我正在使用 javax.imageio 从 PNG 图像中提取元数据。这很好用。但获取实际元数据的 getAsTree 方法返回的 XML 无效。所以我不知道如何解析此 XML 以获得某些元数据:
run:
Format name: javax_imageio_png_1.0
<javax_imageio_png_1.0>
<IHDR width="256" height="256" bitDepth="8" colorType="RGBAlpha" compressionMethod="deflate" filterMethod="adaptive" interlaceMethod="none"/>
<cHRM whitePointX="31269" whitePointY="32899" redX="63999" redY="33001" greenX="30000" greenY="60000" blueX="15000" blueY="5999"/>
<gAMA value="45454"/>
<iTXt>
<iTXtEntry keyword="XML:com.adobe.xmp" compressionFlag="FALSE" compressionMethod="0" languageTag="" translatedKeyword="" text="<?xpacket begin="" id="W5M0MpCehiHzreSzNTczkc9d"?>
<x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="Adobe XMP Core 5.0-c061 64.140949, 2010/12/07-10:57:01 ">
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
<rdf:Description rdf:about=""
xmlns:xmp="http://ns.adobe.com/xap/1.0/"
xmlns:xmpMM="http://ns.adobe.com/xap/1.0/mm/"
xmlns:stEvt="http://ns.adobe.com/xap/1.0/sType/ResourceEvent#"
xmlns:lr="http://ns.adobe.com/lightroom/1.0/"
xmlns:dc="http://purl.org/dc/elements/1.1/"
xmp:MetadataDate="2012-12-05T21:36:19+01:00"
xmpMM:InstanceID="xmp.iid:EF7F11740720681192B08F682498C71D"
xmpMM:DocumentID="xmp.did:FC7F11740720681192B0AE5890E66CAE"
xmpMM:OriginalDocumentID="xmp.did:FC7F11740720681192B0AE5890E66CAE">
<xmpMM:History>
<rdf:Seq>
<rdf:li
stEvt:action="saved"
stEvt:instanceID="xmp.iid:FC7F11740720681192B0AE5890E66CAE"
stEvt:when="2012-12-04T00:23:34+01:00"
stEvt:changed="/metadata"/>
<rdf:li
stEvt:action="saved"
stEvt:instanceID="xmp.iid:EF7F11740720681192B08F682498C71D"
stEvt:when="2012-12-05T21:36:19+01:00"
stEvt:changed="/metadata"/>
</rdf:Seq>
</xmpMM:History>
<lr:hierarchicalSubject>
<rdf:Bag>
<rdf:li>Component|Software</rdf:li>
<rdf:li>Places|Paris</rdf:li>
<rdf:li>Product|Christensen</rdf:li>
<rdf:li>Product|Simba</rdf:li>
</rdf:Bag>
</lr:hierarchicalSubject>
<dc:subject>
<rdf:Bag>
<rdf:li>Christensen</rdf:li>
<rdf:li>Paris</rdf:li>
<rdf:li>Simba</rdf:li>
<rdf:li>Software</rdf:li>
</rdf:Bag>
</dc:subject>
</rdf:Description>
</rdf:RDF>
</x:xmpmeta>
<?xpacket end="r"?>"/>
</iTXt>
<pHYs pixelsPerUnitXAxis="2835" pixelsPerUnitYAxis="2835" unitSpecifier="meter"/>
</javax_imageio_png_1.0>
Format name: javax_imageio_1.0
<javax_imageio_1.0>
<Chroma>
<ColorSpaceType name="RGB"/>
<NumChannels value="4"/>
<Gamma value="0.45453998"/>
<BlackIsZero value="TRUE"/>
</Chroma>
<Compression>
<CompressionTypeName value="deflate"/>
<Lossless value="TRUE"/>
<NumProgressiveScans value="1"/>
</Compression>
<Data>
<PlanarConfiguration value="PixelInterleaved"/>
<SampleFormat value="UnsignedIntegral"/>
<BitsPerSample value="8 8 8 8"/>
</Data>
<Dimension>
<PixelAspectRatio value="1.0"/>
<ImageOrientation value="Normal"/>
<HorizontalPixelSize value="0.35273367"/>
<VerticalPixelSize value="0.35273367"/>
</Dimension>
<Text>
<TextEntry keyword="XML:com.adobe.xmp" value="<?xpacket begin="" id="W5M0MpCehiHzreSzNTczkc9d"?>
<x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="Adobe XMP Core 5.0-c061 64.140949, 2010/12/07-10:57:01 ">
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
<rdf:Description rdf:about=""
xmlns:xmp="http://ns.adobe.com/xap/1.0/"
xmlns:xmpMM="http://ns.adobe.com/xap/1.0/mm/"
xmlns:stEvt="http://ns.adobe.com/xap/1.0/sType/ResourceEvent#"
xmlns:lr="http://ns.adobe.com/lightroom/1.0/"
xmlns:dc="http://purl.org/dc/elements/1.1/"
xmp:MetadataDate="2012-12-05T21:36:19+01:00"
xmpMM:InstanceID="xmp.iid:EF7F11740720681192B08F682498C71D"
xmpMM:DocumentID="xmp.did:FC7F11740720681192B0AE5890E66CAE"
xmpMM:OriginalDocumentID="xmp.did:FC7F11740720681192B0AE5890E66CAE">
<xmpMM:History>
<rdf:Seq>
<rdf:li
stEvt:action="saved"
stEvt:instanceID="xmp.iid:FC7F11740720681192B0AE5890E66CAE"
stEvt:when="2012-12-04T00:23:34+01:00"
stEvt:changed="/metadata"/>
<rdf:li
stEvt:action="saved"
stEvt:instanceID="xmp.iid:EF7F11740720681192B08F682498C71D"
stEvt:when="2012-12-05T21:36:19+01:00"
stEvt:changed="/metadata"/>
</rdf:Seq>
</xmpMM:History>
<lr:hierarchicalSubject>
<rdf:Bag>
<rdf:li>Component|Software</rdf:li>
<rdf:li>Places|Paris</rdf:li>
<rdf:li>Product|Christensen</rdf:li>
<rdf:li>Product|Simba</rdf:li>
</rdf:Bag>
</lr:hierarchicalSubject>
<dc:subject>
<rdf:Bag>
<rdf:li>Christensen</rdf:li>
<rdf:li>Paris</rdf:li>
<rdf:li>Simba</rdf:li>
<rdf:li>Software</rdf:li>
</rdf:Bag>
</dc:subject>
</rdf:Description>
</rdf:RDF>
</x:xmpmeta>
<?xpacket end="r"?>" language="" compression="none"/>
</Text>
<Transparency>
<Alpha value="nonpremultipled"/>
</Transparency>
</javax_imageio_1.0>
BUILD SUCCESSFUL (total time: 3 seconds)
无效的 XML 从 iTXtEntry 元素开始，该元素具有 xpacket 位并包含子元素，尽管它具有自闭合标记格式，而不是结束标记。因此，当我尝试使用 DOM 文档和 xpath 解析它时，我收到一条错误消息，指出该元素的内容中不能包含“">”。
我已在 DocumentBuilderFactory 上禁用 DTD 验证。这没有帮助。我觉得我要使用正则表达式，但这似乎不对。为什么我首先从 imageio 中的 getAsTree 方法得到无效的 XML，对此我该怎么办？
最佳答案
你的问题是无意义的，因为IIOMetaData.getAsTree()返回一个DOM Node对象，它是Node树的根。这是 XML 的内存中表示形式。它不是从任何地方解析的，所以它不可能是无效的。 xml 文档字符串可能无效，但这里没有正在解析的字符串。 getAsTree 方法直接在内存中创建 XML。
问题在于您的输出生成了无效的 XML。无论从 getAsTree() 序列化您的节点，都是错误的。也就是说，它没有正确转义 text 属性的值，该属性本身就是一个 XML 文档字符串。
下面是一个完整的示例，演示了如何获取图像元数据并序列化为(有效的)XML 字符串。
import java.io.*;
import java.util.*;
// for imageio metadata
import javax.imageio.*;
import javax.imageio.stream.*;
import javax.imageio.metadata.*;
// for xml handling
import org.w3c.dom.*;
import javax.xml.transform.*;
import javax.xml.transform.dom.*;
import javax.xml.transform.stream.*;
public class imgmeta {
// Very lazy exception handling
// This is just a quick example
public static void main(String[] args) throws Exception {
String filename = args[0];
File file = new File(filename);
ImageInputStream imagestream = ImageIO.createImageInputStream(file);
// get a reader which is able to read this file
Iterator<ImageReader> readers = ImageIO.getImageReaders(imagestream);
ImageReader reader = readers.next();
// feed image to reader
reader.setInput(imagestream, true);
// get metadata of first image
IIOMetadata metadata = reader.getImageMetadata(0);
// get any metadata format name
// (you should prefer the native one, but not all images have one)
// String mdataname = metadata.getNativeMetadataFormatName(); // might be null
String[] mdatanames = metadata.getMetadataFormatNames();
String mdataname = mdatanames[0];
Node metadatadom = metadata.getAsTree(mdataname);
// metadatadom is now a DOM Node root of a DOM tree
// representing metadata in the image
// Since it's in-memory, it can't be "invalid"
// because it's already been parsed
// now let's serialize to an XML string
// javax.xml.transform.Transformer takes xml sources
// in one representation and transforms them to xml
// in another representation
// Representations include: DOM, JAXB, SAX, stream, etc
DOMSource source = new DOMSource(metadatadom);
StringWriter writer = new StringWriter();
StreamResult result = new StreamResult(writer);
Transformer transformer = TransformerFactory.newInstance().newTransformer();
transformer.transform(source, result);
// THIS is what you want:
String metadata_in_xml = writer.toString();
// now print it:
System.out.print(metadata_in_xml);
}
}
这是使用我周围的图像运行的测试输出:
$ java imgtest testimage.png | xmllint --format -
<?xml version="1.0" encoding="UTF-8"?>
<javax_imageio_png_1.0>
<IHDR width="149" height="237" bitDepth="8" colorType="RGBAlpha" compressionMethod="deflate" filterMethod="adaptive" interlaceMethod="none"/>
<iTXt>
