Question

我想知道为什么我会用新的日食Juno得到这个警告，尽管我认为我正确地关闭了所有东西。您能告诉我为什么我会在下面的代码中收到此警告吗？

public static boolean copyFile(String fileSource, String fileDestination)
{
    try
    {
        // Create channel on the source (the line below generates a warning unassigned closeable value) 
        FileChannel srcChannel = new FileInputStream(fileSource).getChannel(); 

        // Create channel on the destination (the line below generates a warning unassigned closeable value)
        FileChannel dstChannel = new FileOutputStream(fileDestination).getChannel();

        // Copy file contents from source to destination
        dstChannel.transferFrom(srcChannel, 0, srcChannel.size());

        // Close the channels
        srcChannel.close();
        dstChannel.close();

        return true;
    }
    catch (IOException e)
    {
        return false;
    } 
 }

Answer 1

如果你在Java 7上运行，你可以使用像这样的新try-with-resources块，你的流将自动关闭：

public static boolean copyFile(String fileSource, String fileDestination)
{
    try(
      FileInputStream srcStream = new FileInputStream(fileSource); 
      FileOutputStream dstStream = new FileOutputStream(fileDestination) )
    {
        dstStream.getChannel().transferFrom(srcStream.getChannel(), 0, srcStream.getChannel().size());
        return true;
    }
    catch (IOException e)
    {
        return false;
    } 
}

您无需显式关闭基础渠道。但是，如果您不使用Java 7，则应该以一种繁琐的旧方式编写代码，最后使用块：

public static boolean copyFile(String fileSource, String fileDestination)
{
    FileInputStream srcStream=null;
    FileOutputStream dstStream=null;
    try {
      srcStream = new FileInputStream(fileSource); 
      dstStream = new FileOutputStream(fileDestination)
      dstStream.getChannel().transferFrom(srcStream.getChannel(), 0, srcStream.getChannel().size());
        return true;
    }
    catch (IOException e)
    {
        return false;
    } finally {
      try { srcStream.close(); } catch (Exception e) {}
      try { dstStream.close(); } catch (Exception e) {}
    }
}

看看Java 7版本有多好：）

Answer 2

您应始终在finally关闭，因为如果异常增加，您将无法关闭资源。

FileChannel srcChannel = null
try {
   srcChannel = xxx;
} finally {
  if (srcChannel != null) {
    srcChannel.close();
  }
}

注意：即使您在catch块中添加了回复，也会完成finally块。

Answer 3

eclipse警告你，你不能再引用FileInputStream和FileOutputStream。

Eclipse Juno：未分配的可关闭值

3 个答案: