public class DeferredFileOutputStream extends ThresholdingOutputStreamAn 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.
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).
All Methods Instance Methods Concrete Methods Modifier and Type Method Description
close()Closes underlying output stream, and mark this as closed
getData()Returns the data for this output stream as an array of bytes, assuming that the data has been retained in memory.
getFile()Returns either the output file specified in the constructor or the temporary file created or null.
getStream()Returns the current output stream.
isInMemory()Determines whether or not the data for this output stream has been retained in memory.
thresholdReached()Switches the underlying output stream from a memory based stream to one that is backed by disk.
Methods inherited from class org.apache.tomcat.util.http.fileupload.ThresholdingOutputStream
checkThreshold, flush, isThresholdExceeded, write, write, write
public DeferredFileOutputStream(int threshold, 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.
threshold- The number of bytes at which to trigger an event.
outputFile- The file to which data is saved beyond the threshold.
protected OutputStream getStream() throws IOExceptionReturns the current output stream. This may be memory based or disk based, depending on the current state with respect to the threshold.
protected void thresholdReached() throws IOExceptionSwitches the underlying output stream from a memory based stream to one that is backed by disk. This is the point at which we realise that too much data is being written to keep in memory, so we elect to switch to disk-based storage.
public boolean isInMemory()Determines whether or not the data for this output stream has been retained in memory.
trueif the data is available in memory;
public byte getData()Returns 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
- The data for this output stream, or
nullif no such data is available.
public File getFile()Returns 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
- The file for this output stream, or
nullif no such file exists.