当Inputstream中没有数据时跳过在FileOutputStream中创建文件

Question

这是一个日志记录功能，用于记录外部程序执行过程中的错误流。一切正常。但我不想在错误流中没有数据时生成日志文件。目前它正在创建零大小的文件。请帮忙。

FileOutputStream fos = new FileOutputStream(logFile);
PrintWriter pw = new PrintWriter(fos);

Process proc = Runtime.getRuntime().exec(externalProgram);

InputStreamReader isr = new InputStreamReader(proc.getErrorStream());
BufferedReader br = new BufferedReader(isr);
String line=null;
while ( (line = br.readLine()) != null)
{
   if (pw != null){
      pw.println(line);
      pw.flush(); 
   }
}

谢谢。

Answer 1

显而易见的事情是更改

FileOutputStream fos = new FileOutputStream(logFile);
PrintWriter pw = new PrintWriter(fos);
....
   if (pw != null){
   ...
   }

为

FileOutputStream rawLog = null;
try {
    PrintWriter Log = null;
    ....
       if (log == null) {
           rawLog = new FileOutputStream(logFile);
           log = new PrintWriter(log, "UTF-8");
       }
       ...
} finally {
    // Thou shalt close thy resources.
    // Icky null check - might want to split this using the Execute Around idiom.
    if (rawLog != null) {
        rawLog.close();
    }
}

Answer 2

只需推迟 FileOutputStream 和 PrintWriter 的创建，直到您需要它：

PrintWriter pw = null;

Process proc = Runtime.getRuntime().exec(externalProgram);

InputStreamReader isr = new InputStreamReader(proc.getErrorStream());
BufferedReader br = new BufferedReader(isr);
String line;
while ( (line = br.readLine()) != null)
{
   if (pw == null)
   {
      pw = new PrintWriter(new FileOutputStream(logFile));
   }
   pw.println(line);
   pw.flush(); 
}

就我个人而言，我不是 PrintWriter 的忠实粉丝 - 事实上，它只是吞掉了所有与我有关的例外情况。我还使用 OutputStreamWriter 以便您可以显式指定编码。无论如何，这与这里真正的问题无关。