OpenCSV引用空值

Question

使用OpenCSV库，将StatefulBeanToCsv.write()调用为null值是用引号包装的。

示例：

String[] columns = new String[] {
    "Col1",
    "Col2",
    "Col3"
};

ColumnPositionMappingStrategy strat = new ColumnPositionMappingStrategy();
strat.setColumnMapping(columns);

Writer writer = new FileWriter(outputFilePath);
StatefulBeanToCsv beanToCsv = new StatefulBeanToCsvBuilder(writer)
        .withMappingStrategy(strat)
        .build();
beanToCsv.write(items);
writer.close();

将产生：

1,"",3

当我期待：

"1",,"3"

我还没有通过.withApplyQuotesToAll(true)为所有字段设置引号。

如果我确实使用了.withApplyQuotesToAll(true)，我就会

"1","","3"

在某种程度上，这个库似乎与此正好相反：

OpenCSV CSVWriter does not add quote character for null element

如何将空值写入空/空值，而不是空字符串？

Answer 1

看起来，您提到的不调用的方法实际上需要一个布尔值。你试过以下几种方法吗？

.withApplyQuotesToAll(false)

Answer 2

有办法做到这一点。设置.withApplyQuotesToAll(false)告诉OpenCSV只引用具有特殊字符的元素，但是我们可以更改OpenCSV理解的内容，像这样扩展CSVWrite类：

public class CustomCsvWriter extends CSVWriter {

    public CustomCsvWriter(Writer writer) {
        super(writer);
    }

    @Override
    protected boolean stringContainsSpecialCharacters(String line) {
        return !line.isEmpty();
     }
}

因此，您可以创建这样的StatefulBeanToCsv：

new StatefulBeanToCsvBuilder<>(new CustomCsvWriter(writer))
   .withMappingStrategy(strat)
   .withApplyQuotesToAll(false)
   .build();

用OpenCSV 5.3测试