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/util/JsonParserSequence.java

package com.fasterxml.jackson.core.util;

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

import com.fasterxml.jackson.core.*;

/**
 * Helper class that can be used to sequence multiple physical
 * {@link JsonParser}s to create a single logical sequence of
 * tokens, as a single {@link JsonParser}.
 *<p>
 * Fairly simple use of {@link JsonParserDelegate}: only need
 * to override {@link #nextToken} to handle transition
 */
public class JsonParserSequence extends JsonParserDelegate
{
    /**
     * Parsers other than the first one (which is initially assigned
     * as delegate)
     */
    protected final JsonParser[] _parsers;

    /**
     * Configuration that determines whether state of parsers is first verified
     * to see if parser already points to a token (that is,
     * {@link JsonParser#hasCurrentToken()} returns <code>true</code>), and if so
     * that token is first return before {@link JsonParser#nextToken} is called.
     * If enabled, this check is made; if disabled, no check is made and
     * {@link JsonParser#nextToken} is always called for all parsers.
     *<p>
     * Default setting is <code>false</code> (for backwards-compatibility)
     * so that possible existing token is not considered for parsers.
     * 
     * @since 2.8
     */
    protected final boolean _checkForExistingToken;

    /**
     * Index of the next parser in {@link #_parsers}.
     */
    protected int _nextParserIndex;

    /**
     * Flag used to indicate that `JsonParser.nextToken()` should not be called,
     * due to parser already pointing to a token.
     *
     * @since 2.8
     */
    protected boolean _hasToken;

    /*
     *******************************************************
     * Construction
     *******************************************************
     */

    @Deprecated // since 2.8
    protected JsonParserSequence(JsonParser[] parsers) {
        this(false, parsers);
    }

    // @since 2.8
    protected JsonParserSequence(boolean checkForExistingToken, JsonParser[] parsers)
    {
        super(parsers[0]);
        _checkForExistingToken = checkForExistingToken;
        _hasToken = checkForExistingToken && delegate.hasCurrentToken();
        _parsers = parsers;
        _nextParserIndex = 1;
    }

    /**
     * Method that will construct a sequence (possibly a sequence) that
     * contains all given sub-parsers.
     * All parsers given are checked to see if they are sequences: and
     * if so, they will be "flattened", that is, contained parsers are
     * directly added in a new sequence instead of adding sequences
     * within sequences. This is done to minimize delegation depth,
     * ideally only having just a single level of delegation.
     *
     * @param checkForExistingToken Flag passed to be assigned as
     *   {@link #_checkForExistingToken} for resulting sequence
     * @param first First parser to traverse
     * @param second Second parser to traverse
     *
     * @return Sequence instance constructed
     */
    public static JsonParserSequence createFlattened(boolean checkForExistingToken,
            JsonParser first, JsonParser second)
    {
        if (!(first instanceof JsonParserSequence || second instanceof JsonParserSequence)) {
            return new JsonParserSequence(checkForExistingToken,
                    new JsonParser[] { first, second });
        }
        ArrayList<JsonParser> p = new ArrayList<JsonParser>();
        if (first instanceof JsonParserSequence) {
            ((JsonParserSequence) first).addFlattenedActiveParsers(p);
        } else {
            p.add(first);
        }
        if (second instanceof JsonParserSequence) {
            ((JsonParserSequence) second).addFlattenedActiveParsers(p);
        } else {
            p.add(second);
        }
        return new JsonParserSequence(checkForExistingToken,
                p.toArray(new JsonParser[p.size()]));
    }

    @Deprecated // since 2.8
    public static JsonParserSequence createFlattened(JsonParser first, JsonParser second) {
        return createFlattened(false, first, second);
    }
    
    @SuppressWarnings("resource")
    protected void addFlattenedActiveParsers(List<JsonParser> listToAddIn)
    {
        for (int i = _nextParserIndex-1, len = _parsers.length; i < len; ++i) {
            JsonParser p = _parsers[i];
            if (p instanceof JsonParserSequence) {
                ((JsonParserSequence) p).addFlattenedActiveParsers(listToAddIn);
            } else {
                listToAddIn.add(p);
            }
        }
    }

    /*
    /*******************************************************
    /* Overridden methods, needed: cases where default
    /* delegation does not work
    /*******************************************************
     */

    @Override
    public void close() throws IOException {
        do { delegate.close(); } while (switchToNext());
    }

    @Override
    public JsonToken nextToken() throws IOException
    {
        if (delegate == null) {
            return null;
        }
        if (_hasToken) {
            _hasToken = false;
           return delegate.currentToken();
        }
        JsonToken t = delegate.nextToken();
        if (t == null) {
            return switchAndReturnNext();
        }
        return t;
    }

    /**
     * Need to override, re-implement similar to how method defined in
     * {@link com.fasterxml.jackson.core.base.ParserMinimalBase}, to keep
     * state correct here.
     */
    @Override
    public JsonParser skipChildren() throws IOException
    {
        if ((delegate.currentToken() != JsonToken.START_OBJECT)
            && (delegate.currentToken() != JsonToken.START_ARRAY)) {
            return this;
        }
        int open = 1;

        // Since proper matching of start/end markers is handled
        // by nextToken(), we'll just count nesting levels here
        while (true) {
            JsonToken t = nextToken();
            if (t == null) { // not ideal but for now, just return
                return this;
            }
            if (t.isStructStart()) {
                ++open;
            } else if (t.isStructEnd()) {
                if (--open == 0) {
                    return this;
                }
            }
        }
    }

    /*
    /*******************************************************
    /* Additional extended API
    /*******************************************************
     */

    /**
     * Method that is most useful for debugging or testing;
     * returns actual number of underlying parsers sequence
     * was constructed with (nor just ones remaining active)
     *
     * @return Number of actual underlying parsers this sequence has
     */
    public int containedParsersCount() {
        return _parsers.length;
    }

    /*
    /*******************************************************
    /* Helper methods
    /*******************************************************
     */

    /**
     * Method that will switch active delegate parser from the current one
     * to the next parser in sequence, if there is another parser left:
     * if so, the next parser will become the active delegate parser.
     * 
     * @return True if switch succeeded; false otherwise
     *
     * @since 2.8
     */
    protected boolean switchToNext()
    {
        if (_nextParserIndex < _parsers.length) {
            delegate = _parsers[_nextParserIndex++];
            return true;
        }
        return false;
    }

    protected JsonToken switchAndReturnNext() throws IOException
    {
        while (_nextParserIndex < _parsers.length) {
            delegate = _parsers[_nextParserIndex++];
            if (_checkForExistingToken && delegate.hasCurrentToken()) {
                return delegate.getCurrentToken();
            }
            JsonToken t = delegate.nextToken();
            if (t != null) {
                return t;
            }
        }
        return null;
    }
}

⏎ com/fasterxml/jackson/core/util/JsonParserSequence.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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