Allow to configure line endings (and probably indentation)

[digulla]

When writing multi-OS unit tests, it's cumbersome to filter the line endings from Jackson's output.

Please add a config option which allows to configure the line endings to use (and maybe the indentation level or String) so I can write unit tests which always produce a single Line Feed.

If I could configure the indentation, that would allow me to use tabs or four spaces to indent.

[cowtowncoder]

I am guessing you are using default pretty printer (since by default Jackson does not add linefeeds).
If so, you need to implement PrettyPrinter yourself (or sub-class default one), and you can control behavior of indentation and linefeeds.

[digulla]

I tried that but I was unable to figure out how to make Jackson use my instance. Code from ObjectMapper.java:

protected final static PrettyPrinter _defaultPrettyPrinter = new DefaultPrettyPrinter();

final field -> no way to change it.

Also, I couldn't figure out how to make ObjectMapper pass my preferred PrettyPrinter to JsonGenerator instances it creates. Instead, it calls useDefaultPrettyPrinter() which contains new DefaultPrettyPrinter(), so I can't override this as well.

Lastly, I would have to copy the whole class Lf2SpacesIndenter since it's hostile to any kind of reuse.

To add insult to injury, my Eclipse refuses to open GeneratorBase :-(

Would you accept a pull request?

[cowtowncoder]

Ah, no, don't try to change definition of default pretty-printing; rather, assign your own PrettyPrinter, either for mapper, or, via ObjectWriter. Once assigned it will be properly assigned to JsonGenerator that is constructored. Or, if you construct generator yourself, you need to directly assign it (generator.setPrettyPrinter() or such).

You should not have to change anything in JsonGenerator, ObjectMapper or ObjectWriter.
I don't remember if I intended Lf2SpacesIndenter to be easily sub-classable or not, but I am open to changes there.

[digulla]

Suggestion for the indenter:

/**
 * Default linefeed-based indenter uses system-specific linefeeds and
 * 2 spaces for indentation per level.
 */
public class DefaultIndenter
    extends DefaultPrettyPrinter.NopIndenter
{
    public final static String SYS_LF;
    static {
        String lf;
        try {
            lf = System.getProperty("line.separator");
        } catch (Throwable t) {
            lf = "\n"; // fallback when security manager denies access
        }
        SYS_LF = lf;
    }

    public static final DefaultIndenter instance = new DefaultIndenter("  ", SYS_LF);

    private final static int INDENT_LEVELS = 64;
    private final char[] indents;
    private final int charsPerLevel;
    private final String eol;

    /** Create an indenter which uses the <code>indent</code> string to indent one level
     *  and the <code>eol</code> string to separate lines. */
    public DefaultIndenter(String indent, String eol) {
        charsPerLevel = indent.length();

        this.indents = new char[indent.length() * INDENT_LEVELS];
        int offset = 0;
        for (int i=0; i<INDENT_LEVELS; i++) {
            indent.getChars(0, indent.length(), this.indents, offset);
            offset += indent.length();
        }

        this.eol = eol;
    }

    @Override
    public boolean isInline() { return false; }

    @Override
    public void writeIndentation(JsonGenerator jg, int level)
        throws IOException, JsonGenerationException
    {
        jg.writeRaw(eol);
        if (level > 0) { // should we err on negative values (as there's some flaw?)
            level *= charsPerLevel;
            while (level > indents.length) { // should never happen but...
                jg.writeRaw(indents, 0, indents.length); 
                level -= indents.length;
            }
            jg.writeRaw(indents, 0, level);
        }
    }
}

[digulla]

Can you please provide an example how to configure ObjectMapper in such a way that my PrettyPrinter is used everywhere? I can't figure this out from the documentation or the code.

[cowtowncoder]

You will need to use ObjectWriter actually:

ObjectWriter w = mapper.writer(new MyPrettyPrinter());
w.writeValue(output, value);

and either hold on to writer, or just create instances dynamically; they are cheap to create unlike ObjectMapper instances.

Use of ObjectWriter is recommended in general since they are stateless, immutable, light-weight and easily (re)configurable.

[digulla]

Sent you a pull request for the new DefaultIndenter above: FasterXML/jackson-core#166

[derknorton]

Interesting discussion... I know this issue is already closed but it still sounds like a bug to me. I use the ObjectMapper for serialization and deserialization of my POJOs into JSON as part of my jackson based RESTful web services. I don't know a way to do this with the ObjectWriter, perhaps its possible.

So I would like to add my own custom PrettyPrinter subclass that does not use the inline formatting for arrays/collections while serializing the JSON for my web service. I need to do what @digulla was requesting above and have the ObjectMapper use my custom PrettyPrinter everywhere. It seems like this should be something that is possible and if not, perhaps should be considered a bug.

[cowtowncoder]

@derknorton what sounds like a bug? Pull request #166 was merged, included in 2.5.0.

As to semantics, while it's not a huge deal, missing functionality is not a bug, but, well, missing functionality. Creating a new issue for adding things that are missing and you would like to see is perfectly fine; and in fact I prefer it over re-opening old issues (unless it is specific flaw in fix/addition itself).

[james-bjss]

Realise this ticket is closed, but we faced a similar issue when matching messages in unit tests on Windows machines. So adding this here for others who stumble upon this page.

The DefaultPrettyPrinter was adding \r\n but we were expecting \n.

The line-feed char can be set as follows:

private static final ObjectWriter objectWriter = new ObjectMapper().writer(new DefaultPrettyPrinter()
            .withObjectIndenter(new DefaultIndenter().withLinefeed("\n")));