Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ /* $Id: XMPPacketParser.java 750418 2009-03-05 11:03:54Z vhennebert $ */ package org.apache.xmlgraphics.xmp; import java.io.ByteArrayInputStream; import java.io.IOException; import java.io.InputStream; import java.io.OutputStream; import java.io.UnsupportedEncodingException; import javax.xml.transform.TransformerException; import javax.xml.transform.stream.StreamSource; import org.apache.commons.io.output.ByteArrayOutputStream; /** * This class is a parser for XMP packets. By default, it tries to locate the first XMP packet * it finds and parses it. * <p> * Important: Before you use this class to look for an XMP packet in some random file, please read * the chapter on "Scanning Files for XMP Packets" in the XMP specification! */ public class XMPPacketParser { private static final byte[] PACKET_HEADER; private static final byte[] PACKET_HEADER_END; private static final byte[] PACKET_TRAILER; static { try { PACKET_HEADER = "<?xpacket begin=".getBytes("US-ASCII"); PACKET_HEADER_END = "?>".getBytes("US-ASCII"); PACKET_TRAILER = "<?xpacket".getBytes("US-ASCII"); } catch (UnsupportedEncodingException e) { throw new RuntimeException("Incompatible JVM! US-ASCII encoding not supported."); } } /** * Locates an XMP packet in a stream, parses it and returns the XMP metadata. If no * XMP packet is found until the stream ends, null is returned. Note: This method * only finds the first XMP packet in a stream. And it cannot determine whether it * has found the right XMP packet if there are multiple packets. * @param in the InputStream to search * @return the parsed XMP metadata or null if no XMP packet is found * @throws IOException if an I/O error occurs * @throws TransformerException if an error occurs while parsing the XMP packet */ public static Metadata parse(InputStream in) throws IOException, TransformerException { if (!in.markSupported()) { in = new java.io.BufferedInputStream(in); } boolean foundXMP = skipAfter(in, PACKET_HEADER); if (!foundXMP) { return null; } //TODO Inspect "begin" attribute! if (!skipAfter(in, PACKET_HEADER_END)) { throw new IOException("Invalid XMP packet header!"); } //TODO think about not buffering this but for example, parse in another thread //ex. using PipedInput/OutputStream ByteArrayOutputStream baout = new ByteArrayOutputStream(); //TODO Do with TeeInputStream when Commons IO 1.4 is available if (!skipAfter(in, PACKET_TRAILER, baout)) { throw new IOException("XMP packet not properly terminated!"); } Metadata metadata = XMPParser.parseXMP(new StreamSource(new ByteArrayInputStream(baout.toByteArray()))); return metadata; } private static boolean skipAfter(InputStream in, byte[] match) throws IOException { return skipAfter(in, match, null); } private static boolean skipAfter(InputStream in, byte[] match, OutputStream out) throws IOException { int found = 0; int len = match.length; int b; while ((b = in.read()) >= 0) { if (b == match[found]) { found++; if (found == len) { return true; } } else { if (out != null) { if (found > 0) { out.write(match, 0, found); } out.write(b); } found = 0; } } return false; } }