如何使用OpenCSV在同一个CSV文件上写入列，即使该文件是空的？

Question

我必须编写一个代码，该代码必须能够将列（数组字符串[]的值）和该列的头写入CSV文件。在这两种情况下，当列不存在时，以及当已经有一个名为输入值文件的文件时，它必须将列写入到一个output.csv文件中。我当然想在同一个文件上读写。代码如下：

public void afegir_columna_csv(String file, String header, String[] contingut) {
    try {
        FileWriter filewriter = new FileWriter(file, true);
        CSVWriter csvWriter = new CSVWriter(filewriter);
        FileReader filereader = new FileReader(file);
        CSVReader csvReader = new CSVReader(filereader);
        String head = header;
        String[] values = contingut;
        String[] entries = null;
        //Adding the header part:
        String[] H = csvReader.readNext();
        ArrayList listH = new ArrayList(Arrays.asList(H));
        listH.add(head);
        csvWriter.writeNext((String[]) listH.toArray());
        Añadimos los valores:
        int i=0;
        while((entries = csvReader.readNext()) != null) {
            ArrayList list = new ArrayList(Arrays.asList(entries));
            list.add(values[i]);
            csvWriter.writeNext((String[]) list.toArray());
        }
        csvWriter.close();
    }
    catch(Exception e) {
        e.printStackTrace();
    }
}

java.lang.ClassCastException: class [Ljava.lang.Object; cannot be cast to class [Ljava.lang.String; ([Ljava.lang.Object; and [Ljava.lang.String; are in module java.base of loader 'bootstrap')

Answer 1

经过一段时间的分析，我找到了一个可行的解决方案。我不太确定它是否超级高效，但它做了它的工作。必须改变我从文件、头和内容中获取信息的方式，以只获取内容。代码如下：

public void add_column_csv(String[] contingut) {
    try {
        String filename = "output_preproces.csv";
        File _file = new File(filename);
        if(_file.createNewFile()) { //If the file doesn't exists, create and add the first column
            FileWriter filewriter = new FileWriter(filename, true);
            CSVWriter csvWriter = new CSVWriter(filewriter);
            List<String[]> data = new ArrayList<String[]>();
            int i=0;
            while(i < contingut.length) {
                data.add(new String[] {contingut[i]});
                i++;
            }
            csvWriter.writeAll(data);
            csvWriter.close();
        }
        else {  //If the file already exists, add a column to it:
            FileReader filereader = new FileReader(filename);
            CSVReader csvReader = new CSVReader(filereader);
            List<String[]> data = new ArrayList<String[]>();
            int i=0;
            while(i < contingut.length) {
                String[] nextLine;
                nextLine = csvReader.readNext();
                String[] aux = new String[nextLine.length + 1];
                aux[nextLine.length] = contingut[i];
                int j = 0;
                while(j < nextLine.length) {aux[j] = nextLine[j]; j++;};
                data.add(aux);
                i++;
            }
            csvReader.close();
            new FileWriter(filename, false).close();  //delete the old content of the file
            FileWriter filewriter = new FileWriter(filename, true);
            CSVWriter csvWriter = new CSVWriter(filewriter);
            csvWriter.writeAll(data);
            csvWriter.close();
        }

    } catch(Exception e) {
        e.printStackTrace();
    }
}

正如您所看到的，我必须将CSVReader与CSVWriter分开，并将所有数据保存在列表中。