The source code to reproduce https://github.com/alibaba/fastjson/issues/1423

FastJson37IssueWithLongParsing.java

package testapp;

import com.alibaba.fastjson.JSON;

import java.math.BigInteger;
import java.util.HashMap;
import java.util.Map;

public class FastJson37IssueWithLongParsing {

    public static class LongVal {
        private long v;
        public void setV(long v) {
            this.v = v;
        }

        @Override
        public String toString() {
            return String.valueOf(v);
        }
    }

    public static void main(String[] args) {
        String fastJsonVersion = JSON.VERSION;
        System.out.println("fastjson version: " + fastJsonVersion);

        BigInteger n = new BigInteger(String.valueOf(Long.MAX_VALUE)).add(new BigInteger("1"));
        Map<String, BigInteger> map = new HashMap<>();
        map.put("v", n);
        String strBad = JSON.toJSONString(map);
        System.out.println("prepare to parse: " + strBad);

        System.out.println("We expect the following line to raise NumberFormatException, but it will print out something:");
        System.out.println(JSON.parseObject(strBad, LongVal.class));

        System.out.println("While Long.parseLong(String) call does raise NumberFormatException:");
        System.out.println(Long.parseLong(n.toString()));
    }

}