<iTXtEntry keyword="XML:com.adobe.xmp" compressionFlag="0" compressionMethod="0" languageTag="" translatedKeyword="" text="<?xpacket begin="?" id="W5M0MpCehiHzreSzNTczkc9d"?> <x:xmpmeta xmlns:x="adobe:ns:meta/" x:xmptk="Adobe XMP Core 5.0-c061 64.140949, 2010/12/07-10:57:01 "> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"> <rdf:Description rdf:about="" xmlns:xmp="http://ns.adobe.com/xap/1.0/" xmlns:xmpMM="http://ns.adobe.com/xap/1.0/mm/" xmlns:stRef="http://ns.adobe.com/xap/1.0/sType/ResourceRef#" xmp:CreatorTool="Adobe Photoshop CS5.1 Macintosh" xmpMM:InstanceID="xmp.iid:D281E43D34DC11E2BFE69DA1E5D17E5F" xmpMM:DocumentID="xmp.did:D281E43E34DC11E2BFE69DA1E5D17E5F"> <xmpMM:DerivedFrom stRef:instanceID="xmp.iid:D281E43B34DC11E2BFE69DA1E5D17E5F" stRef:documentID="xmp.did:D281E43C34DC11E2BFE69DA1E5D17E5F"/> </rdf:Description> </rdf:RDF> </x:xmpmeta> <?xpacket end="r"?>"/>
</iTXt>
<tEXt>
<tEXtEntry keyword="Software" value="Adobe ImageReady"/>
</tEXt>
</javax_imageio_png_1.0>
生成的 XML 有效:
$ java imgmeta testimage.png | xmllint --noout -
$
(无输出表示有效。)
请注意 iTXtEntry 的 text 属性的值是如何转义的。如果要检索此属性内的数据，则需要检索字符串，然后将其解析为它自己的 XML 文档，以获取另一个 DOM(或其他)树。此属性:keyword="XML:com.adobe.xmp" 是一个信号，表明 text 属性的值是一个包含 XMP 数据的 XML 文档。
更新:解析 XMP 数据
下面是一些示例代码，演示了提取属性值并将其解析为 XML 和 DOM 树，以及从 XML 和 DOM 树解析属性值。
public class XMPExample {
public static String transformXML(Node xml) throws Exception {
StringWriter writer = new StringWriter();
Transformer transformer = TransformerFactory.newInstance().newTransformer();
transformer.transform(new DOMSource(xml), new StreamResult(writer));
return writer.toString();
}
public static Document transformXML(String xml) throws Exception {
StringReader reader = new StringReader(xml);
Document doc = DocumentBuilderFactory.newInstance().newDocumentBuilder().newDocument();
Transformer transformer = TransformerFactory.newInstance().newTransformer();
transformer.transform(new StreamSource(reader), new DOMResult(doc));
return doc;
}
public static String getXMP(Element metadata_dom) throws Exception {
// (Element) type because getElementsByTagName() method is required
// There are many more robust ways of selecting nodes
// (e.g. javax.xml.xpath), but this is for a simple example
// that only uses the native DOM methods
// This is very brittle because we're making assumptions about
// the metadata_dom structure. There are two sources of brittleness:
// 1. The metadata format from `metadata.getMetadataFormatNames()`.
// You should probably settle on a standard one you know will
// exist, like 'javax_imageio_1.0'
// 2. How the image stores the metadata. Usually XMP data will
// be in a text field with keyword 'XML:com.adobe.xmp', but
// I don't know that this is *always* the case.
// the code below assumes "javax_imageio_png_1.0" format
NodeList iTXtEntries = metadata_dom.getElementsByTagName("iTXtEntry");
Element iTXtEntry = null;
Element entry = null;
for (int i = 0; i < iTXtEntries.getLength(); i++) {
entry = (Element) iTXtEntries.item(i);
if (entry.getAttribute("keyword").equals("XML:com.adobe.xmp")) {
iTXtEntry = entry;
break;
}
}
if (iTXtEntry == null) {
return null;
}
String xmp_xml_doc = iTXtEntry.getAttribute("text");
return xmp_xml_doc;
}
}
// Use like so:
Node metadatanode = metadata.getAsTree(metadataname);
String xmp_xml = XMPExample.getXMP((Element) metadatanode);
// xmp_xml is now an xml document STRING
System.out.print(xmp_xml);
// If you want to parse it as an XML document, use an XML parser.
Document xmp_dom = XMPExample.transformXML(xmp_xml);
// ...and you can serialize it again when you are done.
String xmp_xml_roundtripped = XMPExample.transformXML(xmp_dom);
关于java - 当无效的 XML 时，如何在 java 中解析 XMP？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/13733787/