Class DeferredFileOutputStream

  • All Implemented Interfaces:
    java.io.Closeable, java.io.Flushable, java.lang.AutoCloseable

    public class DeferredFileOutputStream
    extends ThresholdingOutputStream
    An output stream which will retain data in memory until a specified threshold is reached, and only then commit it to disk. If the stream is closed before the threshold is reached, the data will not be written to disk at all.

    To build an instance, see DeferredFileOutputStream.Builder.

    This class originated in FileUpload processing. In this use case, you do not know in advance the size of the file being uploaded. If the file is small you want to store it in memory (for speed), but if the file is large you want to store it to file (to avoid memory issues).

    • Field Detail

      • memoryOutputStream

        private ByteArrayOutputStream memoryOutputStream
        The output stream to which data will be written prior to the threshold being reached.
      • currentOutputStream

        private java.io.OutputStream currentOutputStream
        The output stream to which data will be written at any given time. This will always be one of memoryOutputStream or diskOutputStream.
      • outputPath

        private java.nio.file.Path outputPath
        The file to which output will be directed if the threshold is exceeded.
      • prefix

        private final java.lang.String prefix
        The temporary file prefix.
      • suffix

        private final java.lang.String suffix
        The temporary file suffix.
      • directory

        private final java.nio.file.Path directory
        The directory to use for temporary files.
      • closed

        private boolean closed
        True when close() has been called successfully.
    • Constructor Detail

      • DeferredFileOutputStream

        @Deprecated
        public DeferredFileOutputStream​(int threshold,
                                        java.io.File outputFile)
        Constructs an instance of this class which will trigger an event at the specified threshold, and save data to a file beyond that point. The initial buffer size will default to 1024 bytes which is ByteArrayOutputStream's default buffer size.
        Parameters:
        threshold - The number of bytes at which to trigger an event.
        outputFile - The file to which data is saved beyond the threshold.
      • DeferredFileOutputStream

        private DeferredFileOutputStream​(int threshold,
                                         java.io.File outputFile,
                                         java.lang.String prefix,
                                         java.lang.String suffix,
                                         java.io.File directory,
                                         int initialBufferSize)
        Constructs an instance of this class which will trigger an event at the specified threshold, and save data either to a file beyond that point.
        Parameters:
        threshold - The number of bytes at which to trigger an event.
        outputFile - The file to which data is saved beyond the threshold.
        prefix - Prefix to use for the temporary file.
        suffix - Suffix to use for the temporary file.
        directory - Temporary file directory.
        initialBufferSize - The initial size of the in memory buffer.
        Throws:
        java.lang.IllegalArgumentException - if initialBufferSize < 0.
      • DeferredFileOutputStream

        @Deprecated
        public DeferredFileOutputStream​(int threshold,
                                        int initialBufferSize,
                                        java.io.File outputFile)
        Constructs an instance of this class which will trigger an event at the specified threshold, and save data to a file beyond that point.
        Parameters:
        threshold - The number of bytes at which to trigger an event.
        initialBufferSize - The initial size of the in memory buffer.
        outputFile - The file to which data is saved beyond the threshold.
        Since:
        2.5
      • DeferredFileOutputStream

        @Deprecated
        public DeferredFileOutputStream​(int threshold,
                                        int initialBufferSize,
                                        java.lang.String prefix,
                                        java.lang.String suffix,
                                        java.io.File directory)
        Constructs an instance of this class which will trigger an event at the specified threshold, and save data to a temporary file beyond that point.
        Parameters:
        threshold - The number of bytes at which to trigger an event.
        initialBufferSize - The initial size of the in memory buffer.
        prefix - Prefix to use for the temporary file.
        suffix - Suffix to use for the temporary file.
        directory - Temporary file directory.
        Since:
        2.5
      • DeferredFileOutputStream

        @Deprecated
        public DeferredFileOutputStream​(int threshold,
                                        java.lang.String prefix,
                                        java.lang.String suffix,
                                        java.io.File directory)
        Constructs an instance of this class which will trigger an event at the specified threshold, and save data to a temporary file beyond that point. The initial buffer size will default to 32 bytes which is ByteArrayOutputStream's default buffer size.
        Parameters:
        threshold - The number of bytes at which to trigger an event.
        prefix - Prefix to use for the temporary file.
        suffix - Suffix to use for the temporary file.
        directory - Temporary file directory.
        Since:
        1.4
    • Method Detail

      • checkBufferSize

        private static int checkBufferSize​(int initialBufferSize)
      • close

        public void close()
                   throws java.io.IOException
        Closes underlying output stream, and mark this as closed
        Specified by:
        close in interface java.lang.AutoCloseable
        Specified by:
        close in interface java.io.Closeable
        Overrides:
        close in class ThresholdingOutputStream
        Throws:
        java.io.IOException - if an error occurs.
      • getData

        public byte[] getData()
        Gets the data for this output stream as an array of bytes, assuming that the data has been retained in memory. If the data was written to disk, this method returns null.
        Returns:
        The data for this output stream, or null if no such data is available.
      • getFile

        public java.io.File getFile()
        Gets either the output file specified in the constructor or the temporary file created or null.

        If the constructor specifying the file is used then it returns that same output file, even when threshold has not been reached.

        If constructor specifying a temporary file prefix/suffix is used then the temporary file created once the threshold is reached is returned If the threshold was not reached then null is returned.

        Returns:
        The file for this output stream, or null if no such file exists.
      • getStream

        protected java.io.OutputStream getStream()
                                          throws java.io.IOException
        Gets the current output stream. This may be memory based or disk based, depending on the current state with respect to the threshold.
        Overrides:
        getStream in class ThresholdingOutputStream
        Returns:
        The underlying output stream.
        Throws:
        java.io.IOException - if an error occurs.
      • isInMemory

        public boolean isInMemory()
        Tests whether or not the data for this output stream has been retained in memory.
        Returns:
        true if the data is available in memory; false otherwise.
      • thresholdReached

        protected void thresholdReached()
                                 throws java.io.IOException
        Switches the underlying output stream from a memory based stream to one that is backed by disk. This is the point at which we realize that too much data is being written to keep in memory, so we elect to switch to disk-based storage.
        Overrides:
        thresholdReached in class ThresholdingOutputStream
        Throws:
        java.io.IOException - if an error occurs.
      • toInputStream

        public java.io.InputStream toInputStream()
                                          throws java.io.IOException
        Converts the current contents of this byte stream to an InputStream. If the data for this output stream has been retained in memory, the returned stream is backed by buffers of this stream, avoiding memory allocation and copy, thus saving space and time.
        Otherwise, the returned stream will be one that is created from the data that has been committed to disk.
        Returns:
        the current contents of this output stream.
        Throws:
        java.io.IOException - if this stream is not yet closed or an error occurs.
        Since:
        2.9.0
        See Also:
        ByteArrayOutputStream.toInputStream()
      • toPath

        private java.nio.file.Path toPath​(java.io.File file,
                                          java.util.function.Supplier<java.nio.file.Path> defaultPathSupplier)
      • writeTo

        public void writeTo​(java.io.OutputStream outputStream)
                     throws java.io.IOException
        Writes the data from this output stream to the specified output stream, after it has been closed.
        Parameters:
        outputStream - output stream to write to.
        Throws:
        java.lang.NullPointerException - if the OutputStream is null.
        java.io.IOException - if this stream is not yet closed or an error occurs.