Question

There’s a project use Jackson, and have a Java object Data. In the object, there’s a property, and it’s also a object Raw. In this object,there’s a property List<Object[]>
e.g:

public class Data{
    Raw raw;
}

public class Raw{
    List<Object[]> list;
}

If the Object[] have a data type: long, and I give a value: 123, then the Jackson will convert this data type to int,

i.e: If the value’s length < long && > int , the data type is also long, if length < int, the data type will become int.

I use the method:

 byte[] bytes = writeValueAsBytes(Data), Data data = readValue(bytes, Data.class)

How could I keep the original data type when it is converted?

Answer 1

Jackson does what I think you want:

@Test
public void testJackson() throws Exception {
    List<Number> numbers = new ArrayList<Number>();
    numbers.add(100L);
    numbers.add(new Long(Integer.MAX_VALUE) + 1000L);
    numbers.add(10.0);
    ObjectMapper om = new ObjectMapper();
    System.out.println(om.writeValueAsString(numbers));
    List<Number> newNumbers = om.readValue(om.writeValueAsString(numbers), ArrayList.class);
    System.out.println(newNumbers);
    assertEquals(Integer.class, newNumbers.get(0).getClass());
    assertEquals(newNumbers.get(1).getClass(), Long.class);
    assertTrue(! numbers.equals(newNumbers) );
}

However numbers will not equal newNumbers because 100L should be an integer.
The maximum number that JSON can handle is a 64 bit double precision.

If your doing data serialization like for binary images then I would encode the data in Base64.