How to configure Jackson PrettyPrinter format json as Gson

Question

Jackson DefaultPrettyPrinter format json as

{
  "field" : [ 1, 2 ]
}

How to configure it to format json without space before colon and with each element of array starting from a new line as GSON does?

{
  "field": [
    1,
    2
  ]
}

` mapper.writerWithDefaultPrettyPrinter().writeValueAsString(...)`? — pirho, Nov 03 '20 at 20:16
@pirho `mapper.writerWithDefaultPrettyPrinter().writeValueAsString(...)` formats exactly as I wrote in question `"field" : [ 1, 2 ]` — anton, Nov 03 '20 at 20:20
Does this answer your question? [Custom pretty printer using Jackson library](https://stackoverflow.com/questions/18098513/custom-pretty-printer-using-jackson-library) — pirho, Nov 03 '20 at 20:41
Take a look at [Jackson JSON Not Formatting Correctly](https://stackoverflow.com/questions/17411586/jackson-json-not-formatting-correctly), [How to add line drop and appropriate tabs between Json fields?](https://stackoverflow.com/questions/64459378/how-to-add-line-drop-and-appropriate-tabs-between-json-fields) — Michał Ziober, Nov 03 '20 at 20:54

anton · Accepted Answer · 2020-11-04T07:54:29.637

I implemented PrettyPrinter which formats json exactly like GSON

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.util.DefaultIndenter;
import com.fasterxml.jackson.core.util.DefaultPrettyPrinter;
import com.fasterxml.jackson.core.util.Separators;

import java.io.IOException;


public class MyPrettyPrinter extends DefaultPrettyPrinter {

    public MyPrettyPrinter() {
        _arrayIndenter = DefaultIndenter.SYSTEM_LINEFEED_INSTANCE;
        _objectIndenter = DefaultIndenter.SYSTEM_LINEFEED_INSTANCE;
    }

    public MyPrettyPrinter(DefaultPrettyPrinter base) {
        super(base);
    }

    @Override
    public MyPrettyPrinter createInstance() {
        if (getClass() != MyPrettyPrinter.class) {
            throw new IllegalStateException("Failed `createInstance()`: " + getClass().getName()
                    + " does not override method; it has to");
        }
        return new MyPrettyPrinter(this);
    }

    @Override
    public MyPrettyPrinter withSeparators(Separators separators) {
        this._separators = separators;
        this._objectFieldValueSeparatorWithSpaces = separators.getObjectFieldValueSeparator() + " ";
        return this;
    }

    @Override
    public void writeEndArray(JsonGenerator g, int nrOfValues) throws IOException {
        if (!_arrayIndenter.isInline()) {
            --_nesting;
        }
        if (nrOfValues > 0) {
            _arrayIndenter.writeIndentation(g, _nesting);
        }
        g.writeRaw(']');
    }

    @Override
    public void writeEndObject(JsonGenerator g, int nrOfEntries) throws IOException {
        if (!_objectIndenter.isInline()) {
            --_nesting;
        }
        if (nrOfEntries > 0) {
            _objectIndenter.writeIndentation(g, _nesting);
        }
        g.writeRaw('}');
    }
}

Overriding withSeparators is needed to remove space before colon. Overriding writeEndArray and writeEndObject is for removing space in empty array and empty object [] {}.

score -1 · Answer 2 · answered Nov 03 '20 at 20:58

-1

The dupe I pointed has a bit older information. I made it by configuring DefaultPrettyPrinter:

ObjectMapper om = new ObjectMapper();
DefaultPrettyPrinter dpp = new DefaultPrettyPrinter();
dpp.indentArraysWith(new DefaultIndenter("  ", "\n"));
om.setDefaultPrettyPrinter(dpp);

answered Nov 03 '20 at 20:58

pirho

11,565
12
43
70

1

Thanks. It is almost what I needed. But I also wanted to remove space before colon. Also, it prints an empty array as `[ ]` but I wanted `[]`. – anton Nov 03 '20 at 21:19

score -1 · Answer 3 · answered Nov 03 '20 at 21:20

-1

You have to configure the writer eventually,

ObjectMapper mapper = new ObjectMapper();
String String = "{\"field\" : [ 1, 2 ]}";
Object obj = mapper.readValue(String, Object.class);

DefaultPrettyPrinter prettyPrinter = new DefaultPrettyPrinter();
prettyPrinter.indentArraysWith(DefaultIndenter.SYSTEM_LINEFEED_INSTANCE);

System.out.println(mapper.writer(prettyPrinter).writeValueAsString(obj));

Output

{
  "field" : [
    1,
    2
  ]
}

answered Nov 03 '20 at 21:20

Aman

1,627
13
19

1

This only solves array formatting but I also needed to remove space before colon. – anton Nov 04 '20 at 07:35

How to configure Jackson PrettyPrinter format json as Gson

3 Answers3