默认配置会使用BigInteger来parse大数值，无法设置为Long

[xubotian]

问题：
测试fastjson1默认反序列化大数值为long：

fastjson2默认反序列化大数值为BigInteger，且无法修改：

只能通过自定义setter方法进行设置：

小数有类似的配置，但是整数没有找到：

希望添加类似配置，可以选择反序列化大数值的默认行为。

[wenshao]

为什么有这个需求啊？

[wenshao]

https://oss.sonatype.org/content/repositories/snapshots/com/alibaba/fastjson2/fastjson2/2.0.51-SNAPSHOT/
新增加了两个JSONReader.Feature，UseBigIntegerForInts和UseLongForInts。 请帮忙用2.0.51-SNAPSHOT版本验证

public abstract class JSONReader {
    public enum Feature {
         /**
         * Feature that determines whether JSON integral (non-floating-point)
         * numbers are to be deserialized into {@link java.math.BigInteger}s
         * if only generic type description (either {@link Object} or
         * {@link Number}, or within untyped {@link java.util.Map}
         * or {@link java.util.Collection} context) is available.
         * If enabled such values will be deserialized as
         * {@link java.math.BigInteger}s;
         * if disabled, will be deserialized as "smallest" available type,
         * which is either {@link Integer}, {@link Long} or
         * {@link java.math.BigInteger}, depending on number of digits.
         * <p>
         * Feature is disabled by default, meaning that "untyped" integral
         * numbers will by default be deserialized using whatever
         * is the most compact integral type, to optimize efficiency.
         * @since 2.0.51
         */
        UseBigIntegerForInts(1 << 29),

        /**
         * Feature that determines how "small" JSON integral (non-floating-point)
         * numbers -- ones that fit in 32-bit signed integer (`int`) -- are bound
         * when target type is loosely typed as {@link Object} or {@link Number}
         * (or within untyped {@link java.util.Map} or {@link java.util.Collection} context).
         * If enabled, such values will be deserialized as {@link java.lang.Long};
         * if disabled, they will be deserialized as "smallest" available type,
         * {@link Integer}.
         *<p>
         * Note: if {@link #UseBigIntegerForInts} is enabled, it has precedence
         * over this setting, forcing use of {@link java.math.BigInteger} for all
         * integral values.
         *<p>
         * Feature is disabled by default, meaning that "untyped" integral
         * numbers will by default be deserialized using {@link java.lang.Integer}
         * if value fits.
         *
         * @since 2.0.51
         */
        UseLongForInts(1 << 30);
    }
}

[xubotian]

为什么有这个需求啊？

最近在做fastjson1到2升级时，默认行为被更改了，导致很多地方需要手动修改，希望可以通过参数全局配置，感谢大佬！

[wenshao]

https://github.com/alibaba/fastjson2/releases/tag/2.0.51
请用新版本，可以通过JSON.config全局配置