所谓图片元数据，就是除了我们肉眼看到的图片内容外，隐藏在这些内容背后的一些技术数据。
本文介绍如何使用Java代码将一张图片的隐藏信息读取出来。
首先不需要下载任何额外的Java库，用JDK自带的库就能工作。
import java.io.ByteArrayInputStream;import java.io.File;import java.io.FileInputStream;import java.io.IOException;import javax.imageio.ImageIO;import javax.imageio.ImageReader;import javax.imageio.metadata.IIOMetadata;import javax.imageio.metadata.IIOMetadataNode;import org.w3c.dom.NamedNodeMap;import org.w3c.dom.Node;import org.w3c.dom.NodeList;import com.sun.imageio.plugins.png.PNGMetadata;新建一个Java类，这个类的main方法也是非常直接的：static public void main(String[] arg) throws IOException{byte[] content = getContent("C:\Users\i042416\Desktop\test\clipboard1.png");readCustomData(content);}首先把桌面上名叫clipboard1.png的图片文件的内容读到字节数组content中。
getContent方法的代码：
一张png图片的元数据，散布在下面这些节点里：
printNode(pngmeta.getStandardChromaNode());printNode(pngmeta.getStandardCompressionNode());printNode(pngmeta.getStandardDataNode());printNode(pngmeta.getStandardDimensionNode());printNode(pngmeta.getStandardDocumentNode());printNode(pngmeta.getStandardTextNode());printNode(pngmeta.getStandardTransparencyNode());通过printNode打印出来：
printNode方法的源代码：
打印出来的元数据：
如果大家想要复制粘贴，这是全部的源代码：
package image;import java.io.ByteArrayInputStream;import java.io.File;import java.io.FileInputStream;import java.io.IOException;import javax.imageio.ImageIO;import javax.imageio.ImageReader;import javax.imageio.metadata.IIOMetadata;import javax.imageio.metadata.IIOMetadataNode;import org.w3c.dom.NamedNodeMap;import org.w3c.dom.Node;import org.w3c.dom.NodeList;import com.sun.imageio.plugins.png.PNGMetadata;public class pngTest {static private byte[] getContent(String filePath) throws IOException {File file = new File(filePath);long fileSize = file.length();if (fileSize > Integer.MAX_VALUE) {System.out.println("file too big...");return null;}FileInputStream fi = new FileInputStream(file);byte[] buffer = new byte[(int) fileSize];int offset = 0;int numRead = 0;while (offset < buffer.length&& (numRead = fi.read(buffer, offset, buffer.length - offset)) >= 0) {offset += numRead;}if (offset != buffer.length) {fi.close();throw new IOException("Could not completely read file "+ file.getName());}fi.close();return buffer;}static private void readCustomData(byte[] imageData) throws IOException{ImageReader imageReader = ImageIO.getImageReadersByFormatName("png").next();imageReader.setInput(ImageIO.createImageInputStream(new ByteArrayInputStream(imageData)), true);IIOMetadata metadata = imageReader.getImageMetadata(0);PNGMetadata pngmeta = (PNGMetadata) metadata;printNode(pngmeta.getStandardChromaNode());printNode(pngmeta.getStandardCompressionNode());printNode(pngmeta.getStandardDataNode());printNode(pngmeta.getStandardDimensionNode());printNode(pngmeta.getStandardDocumentNode());printNode(pngmeta.getStandardTextNode());printNode(pngmeta.getStandardTransparencyNode());}static private void printNode(IIOMetadataNode metanode){if (metanode == null)return;NodeList childNodes = metanode.getChildNodes();if( childNodes == null)return;for (int i = 0; i < childNodes.getLength(); i++) {Node node = childNodes.item(i);NamedNodeMap attribute = node.getAttributes();if( attribute == null)continue;int length = attribute.getLength();for( int j = 0; j < length; j++){Node each = attribute.item(j);String value = each.getNodeValue();String name = each.getNodeName();System.out.println("Name: " + name + " value: " + value);}}}static public void main(String[] arg) throws IOException{byte[] content = getContent("C:\Users\i042416\Desktop\test\clipboard1.png");readCustomData(content);}}要获取更多Jerry的原创文章，请关注公众号"汪子熙":
