Jackson is "the Java JSON library" or "the best JSON parser for Java". Or simply as "JSON for Java".

Jackson Core Source Code files are provided in the source packge (jackson-core-2.14.0-sources.jar). You can download it at Jackson Maven Website.

You can also browse Jackson Core Source Code below:

⏎ com/fasterxml/jackson/core/json/JsonReadFeature.java

package com.fasterxml.jackson.core.json;

import com.fasterxml.jackson.core.*;

/**
 * Token reader (parser) features specific to JSON backend.
 * Eventual replacement for JSON-specific {@link com.fasterxml.jackson.core.JsonParser.Feature}s.
 *
 * @since 2.10
 */
public enum JsonReadFeature
    implements FormatFeature
{
    // // // Support for non-standard data format constructs: comments

    /**
     * Feature that determines whether parser will allow use
     * of Java/C/C++ style comments (both '/'+'*' and
     * '//' varieties) within parsed content or not.
     *<p>
     * Since JSON specification does not mention comments as legal
     * construct,
     * this is a non-standard feature; however, in the wild
     * this is extensively used. As such, feature is
     * <b>disabled by default</b> for parsers and must be
     * explicitly enabled.
     */
    ALLOW_JAVA_COMMENTS(false, JsonParser.Feature.ALLOW_COMMENTS),

    /**
     * Feature that determines whether parser will allow use
     * of YAML comments, ones starting with '#' and continuing
     * until the end of the line. This commenting style is common
     * with scripting languages as well.
     *<p>
     * Since JSON specification does not mention comments as legal
     * construct,
     * this is a non-standard feature. As such, feature is
     * <b>disabled by default</b> for parsers and must be
     * explicitly enabled.
     */
    ALLOW_YAML_COMMENTS(false, JsonParser.Feature.ALLOW_YAML_COMMENTS),

    // // // Support for non-standard data format constructs: quoting/escaping

    /**
     * Feature that determines whether parser will allow use
     * of single quotes (apostrophe, character '\'') for
     * quoting Strings (names and String values). If so,
     * this is in addition to other acceptable markers.
     *<p>
     * Since JSON specification requires use of double quotes for
     * field names,
     * this is a non-standard feature, and as such disabled by default.
     */
    ALLOW_SINGLE_QUOTES(false, JsonParser.Feature.ALLOW_SINGLE_QUOTES),

    /**
     * Feature that determines whether parser will allow use
     * of unquoted field names (which is allowed by Javascript,
     * but not by JSON specification).
     *<p>
     * Since JSON specification requires use of double quotes for
     * field names,
     * this is a non-standard feature, and as such disabled by default.
     */
    ALLOW_UNQUOTED_FIELD_NAMES(false, JsonParser.Feature.ALLOW_UNQUOTED_FIELD_NAMES),

    /**
     * Feature that determines whether parser will allow
     * JSON Strings to contain unescaped control characters
     * (ASCII characters with value less than 32, including
     * tab and line feed characters) or not.
     * If feature is set false, an exception is thrown if such a
     * character is encountered.
     *<p>
     * Since JSON specification requires quoting for all control characters,
     * this is a non-standard feature, and as such disabled by default.
     */
    @SuppressWarnings("deprecation")
    ALLOW_UNESCAPED_CONTROL_CHARS(false, JsonParser.Feature.ALLOW_UNQUOTED_CONTROL_CHARS),

    /**
     * Feature that can be enabled to accept quoting of all character
     * using backslash quoting mechanism: if not enabled, only characters
     * that are explicitly listed by JSON specification can be thus
     * escaped (see JSON spec for small list of these characters)
     *<p>
     * Since JSON specification requires quoting for all control characters,
     * this is a non-standard feature, and as such disabled by default.
     */
    @SuppressWarnings("deprecation")
    ALLOW_BACKSLASH_ESCAPING_ANY_CHARACTER(false, JsonParser.Feature.ALLOW_BACKSLASH_ESCAPING_ANY_CHARACTER),

    // // // Support for non-standard data format constructs: number representations
    
    /**
     * Feature that determines whether parser will allow
     * JSON integral numbers to start with additional (ignorable) 
     * zeroes (like: 000001). If enabled, no exception is thrown, and extra
     * nulls are silently ignored (and not included in textual representation
     * exposed via {@link JsonParser#getText}).
     *<p>
     * Since JSON specification does not allow leading zeroes,
     * this is a non-standard feature, and as such disabled by default.
     */
    @SuppressWarnings("deprecation")
    ALLOW_LEADING_ZEROS_FOR_NUMBERS(false, JsonParser.Feature.ALLOW_NUMERIC_LEADING_ZEROS),

    /**
     * Feature that determines whether parser will allow
     * JSON decimal numbers to start with a plus sign
     * (like: +123). If enabled, no exception is thrown, and the number
     * is parsed as though a leading sign had not been present.
     *<p>
     * Since JSON specification does not allow leading plus signs,
     * this is a non-standard feature, and as such disabled by default.
     *
     * @since 2.14
     */
    @SuppressWarnings("deprecation")
    ALLOW_LEADING_PLUS_SIGN_FOR_NUMBERS(false, JsonParser.Feature.ALLOW_LEADING_PLUS_SIGN_FOR_NUMBERS),


