How to add number list in ppt using apache poi?

Numbered lists are not yet implemented in XSLF. But the underlying org.openxmlformats.schemas.drawingml.x2006.main.* classes are there. So one could use this classes.

But what and how?

All Office Open XML files are ZIP archives. So one can simply unzip a *.pptx file and have a look into the XML of /ppt/slides/slide1.xml. There one will find something like:

<a:p>
 <a:pPr marL="406400" indent="-406400">
  <a:buAutoNum type="arabicPeriod"/>
 </a:pPr>
 <a:r>
  <a:rPr sz="2200"/>
  <a:t>First list item</a:t>
  </a:r>
</a:p>

for a paragraph in a numbered list.

So the paragraph p contains a paragraph properties pPr element, having margin left set and a negative indent for the first text line (hanging indent). In pPr is a bullet auto number (sic) buAutoNum element having the type Arabic numbers followed by period arabicPeriod.

Unfortunately there is no API documentation for the org.openxmlformats.schemas.drawingml.x2006.main.* classes public available. So one would need getting the sources of ooxml-schemas or poi-ooxml-full to create the API documentation using javadoc.

Complete example:

import java.io.FileOutputStream;

import org.apache.poi.xslf.usermodel.*;
import org.apache.poi.sl.usermodel.*;

public class CreatePPTXNunberings {
    
 static void createBulletpointList(XSLFTextShape textShape, String[] items) {
  XSLFTextParagraph paragraph = null;
  XSLFTextRun run = null;
  double fontSize = 22d;
  double indent = 22d;
  for (String item : items) {
   paragraph = textShape.addNewTextParagraph();
   paragraph.setBullet(true); //XSLFTextParagraph.setBullet sets pPr too
   paragraph.getXmlObject().getPPr().setMarL(org.apache.poi.util.Units.toEMU(indent));
   paragraph.setIndent(-indent);
   run = paragraph.addNewTextRun();
   run.setFontSize(fontSize);
   run.setText(item);
  }   
 }
 
 static void createNumberedList(XSLFTextShape textShape, String[] items) {
  XSLFTextParagraph paragraph = null;
  XSLFTextRun run = null;
  double fontSize = 22d;
  double indent = 32d;
  for (String item : items) {
   paragraph = textShape.addNewTextParagraph();
   if (paragraph.getXmlObject().getPPr() == null) paragraph.getXmlObject().addNewPPr();
   if (paragraph.getXmlObject().getPPr().getBuAutoNum() == null) paragraph.getXmlObject().getPPr().addNewBuAutoNum();
   paragraph.getXmlObject().getPPr().getBuAutoNum().setType(org.openxmlformats.schemas.drawingml.x2006.main.STTextAutonumberScheme.ARABIC_PERIOD);
   paragraph.getXmlObject().getPPr().setMarL(org.apache.poi.util.Units.toEMU(indent));
   paragraph.setIndent(-indent);
   run = paragraph.addNewTextRun();
   run.setFontSize(fontSize);
   run.setText(item);
  }   
 }

 public static void main(String[] args) throws Exception {

  XMLSlideShow slideShow = new XMLSlideShow();
  
  XSLFSlide slide = slideShow.createSlide();
  
  XSLFTextShape textShape = slide.createAutoShape();
  java.awt.Rectangle rect = new java.awt.Rectangle(100, 100, 500, 300);
  textShape.setAnchor(rect.getBounds2D());
  textShape.setShapeType(ShapeType.RECT);

  XSLFTextParagraph paragraph = null;
  XSLFTextRun run = null;
  double fontSize = 22d;
  
  paragraph = textShape.addNewTextParagraph();
  run = paragraph.addNewTextRun();
  run.setFontSize(fontSize);
  run.setText("Following is a bullet point list:");
  
  createBulletpointList(textShape, 
   new String[]{"First list item", "Second list item, a little bit longer to show automatic line breaks", "Third list item"}
  );
  
  paragraph = textShape.addNewTextParagraph();
  
  paragraph = textShape.addNewTextParagraph();
  run = paragraph.addNewTextRun();
  run.setFontSize(fontSize);
  run.setText("Following is a numbered list:");
  
  createNumberedList(textShape, 
   new String[]{"First list item", "Second list item, a little bit longer to show automatic line breaks", "Third list item"}
  );

  FileOutputStream out = new FileOutputStream("./CreatePPTXNunberings.pptx");
  slideShow.write(out);
  out.close();
  slideShow.close();

 }
}

This code needs the full jar of all of the schemas, which is poi-ooxml-full-5.2.2.jar for apache poi 5.2.2, as mentioned in FAQ. Note, since apache poi 5.* the formerly used ooxml-schemas-*.jar cannot be used anymore. There must not be any ooxml-schemas-*.jar in class path when using apache poi 5.*.