使用BufferReader和BufferWriter写入文件时，文件创建为空

Question

I'm trying to load a JSON from webservice and write it to a file using the following code:

File cacheDir = new File(context.getCacheDir(), "texts");
cacheDir.mkdirs();
File cacheFile = new File(cacheDir, "" + articleId);
try {
    if (!cacheFile.exists()) {
        try {
            HttpURLConnection c = (HttpURLConnection) new URL(url).openConnection();
            try {
                InputStream in = c.getInputStream();
                BufferedReader reader = new BufferedReader(new InputStreamReader(in));

                // this approach fails
                /*
                BufferedWriter writer = new BufferedWriter(new FileWriter(cacheFile.getAbsolutePath()));

                String line = null;
                while ((line = reader.readLine()) != null) {
                    writer.write(line);
                    writer.newLine();
                }
                writer.flush();
                reader.close();
                writer.close();
                */

                // this approach works
                Gson g = new Gson();
                Article article = g.fromJson(reader, Article.class);
                String json = g.toJson(article);

                PrintWriter out = new PrintWriter(new FileWriter(cacheFile.getAbsolutePath()));
                out.print(json);

                out.flush();
                out.close();
                reader.close();

            } catch (IOException e) {
                Log.e(getClass().getSimpleName(), "Exception parsing JSON", e);
            } finally {
                c.disconnect();
            }
        } catch (Exception e) {
            Log.e(getClass().getSimpleName(), "Exception parsing JSON", e);
        }
    }
}

I've checked with adb shell and Android Monitor file browswer and the files seem to be created:

However, when I do cat filename from adata/data/appdir/cache no file content is printed (only command is printed again cat filename ). What is wrong with my approach?

Answer 1

You are doing all the operations inside

if (!cacheFile.exists()) {
   //your code here
}

The file.exists() method returns true if a file denoted by the path exists. So in effect what you are saying is 'do my operations if the file does not exist' which does not make sense.

Instead you could

if (!cacheFile.exists()) {
    cacheFile.createNewFile() 
}
//do the rest of your stuff here

Answer 2

Instead of use readLine to read from the InputStream, try with read and a char[]

if (in != null) {
    StringBuffer stringBuffer = new StringBuffer();
    final char[] charBuffer = new char[8 * 1024];
    reader = new BufferedReader(new InputStreamReader(in), charBuffer.length);
    int read;  
    while ((read = reader.read(charBuffer)) != -1) {
         stringBuffer.append(charBuffer, 0, read);
    }
    PrintWriter out = new PrintWriter(new FileWriter(cacheFile.getAbsolutePath()));
    out.print(stringBuffer.toString());
    out.flush();
    out.close();
    reader.close();
    Gson g = new Gson();
    Article article = g.fromJson(stringBuffer.toString(), Article.class);
}