iText - Choosing a Writer

Allegedly there are several classes derived from the abstract DocWriter class which can be used for different kinds of output files - pdf, rtf and html. However, using iText 5.0.2 it seems that both the .rft and the .html options have been removed. So let's focus on pdf creation for now.

You can either write a document to file, memory or the output stream (e.g. stdout).

Document document = new Document();

// write to file

PdfWriter.getInstance(document, new FileOutputStream("Output.pdf");

//write to memory

ByteArrayOutputStream buffer = new ByteArrayOutputStream();

PdfWriter.getInstance(document, buffer);

//write to System.out

PdfWriter.getInstance(document, System.out);

Note that when using the file output or System.out the document is outputted directly but with the ByteArrayOutputStream it is buffered for use at a later date. To retrieve it, the reader needs to be passed the ByteArrayOutputStream cast as a ByteArray.

//read from memory

PdfReader reader = new PdfReader(buffer.toByteArray());

This is extremely useful when you need to do multiple passes on a pdf document. For example, you may want to read in multiple pdfs and write page numbers for the new combined document on each page. The pdfs can be read in, merged together and stored in memory then the whole new document can be manipulated and annotated. This saves writing an intermediary file to disk.

In-depth iText information can be found in Bruno Lowagie's excellent book iText In Action http://www.manning.com/lowagie2/