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Core Jackson processing abstractions (aka Streaming API), implementation for JSON
There is a newer version: 2.17.0
package com.fasterxml.jackson.core.json;

import com.fasterxml.jackson.core.*;

/**
 * Extension of {@link JsonStreamContext}, which implements
 * core methods needed, and also exposes
 * more complete API to parser implementation classes.
 */
public final class JsonReadContext extends JsonStreamContext
{
    // // // Configuration

    /**
     * Parent context for this context; null for root context.
     */
    protected final JsonReadContext _parent;
    
    // // // Optional duplicate detection

    protected DupDetector _dups;

    /*
    /**********************************************************
    /* Simple instance reuse slots; speeds up things
    /* a bit (10-15%) for docs with lots of small
    /* arrays/objects (for which allocation was
    /* visible in profile stack frames)
    /**********************************************************
     */

    protected JsonReadContext _child;

    /*
    /**********************************************************
    /* Location/state information (minus source reference)
    /**********************************************************
     */

    protected String _currentName;

    /**
     * @since 2.5
     */
    protected Object _currentValue;
    
    protected int _lineNr;
    protected int _columnNr;

    /*
    /**********************************************************
    /* Instance construction, config, reuse
    /**********************************************************
     */

    public JsonReadContext(JsonReadContext parent, DupDetector dups, int type, int lineNr, int colNr) {
        super();
        _parent = parent;
        _dups = dups;
        _type = type;
        _lineNr = lineNr;
        _columnNr = colNr;
        _index = -1;
    }

    protected void reset(int type, int lineNr, int colNr) {
        _type = type;
        _index = -1;
        _lineNr = lineNr;
        _columnNr = colNr;
        _currentName = null;
        _currentValue = null;
        if (_dups != null) {
            _dups.reset();
        }
    }

    /*
    public void trackDups(JsonParser p) {
        _dups = DupDetector.rootDetector(p);
    }
    */

    public JsonReadContext withDupDetector(DupDetector dups) {
        _dups = dups;
        return this;
    }

    @Override
    public Object getCurrentValue() {
        return _currentValue;
    }

    @Override
    public void setCurrentValue(Object v) {
        _currentValue = v;
    }

    /*
    /**********************************************************
    /* Factory methods
    /**********************************************************
     */

    public static JsonReadContext createRootContext(int lineNr, int colNr, DupDetector dups) {
        return new JsonReadContext(null, dups, TYPE_ROOT, lineNr, colNr);
    }

    public static JsonReadContext createRootContext(DupDetector dups) {
        return new JsonReadContext(null, dups, TYPE_ROOT, 1, 0);
    }

    public JsonReadContext createChildArrayContext(int lineNr, int colNr) {
        JsonReadContext ctxt = _child;
        if (ctxt == null) {
            _child = ctxt = new JsonReadContext(this,
                    (_dups == null) ? null : _dups.child(), TYPE_ARRAY, lineNr, colNr);
        } else {
            ctxt.reset(TYPE_ARRAY, lineNr, colNr);
        }
        return ctxt;
    }

    public JsonReadContext createChildObjectContext(int lineNr, int colNr) {
        JsonReadContext ctxt = _child;
        if (ctxt == null) {
            _child = ctxt = new JsonReadContext(this,
                    (_dups == null) ? null : _dups.child(), TYPE_OBJECT, lineNr, colNr);
            return ctxt;
        }
        ctxt.reset(TYPE_OBJECT, lineNr, colNr);
        return ctxt;
    }

    /*
    /**********************************************************
    /* Abstract method implementations, overrides
    /**********************************************************
     */

    @Override public String getCurrentName() { return _currentName; }

    // @since 2.9
    @Override public boolean hasCurrentName() { return _currentName != null; }

    @Override public JsonReadContext getParent() { return _parent; }

    @Override
    public JsonLocation getStartLocation(Object srcRef) {
        // We don't keep track of offsets at this level (only reader does)
        long totalChars = -1L;
        return new JsonLocation(srcRef, totalChars, _lineNr, _columnNr);
    }

    /*
    /**********************************************************
    /* Extended API
    /**********************************************************
     */

    /**
     * Method that can be used to both clear the accumulated references
     * (specifically value set with {@link #setCurrentValue(Object)})
     * that should not be retained, and returns parent (as would
     * {@link #getParent()} do). Typically called when closing the active
     * context when encountering {@link JsonToken#END_ARRAY} or
     * {@link JsonToken#END_OBJECT}.
     *
     * @since 2.7
     */
    public JsonReadContext clearAndGetParent() {
        _currentValue = null;
        // could also clear the current name, but seems cheap enough to leave?
        return _parent;
    }

    public DupDetector getDupDetector() {
        return _dups;
    }

    /*
    /**********************************************************
    /* State changes
    /**********************************************************
     */

    public boolean expectComma() {
        /* Assumption here is that we will be getting a value (at least
         * before calling this method again), and
         * so will auto-increment index to avoid having to do another call
         */
        int ix = ++_index; // starts from -1
        return (_type != TYPE_ROOT && ix > 0);
    }

    public void setCurrentName(String name) throws JsonProcessingException {
        _currentName = name;
        if (_dups != null) { _checkDup(_dups, name); }
    }

    private void _checkDup(DupDetector dd, String name) throws JsonProcessingException {
        if (dd.isDup(name)) {
            Object src = dd.getSource();
            throw new JsonParseException(((src instanceof JsonParser) ? ((JsonParser) src) : null),
                    "Duplicate field '"+name+"'");
        }
    }
}