WebSockets and JSON-P - Introducing Java EE 7 - page 141

The javax.json.Json class contains a static factory method , createParser() , that accepts a bevy of input,
and returns an iterable JsonParser . Table 9-3 lists the different possible input types that are accepted via the
createParser() method.

Table 9-3. createParser Method Input Types

Input Type Method Call

InputStream createParser(InputStream in)

JsonArray createParser(JsonArray arr)

JsonObject createParser(JsonObject obj)

Reader createParser(Reader reader)

Once a JsonParser has been created, it can be made into an Iterator of Event objects. Each Event correlates to
a different structure within the JSON object. For instance, when the JSON object is created, a START_OBJECT event
occurs, adding a name\value pair that will trigger both a KEY_NAME and VALUE_STRING event. These events can be
utilized to obtain the desired information from a JSON object. In the example, the event names are merely printed to
a server log. However, in a real-life application, a conditional would most likely test each iteration to find a particular
event, and then perform some processing. Table 9-4 lists the different JSON events, along with a description of when
each occurs.

Table 9-4. JSON Object Events

Event Occurrence

START_OBJECT start of an object

END_OBJECT end of an object

START_ARRAY start of an array

END_ARRAY end of an array

KEY_NAME name of a key

VALUE_STRING value of a name\value pair in String format

VALUE_NUMBER value of a name\value pair in numeric format

VALUE_TRUE value of a name\value pair in Boolean format

VALUE_FALSE value of a name\value pair in Boolean format

VALUE_NULL value of a name\value pair as NULL

Obtain a JSON object that you would like to parse, and then parse it using the javax.json.Json createParser
utility. In the following example, a JSON file is read from disk, and then parsed to determine the hierarchy of events
within. Each of the events is printed to the server log as the JSON is being parsed.

public void parseObject() {
Reader fileReader = new InputStreamReader(getClass().getResourceAsStream("BookObject.json"));
JsonParser parser = Json.createParser(fileReader);
Iterator<Event> it = parser.iterator();