import java.math.RoundingMode;

import java.text.NumberFormat;

import java.util.Locale;

import net.sf.json.JsonConfig;

import net.sf.json.processors.JsonValueProcessor;

class FloatJsonValueProcessor implements JsonValueProcessor {

    public FloatJsonValueProcessor() { }

    /**

     * 处理数组类型

     */

    public Object processArrayValue(Object value, JsonConfig jsonConfig) {

        if (value instanceof float[]) {

            String[] obj = {};

            float[] nums = (float[]) value;

            for (int i = 0; i < nums.length; i++) {

                obj[i] = roundHalfUp(nums[i], 3);

            }

            return obj;

        }

        return value;

    }

    /**

     * 处理单个对象

     */

    public Object processObjectValue(String key, Object value, JsonConfig jsonConfig) {

        if (value instanceof Float) {

            return roundHalfUp((Float)value, 3);

        }

        return value;

    }

    /**

     * 四舍五入。

     *

     * @param number 数值

     * @return 舍入后的数值

     * @see java.text.RoundingMode.HALF_UP

     */

    public String roundHalfUp(double number, int frac) {

        NumberFormat fmt = NumberFormat.getInstance(Locale.CHINA);

        fmt.setMaximumFractionDigits(frac);

        fmt.setRoundingMode(RoundingMode.HALF_UP);

        return fmt.format(number);

    }

}

JsonConfig jsonConfig = new JsonConfig();

jsonConfig.registerJsonValueProcessor(Float.class, new FloatJsonValueProcessor());

float f = 0.1f;

JSONArray array = JSONArray.fromObject(f，jsonConfig);