我使用以下代码提取一些数据并将其保存为CSV文件。但现在的问题是程序将数据写入CSV文件，每当代码再次运行时，该代码将被删除，旧结果将被替换为新结果！ 问题是，有没有办法保存结果并将新结果存储到新行？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;
}
}
答案 0 :(得分：1)
查看此库Apache POI。
以下是一些示例代码（摘自org.apache.poi.hssf.dev.HSSF测试类）： 简短的rownum;
// 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();
阅读或修改现有文件
阅读文件同样简单。要读入文件，请创建org.apache.poi.poifs.Filesystem的新实例，将开放的InputStream（例如XLS的FileInputStream）传递给构造函数。构造一个新的org.apache.poi.hssf.usermodel.HSSFWorkbook实例，将Filesystem实例传递给构造函数。从那里，您可以通过评估方法(workbook.getSheet(sheetNum)，sheet.getRow(rownum), etc)访问所有高级模型对象。
修改您已读入的文件很简单。您可以通过评估方法检索对象，通过父对象的删除方法(sheet.removeRow(hssfrow))删除它，并像创建新的xls一样创建对象。完成修改单元格后，只需像上面一样调用workbook.write(outputstream)。
答案 1 :(得分：1)
FileWriter类有另一个构造函数，它接受一个布尔值来确定是否附加到现有文件。
FileWriter(File file, boolean append)
答案 2 :(得分：1)
确定文件是否已存在
File file = new File("out.csv");
boolean exists = file.exists();
然后在文件存在的情况下以追加模式打开编写器
FileWriter fstream = new FileWriter(file, exists /*=append*/);
并仅在文件尚不存在时编写标题。
if (!exists) {
out.write("File Name;");
...
out.write(System.getProperty("line.separator"));
}
// write new rows
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"));
答案 3 :(得分：0)
你做得对（想法）只是用csv扩展名创建文件。 Check this out !
答案 4 :(得分：0)
我只想使用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。