Class DeferredFileOutputStream
java.lang.Object
java.io.OutputStream
org.apache.tomcat.util.http.fileupload.ThresholdingOutputStream
org.apache.tomcat.util.http.fileupload.DeferredFileOutputStream
- All Implemented Interfaces:
Closeable
,Flushable
,AutoCloseable
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.
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).
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Constructor Summary
ConstructorDescriptionDeferredFileOutputStream
(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. -
Method Summary
Modifier and TypeMethodDescriptionvoid
close()
Closes underlying output stream, and mark this as closedbyte[]
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.protected OutputStream
Returns the current output stream.boolean
Determines whether or not the data for this output stream has been retained in memory.protected void
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
Methods inherited from class java.io.OutputStream
nullOutputStream
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Constructor Details
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DeferredFileOutputStream
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.
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Method Details
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getStream
Returns the current output stream. This may be memory based or disk based, depending on the current state with respect to the threshold.- Specified by:
getStream
in classThresholdingOutputStream
- Returns:
- The underlying output stream.
- Throws:
IOException
- if an error occurs.
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thresholdReached
Switches 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.- Specified by:
thresholdReached
in classThresholdingOutputStream
- Throws:
IOException
- if an error occurs.
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isInMemory
public boolean isInMemory()Determines 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.
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getData
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 returnsnull
.- Returns:
- The data for this output stream, or
null
if no such data is available.
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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
null
is returned.- Returns:
- The file for this output stream, or
null
if no such file exists.
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close
Closes underlying output stream, and mark this as closed- Specified by:
close
in interfaceAutoCloseable
- Specified by:
close
in interfaceCloseable
- Overrides:
close
in classThresholdingOutputStream
- Throws:
IOException
- if an error occurs.
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