PDF 页面的缩略图 (Java)
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时间：2020-08-14 16:55:33 来源:igfitidea点击:
Thumbnail of a PDF page (Java)
提问by Tony the Pony
How can I generate a thumbnail image of pages in a PDF document, using Java?
如何使用 Java 生成 PDF 文档中页面的缩略图？
采纳答案by dstarh
I think http://pdfbox.apache.org/will do what you're looking for since you can create an image from a page and then scale the image
我认为http://pdfbox.apache.org/ 可以满足您的需求，因为您可以从页面创建图像，然后缩放图像
From their example code -
从他们的示例代码 -
/*
* 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.
*/
package org.apache.pdfbox;
import java.awt.HeadlessException;
import java.awt.Toolkit;
import java.awt.image.BufferedImage;
import javax.imageio.ImageIO;
import java.util.List;
import org.apache.pdfbox.exceptions.InvalidPasswordException;
import org.apache.pdfbox.pdmodel.PDDocument;
import org.apache.pdfbox.pdmodel.PDPage;
import org.apache.pdfbox.pdmodel.common.PDRectangle;
import org.apache.pdfbox.util.PDFImageWriter;
/**
* Convert a PDF document to an image.
*
* @author <a href="[email protected]">Ben Litchfield</a>
* @version $Revision: 1.6 $
*/
public class PDFToImage
{
private static final String PASSWORD = "-password";
private static final String START_PAGE = "-startPage";
private static final String END_PAGE = "-endPage";
private static final String IMAGE_FORMAT = "-imageType";
private static final String OUTPUT_PREFIX = "-outputPrefix";
private static final String COLOR = "-color";
private static final String RESOLUTION = "-resolution";
private static final String CROPBOX = "-cropbox";
/**
* private constructor.
*/
private PDFToImage()
{
//static class
}
/**
* Infamous main method.
*
* @param args Command line arguments, should be one and a reference to a file.
*
* @throws Exception If there is an error parsing the document.
*/
public static void main( String[] args ) throws Exception
{
String password = "";
String pdfFile = null;
String outputPrefix = null;
String imageFormat = "jpg";
int startPage = 1;
int endPage = Integer.MAX_VALUE;
String color = "rgb";
int resolution;
float cropBoxLowerLeftX = 0;
float cropBoxLowerLeftY = 0;
float cropBoxUpperRightX = 0;
float cropBoxUpperRightY = 0;
try
{
resolution = Toolkit.getDefaultToolkit().getScreenResolution();
}
catch( HeadlessException e )
{
resolution = 96;
}
for( int i = 0; i < args.length; i++ )
{
if( args[i].equals( PASSWORD ) )
{
i++;
if( i >= args.length )
{
usage();
}
password = args[i];
}
else if( args[i].equals( START_PAGE ) )
{
i++;
if( i >= args.length )
{
usage();
}
startPage = Integer.parseInt( args[i] );
}
else if( args[i].equals( END_PAGE ) )
{
i++;
if( i >= args.length )
{
usage();
}
endPage = Integer.parseInt( args[i] );
}
else if( args[i].equals( IMAGE_FORMAT ) )
{
i++;
imageFormat = args[i];
}
else if( args[i].equals( OUTPUT_PREFIX ) )
{
i++;
outputPrefix = args[i];
}
else if( args[i].equals( COLOR ) )
{
i++;
color = args[i];
}
else if( args[i].equals( RESOLUTION ) )
{
i++;
resolution = Integer.parseInt(args[i]);
}
else if( args[i].equals( CROPBOX ) )
{
i++;
cropBoxLowerLeftX = Float.valueOf(args[i]).floatValue();
i++;
cropBoxLowerLeftY = Float.valueOf(args[i]).floatValue();
i++;
cropBoxUpperRightX = Float.valueOf(args[i]).floatValue();
i++;
cropBoxUpperRightY = Float.valueOf(args[i]).floatValue();
}
else
{
if( pdfFile == null )
{
pdfFile = args[i];
}
}
}
if( pdfFile == null )
{
usage();
}
else
{
if(outputPrefix == null)
{
outputPrefix = pdfFile.substring( 0, pdfFile.lastIndexOf( '.' ));
}
PDDocument document = null;
try
{
document = PDDocument.load( pdfFile );
//document.print();
if( document.isEncrypted() )
{
try
{
document.decrypt( password );
}
catch( InvalidPasswordException e )
{
if( args.length == 4 )//they supplied the wrong password
{
System.err.println( "Error: The supplied password is incorrect." );
System.exit( 2 );
}
else
{
//they didn't supply a password and the default of "" was wrong.
