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/format/DataFormatDetector.java

package com.fasterxml.jackson.core.format;

import java.io.*;
import java.util.*;

import com.fasterxml.jackson.core.*;

/**
 * Simple helper class that allows data format (content type) auto-detection,
 * given an ordered set of {@link JsonFactory} instances to use for actual low-level
 * detection.
 */
public class DataFormatDetector
{
    /**
     * By default we will look ahead at most 64 bytes; in most cases,
     * much less (4 bytes or so) is needed, but we will allow bit more
     * leniency to support data formats that need more complex heuristics.
     */
    public final static int DEFAULT_MAX_INPUT_LOOKAHEAD = 64;
    
    /**
     * Ordered list of factories which both represent data formats to
     * detect (in precedence order, starting with highest) and are used
     * for actual detection.
     */
    protected final JsonFactory[] _detectors;

    /**
     * Strength of match we consider to be good enough to be used
     * without checking any other formats.
     * Default value is {@link MatchStrength#SOLID_MATCH}, 
     */
    protected final MatchStrength _optimalMatch;

    /**
     * Strength of minimal match we accept as the answer, unless
     * better matches are found. 
     * Default value is {@link MatchStrength#WEAK_MATCH}, 
     */
    protected final MatchStrength _minimalMatch;

    /**
     * Maximum number of leading bytes of the input that we can read
     * to determine data format.
     *<p>
     * Default value is {@link #DEFAULT_MAX_INPUT_LOOKAHEAD}.
     */
    protected final int _maxInputLookahead;
    
    /*
    /**********************************************************
    /* Construction
    /**********************************************************
     */
    
    public DataFormatDetector(JsonFactory... detectors) {
        this(detectors, MatchStrength.SOLID_MATCH, MatchStrength.WEAK_MATCH,
            DEFAULT_MAX_INPUT_LOOKAHEAD);
    }

    public DataFormatDetector(Collection<JsonFactory> detectors) {
        this(detectors.toArray(new JsonFactory[0]));
    }

    private DataFormatDetector(JsonFactory[] detectors,
            MatchStrength optMatch, MatchStrength minMatch, int maxInputLookahead) {
        _detectors = detectors;
        _optimalMatch = optMatch;
        _minimalMatch = minMatch;
        _maxInputLookahead = maxInputLookahead;
    }

    /**
     * Method that will return a detector instance that uses given
     * optimal match level (match that is considered sufficient to return, without
     * trying to find stronger matches with other formats).
     *
     * @param optMatch Optimal match level to use
     *
     * @return Format detector instance with specified optimal match level
     */
    public DataFormatDetector withOptimalMatch(MatchStrength optMatch) {
        if (optMatch == _optimalMatch) {
            return this;
        }
        return new DataFormatDetector(_detectors, optMatch, _minimalMatch, _maxInputLookahead);
    }
    /**
     * Method that will return a detector instance that uses given
     * minimal match level; match that may be returned unless a stronger match
     * is found with other format detectors.
     *
     * @param minMatch Minimum match level to use
     *
     * @return Format detector instance with specified minimum match level
     */
    public DataFormatDetector withMinimalMatch(MatchStrength minMatch) {
        if (minMatch == _minimalMatch) {
            return this;
        }
        return new DataFormatDetector(_detectors, _optimalMatch, minMatch, _maxInputLookahead);
    }

    /**
     * Method that will return a detector instance that allows detectors to
     * read up to specified number of bytes when determining format match strength.
     *
     * @param lookaheadBytes Amount of look-ahead allowed
     *
     * @return Format detector instance with specified lookahead settings
     */
    public DataFormatDetector withMaxInputLookahead(int lookaheadBytes) {
        if (lookaheadBytes == _maxInputLookahead) {
            return this;
        }
        return new DataFormatDetector(_detectors, _optimalMatch, _minimalMatch, lookaheadBytes);
    }

    /*
    /**********************************************************
    /* Public API
    /**********************************************************
     */

    /**
     * Method to call to find format that content (accessible via given
     * {@link InputStream}) given has, as per configuration of this detector
     * instance.
     *
     * @param in InputStream from which to read initial content
     *
     * @return Matcher object which contains result; never null, even in cases
     *    where no match (with specified minimal match strength) is found.
     *
     * @throws IOException for read I/O problems
     */
    public DataFormatMatcher findFormat(InputStream in) throws IOException {
        return _findFormat(new InputAccessor.Std(in, new byte[_maxInputLookahead]));
    }

    /**
     * Method to call to find format that given content (full document)
     * has, as per configuration of this detector instance.
     *
     * @param fullInputData Full contents to use for format detection
     *
     * @return Matcher object which contains result; never null, even in cases
     *    where no match (with specified minimal match strength) is found.
     *
     * @throws IOException for read I/O problems
     */
    public DataFormatMatcher findFormat(byte[] fullInputData) throws IOException {
        return _findFormat(new InputAccessor.Std(fullInputData));
    }

    /**
     * Method to call to find format that given content (full document)
     * has, as per configuration of this detector instance.
     * 
     * @param fullInputData Full contents to use for format detection
     * @param offset Offset of the first content byte
     * @param len Length of content
     *
     * @return Matcher object which contains result; never null, even in cases
     *    where no match (with specified minimal match strength) is found.
     *
     * @throws IOException for read I/O problems
     * 
     * @since 2.1
     */
    public DataFormatMatcher findFormat(byte[] fullInputData, int offset, int len) throws IOException {
        return _findFormat(new InputAccessor.Std(fullInputData, offset, len));
    }
    
    /*
    /**********************************************************
    /* Overrides
    /**********************************************************
     */

    @Override public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append('[');
        final int len = _detectors.length;
        if (len > 0) {
            sb.append(_detectors[0].getFormatName());
            for (int i = 1; i < len; ++i) {
                sb.append(", ");
                sb.append(_detectors[i].getFormatName());
            }
        }
        sb.append(']');
        return sb.toString();
    }
    
    /*
    /**********************************************************
    /* Internal methods
    /**********************************************************
     */

    private DataFormatMatcher _findFormat(InputAccessor.Std acc) throws IOException {
        JsonFactory bestMatch = null;
        MatchStrength bestMatchStrength = null;
        for (JsonFactory f : _detectors) {
            acc.reset();
            MatchStrength strength = f.hasFormat(acc);
            // if not better than what we have so far (including minimal level limit), skip
            if (strength == null || strength.ordinal() < _minimalMatch.ordinal()) {
                continue;
            }
            // also, needs to better match than before
            if (bestMatch != null) {
                if (bestMatchStrength.ordinal() >= strength.ordinal()) {
                    continue;
                }
            }
            // finally: if it's good enough match, we are done
            bestMatch = f;
            bestMatchStrength = strength;
            if (strength.ordinal() >= _optimalMatch.ordinal()) {
                break;
            }
        }
        return acc.createMatcher(bestMatch, bestMatchStrength);
    }
}

⏎ com/fasterxml/jackson/core/format/DataFormatDetector.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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