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

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

You can also browse Jackson Databind Source Code below:

⏎ com/fasterxml/jackson/databind/deser/std/NumberDeserializers.java

package com.fasterxml.jackson.databind.deser.std;

import java.io.IOException;
import java.math.BigDecimal;
import java.math.BigInteger;
import java.util.HashSet;

import com.fasterxml.jackson.core.*;
import com.fasterxml.jackson.core.io.NumberInput;
import com.fasterxml.jackson.databind.*;
import com.fasterxml.jackson.databind.annotation.JacksonStdImpl;
import com.fasterxml.jackson.databind.cfg.CoercionAction;
import com.fasterxml.jackson.databind.cfg.CoercionInputShape;
import com.fasterxml.jackson.databind.jsontype.TypeDeserializer;
import com.fasterxml.jackson.databind.type.LogicalType;
import com.fasterxml.jackson.databind.util.AccessPattern;
import com.fasterxml.jackson.databind.util.ClassUtil;

/**
 * Container class for deserializers that handle core JDK primitive
 * (and matching wrapper) types, as well as standard "big" numeric types.
 * Note that this includes types such as {@link java.lang.Boolean}
 * and {@link java.lang.Character} which are not strictly numeric,
 * but are part of primitive/wrapper types.
 */
public class NumberDeserializers
{
    private final static HashSet<String> _classNames = new HashSet<String>();
    static {
        // note: can skip primitive types; other ways to check them:
        Class<?>[] numberTypes = new Class<?>[] {
            Boolean.class,
            Byte.class,
            Short.class,
            Character.class,
            Integer.class,
            Long.class,
            Float.class,
            Double.class,
            // and more generic ones
            Number.class, BigDecimal.class, BigInteger.class
        };
        for (Class<?> cls : numberTypes) {
            _classNames.add(cls.getName());
        }
    }

    public static JsonDeserializer<?> find(Class<?> rawType, String clsName) {
        if (rawType.isPrimitive()) {
            if (rawType == Integer.TYPE) {
                return IntegerDeserializer.primitiveInstance;
            }
            if (rawType == Boolean.TYPE) {
                return BooleanDeserializer.primitiveInstance;
            }
            if (rawType == Long.TYPE) {
                return LongDeserializer.primitiveInstance;
            }
            if (rawType == Double.TYPE) {
                return DoubleDeserializer.primitiveInstance;
            }
            if (rawType == Character.TYPE) {
                return CharacterDeserializer.primitiveInstance;
            }
            if (rawType == Byte.TYPE) {
                return ByteDeserializer.primitiveInstance;
            }
            if (rawType == Short.TYPE) {
                return ShortDeserializer.primitiveInstance;
            }
            if (rawType == Float.TYPE) {
                return FloatDeserializer.primitiveInstance;
            }
            // [databind#2679]: bit odd place for this (Void.class handled in
            // `JdkDeserializers`), due to `void` being primitive type
            if (rawType == Void.TYPE) {
                return NullifyingDeserializer.instance;
            }
        } else if (_classNames.contains(clsName)) {
            // Start with most common types; int, boolean, long, double
            if (rawType == Integer.class) {
                return IntegerDeserializer.wrapperInstance;
            }
            if (rawType == Boolean.class) {
                return BooleanDeserializer.wrapperInstance;
            }
            if (rawType == Long.class) {
                return LongDeserializer.wrapperInstance;
            }
            if (rawType == Double.class) {
                return DoubleDeserializer.wrapperInstance;
            }
            if (rawType == Character.class) {
                return CharacterDeserializer.wrapperInstance;
            }
            if (rawType == Byte.class) {
                return ByteDeserializer.wrapperInstance;
            }
            if (rawType == Short.class) {
                return ShortDeserializer.wrapperInstance;
            }
            if (rawType == Float.class) {
                return FloatDeserializer.wrapperInstance;
            }
            if (rawType == Number.class) {
                return NumberDeserializer.instance;
            }
            if (rawType == BigDecimal.class) {
                return BigDecimalDeserializer.instance;
            }
            if (rawType == BigInteger.class) {
                return BigIntegerDeserializer.instance;
            }
        } else {
            return null;
        }
        // should never occur
        throw new IllegalArgumentException("Internal error: can't find deserializer for "+rawType.getName());
    }

    /*
    /**********************************************************
    /* Then one intermediate base class for things that have
    /* both primitive and wrapper types
    /**********************************************************
     */

    protected abstract static class PrimitiveOrWrapperDeserializer<T>
        extends StdScalarDeserializer<T>
    {
        private static final long serialVersionUID = 1L;

        // @since 2.12
        protected final LogicalType _logicalType;

        protected final T _nullValue;

        // @since 2.9
        protected final T _emptyValue;

        protected final boolean _primitive;

