使用opencsv读取包含'\'字符串和'\ 0'附件的CSV文件？

编程问答 2022-06-05

问题描述

我使用RFC4180Parser读取包含'\'和之前的"的文件。效果很好。

有我的代码，我正在使用RFC4180Parser和CsvToBeanBuilder来读取CSV文件。

final RFC4180Parser rfc4180Parser = new RFC4180ParserBuilder().build();
final CSVReaderBuilder csvReaderBuilder = new CSVReaderBuilder(new FileReader(inputDpaCsvFilePath))
    .withCSVParser(rfc4180Parser);
final List<MyClass> infos = new CsvToBeanBuilder<MyClass>(csvReaderBuilder.build())
    .withType(MyClass.class)
    .withSeparator(',')
    .build().parse();

原始CSV文件： 

"A","B","C","D"
"value 1","value 2","value 3","value 4"
"value\\" 11","value 22\\"","value 33","value 44"

但是现在文件格式改变了。在Header E列中添加了一些逗号。

新的CSV文件： 

"Header A","Header B","Header C","Header D","Header E"
"value1","value2","value3","value4","spA,spB,spC"
"value\\"5","value6\\"","value 7","value8",spC"
"value\\" 9","value 10","value 11","value 12","spC"

将会引发如下异常：

Exception in thread "pool-1-thread-1" java.lang.RuntimeException: com.opencsv.exceptions.CsvrequiredFieldEmptyException: Number of data fields does not match number of headers.
    at com.opencsv.bean.concurrent.ProcessCsvLine.run(ProcessCsvLine.java:101)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at java.lang.Thread.run(Thread.java:748)
Caused by: com.opencsv.exceptions.CsvrequiredFieldEmptyException: Number of data fields does not match number of headers.
    at com.opencsv.bean.HeaderColumnNameMappingStrategy.verifyLineLength(HeaderColumnNameMappingStrategy.java:110)
    at com.opencsv.bean.AbstractMappingStrategy.populateNewBean(AbstractMappingStrategy.java:313)
    at com.opencsv.bean.concurrent.ProcessCsvLine.processLine(ProcessCsvLine.java:132)
    at com.opencsv.bean.concurrent.ProcessCsvLine.run(ProcessCsvLine.java:85)
    ... 3 more

如何更新代码以读取此CSV文件？

解决方法

请参阅RCF4180 specification section 2.4

  1. 在标题和每条记录中，可能有一个或多个 字段，以逗号分隔。每行应包含相同的内容 整个文件中的字段数。 空格被视为一部分 字段，并且不能忽略。最后一个字段 记录后不能带逗号。例如：

    aaa，bbb，ccc

因此发生错误“数据字段数与标题数不匹配。”因为

"value1","value2","value3","value4","spA,spB,spC"

解析为7个字段（请注意前导空格和双引号。）：

value1
     "value2"
    "value3"
   "value4"
   "spA
 spB
 spC

但标头仅包含5个字段。

无需修改csv，我们可以使用CSVParser代替RFC4180Parser和ignoring leading white space。以下程序演示了如何使用CSVParser来解析提供的csv，以及RFC4180Parser如何使用前导空格来解析字段：

import java.io.IOException;
import java.io.StringReader;
import java.util.List;

import com.opencsv.CSVParser;
import com.opencsv.CSVParserBuilder;
import com.opencsv.CSVReaderBuilder;
import com.opencsv.RFC4180Parser;
import com.opencsv.RFC4180ParserBuilder;
import com.opencsv.exceptions.CsvException;

public class ParseCsvFieldContainsCommaAndLeadingSpaceTest {
    public static void main(String[] args) throws IOException,CsvException {
        parseWithCSVParser();
        parseWithRFC4180Parser();
    }

    private static void parseWithCSVParser() throws IOException,CsvException {
        final CSVParser parser = new CSVParserBuilder().withIgnoreLeadingWhiteSpace(true).build();
        final CSVReaderBuilder csvReaderBuilder = new CSVReaderBuilder(
                new StringReader("\"Header A\",\"Header B\",\"Header C\",\"Header D\",\"Header E\"\r\n" +
                        "\"value1\",\"value2\",\"value3\",\"value4\",\"spA,spC\""))
                                .withCSVParser(parser);
        System.out.println("Result from CSVParser");
        List<String[]> lines = csvReaderBuilder.build().readAll();
        for (String[] line : lines) {
            System.out.println(String.join(" | ",line));
        }
    }

    private static void parseWithRFC4180Parser() throws IOException,CsvException {
        final RFC4180Parser rfc4180Parser = new RFC4180ParserBuilder().build();
        final CSVReaderBuilder csvReaderBuilder = new CSVReaderBuilder(
                new StringReader("\"Header A\",spC\""))
                                ////////////////////////////////// Removed space ^ to runnable
                                .withCSVParser(rfc4180Parser);
        System.out.println("Result from RFC4180Parser");
        List<String[]> lines = csvReaderBuilder.build().readAll();
        for (String[] line : lines) {
            System.out.println(String.join(" | ",line));
        }
    }
}
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