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:
    `DeferredFileOutputStream.Builder`

- - ### Nested Class Summary

    Nested Classes
    Modifier and Type | Class and Description
    --- | ---
    `static class` | `DeferredFileOutputStream.Builder` Builds a new `DeferredFileOutputStream`.

  - ### Method Summary

    All Methods Static Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `static DeferredFileOutputStream.Builder` | `builder()` Constructs a new `DeferredFileOutputStream.Builder`.
    `void` | `close()` Closes underlying output stream, and mark this as closed
    `byte[]` | `getData()` Gets the data for this output stream as an array of bytes, assuming that the data has been retained in memory.
    `File` | `getFile()` Gets either the output File specified in the constructor or the temporary File created or null.
    `Path` | `getPath()` Gets either the output Path specified in the constructor or the temporary Path created or null.
    `boolean` | `isInMemory()` Tests whether or not the data for this output stream has been retained in memory.
    `protected void` | `thresholdReached()` Switches the underlying output stream from a memory based stream to one that is backed by disk.
    `InputStream` | `toInputStream()` Converts the current contents of this byte stream to an `InputStream`.
    `void` | `writeTo(OutputStream outputStream)` Writes the data from this output stream to the specified output stream, after it has been closed.

    - ### Methods inherited from class org.apache.commons.io.output.ThresholdingOutputStream

      `checkThreshold, flush, getByteCount, getOutputStream, getThreshold, isThresholdExceeded, resetByteCount, setByteCount, write, write, write`

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Method Detail

    - #### builder

          public static DeferredFileOutputStream.Builder builder()

      Constructs a new `DeferredFileOutputStream.Builder`.
      Returns:
        a new `DeferredFileOutputStream.Builder`.

    - #### close

          public void close()
                     throws IOException

      Closes underlying output stream, and mark this as closed
      Specified by:
        `close` in interface `Closeable`
      Specified by:
        `close` in interface `AutoCloseable`
      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.

    - #### 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.
      See Also:
        `ByteArrayOutputStream.toInputStream()`

    - #### 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.