将两个列表展平为 String .csv 样式格式

Question

我有两个列表，一个 List<String> headers 和一个 List<Row> rows，本质上是一个 List<List<String>> 我正在尝试展平这些列表以获得所需的输出：

Name,ID,Value
John Doe,1111,XXX
Jane Doe,2222,YYY

我目前在迭代器中使用遍历 headers 列表并将它们附加到字符串构建器中

        List<String> headers = ((RowListResult) result).getHeaders();
        List<RowListResult.Row> rows = ((RowListResult) result).getRows();

        output = output.concat(String.join(",", headers)).concat("\n");
        for(RowListResult.Row row: rows) output = output.concat(String.join(",", row.getColumns().toString()).concat("\n")).replace("/[[]]/", "");

        System.out.println(output);
        return null;
    }
}

我打算对行做同样的事情，但我觉得我这样做比我应该做的更难，最后我必须删除每行末尾的逗号。有没有更好的方法来完成这个？向正确的方向推动会有所帮助。我还可以分享您可能需要的任何其他内容，只需发表评论即可。

数据：

Name,ID,Value
[John Doe, 1111, XXX]
[Jane Doe, 2222, YYY]

Answer 1

您可以使用 String.join():

import java.util.Arrays;
import java.util.List;

class Main {
  public static void main(String[] args) {
    List<String> headers = Arrays.asList("header1","header2","header3");

    List<String> row1 = Arrays.asList("cell1","cell2","cell3");
    List<String> row2 = Arrays.asList("cell1","cell2","cell3");
    List<List<String>> rows = Arrays.asList(row1, row2);

    System.out.println(toString(headers, rows));
  }

  private static String toString(List<String> headers, List<List<String>> rows) {
    StringBuilder str = new StringBuilder();
    str.append(String.join(", ", headers)).append("\n");
    for (List<String> row: rows) str.append(String.join(", ", row)).append("\n");
    return str.toString();
  }
}

Answer 2

您可以使用流，然后使用收集器加入。

class Row {
    final List<String> values;
}

class Header {
    final List<String> headers;
}

@Test
public void test() {
    Header header = new Header(Arrays.asList("Name", "Number", "Description"));
    List<Row> row = Arrays.asList(new Row(Arrays.asList("John Doe", "111", "XXX")), new Row(Arrays.asList("John Doe", "112", "XXX")));

    String headerString = header.headers.stream().collect(Collectors.joining(","));
    System.out.println(headerString);

    List<String> listOfValues  = row.stream()
        .map(x -> x.values)
        .map(y -> y.stream().collect(Collectors.joining(",")))
        .collect(Collectors.toList());
    System.out.println(listOfValues);
}

输出：

Name,Number,Description
John Doe,111,XXX
John Doe,112,XXX

Answer 3

按如下操作：

import java.util.List;

public class Main {
    public static void main(String[] args) {
        List<String> header = List.of("Name", "ID", "Value");
        List<List<String>> values = List.of(List.of("John Doe", "1111", "XXX"), List.of("Jane Doe", "2222", "YYY"));
        StringBuilder sb = new StringBuilder();
        sb.append(String.join(",", header).replace("[", "").replace("]", ""));
        for (List<String> valueList : values) {
            sb.append(System.lineSeparator()).append(String.join(",", valueList).replace("[", "").replace("]", ""));
        }

        // Display
        System.out.println(sb);
    }
}

输出：

Name,ID,Value
John Doe,1111,XXX
Jane Doe,2222,YYY

将两个列表展平为 String .csv 样式格式

Flatten two lists to be in String .csv style Format

java

flat-file