        // @since 2.12
        protected PrimitiveOrWrapperDeserializer(Class<T> vc, LogicalType logicalType,
                T nvl, T empty) {
            super(vc);
            _logicalType = logicalType;
            _nullValue = nvl;
            _emptyValue = empty;
            _primitive = vc.isPrimitive();
        }

        @Deprecated // since 2.12
        protected PrimitiveOrWrapperDeserializer(Class<T> vc, T nvl, T empty) {
            this(vc, LogicalType.OtherScalar, nvl, empty);
        }

        @Override
        public AccessPattern getNullAccessPattern() {
            // 02-Feb-2017, tatu: For primitives we must dynamically check (and possibly throw
            //     exception); for wrappers not.
            if (_primitive) {
                return AccessPattern.DYNAMIC;
            }
            if (_nullValue == null) {
                return AccessPattern.ALWAYS_NULL;
            }
            return AccessPattern.CONSTANT;
        }

        @Override
        public final T getNullValue(DeserializationContext ctxt) throws JsonMappingException {
            // 01-Mar-2017, tatu: Alas, not all paths lead to `_coerceNull()`, as `SettableBeanProperty`
            //    short-circuits `null` handling. Hence need this check as well.
            if (_primitive && ctxt.isEnabled(DeserializationFeature.FAIL_ON_NULL_FOR_PRIMITIVES)) {
                ctxt.reportInputMismatch(this,
                        "Cannot map `null` into type %s (set DeserializationConfig.DeserializationFeature.FAIL_ON_NULL_FOR_PRIMITIVES to 'false' to allow)",
                        ClassUtil.classNameOf(handledType()));
            }
            return _nullValue;
        }

        @Override
        public Object getEmptyValue(DeserializationContext ctxt) throws JsonMappingException {
            return _emptyValue;
        }

        @Override // since 2.12
        public final LogicalType logicalType() {
            return _logicalType;
        }
    }

    /*
    /**********************************************************
    /* Then primitive/wrapper types
    /**********************************************************
     */

    @JacksonStdImpl
    public final static class BooleanDeserializer
        extends PrimitiveOrWrapperDeserializer<Boolean>
    {
        private static final long serialVersionUID = 1L;

        final static BooleanDeserializer primitiveInstance = new BooleanDeserializer(Boolean.TYPE, Boolean.FALSE);
        final static BooleanDeserializer wrapperInstance = new BooleanDeserializer(Boolean.class, null);

        public BooleanDeserializer(Class<Boolean> cls, Boolean nvl)
        {
            super(cls, LogicalType.Boolean, nvl, Boolean.FALSE);
        }

        @Override
        public Boolean deserialize(JsonParser p, DeserializationContext ctxt) throws IOException
        {
            JsonToken t = p.currentToken();
            if (t == JsonToken.VALUE_TRUE) {
                return Boolean.TRUE;
            }
            if (t == JsonToken.VALUE_FALSE) {
                return Boolean.FALSE;
            }
            if (_primitive) {
                return _parseBooleanPrimitive(p, ctxt);
            }
            return _parseBoolean(p, ctxt, _valueClass);
        }

        // Since we can never have type info ("natural type"; String, Boolean, Integer, Double):
        // (is it an error to even call this version?)
        @Override
        public Boolean deserializeWithType(JsonParser p, DeserializationContext ctxt,
                TypeDeserializer typeDeserializer)
            throws IOException
        {
            JsonToken t = p.currentToken();
            if (t == JsonToken.VALUE_TRUE) {
                return Boolean.TRUE;
            }
            if (t == JsonToken.VALUE_FALSE) {
                return Boolean.FALSE;
            }
            if (_primitive) {
                return _parseBooleanPrimitive(p, ctxt);
            }
            return _parseBoolean(p, ctxt, _valueClass);
        }
    }

    @JacksonStdImpl
    public static class ByteDeserializer
        extends PrimitiveOrWrapperDeserializer<Byte>
    {
        private static final long serialVersionUID = 1L;

        final static ByteDeserializer primitiveInstance = new ByteDeserializer(Byte.TYPE, (byte) 0);
        final static ByteDeserializer wrapperInstance = new ByteDeserializer(Byte.class, null);

        public ByteDeserializer(Class<Byte> cls, Byte nvl)
        {
            super(cls, LogicalType.Integer, nvl, (byte) 0);
        }

