如何将结果保存到 Excel 文件或 csv 文件？

Question

我正在使用以下代码提取一些数据并将它们保存到 CSV 文件。但现在的问题是程序将数据写入 CSV 文件，并且每当代码再次运行时，它就会被删除，旧的结果将被新的结果替换！ 问题是，有没有办法保存结果并将新结果存储在新行中？如果是，那该怎么做？

这是我的代码：

 private void writeReport() {
    BufferedWriter out = null;
   try {
        FileWriter fstream = new FileWriter("out.csv");
        out = new BufferedWriter(fstream);
        out.write("File Name;");
        out.write("Total Lines of Code;");
        out.write("Executable Lines;");
        out.write("Lines of Comments;");
        out.write("Trivial Lines;");
        out.write("Empty Lines;");
        out.write("Code Complexity;");
        out.write("Number of Files;"); //to be changed to numver of files 
        out.write("Average File Complexity;"); //to be changed to averag file complexity
        out.write("Comment Percentage;"); //total
        out.write("Total Lines of Test Code;");
        out.write("Total Comments in Tests;");
        out.write("Total Trivial Lines in Tests;");
        out.write("Total Empty Lines in Tests;");
        out.write("Total Number of Test Files;");
        out.write("Comment Presentage in Test;");

        out.write(System.getProperty("line.separator"));

      //  for (int i = 0; i < newFiles.getNrOfFiles(); i++) {
            out.write("test" + ";");
        //    out.write(newFiles.getParser(i).getSourceFile().getName()+ ";");
            out.write(String.valueOf(newFiles.sumLinesOfCode()) + ";");
            out.write(String.valueOf(newFiles.sumLinesOfStatements()) + ";");
            out.write(String.valueOf(newFiles.sumLinesOfComments()) + ";");
            out.write(String.valueOf(newFiles.sumTrivialLines()) + ";");
            out.write(String.valueOf(newFiles.sumEmptyLines()) + ";");
            out.write(String.valueOf(newFiles.sumComplexity())+ ";");
            out.write(String.valueOf(newFiles.getNrOfFiles()) + ";");
            out.write(String.valueOf(newFiles.sumAvgComplexity()) + ";");
            out.write(String.valueOf((100 * newFiles.sumLinesOfComments()) / newFiles.sumLinesOfCode() + "%") + ";");

            out.write(System.getProperty("line.separator"));

        //Close the output stream
        out.close();
    } catch (Exception e) {
        System.err.println("Error: " + e.getMessage());
      //  return;
    }
}

Answer 1

判断文件是否已经存在

File file = new File("out.csv");
boolean exists = file.exists();

如果文件存在则以追加模式打开写入器

FileWriter fstream = new FileWriter(file, exists /*=append*/);

仅在文件尚不存在时才写入标题。

if (!exists) {
    out.write("File Name;");
    ...
    out.write(System.getProperty("line.separator"));
}
// write new rows

当您使用PrintWriter 时，有些事情会变得更容易：

PrintWriter out;
...
PrintWriter out = new PrintWriter(new BufferedWriter(fstream));
...
out.println(); // easier than out.write(System.getProperty("line.separator"));

Answer 2

FileWriter 类有另一个构造函数，它接受一个布尔值来确定是否追加到现有文件。

FileWriter(File file, boolean append)

Answer 3

查看这个库Apache POI。

这里是一些示例代码（摘自并改编自 org.apache.poi.hssf.dev.HSSF 测试类）： 短行号；

// create a new file
FileOutputStream out = new FileOutputStream("workbook.xls");
// create a new workbook
Workbook wb = new HSSFWorkbook();
// create a new sheet
Sheet s = wb.createSheet();
// declare a row object reference
Row r = null;
// declare a cell object reference
Cell c = null;
// create 3 cell styles
CellStyle cs = wb.createCellStyle();
CellStyle cs2 = wb.createCellStyle();
CellStyle cs3 = wb.createCellStyle();
DataFormat df = wb.createDataFormat();
// create 2 fonts objects
Font f = wb.createFont();
Font f2 = wb.createFont();

//set font 1 to 12 point type
f.setFontHeightInPoints((short) 12);
//make it blue
f.setColor( (short)0xc );
// make it bold
//arial is the default font
f.setBoldweight(Font.BOLDWEIGHT_BOLD);

//set font 2 to 10 point type
f2.setFontHeightInPoints((short) 10);
//make it red
f2.setColor( (short)Font.COLOR_RED );
//make it bold
f2.setBoldweight(Font.BOLDWEIGHT_BOLD);

f2.setStrikeout( true );