System.err.println( "Error: The document is encrypted." );
usage();
}
}
}
int imageType = 24;
if ("bilevel".equalsIgnoreCase(color))
{
imageType = BufferedImage.TYPE_BYTE_BINARY;
}
else if ("indexed".equalsIgnoreCase(color))
{
imageType = BufferedImage.TYPE_BYTE_INDEXED;
}
else if ("gray".equalsIgnoreCase(color))
{
imageType = BufferedImage.TYPE_BYTE_GRAY;
}
else if ("rgb".equalsIgnoreCase(color))
{
imageType = BufferedImage.TYPE_INT_RGB;
}
else if ("rgba".equalsIgnoreCase(color))
{
imageType = BufferedImage.TYPE_INT_ARGB;
}
else
{
System.err.println( "Error: the number of bits per pixel must be 1, 8 or 24." );
System.exit( 2 );
}
//si une cropBox a ete specifier, appeler la methode de modification de cropbox
//changeCropBoxes(PDDocument document,float a, float b, float c,float d)
if ( cropBoxLowerLeftX!=0 || cropBoxLowerLeftY!=0 || cropBoxUpperRightX!=0 || cropBoxUpperRightY!=0 )
{
changeCropBoxes(document,cropBoxLowerLeftX, cropBoxLowerLeftY, cropBoxUpperRightX, cropBoxUpperRightY);
}
//Make the call
PDFImageWriter imageWriter = new PDFImageWriter();
boolean success = imageWriter.writeImage(document, imageFormat, password,
startPage, endPage, outputPrefix, imageType, resolution);
if (!success)
{
System.err.println( "Error: no writer found for image format '"
+ imageFormat + "'" );
System.exit(1);
}
}
catch (Exception e)
{
System.err.println(e);
}
finally
{
if( document != null )
{
document.close();
}
}
}
}
/**
* This will print the usage requirements and exit.
*/
private static void usage()
{
System.err.println( "Usage: java org.apache.pdfbox.PDFToImage [OPTIONS] <PDF file>\n" +
" -password <password> Password to decrypt document\n" +
" -imageType <image type> (" + getImageFormats() + ")\n" +
" -outputPrefix <output prefix> Filename prefix for image files\n" +
" -startPage <number> The first page to start extraction(1 based)\n" +
" -endPage <number> The last page to extract(inclusive)\n" +
" -color <string> The color depth (valid: bilevel, indexed, gray, rgb, rgba)\n" +
" -resolution <number> The bitmap resolution in dpi\n" +
" -cropbox <number> <number> <number> <number> The page area to export\n" +
" <PDF file> The PDF document to use\n"
);
System.exit( 1 );
}
private static String getImageFormats()
{
StringBuffer retval = new StringBuffer();
String[] formats = ImageIO.getReaderFormatNames();
for( int i = 0; i < formats.length; i++ )
{
retval.append( formats[i] );
if( i + 1 < formats.length )
{
retval.append( "," );
}
}
return retval.toString();
}
private static void changeCropBoxes(PDDocument document,float a, float b, float c,float d)
{
List pages = document.getDocumentCatalog().getAllPages();
for( int i = 0; i < pages.size(); i++ )
{
System.out.println("resizing page");
PDPage page = (PDPage)pages.get( i );
PDRectangle rectangle = new PDRectangle();
rectangle.setLowerLeftX(a);
rectangle.setLowerLeftY(b);
rectangle.setUpperRightX(c);
rectangle.setUpperRightY(d);
page.setMediaBox(rectangle);
page.setCropBox(rectangle);
}
}
}
回答by mark stephens
You could also have a look at JPedal (details at http://www.jpedal.org/pdf_thumbnail.php)
你也可以看看 JPedal（详情见http://www.jpedal.org/pdf_thumbnail.php）
回答by Reverend Gonzo
IcePdf is the best that I've seen (that's free) for reading pdfs. JPedal is awesome, but not free.
IcePdf 是我见过的最好的（免费的）阅读 pdf 文件。JPedal 很棒，但不是免费的。
If you're going to be generating images from pdfs that the general public can send you, I assure you (from experience) that you'll get pdfs that will crash the JVM. (ie: If they're many-layered pdfs with all vector graphics). This pdfis an example that will crash many libraries (but is a perfectly valid PDF without anything funny like Javascript, etc).
如果您要从公众可以发送给您的 pdf 生成图像，我向您保证（根据经验）您将获得会使 JVM 崩溃的 pdf。（即：如果它们是带有所有矢量图形的多层 pdf）。这个 pdf是一个会导致许多库崩溃的例子（但它是一个完全有效的 PDF，没有任何有趣的东西，比如 Javascript 等）。
We've gone down the route of trying to use a multitude of libraries and eventually resorting to delegating the work of creating a thumbnail to ImageMagick, which is a highly optimized C program for image manipulation.
我们已经尝试使用大量库，并最终将创建缩略图的工作委托给 ImageMagick，这是一个高度优化的用于图像处理的 C 程序。
