Create a new Java project with Maven
Let's start by creating a new Java project, named pdf_utils, with Maven:
mvn archetype:generate \
-DgroupId=com.pdf.pdf_utils \
-DartifactId=pdf_utils \
-DarchetypeArtifactId=maven-archetype-quickstart \
-DarchetypeVersion=1.4 \
-DinteractiveMode=false
Then, open the pdf_utils/pom.xml file and add a dependency to PDFBox, in the dependencies section:
<dependencies>
...
<dependency>
<groupId>org.apache.pdfbox</groupId>
<artifactId>pdfbox</artifactId>
<version>2.0.27</version>
</dependency>
...
</dependencies>
Also change the target & source compiler versions:
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<configuration>
<source>17</source>
<target>17</target>
</configuration>
</plugin>
</plugins>
Then rename the generated src/main/java/com/pdf/pdf_utils/App.java class to PDFUtils
How to crop a PDF
We will now develop a Java function that crops each page within a PDF document and saves the cropped content in a new PDF file. The cropping coordinates, specified in millimeters, will serve as inputs to the function.
- Add helper functions to convert between mm <-> units
- Convert mm to units
- Extract the doc's file name
- Crop each page
- Save the result & append "-cropped" to the ouyput file's name
public String cropPDFMM(float x, float y, float width, float height, String srcFilePath) throws IOException {
// helper functions to convert between mm <-> units
Function<Float, Float> mmToUnits = (Float a) -> a / 0.352778f;
Function<Float, Float> unitsToMm = (Float a) -> a * 0.352778f;
// convert mm to units
float xUnits = mmToUnits.apply(x);
float yUnits = mmToUnits.apply(y);
float widthUnits = mmToUnits.apply(width);
float heightUnits = mmToUnits.apply(height);
// extract the doc's file name
File srcFile = new File(srcFilePath);
String fileName = srcFile.getName();
int dotIndex = fileName.lastIndexOf('.');
String fileNameWithoutExtension = (dotIndex == -1) ? fileName : fileName.substring(0, dotIndex);
// crop each page
PDDocument doc = PDDocument.load(srcFile);
int nrOfPages = doc.getNumberOfPages();
PDRectangle newBox = new PDRectangle(
xUnits,
yUnits,
widthUnits,
heightUnits);
for (int i = 0; i < nrOfPages; i++) {
doc.getPage(i).setCropBox(newBox);
}
// save the result & append -cropped to the file name
File outFile = new File(fileNameWithoutExtension + "-cropped.pdf");
doc.save(outFile);
doc.close();
return outFile.getCanonicalPath();
}
Let's test cropPDFMM by calling it from the main function:
public static void main( String[] args )
{
String srcFilePath = "/Users/user/.../file.pdf";
PDFUtils app = new PDFUtils();
try {
///// crop pdf
float x = 18f;
float y = 20f;
float width = 140f;
float height = 210f;
String resultFilePath = app.cropPDFMM(x, y, width, height, srcFilePath);
System.out.println( "Done!" );
} catch (Exception e) {
System.out.println(e);
}
}
You should see a file named file-cropped.pdf in the current directory.
How to remove pages from a PDF
To remove specific pages from a document, we can utilize an array of integer ranges. Each range consists of a start page and an end page ([startPage1, endPage1, startPage2, endPage2, ...]). The function iterates through each page of the document and checks if the page number falls outside of any of the specified ranges in the array. If a page is not within any range, it is appended to a new document.
- Add a helper function to test if a page is within a range
- Test each page number -> append it to a temp. doc
- Save the temp. doc. -> overwrite the input file
public void removePages(String srcFilePath, Integer[] pageRanges) throws IOException {
// a helper function to test if a page is within a range
BiPredicate<Integer, Integer[]> pageInInterval = (Integer page, Integer[] allPages) -> {
for (int j = 0; j < allPages.length; j+=2) {
int startPage = allPages[j];
int endPage = allPages[j+1];
if (page >= startPage-1 && page < endPage) {
return true;
}
}
return false;
};
File srcFile = new File(srcFilePath);
PDDocument pdfDocument = PDDocument.load(srcFile);
PDDocument tmpDoc = new PDDocument();
// test if a page is within a range
// if not, append the page to a temp. doc.
for (int i = 0; i < pdfDocument.getNumberOfPages(); i++) {
if (pageInInterval.test(i, pageRanges)) {
continue;
}
tmpDoc.addPage(pdfDocument.getPage(i));
}
// save the temporary doc.
tmpDoc.save(new File(srcFilePath));
tmpDoc.close();
pdfDocument.close();
}
Let's test it by calling removePages in the main function:
///// remove pages
app.removePages(resultFilePath, new Integer[] {1, 21, 376, 428});
It will overwrite the input (cropped) file.
How to split a PDF
We will now introduce a function that enables the splitting of a PDF into multiple separate PDFs, with each resulting file containing a specified number of pages. The function expects two inputs: the path to the source PDF document and the desired number of pages in each split file.