        @Override
        public Byte deserialize(JsonParser p, DeserializationContext ctxt) throws IOException
        {
            if (p.isExpectedNumberIntToken()) {
                return p.getByteValue();
            }
            if (_primitive) {
                return _parseBytePrimitive(p, ctxt);
            }
            return _parseByte(p, ctxt);
        }

        protected Byte _parseByte(JsonParser p, DeserializationContext ctxt)
                throws IOException
        {
            String text;

            switch (p.currentTokenId()) {
            case JsonTokenId.ID_STRING: // let's do implicit re-parse
                text = p.getText();
                break;
            case JsonTokenId.ID_NUMBER_FLOAT:
                final CoercionAction act = _checkFloatToIntCoercion(p, ctxt, _valueClass);
                if (act == CoercionAction.AsNull) {
                    return (Byte) getNullValue(ctxt);
                }
                if (act == CoercionAction.AsEmpty) {
                    return (Byte) getEmptyValue(ctxt);
                }
                return p.getByteValue();
            case JsonTokenId.ID_NULL: // null fine for non-primitive
                return (Byte) getNullValue(ctxt);
            case JsonTokenId.ID_NUMBER_INT:
                return p.getByteValue();
            case JsonTokenId.ID_START_ARRAY:
                return (Byte) _deserializeFromArray(p, ctxt);
            // 29-Jun-2020, tatu: New! "Scalar from Object" (mostly for XML)
            case JsonTokenId.ID_START_OBJECT:
                text = ctxt.extractScalarFromObject(p, this, _valueClass);
                break;
            default:
                return (Byte) ctxt.handleUnexpectedToken(getValueType(ctxt), p);
            }

            // Rest of the processing is for coercion from String
            final CoercionAction act = _checkFromStringCoercion(ctxt, text);
            if (act == CoercionAction.AsNull) {
                return (Byte) getNullValue(ctxt);
            }
            if (act == CoercionAction.AsEmpty) {
                return (Byte) getEmptyValue(ctxt);
            }
            text = text.trim();
            if (_checkTextualNull(ctxt, text)) {
                return (Byte) getNullValue(ctxt);
            }
            int value;
            try {
                value = NumberInput.parseInt(text);
            } catch (IllegalArgumentException iae) {
                return (Byte) ctxt.handleWeirdStringValue(_valueClass, text,
                        "not a valid Byte value");
            }
            // So far so good: but does it fit?
            // as per [JACKSON-804], allow range up to 255, inclusive
            if (_byteOverflow(value)) {
                return (Byte) ctxt.handleWeirdStringValue(_valueClass, text,
                        "overflow, value cannot be represented as 8-bit value");
                // fall-through for deferred fails
            }
            return Byte.valueOf((byte) value);
        }
    }

    @JacksonStdImpl
    public static class ShortDeserializer
        extends PrimitiveOrWrapperDeserializer<Short>
    {
        private static final long serialVersionUID = 1L;

        final static ShortDeserializer primitiveInstance = new ShortDeserializer(Short.TYPE, Short.valueOf((short)0));
        final static ShortDeserializer wrapperInstance = new ShortDeserializer(Short.class, null);
        
        public ShortDeserializer(Class<Short> cls, Short nvl)
        {
            super(cls, LogicalType.Integer, nvl, (short)0);
        }

        @Override
        public Short deserialize(JsonParser p, DeserializationContext ctxt)
            throws IOException
        {
            if (p.isExpectedNumberIntToken()) {
                return p.getShortValue();
            }
            if (_primitive) {
                return _parseShortPrimitive(p, ctxt);
            }
            return _parseShort(p, ctxt);
        }

        protected Short _parseShort(JsonParser p, DeserializationContext ctxt)
                throws IOException
        {
            String text;
            switch (p.currentTokenId()) {
            case JsonTokenId.ID_STRING: // let's do implicit re-parse
                text = p.getText();
                break;
            case JsonTokenId.ID_NUMBER_FLOAT:
                final CoercionAction act = _checkFloatToIntCoercion(p, ctxt, _valueClass);
                if (act == CoercionAction.AsNull) {
                    return (Short) getNullValue(ctxt);
                }
                if (act == CoercionAction.AsEmpty) {
                    return (Short) getEmptyValue(ctxt);
                }
                return p.getShortValue();
            case JsonTokenId.ID_NULL: // null fine for non-primitive
                return (Short) getNullValue(ctxt);
            case JsonTokenId.ID_NUMBER_INT:
                return p.getShortValue();
            // 29-Jun-2020, tatu: New! "Scalar from Object" (mostly for XML)
            case JsonTokenId.ID_START_OBJECT:
                text = ctxt.extractScalarFromObject(p, this, _valueClass);
                break;
            case JsonTokenId.ID_START_ARRAY:
                return (Short)_deserializeFromArray(p, ctxt);
            default:
                return (Short) ctxt.handleUnexpectedToken(getValueType(ctxt), p);
            }

