Scanner读取10万条数据抛出InputMismatchException求助

问题描述 #

输入几千条数据时程序无报错，但数据量增至100000条时，抛出异常：Exception in thread "main" java.util.InputMismatchException，怀疑是Scanner的问题，请求排查。

程序代码 #

import java.math.BigInteger;
import java.util.*;

class Work {
    public long end;
    public long money;
    Work(long end, long money){
        this.end = end;
        this.money = money;
    }
}
public class TanXin {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        int n = scanner.nextInt();
        List<Work> works = new ArrayList<>();

        for (int i = 0; i < n; i++) {
            long end = scanner.nextLong();
            long money = scanner.nextLong();
            works.add(new Work(end ,money));
        }
        Collections.sort(works, new Comparator<Work>() {
            @Override
            public int compare(Work o1, Work o2) {
                return Long.compare(o1.end, o2.end);
            }
        });
        scanner.nextLine();
        long curEnd =  works.get(0).end;
        long money = works.get(0).money;
        BigInteger result = BigInteger.valueOf(0);
        for (int i = 1; i < works.size(); i++) {
            Work work = works.get(i);
            if(work.end == curEnd){
                money = Math.max(money, work.money);
            }
            else {
                result=result.add(BigInteger.valueOf(money));
                money = work.money;
                curEnd = work.end;
            }
        }
        result=result.add(BigInteger.valueOf(money));
        System.out.println(result);
    }
}

输入示例 #

100000
801615855 349230664
887145852 256709348
543490607 406712523
290306792 866994656
761434274 614622174
523543132 477488683
416651127 515580101
610336950 152185241
337713494 547698342
6453239 251894056
17161871 278487265
309123183 826630026
22171935 97670396
937046566 551871611
338360787 511206428
234499030 12274630
999066863 377262036
498450141 907352279
699130053 40056368
341503872 598356413
92329093 58969313
839293680 912223354
435852220 370051435
328226392 703616380
84394712 320189993
89139302 692379179
668921100 37915667
750500527 980565603
951214595 443240740
342283327 733767608
674959282 407118651
114057416 595985258
908001458 748864346
406064066 170499053

排查分析 #

• 输入数据格式问题：InputMismatchException本质是Scanner读取的内容与预期类型不匹配，大概率是10万条数据中存在非法内容——比如非数字字符、超出long范围的数值（long取值范围为-9223372036854775808至9223372036854775807）。
• Scanner性能瓶颈：Scanner在处理超大量输入时，默认的缓冲区机制可能出现读取不完整的情况，导致某一行数据被截断，后续读取时触发类型不匹配异常。
• 代码冗余操作：读取完所有数据后调用的scanner.nextLine();属于冗余操作，若输入末尾存在空行或残留字符，可能干扰后续逻辑，但不是触发异常的核心原因。

解决方案 #

1. 校验输入数据完整性 #

检查10万条数据的每一行，确保两个数值均为合法的long类型，无格式错误、非数字字符或超出范围的数值。

2. 替换为高效的读取方式 #

改用BufferedReader配合StringTokenizer处理大输入，比Scanner效率更高、稳定性更强，避免缓冲区问题：

import java.math.BigInteger;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.*;

class Work {
    public long end;
    public long money;
    Work(long end, long money){
        this.end = end;
        this.money = money;
    }
}
public class TanXin {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int n = Integer.parseInt(br.readLine());
        List<Work> works = new ArrayList<>();

        StringTokenizer st;
        for (int i = 0; i < n; i++) {
            String line = br.readLine();
            st = new StringTokenizer(line);
            long end = Long.parseLong(st.nextToken());
            long money = Long.parseLong(st.nextToken());
            works.add(new Work(end, money));
        }
        Collections.sort(works, Comparator.comparingLong(o -> o.end));
        
        long curEnd = works.get(0).end;
        long money = works.get(0).money;
        BigInteger result = BigInteger.ZERO;
        for (int i = 1; i < works.size(); i++) {
            Work work = works.get(i);
            if(work.end == curEnd){
                money = Math.max(money, work.money);
            } else {
                result = result.add(BigInteger.valueOf(money));
                money = work.money;
                curEnd = work.end;
            }
        }
        result = result.add(BigInteger.valueOf(money));
        System.out.println(result);
        br.close();
    }
}

3. 添加异常定位日志 #

在读取数据时加入异常捕获，打印出错的行号和内容，快速定位问题数据：

for (int i = 0; i < n; i++) {
    try {
        String line = br.readLine();
        st = new StringTokenizer(line);
        long end = Long.parseLong(st.nextToken());
        long money = Long.parseLong(st.nextToken());
        works.add(new Work(end, money));
    } catch (NumberFormatException e) {
        System.err.println("第" + (i+1) + "行数据格式错误：" + br.readLine());
        e.printStackTrace();
        return;
    }
}

内容的提问来源于stack exchange，提问作者little little