需要实现看门狗功能，定时检测另外一个程序是否在运行，使用 crontab 仅可以实现检测程序是否正在运行，无法做到扩展，如：手动重启、程序升级(如果只需要实现自动升级功能可以使用 inotify)等功能；最后决定使用 Spring Boot 调用 Shell 脚本来实现

一、脚本

1.1 启动脚本

#!/bin/bash

ps -ef | grep "demo-app-0.0.1-SNAPSHOT.jar" | grep -v "grep"

if [ "$?" -eq 0 ]

then

# sleep

echo $(date "+%Y-%m-%d %H:%M:%S") "process already started!"

else

nohup java -jar -server /project/watchdog/demo-app-0.0.1-SNAPSHOT.jar &

echo $(date "+%Y-%m-%d %H:%M:%S") "process has been started!"

fi

1.2 重启脚本

#!/bin/bash

pid=`ps -ef | grep "demo-app-0.0.1-SNAPSHOT.jar" | grep -v "grep" | awk '{print $2}'`

for id in $pid

do

    kill -9 $id

    echo "killed $id"

done

nohup java -jar -server /project/watchdog/demo-app-0.0.1-SNAPSHOT.jar &

echo $(date "+%Y-%m-%d %H:%M:%S") "process has been restarted!"

二、功能实现

将脚本放置在程序的资源目录下，每次程序启动时将脚本读取到指定位置，然后再通过定时任务执行脚本

配置内容：

shell:

  directory: /project/watchdog

  startupFileName: startup.sh

  restartFileName: restart.sh

@Configuration

@ConfigurationProperties(prefix = "shell")

public class ShellProperties {

    private String directory;

    private String startupFileName;

    private String restartFileName;

    /* getter & setter */

    public String getFullName(String fileName) {

        return directory + File.separator + fileName;

    }

}

2.1 启动时将脚本读取到指定位置

@Component

public class InitRunner implements CommandLineRunner {

    @Autowired

    private ShellProperties shellProperties;

    @Autowired

    ResourceLoader resourceLoader;

    @Override

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

        generateFile(shellProperties.getStartupFileName());

        generateFile(shellProperties.getRestartFileName());

    }

    private void generateFile(String fileName) throws IOException {

        String fileFullName = shellProperties.getFullName(fileName);

        File file = new File(fileFullName);

        if(file.exists()) {

            return;

        }

        // 如果文件已存在，FileWriter 会先删除再新建

        FileWriter fileWriter = new FileWriter(fileFullName);

        Resource resource = resourceLoader.getResource("classpath:" + fileName);

        InputStream inputStream = resource.getInputStream();

        InputStreamReader inputStreamReader = new InputStreamReader(inputStream);

        BufferedReader bufferedReader = new BufferedReader(inputStreamReader);

        String data;

        while ((data = bufferedReader.readLine()) != null) {

            fileWriter.write(data + "\n");

        }

        bufferedReader.close();

        inputStreamReader.close();

        inputStream.close();

        fileWriter.close();

        // 设置权限，否则会报 Permission denied

        file.setReadable(true);

        file.setWritable(true);

        file.setExecutable(true);

    }

}

2.2 定时任务定时任务执行脚本

@Component

public class ShellTask {

    private static final Logger logger = LoggerFactory.getLogger(ShellTask.class);

    @Autowired

    private ShellProperties shellProperties;

    @Scheduled(cron = "0/10 * * * * ? ")

    public void start() throws IOException {

        executeShell(shellProperties.getStartupFileName());

    }

    private void executeShell(String fileName) throws IOException {

        String fileFullName = shellProperties.getFullName(fileName);

        File file = new File(fileFullName);

        if(!file.exists()) {

            logger.error("file {} not existed!", fileFullName);

            return;

        }

        ProcessBuilder processBuilder = new ProcessBuilder(fileFullName);

        processBuilder.directory(new File(shellProperties.getDirectory()));

        Process process = processBuilder.start();

//        String input;

//        BufferedReader stdInput = new BufferedReader(new InputStreamReader(process.getInputStream()));

//        BufferedReader stdError = new BufferedReader(new InputStreamReader(process.getErrorStream()));

//        while ((input = stdInput.readLine()) != null) {

//            logger.info(input);

//        }

//        while ((input = stdError.readLine()) != null) {

//            logger.error(input);

//        }

        int runningStatus = 0;

        try {

            runningStatus = process.waitFor();

        } catch (InterruptedException e) {

            logger.error("shell", e);

        }

        if(runningStatus != 0) {

            logger.error("failed.");

        }else {

            logger.info("success.");

        }

    }

}

2.3 扩展

1. 本例只实现了定时检测程序是否运行，如果没有运行则启动程序；如有需要可以添加接口，调用接口重启程序；或者添加定时任务定时检测程序是否有更新，如果有更新则下载新的 jar 包然后重启程序
2. 看门狗程序自己可以使用 crontab 定时检测是否正在运行，模仿上面的启动脚本编写看门狗的启动脚本，然后添加定时任务：

crontab -e

*/10 * * * * /project/watchdog/watchdog.sh

sudo systemctl reload crond.service

完整代码：GitHub

参考：java去调用并执行shell脚本以及问题总结