org.jvnet.staxex.StreamingDataHandler Maven / Gradle / Ivy
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package org.jvnet.staxex;
import javax.activation.DataHandler;
import javax.activation.DataSource;
import java.io.BufferedInputStream;
import java.io.Closeable;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
/**
* {@link DataHandler} extended to offer better buffer management
* in a streaming environment.
*
*
* {@link DataHandler} is used commonly as a data format across
* multiple systems (such as JAXB/WS.) Unfortunately, {@link 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.
*
*
* {@link StreamingDataHandler} solves this problem by offering methods
* that enable faster bulk "consume once" read operation.
*
* @author Jitendra Kotamraju
*/
public abstract class StreamingDataHandler extends DataHandler implements Closeable {
public StreamingDataHandler(Object o, String s) {
super(o, s);
}
public StreamingDataHandler(URL url) {
super(url);
}
public StreamingDataHandler(DataSource dataSource) {
super(dataSource);
}
/**
* Works like {@link #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 {@link #getInputStream()} invocation nor
* {@link #readOnce()} invocation on this object (which would
* result in {@link IOException}.)
*
*
* When {@link 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 {@link #getInputStream()}
* multiple times and then call {@link #readOnce()} afterward.
* Streams created such a way can be read in any order —
* there's no requirement that streams created earlier must be read
* first.
*
* @return
* 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
* {@link BufferedInputStream}.
* @throws IOException
* if any i/o error
*/
public abstract InputStream readOnce() throws IOException;
/**
* 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
* {@link 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 calling {@link File#renameTo(File)}.
*
*
* This method shouldn't be called when there are any
* open streams.
*
*
* After this method is invoked, {@link #readOnce()} and
* {@link #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.
*/
public abstract void moveTo(File dst) throws IOException;
/**
* 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.
*/
public abstract void close() throws IOException;
}