            // Rest of the processing is for coercion from String
            final CoercionAction act = _checkFromStringCoercion(ctxt, text);
            if (act == CoercionAction.AsNull) {
                return (Short) getNullValue(ctxt);
            }
            if (act == CoercionAction.AsEmpty) {
                return (Short) getEmptyValue(ctxt);
            }
            text = text.trim();
            if (_checkTextualNull(ctxt, text)) {
                return (Short) getNullValue(ctxt);
            }
            int value;
            try {
                value = NumberInput.parseInt(text);
            } catch (IllegalArgumentException iae) {
                return (Short) ctxt.handleWeirdStringValue(_valueClass, text,
                        "not a valid Short value");
            }
            // So far so good: but does it fit?
            if (_shortOverflow(value)) {
                return (Short) ctxt.handleWeirdStringValue(_valueClass, text,
                        "overflow, value cannot be represented as 16-bit value");
            }
            return (short) value;
        }
    }

    @JacksonStdImpl
    public static class CharacterDeserializer
        extends PrimitiveOrWrapperDeserializer<Character>
    {
        private static final long serialVersionUID = 1L;

        final static CharacterDeserializer primitiveInstance = new CharacterDeserializer(Character.TYPE, '\0');
        final static CharacterDeserializer wrapperInstance = new CharacterDeserializer(Character.class, null);
        
        public CharacterDeserializer(Class<Character> cls, Character nvl)
        {
            super(cls,
                    // 07-Jun-2020, tatu: Debatable if it should be "OtherScalar" or Integer but...
                    LogicalType.Integer, nvl, '\0');
        }

        @Override
        public Character deserialize(JsonParser p, DeserializationContext ctxt)
            throws IOException
        {
            String text;
            switch (p.currentTokenId()) {
            case JsonTokenId.ID_STRING:
                // 23-Jun-2020, tatu: Unlike real numeric types, Character/char does not
                //   have canonical shape in JSON, and String in particular does not need
                //   coercion -- as long as it has length of 1.
                text = p.getText();
                break;
            case JsonTokenId.ID_NUMBER_INT: // ok iff Unicode value
                CoercionAction act = ctxt.findCoercionAction(logicalType(), _valueClass, CoercionInputShape.Integer);
                switch (act) {
                case Fail:
                    _checkCoercionFail(ctxt, act, _valueClass, p.getNumberValue(),
                            "Integer value ("+p.getText()+")");
                    // fall-through in unlikely case of returning
                case AsNull:
                    return getNullValue(ctxt);
                case AsEmpty:
                    return (Character) getEmptyValue(ctxt);
                default:
                }
                int value = p.getIntValue();
                if (value >= 0 && value <= 0xFFFF) {
                    return Character.valueOf((char) value);
                }
                return (Character) ctxt.handleWeirdNumberValue(handledType(), value,
                        "value outside valid Character range (0x0000 - 0xFFFF)");
            case JsonTokenId.ID_NULL:
                if (_primitive) {
                    _verifyNullForPrimitive(ctxt);
                }
                return (Character) getNullValue(ctxt);
            // 29-Jun-2020, tatu: New! "Scalar from Object" (mostly for XML)
            case JsonTokenId.ID_START_OBJECT:
                text = ctxt.extractScalarFromObject(p, this, _valueClass);
                break;
            case JsonTokenId.ID_START_ARRAY:
                return _deserializeFromArray(p, ctxt);
            default:
                return (Character) ctxt.handleUnexpectedToken(getValueType(ctxt), p);
            }

            if (text.length() == 1) {
                return Character.valueOf(text.charAt(0));
            }
            CoercionAction act = _checkFromStringCoercion(ctxt, text);
            if (act == CoercionAction.AsNull) {
                return getNullValue(ctxt);
            }
            if (act == CoercionAction.AsEmpty) {
                return (Character) getEmptyValue(ctxt);
            }
            text = text.trim();
            if (_checkTextualNull(ctxt, text)) {
                return (Character) getNullValue(ctxt);
            }
            return (Character) ctxt.handleWeirdStringValue(handledType(), text,
                    "Expected either Integer value code or 1-character String");
        }
    }

    @JacksonStdImpl
    public final static class IntegerDeserializer
        extends PrimitiveOrWrapperDeserializer<Integer>
    {
        private static final long serialVersionUID = 1L;

        final static IntegerDeserializer primitiveInstance = new IntegerDeserializer(Integer.TYPE, 0);
        final static IntegerDeserializer wrapperInstance = new IntegerDeserializer(Integer.class, null);
        
        public IntegerDeserializer(Class<Integer> cls, Integer nvl) {
            super(cls, LogicalType.Integer, nvl, 0);
        }

        // since 2.6, slightly faster lookups for this very common type
        @Override
        public boolean isCachable() { return true; }

        @Override
        public Integer deserialize(JsonParser p, DeserializationContext ctxt) throws IOException {
            if (p.isExpectedNumberIntToken()) {
                return p.getIntValue();
            }
            if (_primitive) {
                return _parseIntPrimitive(p, ctxt);
            }
            return _parseInteger(p, ctxt, Integer.class);
        }

