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A Minimal JSON Parser and Writer
/*******************************************************************************
* Copyright (c) 2008, 2013 EclipseSource.
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* which accompanies this distribution, and is available at
* http://www.eclipse.org/legal/epl-v10.html
*
* Contributors:
* Ralf Sternberg - initial implementation and API
******************************************************************************/
package com.eclipsesource.json;
import java.io.IOException;
import java.io.Reader;
import java.io.Serializable;
import java.io.StringWriter;
import java.io.Writer;
/**
* Represents a JSON value. This can be a JSON object, an array,
* a number, a string, or one of the literals
* true, false, and null.
*
* The literals true, false, and null are
* represented by the constants {@link #TRUE}, {@link #FALSE}, and {@link #NULL}.
*
*
* JSON objects and arrays are represented by the subtypes
* {@link JsonObject} and {@link JsonArray}. Instances of these types can be created using the
* public constructors of these classes.
*
*
* Instances that represent JSON numbers, strings and
* boolean values can be created using the static factory methods
* {@link #valueOf(String)}, {@link #valueOf(long)}, {@link #valueOf(double)}, etc.
*
*
* In order to find out whether an instance of this class is of a certain type, the methods
* {@link #isObject()}, {@link #isArray()}, {@link #isString()}, {@link #isNumber()} etc. can be
* used.
*
*
* If the type of a JSON value is known, the methods {@link #asObject()}, {@link #asArray()},
* {@link #asString()}, {@link #asInt()}, etc. can be used to get this value directly in the
* appropriate target type.
*
*
* This class is not supposed to be extended by clients.
*
*/
@SuppressWarnings( "serial" ) // use default serial UID
public abstract class JsonValue implements Serializable {
/**
* Represents the JSON literal true.
*/
public static final JsonValue TRUE = new JsonLiteral( "true" );
/**
* Represents the JSON literal false.
*/
public static final JsonValue FALSE = new JsonLiteral( "false" );
/**
* The JSON literal null.
*/
public static final JsonValue NULL = new JsonLiteral( "null" );
JsonValue() {
// prevent subclasses outside of this package
}
/**
* Reads a JSON value from the given reader.
*
* Characters are read in chunks and buffered internally, therefore wrapping an existing reader in
* an additional BufferedReader does not improve reading
* performance.
*
*
* @param reader
* the reader to read the JSON value from
* @return the JSON value that has been read
* @throws IOException
* if an I/O error occurs in the reader
* @throws ParseException
* if the input is not valid JSON
*/
public static JsonValue readFrom( Reader reader ) throws IOException {
return new JsonParser( reader ).parse();
}
/**
* Reads a JSON value from the given string.
*
* @param text
* the string that contains the JSON value
* @return the JSON value that has been read
* @throws ParseException
* if the input is not valid JSON
*/
public static JsonValue readFrom( String text ) {
try {
return new JsonParser( text ).parse();
} catch( IOException exception ) {
// JsonParser does not throw IOException for String
throw new RuntimeException( exception );
}
}
/**
* Returns a JsonValue instance that represents the given int value.
*
* @param value
* the value to get a JSON representation for
* @return a JSON value that represents the given value
*/
public static JsonValue valueOf( int value ) {
return new JsonNumber( Integer.toString( value, 10 ) );
}
/**
* Returns a JsonValue instance that represents the given long value.
*
* @param value
* the value to get a JSON representation for
* @return a JSON value that represents the given value
*/
public static JsonValue valueOf( long value ) {
return new JsonNumber( Long.toString( value, 10 ) );
}
/**
* Returns a JsonValue instance that represents the given float value.
*
* @param value
* the value to get a JSON representation for
* @return a JSON value that represents the given value
*/
public static JsonValue valueOf( float value ) {
if( Float.isInfinite( value ) || Float.isNaN( value ) ) {
throw new IllegalArgumentException( "Infinite and NaN values not permitted in JSON" );
}
return new JsonNumber( cutOffPointZero( Float.toString( value ) ) );
}
/**
* Returns a JsonValue instance that represents the given double value.
*
* @param value
* the value to get a JSON representation for
* @return a JSON value that represents the given value
*/
public static JsonValue valueOf( double value ) {
if( Double.isInfinite( value ) || Double.isNaN( value ) ) {
throw new IllegalArgumentException( "Infinite and NaN values not permitted in JSON" );
}
return new JsonNumber( cutOffPointZero( Double.toString( value ) ) );
}
/**
* Returns a JsonValue instance that represents the given string.
*
* @param string
* the string to get a JSON representation for
* @return a JSON value that represents the given string
*/
public static JsonValue valueOf( String string ) {
return string == null ? NULL : new JsonString( string );
}
/**
* Returns a JsonValue instance that represents the given boolean value.
*
* @param value
* the value to get a JSON representation for
* @return a JSON value that represents the given value
*/
public static JsonValue valueOf( boolean value ) {
return value ? TRUE : FALSE;
}
/**
* Detects whether this value represents a JSON object. If this is the case, this value is an
* instance of {@link JsonObject}.
*
* @return true if this value is an instance of JsonObject
*/
public boolean isObject() {
return false;
}
/**
* Detects whether this value represents a JSON array. If this is the case, this value is an
* instance of {@link JsonArray}.
*
* @return true if this value is an instance of JsonArray
*/
public boolean isArray() {
return false;
}
/**
* Detects whether this value represents a JSON number.
*
* @return true if this value represents a JSON number
*/
public boolean isNumber() {
return false;
}
/**
* Detects whether this value represents a JSON string.
*
* @return true if this value represents a JSON string
*/
public boolean isString() {
return false;
}
/**
* Detects whether this value represents a boolean value.
