Java代码规范总结，更新持续中

1. 实例的开启与关闭

var zkClient: ZooKeeper = null
      try {
        zkClient = new ZooKeeper(getZkUrl(), 2000, new Watcher {
          override def process(watchedEvent: WatchedEvent): Unit = {}
        })

        val data = zkClient.getData(s"/hadoop-ha/" + hdfsNameServiceHost + s"/ActiveBreadCrumb", new Watcher {
          override def process(watchedEvent: WatchedEvent): Unit = {}
        }, new Stat())

        val activeNodeInfo = HAZKInfoProtos.ActiveNodeInfo.parseFrom(data)

        activeNodeInfo.getHostname
      } catch {
        case ex: Exception => {
          logError(s"ERROR: zookeeper connect failure, can not get the active hdfs namenode according to ${hdfsNameServiceHost}", ex)
          ""
        }
      }finally {
        if (zkClient != null){
          zkClient.close()
        }
      }

　　如上述，代码 zkClient 在try中开启，不能再在try中关闭，因为发生异常的时候是关闭不掉的，切记切记切记！！！必须在finally中zkClient.close()才能把zkClient关闭，不这样做的后果就是会不断报连接zkserver失败

2. 异常捕获

2.1 每个方法都需要try catch，内或外的区别

　　每个方法里面或者外面都需要try catch。不然会导致程序挂死，占用资源。

2.1 异常后的代码不会执行

　　注意：try catch里面需要代码异常之后，异常代码剩下的代码将不会执行，如下示例：

try{
      assert(argsCheck(args))
      if (dbName != null && dbName != "") {
        logInfo(s"use $dbName")
        sparkSession.sql(s"use $dbName")
      }
      processSparkPara
      run
      sparkSession.stop()
      result = true

      // determine if the taskVars json file exists, if not write the file, if exists overwrite the file
      val taskVarsJson = JsonProtocal.taskVarsToJson(TaskVars(systemVars, runtimeVars))
      logInfo(s"write taskVarsJsonStr:$taskVarsJson")
      //    if (!isLocal){
      HDFSUtil.writeHDFSFile(taskVarsJsonPath, taskVarsJson)
      //    }else{
      //      createLocalFile(taskVarsJsonPath, taskVarsJson)
      //    }
    }catch {
      case e: Throwable => {
        logError(s"== process failed, please check.",e)
        cause = e.getMessage
        result = false
      }
    }

　　示例中的run方法发生异常之后，taskVarsJson文件将不会生成，而这将会导致后续的程序异常。如果taskVarsJson文件是程序所必须的，则不能放在try catch里面

try{
      assert(argsCheck(args))
      if (dbName != null && dbName != "") {
        logInfo(s"use $dbName")
        sparkSession.sql(s"use $dbName")
      }
      processSparkPara
      run
      sparkSession.stop()
      result = true
      
    }catch {
      case e: Throwable => {
        logError(s"== process failed, please check.",e)
        cause = e.getMessage
        result = false
      }
    }

    // determine if the taskVars json file exists, if not write the file, if exists overwrite the file
    val taskVarsJson = JsonProtocal.taskVarsToJson(TaskVars(systemVars, runtimeVars))
    logInfo(s"write taskVarsJsonStr:$taskVarsJson")
    //    if (!isLocal){
    HDFSUtil.writeHDFSFile(taskVarsJsonPath, taskVarsJson)
    //    }else{
    //      createLocalFile(taskVarsJsonPath, taskVarsJson)
    //    }

3. 测试规范

　　测试成功，测试不成功两种。不要只测试成功的，遗留不成功，程序不成功也会导致程序线程挂死（占用资源）、不断打印连接不上日志等等异常情况。好像给别人造成不少麻烦...

4. scala的 case class 类构造优化

原代码：
case class Desc(name:String)
val taskDesc = TaskDesc("hello")

类扩展：
case class Desc(name:String, config: Config)
val taskDesc = TaskDesc("hello", null)

　　评：上述代码扩展性不好，需要修改原来的老代码。参考如下设计，可以在扩展类的时候，避免修改其他老代码：

原代码：
case class Desc(name:String)
val taskDesc = TaskDesc("hello")

类扩展：
case class Desc(name:String, config: Config = null)
val taskDesc = TaskDesc("hello)

5. File文件与文件夹

def cleanExpiredLog(pathname: String, task: String): Unit ={
    System.out.println("clean expired log start")
    try{
      var lifeCycle = 3
      if (lifeCycle < 1) lifeCycle = 3
      val sdfDay = new java.text.SimpleDateFormat("yyyy-MM-dd")
      val strDay = sdfDay.format(System.currentTimeMillis() - lifeCycle * 24 * 60 * 60 * 1000)
      val tasksFile = new File(pathname  + File.separator + task + File.separator)
      val tasksSubFiles = tasksFile.listFiles()
      for(taskFile <- tasksSubFiles){
          // 筛选task任务目录下过期的文件夹
          val filterFiles = filterExpiredLog(taskFile, strDay)
          // 删除过期日志
          deleteExpiredLog(filterFiles)
      }
    }catch{
      case ex: Exception =>
        System.out.println("clean expired log error, " + ex.getMessage)
    }
    System.out.println("clean expired log end")
  } 

　　评：对文件进行操作时，需判断该文件父类是文件还是文件夹，

def cleanExpiredLog(pathname: String, task: String): Unit ={
    System.out.println("clean expired log start")
    try{
      var lifeCycle = 3
      if (lifeCycle < 1) lifeCycle = 3
      val sdfDay = new java.text.SimpleDateFormat("yyyy-MM-dd")
      val strDay = sdfDay.format(System.currentTimeMillis() - lifeCycle * 24 * 60 * 60 * 1000)
      val tasksFile = new File(pathname  + File.separator + task + File.separator)
      val tasksSubFiles = tasksFile.listFiles()
      for(taskFile <- tasksSubFiles){
 
       //这里需要判断文件还是文件夹，否则文件的listFiles会报错   
        if (tasksFile.isDirectory){
          // 筛选task任务目录下过期的文件夹
          val filterFiles = filterExpiredLog(taskFile, strDay)
          // 删除过期日志
          deleteExpiredLog(filterFiles)
        }
      }
    }catch{
      case ex: Exception =>
        System.out.println("clean expired log error, " + ex.getMessage)
    }
    System.out.println("clean expired log end")
  }