        // Since we can never have type info ("natural type"; String, Boolean, Integer, Double):
        // (is it an error to even call this version?)
        @Override
        public Integer deserializeWithType(JsonParser p, DeserializationContext ctxt,
                TypeDeserializer typeDeserializer) throws IOException
        {
            if (p.isExpectedNumberIntToken()) {
                return p.getIntValue();
            }
            if (_primitive) {
                return _parseIntPrimitive(p, ctxt);
            }
            return _parseInteger(p, ctxt, Integer.class);
        }
    }

    @JacksonStdImpl
    public final static class LongDeserializer
        extends PrimitiveOrWrapperDeserializer<Long>
    {
        private static final long serialVersionUID = 1L;

        final static LongDeserializer primitiveInstance = new LongDeserializer(Long.TYPE, 0L);
        final static LongDeserializer wrapperInstance = new LongDeserializer(Long.class, null);
        
        public LongDeserializer(Class<Long> cls, Long nvl) {
            super(cls, LogicalType.Integer, nvl, 0L);
        }

        // since 2.6, slightly faster lookups for this very common type
        @Override
        public boolean isCachable() { return true; }
        
        @Override
        public Long deserialize(JsonParser p, DeserializationContext ctxt) throws IOException {
            if (p.isExpectedNumberIntToken()) {
                return p.getLongValue();
            }
            if (_primitive) {
                return _parseLongPrimitive(p, ctxt);
            }
            return _parseLong(p, ctxt, Long.class);
        }
    }

    @JacksonStdImpl
    public static class FloatDeserializer
        extends PrimitiveOrWrapperDeserializer<Float>
    {
        private static final long serialVersionUID = 1L;

        final static FloatDeserializer primitiveInstance = new FloatDeserializer(Float.TYPE, 0.f);
        final static FloatDeserializer wrapperInstance = new FloatDeserializer(Float.class, null);
        
        public FloatDeserializer(Class<Float> cls, Float nvl) {
            super(cls, LogicalType.Float, nvl, 0.f);
        }

        @Override
        public Float deserialize(JsonParser p, DeserializationContext ctxt) throws IOException
        {
            if (p.hasToken(JsonToken.VALUE_NUMBER_FLOAT)) {
                return p.getFloatValue();
            }
            if (_primitive) {
                return _parseFloatPrimitive(p, ctxt);
            }
            return _parseFloat(p, ctxt);
        }

        protected final Float _parseFloat(JsonParser p, DeserializationContext ctxt)
            throws IOException
        {
            String text;
            switch (p.currentTokenId()) {
            case JsonTokenId.ID_STRING:
                text = p.getText();
                break;
            case JsonTokenId.ID_NULL: // null fine for non-primitive
                return (Float) getNullValue(ctxt);
            case JsonTokenId.ID_NUMBER_INT:
                final CoercionAction act = _checkIntToFloatCoercion(p, ctxt, _valueClass);
                if (act == CoercionAction.AsNull) {
                    return (Float) getNullValue(ctxt);
                }
                if (act == CoercionAction.AsEmpty) {
                    return (Float) getEmptyValue(ctxt);
                }
                // fall through to coerce
            case JsonTokenId.ID_NUMBER_FLOAT:
                return p.getFloatValue();
            // 29-Jun-2020, tatu: New! "Scalar from Object" (mostly for XML)
            case JsonTokenId.ID_START_OBJECT:
                text = ctxt.extractScalarFromObject(p, this, _valueClass);
                break;
            case JsonTokenId.ID_START_ARRAY:
                return _deserializeFromArray(p, ctxt);
            default:
                return (Float) ctxt.handleUnexpectedToken(getValueType(ctxt), p);
            }

            // 18-Nov-2020, tatu: Special case, Not-a-Numbers as String need to be
            //     considered "native" representation as JSON does not allow as numbers,
            //     and hence not bound by coercion rules
            {
                Float nan = _checkFloatSpecialValue(text);
                if (nan != null) {
                    return nan;
                }
            }
            final CoercionAction act = _checkFromStringCoercion(ctxt, text);
            if (act == CoercionAction.AsNull) {
                return (Float) getNullValue(ctxt);
            }
            if (act == CoercionAction.AsEmpty) {
                return (Float) getEmptyValue(ctxt);
            }
            text = text.trim();
            if (_checkTextualNull(ctxt, text)) {
                return (Float) getNullValue(ctxt);
            }
            try {
                return NumberInput.parseFloat(text, p.isEnabled(StreamReadFeature.USE_FAST_DOUBLE_PARSER));
            } catch (IllegalArgumentException iae) { }
            return (Float) ctxt.handleWeirdStringValue(_valueClass, text,
                    "not a valid `Float` value");
        }
    }

