Android 将光标导出到CSV文件。CSV文件丢失

我有一个使用Room数据库体系结构的客户数据库。在后台，我有一个客户实体、一个客户Dao、一个客户数据存储库和一个客户视图模型。我创建的应用程序具有这4个组件。现在我需要将数据下载到CSV文件中，我正在寻找最好的方法

到目前为止，我已经根据我的研究提出了这个解决方案

拥有CSV文件写入实用程序（从internet获得）

最后，在Android清单中，我拥有以下权限：

---

命令Log.v（“MainActivity1”，arrStr[0]+arrStr[1]+arrStr[2]）；显示我的日志文件中的所有数据。。但是文件不在哪里可以找到。没有出现错误。我能够检索数据并显示在日志中，但CSV编写器似乎不工作，或者我没有获得正确的目录或其他信息。需要一切帮助

它起作用了。。我在线复制的代码缺少文件夹名称： File exportDir=新文件（Environment.getExternalStorageDirectory（），“/TestFolder”）

  import java.io.IOException;
  import java.io.PrintWriter;
  import java.io.Writer;

  public class CSVWriter {
        private PrintWriter pw;
        private char separator;
        private char quotechar;
        private char escapechar;
        private String lineEnd;

        /** The character used for escaping quotes. */
        public static final char DEFAULT_ESCAPE_CHARACTER = '"';

        /** The default separator to use if none is supplied to the constructor. */
        public static final char DEFAULT_SEPARATOR = ',';

        /**
        * The default quote character to use if none is supplied to the
        * constructor.
        */
        public static final char DEFAULT_QUOTE_CHARACTER = '"';

        /** The quote constant to use when you wish to suppress all quoting. */
        public static final char NO_QUOTE_CHARACTER = '\u0000';

        /** The escape constant to use when you wish to suppress all escaping. */
        public static final char NO_ESCAPE_CHARACTER = '\u0000';

        /** Default line terminator uses platform encoding. */
        public static final String DEFAULT_LINE_END = "\n";

        /**
         * Constructs CSVWriter using a comma for the separator.
         *
         * @param writer
         *            the writer to an underlying CSV source.
         */
         public CSVWriter(Writer writer) {
               this(writer, DEFAULT_SEPARATOR, DEFAULT_QUOTE_CHARACTER,
                  DEFAULT_ESCAPE_CHARACTER, DEFAULT_LINE_END);
         } 

         /**
          * Constructs CSVWriter with supplied separator, quote char, escape char and 
             line ending.
          *
          * @param writer
          *            the writer to an underlying CSV source.
          * @param separator
          *            the delimiter to use for separating entries
          * @param quotechar
          *            the character to use for quoted elements
          * @param escapechar
          *            the character to use for escaping quotechars or escapechars
          * @param lineEnd
          *               the line feed terminator to use
          */
          public CSVWriter(Writer writer, char separator, char quotechar, char 
       escapechar, String lineEnd) {
                this.pw = new PrintWriter(writer);
                this.separator = separator;
                this.quotechar = quotechar;
                this.escapechar = escapechar;
                this.lineEnd = lineEnd;
        }

        /**
        * Writes the next line to the file.
        *
        * @param nextLine
        *            a string array with each comma-separated element as a separate
        *            entry.
        */
        public void writeNext(String[] nextLine) {

               if (nextLine == null)
               return;

               StringBuffer sb = new StringBuffer();
               for (int i = 0; i < nextLine.length; i++) {

                      if (i != 0) {
                           sb.append(separator);
                      }  

                      String nextElement = nextLine[i];
                      if (nextElement == null)
                           continue;
                      if (quotechar !=  NO_QUOTE_CHARACTER)
                           sb.append(quotechar);
                      for (int j = 0; j < nextElement.length(); j++) {
                           char nextChar = nextElement.charAt(j);
                           if (escapechar != NO_ESCAPE_CHARACTER && nextChar == quotechar) {
                              sb.append(escapechar).append(nextChar);
                           } else if (escapechar != NO_ESCAPE_CHARACTER && nextChar == 
                                  escapechar) {
                              sb.append(escapechar).append(nextChar);
                           } else {
                              sb.append(nextChar);
                           }
                      }
                      if (quotechar != NO_QUOTE_CHARACTER)
                           sb.append(quotechar);
               }

          sb.append(lineEnd);
          pw.write(sb.toString());

          }

          /**
          * Flush underlying stream to writer.
          *
          * @throws IOException if bad things happen
          */
          public void flush() throws IOException {
               pw.flush();
          }

       /**
        * Close the underlying stream writer flushing any buffered content.
        *
        * @throws IOException if bad things happen
         *
        */
        public void close() throws IOException {
            pw.flush();
            pw.close();
        }

    }

private CustomerViewModel mCustomerViewModel;
private Cursor mCursor;

mCustomerViewModel = new ViewModelProvider(this).get(CustomerViewModel.class);
mCustomerViewModel.getAllCustomers().observe(this, new Observer<List<Customer>>() {
    @Override
    public void onChanged(List<Customer> customers) {
        mCursor = getCursorFromList(customers);
    }
});

public Cursor getCursorFromList(List<Customer> customers) {
     MatrixCursor cursor = new MatrixCursor(
        new String[]{"id", "customerCode", "branchCode", "telephone"}
     );

    for (Customer customer : customers) {
         cursor.newRow()
            .add("id", customer.getId())
            .add("customerCode", customer.getCustomerCode())
            .add("branchCode", customer.getBranchCode())
            .add("telephone", customer.getTelephone());
     }

     return cursor;
  } 

        File exportDir = new File(Environment.getExternalStorageDirectory(), "");
        if (!exportDir.exists()) {
            exportDir.mkdirs();
        }

        File file = new File(exportDir, "customer.csv");
        try {
            file.createNewFile();
            CSVWriter csvWrite = new CSVWriter(new FileWriter(file));
            csvWrite.writeNext(mCursor.getColumnNames());
            while (mCursor.moveToNext()) {
                //Which column you want to exprort
                String arrStr[] = {mCursor.getString(0), mCursor.getString(1), mCursor.getString(2)};
                Log.v("MainActivity1", arrStr[0] + arrStr[1] + arrStr[2]);
                csvWrite.writeNext(arrStr);
            }
            csvWrite.close();
            mCursor.close();
        } catch (Exception sqlEx) {
            Log.e("MainActivity1", sqlEx.getMessage(), sqlEx);
        }