Package org.apache.commons.io.output

Class DeferredFileOutputStream

java.lang.Object
java.io.OutputStream
org.apache.commons.io.output.ThresholdingOutputStream
org.apache.commons.io.output.DeferredFileOutputStream
All Implemented Interfaces:
Closeable, Flushable, 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, use DeferredFileOutputStream.Builder.

The caller is responsible for deleting the output file (getFile(), getPath()) created by a DeferredFileOutputStream when the caller only configured a prefix.

The caller is responsible for deleting the output file passed to a constructor or builder through DeferredFileOutputStream.Builder.setOutputFile(File) or DeferredFileOutputStream.Builder.setOutputFile(Path).

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).

See Also:

  • Constructor Details

    • DeferredFileOutputStream

      @Deprecated public DeferredFileOutputStream(int threshold, File outputFile)
      Deprecated.
      Use builder(), DeferredFileOutputStream.Builder, and DeferredFileOutputStream.Builder.get()
      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

      @Deprecated public DeferredFileOutputStream(int threshold, int initialBufferSize, File outputFile)
      Deprecated.
      Use builder(), DeferredFileOutputStream.Builder, and DeferredFileOutputStream.Builder.get()
      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, String prefix, String suffix, File directory)
      Deprecated.
      Use builder(), DeferredFileOutputStream.Builder, and DeferredFileOutputStream.Builder.get()
      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, String prefix, String suffix, File directory)
      Deprecated.
      Use builder(), DeferredFileOutputStream.Builder, and DeferredFileOutputStream.Builder.get()
      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 Details

    • builder

      public static DeferredFileOutputStream.Builder builder()
      Constructs a new DeferredFileOutputStream.Builder.
      Returns:
      a new DeferredFileOutputStream.Builder.
      Since:
      2.12.0

    • close

      public void close() throws IOException
      Closes underlying output stream, and mark this as closed
      Specified by:
      close in interface AutoCloseable
      Specified by:
      close in interface Closeable
      Overrides:
      close in class ThresholdingOutputStream
      Throws:
      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 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.

    • getPath

      public Path getPath()
      Gets either the output Path specified in the constructor or the temporary Path created or null.

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

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

      Returns:
      The Path for this output stream, or null if no such Path exists.
      Since:
      2.14.0

    • getStream

      protected OutputStream getStream() throws 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:
      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 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:
      IOException - if an error occurs.

    • toInputStream

      public InputStream toInputStream() throws 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:
      IOException - if this stream is not yet closed or an error occurs.
      Since:
      2.9.0
      See Also:

    • writeTo

      public void writeTo(OutputStream outputStream) throws 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:
      NullPointerException - if the OutputStream is null.
      IOException - if this stream is not yet closed or an error occurs.