- Extract source file's name
- for each nrOfPages
- append them to a temporary document
- save the temp doc with the source file's name + index
public void splitPDF(String srcFilePath, int nrOfPages) throws IOException {
// extract file's name
File srcFile = new File(srcFilePath);
String fileName = srcFile.getName();
int dotIndex = fileName.lastIndexOf('.');
String fileNameWithoutExtension = (dotIndex == -1) ? fileName : fileName.substring(0, dotIndex);
PDDocument pdfDocument = PDDocument.load(srcFile);
// extract every nrOfPages to a temporary document
// append an index to its name and save it
for (int i = 1; i < pdfDocument.getNumberOfPages(); i+=nrOfPages) {
Splitter splitter = new Splitter();
int fromPage = i;
int toPage = i+nrOfPages;
splitter.setStartPage(fromPage);
splitter.setEndPage(toPage);
splitter.setSplitAtPage(toPage - fromPage );
List<PDDocument> lst = splitter.split(pdfDocument);
PDDocument pdfDocPartial = lst.get(0);
File f = new File(fileNameWithoutExtension + "-" + i + ".pdf");
pdfDocPartial.save(f);
pdfDocPartial.close();
}
pdfDocument.close();
}
Here is the full main() function:
public static void main( String[] args ){
String srcFilePath = "/Users/user/pdfs/file.pdf";
PDFUtils app = new PDFUtils();
try {
///// crop pdf
float x = 18f;
float y = 20f;
float width = 140f;
float height = 210f;
String resultFilePath = app.cropPDFMM(x, y, width, height, srcFilePath);
///// remove pages
app.removePages(resultFilePath, new Integer[] {1, 21, 376, 428});
///// split pages
app.splitPDF(resultFilePath, 20);
System.out.println( "Done!" );
} catch (Exception e) {
System.out.println(e);
}
}
Merge 2 pages per sheet (2up)
This function is inspired from https://stackoverflow.com/questions/12093408/pdfbox-merge-2-portrait-pages-onto-a-single-side-by-side-landscape-page.
- Create a temporary document
- Iterate over the pages of the original doc. -> get the left & right pages
- Create a new "output" page with the right dimensions
- Append the left page at (0,0)
- Append the right page, translated to (left page's width, 0)
- Save the temp. doc -> overwrite the source file
public void mergePages(String srcFilePath) throws IOException {
// SOURCE: https://stackoverflow.com/questions/12093408/pdfbox-merge-2-portrait-pages-onto-a-single-side-by-side-landscape-page
File srcFile = new File(srcFilePath);
PDDocument pdfDocument = PDDocument.load(srcFile);
PDDocument outPdf = new PDDocument();
for (int i = 0; i < pdfDocument.getNumberOfPages(); i+=2) {
PDPage page1 = pdfDocument.getPage(i);
PDPage page2 = pdfDocument.getPage(i+1);
PDRectangle pdf1Frame = page1.getCropBox();
PDRectangle pdf2Frame = page2.getCropBox();
PDRectangle outPdfFrame = new PDRectangle(pdf1Frame.getWidth()+pdf2Frame.getWidth(), Math.max(pdf1Frame.getHeight(), pdf2Frame.getHeight()));
// Create output page with calculated frame and add it to the document
COSDictionary dict = new COSDictionary();
dict.setItem(COSName.TYPE, COSName.PAGE);
dict.setItem(COSName.MEDIA_BOX, outPdfFrame);
dict.setItem(COSName.CROP_BOX, outPdfFrame);
dict.setItem(COSName.ART_BOX, outPdfFrame);
PDPage newP = new PDPage(dict);
outPdf.addPage(newP);
// Source PDF pages has to be imported as form XObjects to be able to insert them at a specific point in the output page
LayerUtility layerUtility = new LayerUtility(outPdf);
PDFormXObject formPdf1 = layerUtility.importPageAsForm(pdfDocument, page1);
PDFormXObject formPdf2 = layerUtility.importPageAsForm(pdfDocument, page2);
AffineTransform afLeft = new AffineTransform();
layerUtility.appendFormAsLayer(newP, formPdf1, afLeft, "left" + i);
AffineTransform afRight = AffineTransform.getTranslateInstance(pdf1Frame.getWidth(), 0.0);
layerUtility.appendFormAsLayer(newP, formPdf2, afRight, "right" + i);
}
outPdf.save(srcFile);
outPdf.close();
pdfDocument.close();
}
Update main() to test it:
...
///// 2 pages per sheet
app.mergePages(resultFilePath);
...
Here is the full list of imports:
package com.pdf.pdf_utils;
import org.apache.pdfbox.cos.COSDictionary;
import org.apache.pdfbox.cos.COSName;
import org.apache.pdfbox.multipdf.LayerUtility;
import org.apache.pdfbox.multipdf.Splitter;
import org.apache.pdfbox.pdmodel.PDDocument;
import org.apache.pdfbox.pdmodel.PDPage;
import org.apache.pdfbox.pdmodel.common.PDRectangle;
import org.apache.pdfbox.pdmodel.graphics.form.PDFormXObject;
import java.awt.geom.AffineTransform;
import java.io.File;
import java.io.IOException;
import java.util.List;
import java.util.function.BiPredicate;
import java.util.function.Function;
The source code is available here.
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