jakarta.json.stream.JsonParser Maven / Gradle / Ivy
/*
* Copyright (c) 2011, 2020 Oracle and/or its affiliates. All rights reserved.
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Public License v. 2.0, which is available at
* http://www.eclipse.org/legal/epl-2.0.
*
* This Source Code may also be made available under the following Secondary
* Licenses when the conditions for such availability set forth in the
* Eclipse Public License v. 2.0 are satisfied: GNU General Public License,
* version 2 with the GNU Classpath Exception, which is available at
* https://www.gnu.org/software/classpath/license.html.
*
* SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
*/
package jakarta.json.stream;
import java.io.Closeable;
import java.math.BigDecimal;
import java.util.stream.Stream;
import java.util.Map;
import jakarta.json.JsonValue;
import jakarta.json.JsonObject;
import jakarta.json.JsonArray;
/**
* Provides forward, read-only access to JSON data in a streaming way. This
* is the most efficient way for reading JSON data.
* This is the only way to parse and process JSON data that are too big to be loaded in memory.
* The class
* {@link jakarta.json.Json} contains methods to create parsers from input
* sources ({@link java.io.InputStream} and {@link java.io.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 {@link JsonParserFactory} also contains methods to create
* {@code JsonParser} instances. {@link 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(...);
*
*
*
*
* {@code JsonParser} parses JSON using the pull parsing programming model.
* In this model the client code controls the thread and calls the method
* {@code next()} to advance the parser to the next state after
* processing each element. The parser can generate the following events:
* {@code START_OBJECT}, {@code END_OBJECT}, {@code START_ARRAY},
* {@code END_ARRAY}, {@code KEY_NAME}, {@code VALUE_STRING},
* {@code VALUE_NUMBER}, {@code VALUE_TRUE}, {@code VALUE_FALSE},
* and {@code VALUE_NULL}.
*
*
* For example, for an empty JSON object ({ }), the parser generates the event
* {@code START_OBJECT} with the first call to the method {@code next()} and the
* event {@code END_OBJECT} with the second call to the method {@code 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 {@code 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 {@link #next()} and {@link #hasNext()} enable iteration over
* parser events to process JSON data. {@code 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"
*
*
*
* Starting in version 1.1, it is possible to build a partial JSON object
* model from the stream, at the current parser position.
* The methods {@link #getArray} and {@link #getObject} can be used to read in
* a {@code JsonArray} or {@code JsonObject}. For example, the following code
* shows how to obtain the phoneNumber in a JsonArray, from the JSON above:
*
*
* while (parser.hasNext() {
* Event event = parser.next();
* if (event == JsonParser.Event.KEY_NAME ) {
* String key = getString();
* event = parser.next();
* if (key.equals("phoneNumber") {
* JsonArray phones = parser.getArray();
* }
* }
* }
*
*
* The methods {@link #getArrayStream} and {@link #getObjectStream} can be used
* to get a stream of the elements of a {@code JsonArray} or {@code JsonObject}.
* For example, the following code shows another way to obtain John's phoneNumber
* in a {@code JsonArray} :
*
* {@code
* Event event = parser.next(); // START_OBJECT
* JsonArray phones = (JsonArray)
* parser.getObjectStream().filter(e->e.getKey().equals("phoneNumber"))
* .map(e->e.getValue())
* .findFirst()
* .get();
* }
*
* The methods {@link #skipArray} and {@link #skipObject} can be used to
* skip tokens and position the parser to {@code END_ARRAY} or
* {@code END_OBJECT}.
*
* {@code JsonParser} can be used to parse sequence of JSON values that are not
* enclosed in a JSON array, e.g. { } { }. The following code demonstrates how
* to parse such sequence.
*
* JsonParser parser = Json.createParser(...);
* while (parser.hasNext) {
* parser.next(); // advance parser state
* JsonValue value = parser.getValue();
* }
*
*
* @see jakarta.json.Json
* @see JsonParserFactory
*/
public interface JsonParser extends /*Auto*/Closeable {
/**
* An event from {@code JsonParser}.