    @JacksonStdImpl
    public static class DoubleDeserializer
        extends PrimitiveOrWrapperDeserializer<Double>
    {
        private static final long serialVersionUID = 1L;

        final static DoubleDeserializer primitiveInstance = new DoubleDeserializer(Double.TYPE, 0.d);
        final static DoubleDeserializer wrapperInstance = new DoubleDeserializer(Double.class, null);
        
        public DoubleDeserializer(Class<Double> cls, Double nvl) {
            super(cls, LogicalType.Float, nvl, 0.d);
        }

        @Override
        public Double deserialize(JsonParser p, DeserializationContext ctxt) throws IOException {
            if (p.hasToken(JsonToken.VALUE_NUMBER_FLOAT)) {
                return p.getDoubleValue();
            }
            if (_primitive) {
                return _parseDoublePrimitive(p, ctxt);
            }
            return _parseDouble(p, ctxt);
        }

        // Since we can never have type info ("natural type"; String, Boolean, Integer, Double):
        // (is it an error to even call this version?)
        @Override
        public Double deserializeWithType(JsonParser p, DeserializationContext ctxt,
                TypeDeserializer typeDeserializer) throws IOException
        {
            if (p.hasToken(JsonToken.VALUE_NUMBER_FLOAT)) {
                return p.getDoubleValue();
            }
            if (_primitive) {
                return _parseDoublePrimitive(p, ctxt);
            }
            return _parseDouble(p, ctxt);
        }

        protected final Double _parseDouble(JsonParser p, DeserializationContext ctxt) throws IOException
        {
            String text;
            switch (p.currentTokenId()) {
            case JsonTokenId.ID_STRING:
                text = p.getText();
                break;
            case JsonTokenId.ID_NULL: // null fine for non-primitive
                return (Double) getNullValue(ctxt);
            case JsonTokenId.ID_NUMBER_INT:
                final CoercionAction act = _checkIntToFloatCoercion(p, ctxt, _valueClass);
                if (act == CoercionAction.AsNull) {
                    return (Double) getNullValue(ctxt);
                }
                if (act == CoercionAction.AsEmpty) {
                    return (Double) getEmptyValue(ctxt);
                }
                // fall through to coerce
            case JsonTokenId.ID_NUMBER_FLOAT: // safe coercion
                return p.getDoubleValue();
            // 29-Jun-2020, tatu: New! "Scalar from Object" (mostly for XML)
            case JsonTokenId.ID_START_OBJECT:
                text = ctxt.extractScalarFromObject(p, this, _valueClass);
                break;
            case JsonTokenId.ID_START_ARRAY:
                return _deserializeFromArray(p, ctxt);
            default:
                return (Double) ctxt.handleUnexpectedToken(getValueType(ctxt), p);
            }

            // 18-Nov-2020, tatu: Special case, Not-a-Numbers as String need to be
            //     considered "native" representation as JSON does not allow as numbers,
            //     and hence not bound by coercion rules
            {
                Double nan = this._checkDoubleSpecialValue(text);
                if (nan != null) {
                    return nan;
                }
            }

            // Coercion from String most complicated
            final CoercionAction act = _checkFromStringCoercion(ctxt, text);
            if (act == CoercionAction.AsNull) {
                return (Double) getNullValue(ctxt);
            }
            if (act == CoercionAction.AsEmpty) {
                return (Double) getEmptyValue(ctxt);
            }
            text = text.trim();
            if (_checkTextualNull(ctxt, text)) {
                return (Double) getNullValue(ctxt);
            }
            try {
                return _parseDouble(text, p.isEnabled(StreamReadFeature.USE_FAST_DOUBLE_PARSER));
            } catch (IllegalArgumentException iae) { }
            return (Double) ctxt.handleWeirdStringValue(_valueClass, text,
                    "not a valid `Double` value");
        }
    }

    /**
     * For type <code>Number.class</code>, we can just rely on type
     * mappings that plain {@link JsonParser#getNumberValue} returns.
     *<p>
     * There is one additional complication: some numeric
     * types (specifically, int/Integer and double/Double) are "non-typed";
     * meaning that they will NEVER be output with type information.
     * But other numeric types may need such type information.
     * This is why {@link #deserializeWithType} must be overridden.
     */
    @SuppressWarnings("serial")
    @JacksonStdImpl
    public static class NumberDeserializer
        extends StdScalarDeserializer<Object>
    {
        public final static NumberDeserializer instance = new NumberDeserializer();
        
        public NumberDeserializer() {
            super(Number.class);
        }

        @Override // since 2.12
        public final LogicalType logicalType() {
            // 07-Jun-2020, tatu: Hmmh... tricky choice. For now, use:
            return LogicalType.Integer;
        }

