需要實現看門狗功能，定時檢測另外一個程式是否在執行，使用 crontab 僅可以實現檢測程式是否正在執行，無法做到擴充套件，如：手動重啟、程序升級(如果只需要實現自動升級功能可以使用 inotify)等功能；最後決定使用 Spring Boot 呼叫 Shell 指令碼來實現

一、指令碼

1.1 啟動指令碼

#!/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 重啟指令碼

#!/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、功能實現

將指令碼放置在程式的資源目錄下，每次程式啟動時將指令碼讀取到指定位置，然後再通過定時任務執行指令碼

配置內容：

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 啟動時將指令碼讀取到指定位置

@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;
  }

  // 如果檔案已存在，FileWriter 會先刪除再新建
  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();

  // 設定許可權，否則會報 Permission denied
  file.setReadable(true);
  file.setWritable(true);
  file.setExecutable(true);
 }
}

2.2 定時任務定時任務執行指令碼

@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 擴充套件

本例只實現了定時檢測程式是否執行，如果沒有執行則啟動程式；如有需要可以新增介面，呼叫介面重啟程式；或者新增定時任務定時檢測程式是否有更新，如果有更新則下載新的 jar 包然後重啟程式

看門狗程式自己可以使用 crontab 定時檢測是否正在執行，模仿上面的啟動指令碼編寫看門狗的啟動指令碼，然後新增定時任務：

crontab -e
*/10 * * * * /project/watchdog/watchdog.sh
sudo systemctl reload crond.service

完整程式碼：GitHub

參考：java去呼叫並執行shell指令碼以及問題總結

總結

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