@SpringBootApplication

@EnableDiscoveryClient

@EnableDuduAuthClient

@EnableFeignClients({"com.yc.dudu.auth.client.feign", "com.yc.dudu.gate.admin.feign"})

public class AdminGatewayApplication {

    public static void main(String[] args) {

        SpringApplication.run(AdminGatewayApplication.class, args);

        System.out.println("AdminGatewayApplication is started!~~~~~~~~");

    }

    /**

     * 链路跟踪信息输出log

     */

    private static Logger sleuthLog = LoggerFactory.getLogger("sleuthLog");

    /**

     * 将链路跟踪信息输出到日志文件

     *

     * @return

     */

    @Bean

    public Reporter<Span> spanReporter() {

        Reporter<Span> reporter = span -> sleuthLog.info(span.toString());

        return reporter;

    }

}

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