Java - Variable number of variables

Question

I wrote a code to find all URLs within a PDF file and replace the one(s) that matches the parameters that was passed from a PHP script.

It is working fine when a single URL is passed. But I don't know how to handle more than one URL, I'm guessing I would need a loop that reads the array length, and call the changeURL method passing the correct parameters.

I actually made it work with if Statements (if myarray.lenght < 4 do this, if it is < 6, do that, if < 8.....), but I am guessing this is not the optimal way. So I removed it and want to try something else.

Parameters passed from PHP (in this order):

args[0] - Location of original PDF
args[1] - Location of new PDF
args[2] - URL 1 (URL to be changed)
args[3] - URL 1a (URL that will replace URL 1)
args[4] - URL 2 (URL to be changed)
args[5] - URL 2a - (URL that will replace URL 2)
args...

and so on... up to maybe around 16 args, depending on how many URLs the PDF file contains.

Here's the code:

Main.java

public class Main {

public static void main(String[] args) {

    if (args.length >= 4) {
        URLReplacer.changeURL(args);
    } else {
        System.out.println("PARAMETER MISSING FROM PHP");
    }
}
}

URLReplacer.java

public class URLReplacer {

public static void changeURL(String... a) {

    try (PDDocument doc = PDDocument.load(a[0])) {
        List<?> allPages = doc.getDocumentCatalog().getAllPages();
        for (int i = 0; i < allPages.size(); i++) {
            PDPage page = (PDPage) allPages.get(i);
            List annotations = page.getAnnotations();
            for (int j = 0; j < annotations.size(); j++) {
                PDAnnotation annot = (PDAnnotation) annotations.get(j);
                if (annot instanceof PDAnnotationLink) {
                    PDAnnotationLink link = (PDAnnotationLink) annot;
                    PDAction action = link.getAction();
                    if (action instanceof PDActionURI) {
                        PDActionURI uri = (PDActionURI) action;
                        String oldURL = uri.getURI();

                        if (a[2].equals(oldURL)) {
                            //System.out.println("Page " + (i + 1) + ": Replacing " + oldURL + " with " + a[3]);
                            uri.setURI(a[3]);
                        }
                    }
                }
            }
        }
        doc.save(a[1]);
    } catch (IOException | COSVisitorException e) {
        e.printStackTrace();
    }
}
}

I have tried all sort of loops, but with my limited Java skills, did not achieve any success.

Also, if you notice any dodgy code, kindly let me know so I can learn the best practices from more experienced programmers.

you could use an array, and transmit it with JSON. useful if you have dozens of parameters ... — guillaume girod-vitouchkina, Nov 25 '15 at 15:26
I have no experience with JSON, I am just a beginner, but I will make sure to look into that possibility. Thanks! — Teio, Nov 25 '15 at 15:30

score 1 · Answer 1 · edited May 23 '17 at 12:15

Your main problem - as I understand -, is the "variable number of variables". And you have to send from PHP to JAVA.

1 you can transmit one by one as your example

2 or, in a structure. there are several structures. JSON is rather simple at PHP: multiple examples here: encode json using php?

and for java you have: Decoding JSON String in Java.

or others (like XML , which seems too complex for this).

Aragorn · Accepted Answer · 2015-12-02T14:29:51.117

I'd structure your method to accept specific parameters. I used map to accept URLs, a custom object would be another option.

Also notice the way loops are changed, might give you a hint on some Java skills.

public static void changeURL(String originalPdf, String targetPdf, Map<String, String> urls ) {

        try (PDDocument doc = PDDocument.load(originalPdf)) {
            List<PDPage> allPages = doc.getDocumentCatalog().getAllPages();
            for(PDPage page: allPages){
                List annotations = page.getAnnotations();
                for(PDAnnotation annot : page.getAnnotations()){
                    if (annot instanceof PDAnnotationLink) {
                        PDAnnotationLink link = (PDAnnotationLink) annot;
                        PDAction action = link.getAction();
                        if (action instanceof PDActionURI) {
                            PDActionURI uri = (PDActionURI) action;
                            String oldURL = uri.getURI();

                            for (Map.Entry<String, String> url : urls.entrySet()){
                                if (url.getKey().equals(oldURL)) {
                                    uri.setURI(url.getValue());
                                }
                            }

                        }
                    }
                }
            }
            doc.save(targetPdf);
        } catch (IOException | COSVisitorException e) {
            e.printStackTrace();
        }
    }

If you have to get the URL and PDF locations from command line, then call the changeURL function like this:

 public static void main(String[] args) {

        if (args.length >= 4) {
            String originalPdf = args[0];
            String targetPdf = args[1];
            Map<String, String> urls = new HashMap<String, String>();
            for(int i = 2; i< args.length; i+=2){
                urls.put(args[i], args[i+1]);
            }
            URLReplacer.changeURL(originalPdf, targetPdf, urls);
        } else {
            System.out.println("PARAMETER MISSING FROM PHP");
        }
    }

A question though, I noticed you have changed the loops, what is the difference between: for(PDPage page: allPages){} and for (int i = 0; i < allPages.size(); i++) {} — Teio, Dec 02 '15 at 11:52

Giorgos Kritsotakis · Answer 3 · 2015-11-25T15:51:59.650

-1

Of the top of my head, you could do something like this

public static void main(String[] args) {

    if (args.length >= 4 && args.length % 2 == 0) {
        for(int i = 2; i < args.length; i += 2) {
            URLReplacer.changeURL(args[0], args[1], args[i], args[i+1]);
            args[0] = args[1];
        }
    } else {
        System.out.println("PARAMETER MISSING FROM PHP");
    }
}

edited Nov 25 '15 at 15:51

answered Nov 25 '15 at 15:23

Giorgos Kritsotakis

19
1
6

Inefficient, this makes the changeURL process the PDF document several times. – Aragorn Nov 25 '15 at 15:55
@Aragorn The whole way he handles this process is wrong in my opinion, I simply provided a solution that works respecting his interface. I don't believe that my answer deserves your negative vote. – Giorgos Kritsotakis Nov 25 '15 at 16:27
@GiorgosKritsotakis, though I don't think your answer deserves a negative vote, I find that Aragorn's example (accepted answer) is more efficient and elegant. but thank you for your answer, as it also works. – Teio Dec 02 '15 at 11:31

Java - Variable number of variables

3 Answers3