android - 尝试在 Android 中创建文件时出现 FileNotFoundException

Question

我正在尝试使用 Jexcel API 创建一个 excel 文件并使用我手机上的应用程序写入该文件。当我运行该应用程序时，它会抛出一个 FileNotFoundException。我什至尝试根据另一个此类问题的答案创建一个文本文件，但它会引发相同的错误。我已经在 list 中提供了适当的权限，但我似乎仍然无法查明问题所在。请帮忙。

这是我的代码

 public WritableWorkbook createWorkbook(String fileName){

    //Saving file in external storage
        File sdCard = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS);
        File directory = new File(sdCard.getAbsolutePath() + "/bills");

        //create directory if not exist
        if(!directory.isDirectory()){
            directory.mkdirs();
        }

        //file path
        file= new File(directory, fileName);
        if (file.exists())
            Log.e(taf,"file created");
        else
        Log.e(taf,"file not created");

        WorkbookSettings wbSettings = new WorkbookSettings();
        wbSettings.setLocale(new Locale("en", "EN"));
        wbSettings.setUseTemporaryFileDuringWrite(true);
        WritableWorkbook workbook;
        workbook=null;

        try {
            workbook = Workbook.createWorkbook(file, wbSettings);
            Log.i(taf,"workbook created");
            //Excel sheet name. 0 represents first sheet
            WritableSheet sheet = workbook.createSheet("MyShoppingList", 0);

            try {
                sheet.addCell(new Label(0, 0, "Subject")); // column and row
                sheet.addCell(new Label(1, 0, "Description"));


                        String title = "blaj";
                        String desc = "nxjdncj";

                        int i = 1;
                        sheet.addCell(new Label(0, i, title));
                        sheet.addCell(new Label(1, i, desc));
            } catch (WriteException e) {
                e.printStackTrace();
            }
            workbook.write();
            try {
                workbook.close();
            } catch (WriteException e) {
                e.printStackTrace();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    return workbook;
}

执行时，会打印日志消息“文件未创建”。我是 android 的新手，所以即使是最基本的问题也请指出。

谢谢。

Answer 1

实例化 File 不会创建文件，只会为您提供一个 File 实例，无论是否存在具有该特定路径和文件名的文件。

查看构造函数源码:

public File(String dirPath, String name) {
    if (name == null) {
        throw new NullPointerException("name == null");
    }
    if (dirPath == null || dirPath.isEmpty()) {
        this.path = fixSlashes(name);
    } else if (name.isEmpty()) {
        this.path = fixSlashes(dirPath);
    } else {
        this.path = fixSlashes(join(dirPath, name));
    }
}

要实际创建文件，您可以执行以下操作:

if (!file.exists()) {
    // file does not exist, create it
    file.createNewFile();
}