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"
 
 

Author:

Jitendra Kotamraju

See Also:

Json, JsonParserFactory

Nested Class Summary

Nested Classes

Modifier and Type	Interface and Description
static class	JsonParser.Event An event from JsonParser.

Method Summary

Methods

Modifier and Type	Method and 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 Detail

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:

BigDecimal.intValue()

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:

BigDecimal.longValue()

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)