        @Override
        public Object deserialize(JsonParser p, DeserializationContext ctxt) throws IOException
        {
            String text;
            switch (p.currentTokenId()) {
            case JsonTokenId.ID_STRING:
                text = p.getText();
                break;
            case JsonTokenId.ID_NUMBER_INT:
                if (ctxt.hasSomeOfFeatures(F_MASK_INT_COERCIONS)) {
                    return _coerceIntegral(p, ctxt);
                }
                return p.getNumberValue();

            case JsonTokenId.ID_NUMBER_FLOAT:
                if (ctxt.isEnabled(DeserializationFeature.USE_BIG_DECIMAL_FOR_FLOATS)) {
                    // 10-Mar-2017, tatu: NaN and BigDecimal won't mix...
                    if (!p.isNaN()) {
                        return p.getDecimalValue();
                    }
                }
                return p.getNumberValue();
            // 29-Jun-2020, tatu: New! "Scalar from Object" (mostly for XML)
            case JsonTokenId.ID_START_OBJECT:
                text = ctxt.extractScalarFromObject(p, this, _valueClass);
                break;
            case JsonTokenId.ID_START_ARRAY:
                return _deserializeFromArray(p, ctxt);
            default:
                return ctxt.handleUnexpectedToken(getValueType(ctxt), p);
            }

            // Textual values are more difficult... not parsing itself, but figuring
            // out 'minimal' type to use 
            CoercionAction act = _checkFromStringCoercion(ctxt, text);
            if (act == CoercionAction.AsNull) {
                return getNullValue(ctxt);
            }
            if (act == CoercionAction.AsEmpty) {
                return getEmptyValue(ctxt);
            }
            text = text.trim();
            if (_hasTextualNull(text)) {
                // note: no need to call `coerce` as this is never primitive
                return getNullValue(ctxt);
            }
            if (_isPosInf(text)) {
                return Double.POSITIVE_INFINITY;
            }
            if (_isNegInf(text)) {
                return Double.NEGATIVE_INFINITY;
            }
            if (_isNaN(text)) {
                return Double.NaN;
            }
            try {
                if (!_isIntNumber(text)) {
                    if (ctxt.isEnabled(DeserializationFeature.USE_BIG_DECIMAL_FOR_FLOATS)) {
                        return NumberInput.parseBigDecimal(text);
                    }
                    return Double.valueOf(
                            NumberInput.parseDouble(text, p.isEnabled(StreamReadFeature.USE_FAST_DOUBLE_PARSER)));
                }
                if (ctxt.isEnabled(DeserializationFeature.USE_BIG_INTEGER_FOR_INTS)) {
                    return NumberInput.parseBigInteger(text);
                }
                long value = NumberInput.parseLong(text);
                if (!ctxt.isEnabled(DeserializationFeature.USE_LONG_FOR_INTS)) {
                    if (value <= Integer.MAX_VALUE && value >= Integer.MIN_VALUE) {
                        return Integer.valueOf((int) value);
                    }
                }
                return Long.valueOf(value);
            } catch (IllegalArgumentException iae) {
                return ctxt.handleWeirdStringValue(_valueClass, text,
                        "not a valid number");
            }
        }

        /**
         * As mentioned in class Javadoc, there is additional complexity in
         * handling potentially mixed type information here. Because of this,
         * we must actually check for "raw" integers and doubles first, before
         * calling type deserializer.
         */
        @Override
        public Object deserializeWithType(JsonParser p, DeserializationContext ctxt,
                TypeDeserializer typeDeserializer)
            throws IOException
        {
            switch (p.currentTokenId()) {
            case JsonTokenId.ID_NUMBER_INT:
            case JsonTokenId.ID_NUMBER_FLOAT:
            case JsonTokenId.ID_STRING:
                // cannot point to type information: hence must be non-typed (int/double)
                return deserialize(p, ctxt);
            }
            return typeDeserializer.deserializeTypedFromScalar(p, ctxt);
        }
    }

    /*
    /**********************************************************
    /* And then bit more complicated (but non-structured) number types
    /**********************************************************
     */

    /**
     * This is bit trickier to implement efficiently, while avoiding
     * overflow problems.
     */
    @SuppressWarnings("serial")
    @JacksonStdImpl
    public static class BigIntegerDeserializer
        extends StdScalarDeserializer<BigInteger>
    {
        public final static BigIntegerDeserializer instance = new BigIntegerDeserializer();

        public BigIntegerDeserializer() { super(BigInteger.class); }

        @Override
        public Object getEmptyValue(DeserializationContext ctxt) {
            return BigInteger.ZERO;
        }

        @Override // since 2.12
        public final LogicalType logicalType() {
            return LogicalType.Integer;
        }

