Java Reference
In-Depth Information
} else if (event.equals(Event.VALUE_NUMBER)) {
jsonVal = jsonParser.getInt();
}
jsonMap.put(jsonKeyNm, jsonVal);
}
person.setFirstName((String) jsonMap.get("firstName"));
person.setMiddleName((String) jsonMap.get("middleName"));
person.setLastName((String) jsonMap.get("lastName"));
person.setGender((String) jsonMap.get("gender"));
person.setAge((Integer) jsonMap.get("age"));
return "display_populated_obj";
}
}
In order to read and parse JSON data using the JSON-P streaming API, we need
to obtain an implementation of the
JsonParser
interface. The
Json
class has
two overloaded versions of a
createParser()
method we can use to obtain a
JsonParser
implementation. One version of
Json.createParser()
takes an
instance of
java.io.InputStream
(or one of its subclasses) as its sole parameter,
and the other version takes an instance of
java.io.Reader
(or one of its subclasses)
as its sole parameter. In our example, we use the second version, passing an instance
of
java.io.StringReader
(which extends
java.io.Reader
) that contains our JSON
string as a parameter.
Once we obtain a reference to
JsonParser
, we invoke its
hasNext()
method in a
while loop. The
JsonParser.hasNext()
method returns
true
if there are more
property names or values to read from the JSON string, otherwise it returns
false
.
Inside the
while
loop, we invoke
JsonParser.next()
. This method returns an
instance of the
JsonParser.Event
enum. The specific value of the
JsonParser.
Event
enum we get from
JsonParser.next()
lets us know what type of data we
are reading (key name, string value, numeric value, and so on). In our example, our
JSON string contains only string and numeric values, so we only check for those two
value types by comparing the
JsonParser.Event
instance we got from
JsonParser.
next()
against
Event.VALUE_STRING
and
Event.VALUE_NUMBER
, respectively. We
also check for a JSON key name by comparing the obtained value against
Event.KEY_
NAME
. Once we have read a key/value pair combination from our JSON string, what
we do with it depends on our application requirements. In our example, we simply
populate a hash map using the corresponding values from our JSON string.