*/
enum Event {
/**
* Start of a JSON array. The position of the parser is after '['.
*/
START_ARRAY,
/**
* Start of a JSON object. The position of the parser is after '{'.
*/
START_OBJECT,
/**
* Name in a name/value pair of a JSON object. The position of the parser
* is after the key name. The method {@link #getString} returns the key
* name.
*/
KEY_NAME,
/**
* String value in a JSON array or object. The position of the parser is
* after the string value. The method {@link #getString}
* returns the string value.
*/
VALUE_STRING,
/**
* Number value in a JSON array or object. The position of the parser is
* after the number value. {@code JsonParser} provides the following
* methods to access the number value: {@link #getInt},
* {@link #getLong}, and {@link #getBigDecimal}.
*/
VALUE_NUMBER,
/**
* {@code true} value in a JSON array or object. The position of the
* parser is after the {@code true} value.
*/
VALUE_TRUE,
/**
* {@code false} value in a JSON array or object. The position of the
* parser is after the {@code false} value.
*/
VALUE_FALSE,
/**
* {@code null} value in a JSON array or object. The position of the
* parser is after the {@code null} value.
*/
VALUE_NULL,
/**
* End of a JSON object. The position of the parser is after '}'.
*/
END_OBJECT,
/**
* End of a JSON array. The position of the parser is after ']'.
*/
END_ARRAY
}
/**
* Returns {@code true} if there are more parsing states. This method returns
* {@code false} if the parser reaches the end of the JSON text.
*
* @return {@code true} if there are more parsing states.
* @throws jakarta.json.JsonException if an i/o error occurs (IOException
* would be cause of JsonException)
* @throws JsonParsingException if the parser encounters invalid JSON
* when advancing to next state.
*/
boolean hasNext();
/**
* Returns the event for the next parsing state.
*
* @throws jakarta.json.JsonException if an i/o error occurs (IOException
* would be cause of JsonException)
* @throws JsonParsingException if the parser encounters invalid JSON
* when advancing to next state.
* @throws java.util.NoSuchElementException if there are no more parsing
* states.
* @return the event for the next parsing state
*/
Event next();
/**
* Returns a {@code 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 {@link Event#KEY_NAME}, {@link Event#VALUE_STRING},
* or {@link Event#VALUE_NUMBER}.
*
* @return a name when the parser state is {@link Event#KEY_NAME}
* a string value when the parser state is {@link Event#VALUE_STRING}
* a number value when the parser state is {@link Event#VALUE_NUMBER}
* @throws IllegalStateException when the parser state is not
* {@code KEY_NAME}, {@code VALUE_STRING}, or {@code VALUE_NUMBER}
*/
String getString();
/**
* Returns true if the JSON number at the current parser state is a
* integral number. A {@link BigDecimal} may be used to store the value
* internally and this method semantics are defined using its
* {@code 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();
* }
*
*
*
* @return true if this number is a integral number, otherwise false
* @throws IllegalStateException when the parser state is not
* {@code VALUE_NUMBER}
*/
boolean isIntegralNumber();
/**
* Returns a JSON number as an integer. The returned value is equal
* to {@code 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 {@link Event#VALUE_NUMBER}.
*
* @return an integer for a JSON number
* @throws IllegalStateException when the parser state is not
* {@code VALUE_NUMBER}
* @see java.math.BigDecimal#intValue()
*/
int getInt();
/**
* Returns a JSON number as a long. The returned value is equal
* to {@code 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
* {@link Event#VALUE_NUMBER}.
*
* @return a long for a JSON number
* @throws IllegalStateException when the parser state is not
* {@code VALUE_NUMBER}
* @see java.math.BigDecimal#longValue()
*/
long getLong();
/**
* Returns a JSON number as a {@code BigDecimal}. The {@code BigDecimal}
* is created using {@code new BigDecimal(getString())}. This
* method should only called when the parser state is
* {@link Event#VALUE_NUMBER}.
*
* @return a {@code BigDecimal} for a JSON number
* @throws IllegalStateException when the parser state is not
* {@code VALUE_NUMBER}
*/
BigDecimal getBigDecimal();
/**
* 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).