        @Override
        public BigInteger deserialize(JsonParser p, DeserializationContext ctxt) throws IOException
        {
            if (p.isExpectedNumberIntToken()) {
                return p.getBigIntegerValue();
            }

            String text;
            switch (p.currentTokenId()) {
            case JsonTokenId.ID_STRING: // let's do implicit re-parse
                text = p.getText();
                break;
            case JsonTokenId.ID_NUMBER_FLOAT:
                final CoercionAction act = _checkFloatToIntCoercion(p, ctxt, _valueClass);
                if (act == CoercionAction.AsNull) {
                    return (BigInteger) getNullValue(ctxt);
                }
                if (act == CoercionAction.AsEmpty) {
                    return (BigInteger) getEmptyValue(ctxt);
                }
                return p.getDecimalValue().toBigInteger();
            // 29-Jun-2020, tatu: New! "Scalar from Object" (mostly for XML)
            case JsonTokenId.ID_START_OBJECT:
                text = ctxt.extractScalarFromObject(p, this, _valueClass);
                break;
            case JsonTokenId.ID_START_ARRAY:
                return _deserializeFromArray(p, ctxt);
            default:
                // String is ok too, can easily convert; otherwise, no can do:
                return (BigInteger) ctxt.handleUnexpectedToken(getValueType(ctxt), p);
            }

            final CoercionAction act = _checkFromStringCoercion(ctxt, text);
            if (act == CoercionAction.AsNull) {
                return getNullValue(ctxt);
            }
            if (act == CoercionAction.AsEmpty) {
                return (BigInteger) getEmptyValue(ctxt);
            }
            text = text.trim();
            if (_hasTextualNull(text)) {
                // note: no need to call `coerce` as this is never primitive
                return getNullValue(ctxt);
            }
            try {
                return NumberInput.parseBigInteger(text);
            } catch (IllegalArgumentException iae) { }
            return (BigInteger) ctxt.handleWeirdStringValue(_valueClass, text,
                    "not a valid representation");
        }
    }

    @SuppressWarnings("serial")
    @JacksonStdImpl
    public static class BigDecimalDeserializer
        extends StdScalarDeserializer<BigDecimal>
    {
        public final static BigDecimalDeserializer instance = new BigDecimalDeserializer();
 
        public BigDecimalDeserializer() { super(BigDecimal.class); }

        @Override
        public Object getEmptyValue(DeserializationContext ctxt) {
            return BigDecimal.ZERO;
        }

        @Override // since 2.12
        public final LogicalType logicalType() {
            return LogicalType.Float;
        }

        @Override
        public BigDecimal deserialize(JsonParser p, DeserializationContext ctxt)
            throws IOException
        {
            String text;
            switch (p.currentTokenId()) {
            case JsonTokenId.ID_NUMBER_INT:
                final CoercionAction act = _checkIntToFloatCoercion(p, ctxt, _valueClass);
                if (act == CoercionAction.AsNull) {
                    return (BigDecimal) getNullValue(ctxt);
                }
                if (act == CoercionAction.AsEmpty) {
                    return (BigDecimal) getEmptyValue(ctxt);
                }
                // fall through to coerce
            case JsonTokenId.ID_NUMBER_FLOAT:
                return p.getDecimalValue();
            case JsonTokenId.ID_STRING:
                text = p.getText();
                break;
            // 29-Jun-2020, tatu: New! "Scalar from Object" (mostly for XML)
            case JsonTokenId.ID_START_OBJECT:
                text = ctxt.extractScalarFromObject(p, this, _valueClass);
                break;
            case JsonTokenId.ID_START_ARRAY:
                return _deserializeFromArray(p, ctxt);
            default:
                return (BigDecimal) ctxt.handleUnexpectedToken(getValueType(ctxt), p);
            }

            final CoercionAction act = _checkFromStringCoercion(ctxt, text);
            if (act == CoercionAction.AsNull) {
                return getNullValue(ctxt);
            }
            if (act == CoercionAction.AsEmpty) {
                return (BigDecimal) getEmptyValue(ctxt);
            }
            text = text.trim();
            if (_hasTextualNull(text)) {
                // note: no need to call `coerce` as this is never primitive
                return getNullValue(ctxt);
            }
            try {
                return NumberInput.parseBigDecimal(text);
            } catch (IllegalArgumentException iae) { }
            return (BigDecimal) ctxt.handleWeirdStringValue(_valueClass, text,
                    "not a valid representation");
        }
    }
}

⏎ com/fasterxml/jackson/databind/deser/std/NumberDeserializers.java

Or download all of them as a single archive file:

File name: jackson-databind-2.14.0-sources.jar
File size: 1187952 bytes
Release date: 2022-11-05
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