What is the simplest way to configure the indentation spacing on a Jackson ObjectMapper?

Question

I\'m really struggling with the degree of complexity I am perceiving in solving this problem. As the title says: What is a simple way to create a Jackson Objec

Answer 1

I am not sure if this is the simplest way to go but... You can use the ObjectMapper with a custom printer. The DefaultPrettyPrinter can be used if you modify the indent behaviour.

// Create the mapper
ObjectMapper mapper = new ObjectMapper();

// Setup a pretty printer with an indenter (indenter has 4 spaces in this case)
DefaultPrettyPrinter.Indenter indenter = 
        new DefaultIndenter("    ", DefaultIndenter.SYS_LF);
DefaultPrettyPrinter printer = new DefaultPrettyPrinter();
printer.indentObjectsWith(indenter);
printer.indentArraysWith(indenter);

// Some object to serialize
Map<String, Object> value = new HashMap<>();
value.put("foo", Arrays.asList("a", "b", "c"));

// Serialize it using the custom printer
String json = mapper.writer(printer).writeValueAsString(value);

// Print it
System.out.println(json);

The output will be:

{
    "foo" : [
        "a",
        "b",
        "c"
    ]
}

Answer 2

If you intend to write multiple objects, as I did, to get JSON comparison in a JUnit test running in IntelliJ (which has a very nice multiline compare tool):

// could likely be simplified to `new ObjectMapper().writer(new DefaultPrettyPrinter())`
ObjectWriter writer = new ObjectMapper()
        .setDefaultPrettyPrinter(new DefaultPrettyPrinter())
        .writerWithDefaultPrettyPrinter();

try {
    String expected = writer.writeValueAsString(testCase.getThing());
    String actual = writer.writeValueAsString(actual.getThing());
    assertEquals(expected, actual);
} catch (JsonProcessingException e) {
    fail("JSON exception: " + e.toString());
}