Java write to .pdf with color

Question

I would like to create a .pdf file and then write to it in color. Through consoles, I have been able to do that with ansi escape sequences. For example if I want red I put "\u001b[31m" in front of my string and "\u001b[0m" to remove all the formatting. You can change the background and the foreground. I designed my own useful class around this to help with displaying information and even for a text-based chess project I am still working on.

However, now I would like to write to files with colors. I would like to do a similar thing that I did with the ansi escapes but probably not with escapes.

If I want to create color in a .pdf, how would I do that (without utilizing an external source)? Can someone point me in the right direction?

Answer 1

Here a quick hack of a very very simple PDF creator class which can do nothing more than writing Courier text in color on colored background:

public class SimplePdfCreator
{
    /**
     * Creates a {@link SimplePdfCreator} instance writing to the
     * given {@link OutputStream}.
     */
    public SimplePdfCreator(OutputStream os) throws IOException
    {
        pdfOs = os instanceof BufferedOutputStream ? (BufferedOutputStream) os : new BufferedOutputStream(os);

        writeHeader();
        fontObjectNr = writeFont();
        initPage();
    }

    /**
     * Sets the (fill) color for the upcoming operations on the current page.
     */
    public void color(float r, float g, float b)
    {
        pageBuilder.append(r)
                   .append(' ')
                   .append(g)
                   .append(' ')
                   .append(b)
                   .append(" rg\n");
    }

    /**
     * Sets the background (fill) color for the upcoming operations on the current page.
     */
    public void backColor(float r, float g, float b)
    {
        backBuilder.append(r)
                   .append(' ')
                   .append(g)
                   .append(' ')
                   .append(b)
                   .append(" rg\n");
    }

    /**
     * Prints the given text on a baseline starting at the given coordinates
     * on the current page.
     */
    public void print(int x, int y, String string)
    {
        pageBuilder.append(x - xNow)
                   .append(' ')
                   .append(y - yNow)
                   .append(" Td (")
                   .append(string)
                   .append(") Tj\n");
        xNow = x;
        yNow = y;
        fillBack(string);
    }

    /**
     * Prints the given text on the next line on the current page.
     */
    public void print(String string)
    {
        pageBuilder.append("(")
                   .append(string)
                   .append(") '\n");
        yNow -= leading;
        fillBack(string);
    }

    /**
     * Stores the current page with the printed content in the output
     * and creates a new one.
     */
    public void storePage() throws IOException
    {
        writePageContent();
        initPage();
    }

    /**
     * Returns the width of the given String.
     */
    public double getStringWidth(String string)
    {
        return string.length() * fontSize * .6;
    }

    /**
     * Returns the font size
     */
    public int getFontSize()
    {
        return fontSize;
    }

    /**
     * Returns the leading
     */
    public int getLeading()
    {
        return leading;
    }

    /**
     * Finishes the output writing required data to it and closing the
     * target {@link OutputStream}.
     */
    public void close() throws IOException
    {
        int pagesObjectNr = writePages();
        int catalogObjectNr = writeCatalog(pagesObjectNr);
        long xrefPosition = writeXref();
        writeTrailer(catalogObjectNr);
        writeFooter(xrefPosition);
        pdfOs.close();;
    }

    //
    // helper methods
    //
    void writeHeader() throws IOException
    {
        write("%PDF-1.4\n".getBytes(charSet));
        write(new byte[]{'%', (byte)128, (byte)129, (byte)130, '\n'});
    }

    int writeFont() throws IOException
    {
        return writeObject("<</Type/Font/Subtype/Type1/BaseFont/Courier/Encoding/WinAnsiEncoding>>\n".getBytes(charSet));
    }

    void initPage()
    {
        pageBuilder.setLength(0);
        backBuilder.setLength(0);
        pageBuilder.append("BT/F0 ")
                   .append(fontSize)
                   .append(" Tf ")
                   .append(leading)
                   .append(" TL 0 g\n");
        backBuilder.append("1 g\n");
        xNow = 0;
        yNow = 0;
    }

    void fillBack(String string)
    {
        backBuilder.append(xNow)
                   .append(' ')
                   .append(yNow - leading*.2)
                   .append(' ')
                   .append(getStringWidth(string))
                   .append(' ')
                   .append(leading)
                   .append(" re f\n");
    }

    void writePageContent() throws IOException
    {
        pageBuilder.append("ET\n");
        StringBuilder contents = new StringBuilder();
        contents.append("<</Length ")
                .append(pageBuilder.length() + backBuilder.length())
                .append(">>\nstream\n")
                .append(backBuilder)
                .append(pageBuilder)
                .append("\nendstream\n");
        int contentsObjectNr = writeObject(contents.toString().getBytes(charSet));
        pageContentsObjects.add(contentsObjectNr);
    }

