Package javax.json.stream

Interface JsonParser

All Superinterfaces:
AutoCloseable, Closeable
public interface JsonParser extends Closeable
Provides forward, read-only access to JSON data in a streaming way. This is the most efficient way for reading JSON data. The class Json contains methods to create parsers from input sources (InputStream and Reader).

The following example demonstrates how to create a parser from a string that contains an empty JSON array: 

 
 JsonParser parser = Json.createParser(new StringReader("[]"));

The class JsonParserFactory also contains methods to create JsonParser instances. JsonParserFactory is preferred when creating multiple parser instances. A sample usage is shown in the following example: 

 
 JsonParserFactory factory = Json.createParserFactory();
 JsonParser parser1 = factory.createParser(...);
 JsonParser parser2 = factory.createParser(...);

JsonParser parses JSON using the pull parsing programming model. In this model the client code controls the thread and calls the method next() to advance the parser to the next state after processing each element. The parser can generate the following events: START_OBJECT, END_OBJECT, START_ARRAY, END_ARRAY, KEY_NAME, VALUE_STRING, VALUE_NUMBER, VALUE_TRUE, VALUE_FALSE, and VALUE_NULL.

For example, for an empty JSON object ({ }), the parser generates the event START_OBJECT with the first call to the method next() and the event END_OBJECT with the second call to the method next(). The following code demonstrates how to access these events: 

 
 Event event = parser.next(); // START_OBJECT
 event = parser.next();       // END_OBJECT

For example, for the following JSON: 

 {
   "firstName": "John", "lastName": "Smith", "age": 25,
   "phoneNumber": [
       { "type": "home", "number": "212 555-1234" },
       { "type": "fax", "number": "646 555-4567" }
    ]
 }

calls to the method next() result in parse events at the specified locations below (marked in bold): 

 {START_OBJECT
   "firstName"KEY_NAME: "John"VALUE_STRING, "lastName"KEY_NAME: "Smith"VALUE_STRING, "age"KEY_NAME: 25VALUE_NUMBER,
   "phoneNumber"KEY_NAME : [START_ARRAY
       {START_OBJECT "type"KEY_NAME: "home"VALUE_STRING, "number"KEY_NAME: "212 555-1234"VALUE_STRING }END_OBJECT,
       {START_OBJECT "type"KEY_NAME: "fax"VALUE_STRING, "number"KEY_NAME: "646 555-4567"VALUE_STRING }END_OBJECT
    ]END_ARRAY
 }END_OBJECT

The methods next() and hasNext() enable iteration over parser events to process JSON data. JsonParser provides get methods to obtain the value at the current state of the parser. For example, the following code shows how to obtain the value "John" from the JSON above: 

 
 Event event = parser.next(); // START_OBJECT
 event = parser.next();       // KEY_NAME
 event = parser.next();       // VALUE_STRING
 parser.getString();          // "John"
See Also:

  • Nested Class Summary

    Nested Classes
    Modifier and Type
    Interface
    Description
    static enum 
    JsonParser.Event
    An event from JsonParser.

  • Method Summary

    Modifier and Type
    Method
    Description
    void
    close()
    Closes this parser and frees any resources associated with the parser.
    BigDecimal
    getBigDecimal()
    Returns a JSON number as a BigDecimal.
    int
    getInt()
    Returns a JSON number as an integer.
    JsonLocation
    getLocation()
    Return the location that corresponds to the parser's current state in the JSON input source.
    long
    getLong()
    Returns a JSON number as a long.
    String
    getString()
    Returns a String for the name in a name/value pair, for a string value or a number value.
    boolean
    hasNext()
    Returns true if there are more parsing states.
    boolean
    isIntegralNumber()
    Returns true if the JSON number at the current parser state is a integral number.
    JsonParser.Event
    next()
    Returns the event for the next parsing state.

  • Method Details

    • hasNext

      boolean hasNext()
      Returns true if there are more parsing states. This method returns false if the parser reaches the end of the JSON text.
      Returns:
      true if there are more parsing states.
      Throws:
      JsonException - if an i/o error occurs (IOException would be cause of JsonException)
      JsonParsingException - if the parser encounters invalid JSON when advancing to next state.

    • next

      JsonParser.Event next()
      Returns the event for the next parsing state.
      Throws:
      JsonException - if an i/o error occurs (IOException would be cause of JsonException)
      JsonParsingException - if the parser encounters invalid JSON when advancing to next state.
      NoSuchElementException - if there are no more parsing states.

    • getString

      String getString()
      Returns a String for the name in a name/value pair, for a string value or a number value. This method should only be called when the parser state is JsonParser.Event.KEY_NAME, JsonParser.Event.VALUE_STRING, or JsonParser.Event.VALUE_NUMBER.
      Returns:
      a name when the parser state is JsonParser.Event.KEY_NAME a string value when the parser state is JsonParser.Event.VALUE_STRING a number value when the parser state is JsonParser.Event.VALUE_NUMBER
      Throws:
      IllegalStateException - when the parser state is not KEY_NAME, VALUE_STRING, or VALUE_NUMBER

    • isIntegralNumber

      boolean isIntegralNumber()
      Returns true if the JSON number at the current parser state is a integral number. A BigDecimal may be used to store the value internally and this method semantics are defined using its scale(). If the scale is zero, then it is considered integral type. This integral type information can be used to invoke an appropriate accessor method to obtain a numeric value as in the following example: 
       
 JsonParser parser = ...
 if (parser.isIntegralNumber()) {
     parser.getInt();     // or other methods to get integral value
 } else {
     parser.getBigDecimal();
 }
      Returns:
      true if this number is a integral number, otherwise false
      Throws:
      IllegalStateException - when the parser state is not VALUE_NUMBER

    • getInt

      int getInt()
      Returns a JSON number as an integer. The returned value is equal to new BigDecimal(getString()).intValue(). Note that this conversion can lose information about the overall magnitude and precision of the number value as well as return a result with the opposite sign. This method should only be called when the parser state is JsonParser.Event.VALUE_NUMBER.
      Returns:
      an integer for a JSON number
      Throws:
      IllegalStateException - when the parser state is not VALUE_NUMBER
      See Also:

    • getLong

      long getLong()
      Returns a JSON number as a long. The returned value is equal to new BigDecimal(getString()).longValue(). Note that this conversion can lose information about the overall magnitude and precision of the number value as well as return a result with the opposite sign. This method is only called when the parser state is JsonParser.Event.VALUE_NUMBER.
      Returns:
      a long for a JSON number
      Throws:
      IllegalStateException - when the parser state is not VALUE_NUMBER
      See Also:

    • getBigDecimal

      BigDecimal getBigDecimal()
      Returns a JSON number as a BigDecimal. The BigDecimal is created using new BigDecimal(getString()). This method should only called when the parser state is JsonParser.Event.VALUE_NUMBER.
      Returns:
      a BigDecimal for a JSON number
      Throws:
      IllegalStateException - when the parser state is not VALUE_NUMBER

    • getLocation

      JsonLocation getLocation()
      Return the location that corresponds to the parser's current state in the JSON input source. The location information is only valid in the current parser state (or until the parser is advanced to a next state).
      Returns:
      a non-null location corresponding to the current parser state in JSON input source

    • close

      void close()
      Closes this parser and frees any resources associated with the parser. This method closes the underlying input source.
      Specified by:
      close in interface AutoCloseable
      Specified by:
      close in interface Closeable
      Throws:
      JsonException - if an i/o error occurs (IOException would be cause of JsonException)