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 * This code is distributed in the hope that it will be useful, but WITHOUT

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 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

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package com.sun.xml.internal.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.

 *

 * <p>

 * {@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.

 *

 * <p>

 * {@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.

     *

     * <p>

     * 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}.)

     *

     * <p>

     * 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.

     *

     * <p>

     * 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.

     *

     * <p>

     * Semantically, this method is roughly equivalent to the following

     * code, except that the actual implementation is likely to be a lot faster.

     *

     * <pre>

     * InputStream i = getInputStream();

     * OutputStream o = new FileOutputStream(dst);

     * int ch;

     * while((ch=i.read())!=-1)  o.write(ch);

     * i.close();

     * o.close();

     * </pre>

     *

     * <p>

     * 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)}.

     *

     * <p>

     * This method shouldn't be called when there are any

     * open streams.

     *

     * <p>

     * 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;

}