Class StreamingDataHandler
- All Implemented Interfaces:
Transferable
,Closeable
,AutoCloseable
- Direct Known Subclasses:
StreamingDataHandler
DataHandler
extended to offer better buffer management
in a streaming environment.
DataHandler
is used commonly as a data format across
multiple systems (such as JAXB/WS.) Unfortunately, DataHandler
has the semantics of "read as many times as you want", so this makes
it difficult for involving parties to handle a BLOB in a streaming fashion.
StreamingDataHandler
solves this problem by offering methods
that enable faster bulk "consume once" read operation.
- Author:
- Jitendra Kotamraju
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Constructor Summary
ConstructorDescriptionStreamingDataHandler
(Object o, String s) StreamingDataHandler
(URL url) StreamingDataHandler
(javax.activation.DataSource dataSource) -
Method Summary
Modifier and TypeMethodDescriptionabstract void
close()
Releases any resources associated with this DataHandler.abstract void
Obtains the BLOB into a specified file.abstract InputStream
readOnce()
Works likeDataHandler.getInputStream()
except that this method can be invoked only once.void
setHrefCid
(String cid) Methods inherited from class javax.activation.DataHandler
getAllCommands, getBean, getCommand, getContent, getContentType, getDataSource, getInputStream, getName, getOutputStream, getPreferredCommands, getTransferData, getTransferDataFlavors, isDataFlavorSupported, setCommandMap, setDataContentHandlerFactory, writeTo
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Constructor Details
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StreamingDataHandler
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StreamingDataHandler
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StreamingDataHandler
public StreamingDataHandler(javax.activation.DataSource dataSource)
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Method Details
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readOnce
Works likeDataHandler.getInputStream()
except that this method can be invoked only once.This is used as a signal from the caller that there will be no further
DataHandler.getInputStream()
invocation norreadOnce()
invocation on this object (which would result inIOException
.)When
DataHandler
is backed by a streaming BLOB (such as an attachment in a web service read from the network), this allows the callee to avoid unnecessary buffering.Note that it is legal to call
DataHandler.getInputStream()
multiple times and then callreadOnce()
afterward. Streams created such a way can be read in any order — there's no requirement that streams created earlier must be read first.- Returns:
- always non-null. Represents the content of this BLOB.
The returned stream is generally not buffered, so for
better performance read in a big batch or wrap this into
BufferedInputStream
. - Throws:
IOException
- if any i/o error
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moveTo
Obtains the BLOB into a specified file.Semantically, this method is roughly equivalent to the following code, except that the actual implementation is likely to be a lot faster.
InputStream i = getInputStream(); OutputStream o = new FileOutputStream(dst); int ch; while((ch=i.read())!=-1) o.write(ch); i.close(); o.close();
The main motivation behind this method is that often
DataHandler
that reads data from a streaming source will use a temporary file as a data store to hold data (think of commons-fileupload.) In such case this method can be as fast as callingFile.renameTo(File)
.This method shouldn't be called when there are any open streams.
After this method is invoked,
readOnce()
andDataHandler.getInputStream()
will simply open the destination file you've specified as an argument. So if you further move the file or delete this file, those methods will behave in undefined fashion. For a simliar reason, calling this method multiple times will cause undefined behavior.- Throws:
IOException
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close
Releases any resources associated with this DataHandler. (such as an attachment in a web service read from a temp file will be deleted.) After calling this method, it is illegal to call any other methods.- Specified by:
close
in interfaceAutoCloseable
- Specified by:
close
in interfaceCloseable
- Throws:
IOException
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getHrefCid
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setHrefCid
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