*
* @return true if this value represents either the JSON literal
* true or false
*/
public boolean isBoolean() {
return false;
}
/**
* Detects whether this value represents the JSON literal true.
*
* @return true if this value represents the JSON literal
* true
*/
public boolean isTrue() {
return false;
}
/**
* Detects whether this value represents the JSON literal false.
*
* @return true if this value represents the JSON literal
* false
*/
public boolean isFalse() {
return false;
}
/**
* Detects whether this value represents the JSON literal null.
*
* @return true if this value represents the JSON literal
* null
*/
public boolean isNull() {
return false;
}
/**
* Returns this JSON value as {@link JsonObject}, assuming that this value represents a JSON
* object. If this is not the case, an exception is thrown.
*
* @return a JSONObject for this value
* @throws UnsupportedOperationException
* if this value is not a JSON object
*/
public JsonObject asObject() {
throw new UnsupportedOperationException( "Not an object: " + toString() );
}
/**
* Returns this JSON value as {@link JsonArray}, assuming that this value represents a JSON
* array. If this is not the case, an exception is thrown.
*
* @return a JSONArray for this value
* @throws UnsupportedOperationException
* if this value is not a JSON array
*/
public JsonArray asArray() {
throw new UnsupportedOperationException( "Not an array: " + toString() );
}
/**
* Returns this JSON value as an int value, assuming that this value represents a
* JSON number that can be interpreted as Java int. If this is not the case, an
* exception is thrown.
*
* To be interpreted as Java int, the JSON number must neither contain an exponent
* nor a fraction part. Moreover, the number must be in the Integer range.
*
*
* @return this value as int
* @throws UnsupportedOperationException
* if this value is not a JSON number
* @throws NumberFormatException
* if this JSON number can not be interpreted as int value
*/
public int asInt() {
throw new UnsupportedOperationException( "Not a number: " + toString() );
}
/**
* Returns this JSON value as a long value, assuming that this value represents a
* JSON number that can be interpreted as Java long. If this is not the case, an
* exception is thrown.
*
* To be interpreted as Java long, the JSON number must neither contain an exponent
* nor a fraction part. Moreover, the number must be in the Long range.
*
*
* @return this value as long
* @throws UnsupportedOperationException
* if this value is not a JSON number
* @throws NumberFormatException
* if this JSON number can not be interpreted as long value
*/
public long asLong() {
throw new UnsupportedOperationException( "Not a number: " + toString() );
}
/**
* Returns this JSON value as a float value, assuming that this value represents a
* JSON number. If this is not the case, an exception is thrown.
*
* If the JSON number is out of the Float range, {@link Float#POSITIVE_INFINITY} or
* {@link Float#NEGATIVE_INFINITY} is returned.
*
*
* @return this value as float
* @throws UnsupportedOperationException
* if this value is not a JSON number
*/
public float asFloat() {
throw new UnsupportedOperationException( "Not a number: " + toString() );
}
/**
* Returns this JSON value as a double value, assuming that this value represents a
* JSON number. If this is not the case, an exception is thrown.
*
* If the JSON number is out of the Double range, {@link Double#POSITIVE_INFINITY} or
* {@link Double#NEGATIVE_INFINITY} is returned.
*
*
* @return this value as double
* @throws UnsupportedOperationException
* if this value is not a JSON number
*/
public double asDouble() {
throw new UnsupportedOperationException( "Not a number: " + toString() );
}
/**
* Returns this JSON value as String, assuming that this value represents a JSON string. If this
* is not the case, an exception is thrown.
*
* @return the string represented by this value
* @throws UnsupportedOperationException
* if this value is not a JSON string
*/
public String asString() {
throw new UnsupportedOperationException( "Not a string: " + toString() );
}
/**
* Returns this JSON value as a boolean value, assuming that this value is either
* true or false. If this is not the case, an exception is thrown.
*
* @return this value as boolean
* @throws UnsupportedOperationException
* if this value is neither true or false
*/
public boolean asBoolean() {
throw new UnsupportedOperationException( "Not a boolean: " + toString() );
}
/**
* Writes the JSON representation for this object to the given writer.
*
* Single elements are passed directly to the given writer. Therefore, if the writer is not
* buffered, wrapping it in a {@link java.io.BufferedWriter BufferedWriter} can drastically
* improve writing performance.
*
*
* @param writer
* the writer to write this value to
* @throws IOException
* if an I/O error occurs in the writer
*/
public void writeTo( Writer writer ) throws IOException {
write( new JsonWriter( writer ) );
}
/**
* Returns the JSON string for this value in its minimal form, without any additional whitespace.
* The result is guaranteed to be a valid input for the method {@link #readFrom(String)} and to
* create a value that is equal to this object.
*
* @return a JSON string that represents this value
*/
@Override
public String toString() {
StringWriter stringWriter = new StringWriter();
JsonWriter jsonWriter = new JsonWriter( stringWriter );
try {
write( jsonWriter );
} catch( IOException exception ) {
// StringWriter does not throw IOExceptions
throw new RuntimeException( exception );
}
return stringWriter.toString();
}
/**
* Indicates whether some other object is "equal to" this one according to the contract specified
* in {@link Object#equals(Object)}.
*
* Two JsonValues are considered equal if and only if they represent the same JSON text. As a
* consequence, two given JsonObjects may be different even though they contain the same set of
* names with the same values, but in a different order.
*
*
* @param object
* the reference object with which to compare
* @return true if this object is the same as the object argument; false otherwise
*/
@Override
public boolean equals( Object object ) {
return super.equals( object );
}
@Override
public int hashCode() {
return super.hashCode();
}
protected abstract void write( JsonWriter writer ) throws IOException;
private static String cutOffPointZero( String string ) {
if( string.endsWith( ".0" ) ) {
return string.substring( 0, string.length() - 2 );
}
return string;
}
}