我可以在Java中正确关闭输入流吗？ [英] Am I closing my input stream correctly in Java?

问题描述

我创建了一个扩展InputStream的类，以便我可以对正在读取的字节数进行计数，并在超出我定义的最大限制时引发异常。

I created a class that extends InputStream so that I can keep count of the number of bytes being read and throw an exception if it exceeds a max limit that I define.

这是我的课程：

    public class LimitedSizeInputStream extends InputStream
    {

        private final InputStream original;
        private final long maxSize;
        private long total;

        public LimitedSizeInputStream(InputStream original, long maxSize)
        {
            this.original = original;
            this.maxSize = maxSize;
        }

        @Override
        public int read() throws IOException
        {
            int i = original.read();
            if (i >= 0)
            {
                incrementCounter(1);
            }
            return i;
        }

        @Override
        public int read(byte b[]) throws IOException
        {
            return read(b, 0, b.length);
        }

        @Override
        public int read(byte b[], int off, int len) throws IOException
        {
            int i = original.read(b, off, len);
            if (i >= 0)
            {
                incrementCounter(i);
            }
            return i;
        }

        private void incrementCounter(int size) throws IOException
        {
            total += size;
            if (total > maxSize)
            {
                throw new IOException("InputStream exceeded maximum size in bytes.");
            }
        }
    }

这是来自：< a href = https://stackoverflow.com/questions/15445504/copy-inputstream-abort-operation-if-size-exceeds-limit/30072143#30072143>复制InputStream，如果大小超出限制，则中止操作 ，我正在实现一个Jersey API，如果用户上传的文件过大，该API将会失败。

This is coming from: Copy InputStream, abort operation if size exceeds limit, I am implementing a Jersey API that needs to fail if a user is uploading a file that is too large.

这是我的资源类：

    @POST
    @Consumes(MediaType.MULTIPART_FORM_DATA)
    @Path("/test")
    public Response load(
        @Context HttpServletRequest request,
        @FormDataParam(FILE_FIELD) FormDataBodyPart file)
    {
      if (request.getContentLength() > MAX_FILE_SIZE_IN_BYTES)
        {
            // fail fast handle failure
        }

      try (InputStream stream = new LimitedSizeInputStream(
           file.getValueAs(InputStream.class), MAX_FILE_SIZE_IN_BYTES))
        {
            // some logic
        }
      catch (IOException e)
        {
            // handle failure
        }
}

我将LimitedSizeInputStream包装在try资源中，因此我认为流应该正确关闭。对于是否正确处理关闭操作，或者我是否通过LimitedSizeInputStream和file.getValueAs（InputStream.class）技术上打开两个输入流，而只有一个正在关闭，我只是感到困惑？

I wrapped LimitedSizeInputStream in my try resource so I think the stream should close properly. I'm just a bit confused as to whether the close is handled correctly or if I'm technically opening two input streams through LimitedSizeInputStream and file.getValueAs(InputStream.class) and only one is closing?

推荐答案

try-with-resources仅关闭声明的资源。因此只会关闭 metadataStream 。

The try-with-resources only closes the declared resource. So will only close metadataStream.

您应在 LimitedSizeInputStream 中实现 close 方法关闭原始流。

You should implement the close method in LimitedSizeInputStream to close the original stream.

@Override
public void close() throws IOException {
    original.close();
}

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