//set cell stlye
cs.setFont(f);
//set the cell format 
cs.setDataFormat(df.getFormat("#,##0.0"));

//set a thin border
cs2.setBorderBottom(cs2.BORDER_THIN);
//fill w fg fill color
cs2.setFillPattern((short) CellStyle.SOLID_FOREGROUND);
//set the cell format to text see DataFormat for a full list
cs2.setDataFormat(HSSFDataFormat.getBuiltinFormat("text"));

// set the font
cs2.setFont(f2);

// set the sheet name in Unicode
wb.setSheetName(0, "\u0422\u0435\u0441\u0442\u043E\u0432\u0430\u044F " + 
                   "\u0421\u0442\u0440\u0430\u043D\u0438\u0447\u043A\u0430" );
// in case of plain ascii
// wb.setSheetName(0, "HSSF Test");
// create a sheet with 30 rows (0-29)
int rownum;
for (rownum = (short) 0; rownum < 30; rownum++)
{
    // create a row
    r = s.createRow(rownum);
    // on every other row
    if ((rownum % 2) == 0)
    {
        // make the row height bigger  (in twips - 1/20 of a point)
        r.setHeight((short) 0x249);
    }

    //r.setRowNum(( short ) rownum);
    // create 10 cells (0-9) (the += 2 becomes apparent later
    for (short cellnum = (short) 0; cellnum < 10; cellnum += 2)
    {
        // create a numeric cell
        c = r.createCell(cellnum);
        // do some goofy math to demonstrate decimals
        c.setCellValue(rownum * 10000 + cellnum
                + (((double) rownum / 1000)
                + ((double) cellnum / 10000)));

        String cellValue;

        // create a string cell (see why += 2 in the
        c = r.createCell((short) (cellnum + 1));

        // on every other row
        if ((rownum % 2) == 0)
        {
            // set this cell to the first cell style we defined
            c.setCellStyle(cs);
            // set the cell's string value to "Test"
            c.setCellValue( "Test" );
        }
        else
        {
            c.setCellStyle(cs2);
            // set the cell's string value to "\u0422\u0435\u0441\u0442"
            c.setCellValue( "\u0422\u0435\u0441\u0442" );
        }


        // make this column a bit wider
        s.setColumnWidth((short) (cellnum + 1), (short) ((50 * 8) / ((double) 1 / 20)));
    }
}

//draw a thick black border on the row at the bottom using BLANKS
// advance 2 rows
rownum++;
rownum++;

r = s.createRow(rownum);

// define the third style to be the default
// except with a thick black border at the bottom
cs3.setBorderBottom(cs3.BORDER_THICK);

//create 50 cells
for (short cellnum = (short) 0; cellnum < 50; cellnum++)
{
    //create a blank type cell (no value)
    c = r.createCell(cellnum);
    // set it to the thick black border style
    c.setCellStyle(cs3);
}

//end draw thick black border


// demonstrate adding/naming and deleting a sheet
// create a sheet, set its title then delete it
s = wb.createSheet();
wb.setSheetName(1, "DeletedSheet");
wb.removeSheetAt(1);
//end deleted sheet

// write the workbook to the output stream
// close our file.  (don't blow out our file handles
wb.write(out);
out.close();

读取或修改现有文件

读取文件同样简单。要读入文件，请创建org.apache.poi.poifs.Filesystem 的新实例，将打开的InputStream（例如XLS 的FileInputStream）传递给构造函数。构造 org.apache.poi.hssf.usermodel.HSSFWorkbook 的新实例，将 Filesystem 实例传递给构造函数。从那里您可以通过他们的评估方法(workbook.getSheet(sheetNum)、sheet.getRow(rownum), etc) 访问所有高级模型对象。

修改你读入的文件很简单。您通过评估器方法检索对象，通过父对象的删除方法(sheet.removeRow(hssfrow)) 将其删除，然后像创建新 xls 一样创建对象。修改完单元格后，只需像上面那样调用workbook.write(outputstream)。

这方面的一个例子可以在org.apache.poi.hssf.usermodel.examples.HSSFRead中看到

Answer 4

您做得对（想法）只需创建带有 csv 扩展名的文件。 Check this out !

Answer 5

我会简单地使用http://opencsv.sourceforge.net/

 CSVWriter writer = new CSVWriter(new FileWriter("yourfile.csv"), '\t');
     // feed in your array (or convert your data to an array)
     String[] entries = "first#second#third".split("#");
     writer.writeNext(entries);
     writer.close();

使用 Maven 或 Gradle 获取它：http://mvnrepository.com/artifact/com.opencsv/opencsv 或下载并手动将其包含在您的项目中。