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/*
 * Copyright (c) 2010, 2018 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Distribution License v. 1.0, which is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

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 { private String hrefCid; 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; public String getHrefCid() { return hrefCid; } public void setHrefCid(final String cid) { this.hrefCid = cid; } }





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