Interface JsonParser
- All Superinterfaces:
AutoCloseable
,Closeable
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
-
Method Summary
Modifier and TypeMethodDescriptionvoid
close()
Closes this parser and frees any resources associated with the parser.Returns a JSON number as aBigDecimal
.int
getInt()
Returns a JSON number as an integer.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.Returns aString
for the name in a name/value pair, for a string value or a number value.boolean
hasNext()
Returnstrue
if there are more parsing states.boolean
Returns true if the JSON number at the current parser state is a integral number.next()
Returns the event for the next parsing state.
-
Method Details
-
hasNext
boolean hasNext()Returnstrue
if there are more parsing states. This method returnsfalse
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 aString
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 isJsonParser.Event.KEY_NAME
,JsonParser.Event.VALUE_STRING
, orJsonParser.Event.VALUE_NUMBER
.- Returns:
- a name when the parser state is
JsonParser.Event.KEY_NAME
a string value when the parser state isJsonParser.Event.VALUE_STRING
a number value when the parser state isJsonParser.Event.VALUE_NUMBER
- Throws:
IllegalStateException
- when the parser state is notKEY_NAME
,VALUE_STRING
, orVALUE_NUMBER
-
isIntegralNumber
boolean isIntegralNumber()Returns true if the JSON number at the current parser state is a integral number. ABigDecimal
may be used to store the value internally and this method semantics are defined using itsscale()
. 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 notVALUE_NUMBER
-
getInt
int getInt()Returns a JSON number as an integer. The returned value is equal tonew 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 isJsonParser.Event.VALUE_NUMBER
.- Returns:
- an integer for a JSON number
- Throws:
IllegalStateException
- when the parser state is notVALUE_NUMBER
- See Also:
-
getLong
long getLong()Returns a JSON number as a long. The returned value is equal tonew 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 isJsonParser.Event.VALUE_NUMBER
.- Returns:
- a long for a JSON number
- Throws:
IllegalStateException
- when the parser state is notVALUE_NUMBER
- See Also:
-
getBigDecimal
BigDecimal getBigDecimal()Returns a JSON number as aBigDecimal
. TheBigDecimal
is created usingnew BigDecimal(getString())
. This method should only called when the parser state isJsonParser.Event.VALUE_NUMBER
.- Returns:
- a
BigDecimal
for a JSON number - Throws:
IllegalStateException
- when the parser state is notVALUE_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 interfaceAutoCloseable
- Specified by:
close
in interfaceCloseable
- Throws:
JsonException
- if an i/o error occurs (IOException would be cause of JsonException)
-