如何使用零宽度不间断空格字符解决 CsvToBean header 问题？

Question

I have this code snippet that uses OpenCSV:

class Pojo {

    @CsvBindByName(column="point")
    Integer point;

    @CsvBindByName(column="name")
    String name;

}

And:

class Main {

   readFile(){

     CsvReader reader = new Csv(.....);
    
     CsvToBean<Pojo> bean = new CsvToBeanBuilder<Pojo>(reader)...;
     
     List<Pojo> list = bean.parse();
     
   }

}

Why is it - while parsing - not considering header coming with zwnbsp and that column value I am getting as null ?

Example input data:

ZWNBSPpoint

Answer 1

Not a real answer, yet a potential workaround for you, in case all CSV files to be processed share the extra zwnbsp character at the very beginning of the input (file).

In Pojo switch to:

@CsvBindByName(column="\uFEFFpoint")
Integer point;

Given input data

• var input = "point,name\n1,A";

And

CSVReader csvReader = new CSVReader(new StringReader(input));
List<Pojo> beans = new CsvToBeanBuilder<Pojo>(csvReader)
        .withType(Pojo.class)
        .withIgnoreLeadingWhiteSpace(true)
        .build()
        .parse();
System.out.println(beans);

This will produce a valid Pojo[point = 1, name = A] . I tested the above scenario with OpenCSV version 5.7.1, with Java 17 under MacOS.

Without the above adjustment to the mapping annotation ("point" -> "point"), CSVReader will interpret the extra UTF-8 symbolas an extra character for the mapping to the field point which will produce a mismatch finally resulting in a non-populated field value.

However, it seems to be incorrect/invalid CSV input, as others already pointed out in the comments below your question. OpenCSV does not seem to have a flag or switch for HeaderColumnNameMappingStrategy to circumvent such cases as reported by you.

Answer 2

Apologies for misleading you and for some strange reason, missing the BOM problem. This is not extensively tested, but works:

package com.technojeeves.opencsvbeans;

import com.opencsv.bean.CsvToBeanBuilder;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.Objects;
import java.util.List;

import java.io.IOException;
import java.io.Reader;
import java.io.FilterReader;

public class App {
    public static void main(String[] args) {
        try {
            System.out.println(new App().read(Path.of(args[0])));
        } catch (Throwable t) {
            t.printStackTrace();
        }
    }

    public List<Pojo> read(Path path) {
        try (Reader reader = new BomFilterReader(Files.newBufferedReader(path))) {
        //try (Reader reader = Files.newBufferedReader(path)) {
            return new CsvToBeanBuilder(reader).withType(Pojo.class).build().parse();
        } catch (IOException e) {
            throw new RuntimeException("Cannot read file: " + path.toFile().getName() + e);
        }
    }

}

class BomFilterReader extends FilterReader {
    public static final char BOM = '\uFEFF';
    private boolean haveReadBOM = false;
    
    public BomFilterReader(Reader in) {
        super(in);
    }

    @Override
    public int read() throws IOException {
        int c = super.read();
        if (!haveReadBOM && ((char)c == BOM)) {
            return super.read();
        }
        
        haveReadBOM = true;
        return c;
    }


    @Override
    public int read(char[] a) throws IOException {
        return read(a, 0, a.length);
    }

    @Override
    public int read(char a[], int off, int len) throws IOException {
        Objects.checkFromIndexSize(off, len, a.length);
        if (len == 0) {
            return 0;
        }

        int c = read();
        if (c == -1) {
            return -1;
        }
        a[off] = (char) c;

        int i = 1;
        try {
            for (; i < len; i++) {
                c = read();
                if (c == -1) {
                    break;
                }
                a[off + i] = (char) c;
            }
        } catch (IOException ee) {
        }
        return i;
    }

}