PdfPageEventHelper implements PdfPageEvent in Java

Encoder Quick Response Code in Java PdfPageEventHelper implements PdfPageEvent

years.put(text, count + 1); } } }

Instead of B, you could have written GenericTags implements PdfPageEvent, but then you d need to implement all the methods defined in the PdfPageEvent interface. Here you re only interested in the onGenericTag() method, so it s easier to extend the PdfPageEventHelper class. This class contains nothing but empty implementations of the interface s methods. In this example, you override one specific method, and you can safely ignore the other methods. The code in listing 5.8 won t be executed unless you declare the event to a writer. The onGenericTag() method will never be invoked if you don t define generic tags for Chunks.

Listing 5.9 MovieYears.java (continued)

Document document = new Document(); PdfWriter writer = PdfWriter.getInstance( Creates instance document, new FileOutputStream(filename)); of event GenericTags event = new GenericTags(); writer.setPageEvent(event); Declares event ... to writer document.open(); ... Paragraph p; Chunk c; ... p = new Paragraph(22); c = new Chunk(String.format("%d ", movie.getYear()), bold); Sets strip c.setGenericTag("strip"); as generic tag p.add(c); c = new Chunk(movie.getMovieTitle()); Sets year as c.setGenericTag(String.valueOf(movie.getYear())); generic tag p.add(c); c = new Chunk( String.format(" (%d minutes) ", movie.getDuration()), italic); p.add(c); c = new Chunk("IMDB", white); Sets ellipse c.setAnchor("http://www.imdb.com/title/tt" + movie.getImdb()); as generic tag c.setGenericTag("ellipse"); p.add(c); document.add(p); ... document.close();

Before we study the mechanisms used in this code, let s look at the parameters passed to the onGenericTag() method:

writer The PdfWriter object to which the event is added. pdfDocument Not the Document object to which the Paragraph is added. This is a PdfDocument that is created internally when you create a PdfWriter instance.

Use this object just for read-only purposes!

In listing 5.9 you re tagging the Chunks representing the year with a generic tag named strip . When the content is written to the page, the onGenericTag() method is invoked. In the page event implementation, the onGenericTag() method looks at the text, and calls the strip() method to draw a filmstrip over the year.

If a Chunk is split over multiple lines, the onGenericTag() method will be invoked as many times as there are lines. Every line will have its own Rectangle.

The same happens for the IMDB links: the text ellipse corresponds with the ellipse() method. You re using this page event to achieve more or less the same goals as with table and cell events: to add special shapes. But there s more. In listing 5.8, you ll also find a countYear() method. This method is invoked because you re setting the year as a generic tag for the movie titles. A list of these years and the number of times each year occurs is kept in the member variable years. Here is what you can do with this TreeMap.

Listing 5.10 MovieYears.java (continued)

document.newPage(); writer.setPageEvent(null); for (Map.Entry entry : event.years.entrySet()) { p = new Paragraph(String.format("%s: %d movie(s)", entry.getKey(), entry.getValue())); document.add(p); }

You start a new page and remove the page events from the writer by setting the page events to null. You don t want any of the page events to be active, and figure 5.5 shows that GenericTags wasn t the only event used in this example you also used a Paragraph event to draw extra lines. You don t want these lines to appear when you create an overview of the years for which you have a film in the database, along with the number of times each year occurs. This overview is shown in figure 5.6. Listing 5.9 was far from complete the lines in figure 5.5 were added using another type of page event. The following line actually came right after GenericTags was set:

writer.setPageEvent(new ParagraphPositions()); Figure 5.6 Counting movies using the generic tag functionality