*
* @return a non-null location corresponding to the current parser state
* in JSON input source
*/
JsonLocation getLocation();
/**
* Returns a {@code JsonObject} and advances the parser to the
* corresponding {@code END_OBJECT}.
*
* @return the {@code JsonObject} at the current parser position
*
* @throws IllegalStateException when the parser state is not
* {@code START_OBJECT}
*
* @since 1.1
*/
default public JsonObject getObject() {
throw new UnsupportedOperationException();
}
/**
* Returns a {@code JsonValue} at the current parser position.
* If the parser state is {@code START_ARRAY}, the behavior is
* the same as {@link #getArray}. If the parser state is
* {@code START_OBJECT}, the behavior is the same as
* {@link #getObject}. For all other cases, if applicable, the JSON value is
* read and returned.
*
* @return the {@code JsonValue} at the current parser position.
* @throws IllegalStateException when the parser state is
* {@code END_OBJECT} or {@code END_ARRAY}
*
* @since 1.1
*/
default public JsonValue getValue() {
throw new UnsupportedOperationException();
}
/**
* Returns a {@code JsonArray} and advance the parser to the
* the corresponding {@code END_ARRAY}.
*
* @return the {@code JsonArray} at the current parser position
*
* @throws IllegalStateException when the parser state is not
* {@code START_ARRAY}
*
* @since 1.1
*/
default public JsonArray getArray() {
throw new UnsupportedOperationException();
}
/**
* Returns a stream of the {@code JsonArray} elements.
* The parser state must be {@code START_ARRAY}.
* The elements are read lazily, on an as-needed basis, as
* required by the stream operations.
* If the stream operations do not consume
* all of the array elements, {@link skipArray} can be used to
* skip the unprocessed array elements.
*
* @return a stream of elements of the {@code JsonArray}
*
* @throws IllegalStateException when the parser state is not
* {@code START_ARRAY}
*
* @since 1.1
*/
default public Stream getArrayStream() {
throw new UnsupportedOperationException();
}
/**
* Returns a stream of the {@code JsonObject}'s
* name/value pairs. The parser state must be {@code START_OBJECT}.
* The name/value pairs are read lazily, on an as-needed basis, as
* required by the stream operations.
* If the stream operations do not consume
* all of the object's name/value pairs, {@link skipObject} can be
* used to skip the unprocessed elements.
*
* @return a stream of name/value pairs of the {@code JsonObject}
*
* @throws IllegalStateException when the parser state is not
* {@code START_OBJECT}
*
* @since 1.1
*/
default public Stream> getObjectStream() {
throw new UnsupportedOperationException();
}
/**
* Returns a stream of {@code JsonValue} from a sequence of
* JSON values. The values are read lazily, on an as-needed basis,
* as needed by the stream operations.
*
* @return a Stream of {@code JsonValue}
*
* @throws IllegalStateException if the parser is in an array or object.
*
* @since 1.1
*/
default public Stream getValueStream() {
throw new UnsupportedOperationException();
}
/**
* Advance the parser to {@code END_ARRAY}.
* If the parser is in array context, i.e. it has previously
* encountered a {@code START_ARRAY} without encountering the
* corresponding {@code END_ARRAY}, the parser is advanced to
* the corresponding {@code END_ARRAY}.
* If the parser is not in any array context, nothing happens.
*
* @since 1.1
*/
default public void skipArray() {
throw new UnsupportedOperationException();
}
/**
* Advance the parser to {@code END_OBJECT}.
* If the parser is in object context, i.e. it has previously
* encountered a {@code START_OBJECT} without encountering the
* corresponding {@code END_OBJECT}, the parser is advanced to
* the corresponding {@code END_OBJECT}.
* If the parser is not in any object context, nothing happens.
*
* @since 1.1
*/
default public void skipObject() {
throw new UnsupportedOperationException();
}
/**
* Closes this parser and frees any resources associated with the
* parser. This method closes the underlying input source.
*
* @throws jakarta.json.JsonException if an i/o error occurs (IOException
* would be cause of JsonException)
*/
@Override
void close();
}
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