    /**
     * Feature that determines whether parser will allow
     * JSON decimal numbers to start with a decimal point
     * (like: .123). If enabled, no exception is thrown, and the number
     * is parsed as though a leading 0 had been present.
     *<p>
     * Since JSON specification does not allow leading decimal points,
     * this is a non-standard feature, and as such disabled by default.
     *
     * @since 2.11
     */
    @SuppressWarnings("deprecation")
    ALLOW_LEADING_DECIMAL_POINT_FOR_NUMBERS(false, JsonParser.Feature.ALLOW_LEADING_DECIMAL_POINT_FOR_NUMBERS),

    /**
     * Feature that determines whether parser will allow
     * JSON decimal numbers to end with a decimal point
     * (like: 123.). If enabled, no exception is thrown, and the number
     * is parsed as though the trailing decimal point had not been present.
     *<p>
     * Since JSON specification does not allow trailing decimal points,
     * this is a non-standard feature, and as such disabled by default.
     *
     * @since 2.14
     */
    @SuppressWarnings("deprecation")
    ALLOW_TRAILING_DECIMAL_POINT_FOR_NUMBERS(false, JsonParser.Feature.ALLOW_TRAILING_DECIMAL_POINT_FOR_NUMBERS),

    /**
     * Feature that allows parser to recognize set of
     * "Not-a-Number" (NaN) tokens as legal floating number
     * values (similar to how many other data formats and
     * programming language source code allows it).
     * Specific subset contains values that
     * <a href="http://www.w3.org/TR/xmlschema-2/">XML Schema</a>
     * (see section 3.2.4.1, Lexical Representation)
     * allows (tokens are quoted contents, not including quotes):
     *<ul>
     *  <li>"INF" (for positive infinity), as well as alias of "Infinity"
     *  <li>"-INF" (for negative infinity), alias "-Infinity"
     *  <li>"NaN" (for other not-a-numbers, like result of division by zero)
     *</ul>
     *<p>
     * Since JSON specification does not allow use of such values,
     * this is a non-standard feature, and as such disabled by default.
     */
    @SuppressWarnings("deprecation")
    ALLOW_NON_NUMERIC_NUMBERS(false, JsonParser.Feature.ALLOW_NON_NUMERIC_NUMBERS),

    // // // Support for non-standard data format constructs: array/value separators
     
    /**
     * Feature allows the support for "missing" values in a JSON array: missing
     * value meaning sequence of two commas, without value in-between but only
     * optional white space.
     * Enabling this feature will expose "missing" values as {@link JsonToken#VALUE_NULL}
     * tokens, which typically become Java nulls in arrays and {@link java.util.Collection}
     * in data-binding.
     * <p>
     * For example, enabling this feature will represent a JSON array <code>["value1",,"value3",]</code>
     * as <code>["value1", null, "value3", null]</code> 
     * <p>
     * Since the JSON specification does not allow missing values this is a non-compliant JSON
     * feature and is disabled by default.
     */
    @SuppressWarnings("deprecation")
    ALLOW_MISSING_VALUES(false, JsonParser.Feature.ALLOW_MISSING_VALUES),

    /**
     * Feature that determines whether {@link JsonParser} will allow for a single trailing
     * comma following the final value (in an Array) or member (in an Object). These commas
     * will simply be ignored.
     * <p>
     * For example, when this feature is enabled, <code>[true,true,]</code> is equivalent to
     * <code>[true, true]</code> and <code>{"a": true,}</code> is equivalent to
     * <code>{"a": true}</code>.
     * <p>
     * When combined with <code>ALLOW_MISSING_VALUES</code>, this feature takes priority, and
     * the final trailing comma in an array declaration does not imply a missing
     * (<code>null</code>) value. For example, when both <code>ALLOW_MISSING_VALUES</code>
     * and <code>ALLOW_TRAILING_COMMA</code> are enabled, <code>[true,true,]</code> is
     * equivalent to <code>[true, true]</code>, and <code>[true,true,,]</code> is equivalent to
     * <code>[true, true, null]</code>.
     * <p>
     * Since the JSON specification does not permit trailing commas, this is a non-standard
     * feature, and as such disabled by default.
     */
    @SuppressWarnings("deprecation")
    ALLOW_TRAILING_COMMA(false, JsonParser.Feature.ALLOW_TRAILING_COMMA),
    ;

    final private boolean _defaultState;
    final private int _mask;

    /**
     * For backwards compatibility we may need to map to one of existing {@link JsonParser.Feature}s;
     * if so, this is the feature to enable/disable.
     */
    final private JsonParser.Feature _mappedFeature;
    
    /**
     * Method that calculates bit set (flags) of all features that
     * are enabled by default.
     *
     * @return Bit mask of all features that are enabled by default
     */
    public static int collectDefaults()
    {
        int flags = 0;
        for (JsonReadFeature f : values()) {
            if (f.enabledByDefault()) {
                flags |= f.getMask();
            }
        }
        return flags;
    }
    
    private JsonReadFeature(boolean defaultState,
            JsonParser.Feature  mapTo) {
        _defaultState = defaultState;
        _mask = (1 << ordinal());
        _mappedFeature = mapTo;
    }

    @Override
    public boolean enabledByDefault() { return _defaultState; }
    @Override
    public int getMask() { return _mask; }
    @Override
    public boolean enabledIn(int flags) { return (flags & _mask) != 0; }

    public JsonParser.Feature mappedFeature() { return _mappedFeature; }
}

⏎ com/fasterxml/jackson/core/json/JsonReadFeature.java

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File name: jackson-core-2.14.0-sources.jar
File size: 497693 bytes
Release date: 2022-11-05
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