    int writePages() throws IOException
    {
        int pagesObjectNrToBe = xref.size() + pageContentsObjects.size() + 1;
        StringBuilder pages = new StringBuilder();
        pages.append("<</Type /Pages /Count ")
             .append(pageContentsObjects.size())
             .append("/Kids[");
        for (int pageContentObject : pageContentsObjects)
        {
            int pageObjectNr = writeObject(String.format("<</Type/Page/Parent %s 0 R/Contents %s 0 R>>\n", pagesObjectNrToBe, pageContentObject).getBytes(charSet));
            pages.append(pageObjectNr).append(" 0 R ");
        }
        pages.append("]/Resources<</ProcSet[/PDF/Text]/Font<</F0 ")
             .append(fontObjectNr)
             .append(" 0 R>>>>/MediaBox[0 0 612 792]>>\n");
        return writeObject(pages.toString().getBytes(charSet));
    }

    int writeCatalog(int pagesObjectNr) throws IOException
    {
        return writeObject(String.format("<</Type/Catalog/Pages %s 0 R>>\n", pagesObjectNr).getBytes(charSet));
    }

    long writeXref() throws IOException
    {
        long xrefPos = position;
        byte[] eol = new byte[]{'\n'};
        write("xref\n".getBytes(charSet));
        write(String.format("0 %s\n", xref.size() + 1).getBytes(charSet));
        write("0000000000 65535 f ".getBytes(charSet));
        write(eol);
        for(long position: xref)
        {
            write(String.format("%010d 00000 n ", position).getBytes(charSet));
            write(eol);
        }
        return xrefPos;
    }

    void writeTrailer(int catalogObjectNr) throws IOException
    {
        write(String.format("trailer\n<</Size %s/Root %s 0 R>>\n", xref.size() + 1, catalogObjectNr).getBytes(charSet));
    }

    void writeFooter(long xrefPosition) throws IOException
    {
        write(String.format("startxref\n%s\n%%%%EOF\n", xrefPosition).getBytes(charSet));
    }

    int writeObject(byte[] bytes) throws IOException
    {
        int objectNr = startObject();
        write(bytes);
        endObj();
        return objectNr;
    }

    int startObject() throws IOException
    {
        xref.add(position);
        int objectNr = xref.size();
        write(String.format("%s 0 obj\n", objectNr).getBytes(charSet));
        return objectNr;
    }

    void endObj() throws IOException
    {
        write("endobj\n".getBytes(charSet));
    }

    long write(byte[] bytes) throws IOException
    {
        if (bytes != null)
        {
            pdfOs.write(bytes);
            position += bytes.length;
        }
        return position;
    }

    final BufferedOutputStream pdfOs;
    final Charset charSet = Charset.forName("ISO-8859-1");
    final List<Long> xref = new ArrayList<Long>();
    final List<Integer> pageContentsObjects = new ArrayList<Integer>();
    final StringBuilder pageBuilder = new StringBuilder();
    final StringBuilder backBuilder = new StringBuilder();
    final int fontObjectNr;
    long position = 0;

    int xNow = 0;
    int yNow = 0;

    int fontSize = 11;
    int leading = 11;
}

You can use it like this:

public void test() throws IOException
{
    SimplePdfCreator creator = new SimplePdfCreator(new FileOutputStream("target/test-outputs/SimpleGenerated.pdf"));

    creator.print(100, 500, "Test line 1");
    creator.print("Test line 2");

    creator.color(1, 0, 0);
    creator.backColor(0, 1, 1);
    creator.print(100, 450, "Test line red");
    creator.color(0, 1, 0);
    creator.backColor(1, 0, 1);
    creator.print("Test line green");
    creator.color(0, 0, 1);
    creator.backColor(1, 1, 0);
    creator.print("Test line blue");

    creator.color(1, 1, 1);
    creator.backColor(0, 0, 0);

    creator.print(100, 400, "step");
    creator.print(100 + (int)creator.getStringWidth("step"), 400 - creator.getLeading(), "by");
    creator.print(100 + (int)creator.getStringWidth("stepby"), 400 - 2 * creator.getLeading(), "step");

    creator.storePage();

    creator.print(100, 400, "Page 2");

    creator.storePage();

    creator.close();
}

Which creates this:

And remember, as mentioned above, this is a quick hack, maybe a prove of concept, and there is much to improve, e.g. coordinates probably should be double instead of int, strings shall be escaped before adding to the content (especially concerning brackets, ...