PDF Page re-ordering using itext

Question

i am using itext pdf library. can any one know how can i move pages in existing pdf? Actually i want to move few last pages at beginning of file. It is something like below but i don't understand how it work. ``` reader = new PdfReader(baos.toByteArray()); n = reader.getNumberOfPages(); reader.selectPages(String.format("%d, 1-%d", n, n-1)); PdfStamper stamper = new PdfStamper(reader, new FileOutputStream(filename)); stamper.close(); ``` Can any one explain in detail?

Accepted Answer

The `selectPages()` method is explained in chapter 6 of my book (see page 164). In the context of code snippet 6.3 and 6.11, it is used to reduce the number of pages being read by `PdfReader` for consumption by `PdfStamper` or `PdfCopy`. However, it can also be used to reorder pages. First allow me to explain the syntax.

There are different flavors of the `selectPages()` method:

You can pass a `List<Integer>` containing all the page numbers you want to keep. This list can consist of increasing page numbers, 1, 2, 3, 4,... If you change the order, for instance: 1, 3, 2, 4,... `PdfReader` will serve the pages in that changed order.

You can also pass a String (which is what is done in your snippet) using the following syntax:

```
[!][o][odd][e][even]start[-end]
```

You can have multiple ranges separated by commas, and the ! modifier removes pages from what is already selected. The range changes are incremental; numbers are added or deleted as the range appears. The start or the end can be omitted; if you omit both, you need at least o (odd; selects all odd pages) or e (even; selects all even pages).

In your case, we have:

```
String.format("%d, 1-%d", n, n-1)
```

Suppose we have a document with 10 pages, then `n` equals 10 and the result of the formatting operation is: `"10, 1-9"`. In this case, `PdfReader` will present the last page as the first one, followed by pages 1 to 9.

Now suppose that you have a TOC that starts on page 8, and you want to move this TOC to the first pages, then you need something like this: `8-10, 1-7`, or if `toc` equals 8 and `n` equals 10:

```
String.format("%d-%d, 1-%d", toc, n, toc -1)
```

For more info about the `format()` method, see the API docs for `String` and the Format String syntax.

PDF Page re-ordering using itext

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