从文件读取字节？

Question

I need to read some data until file is opened at different times, but I'm not sure if pointer to data that have not been read yet is automatic increased?

My method:

//method for copy binary data from file to binaryDataBuffer
    void readcpy(String fileName, int pos, int len) {       
        try {                                              
            File lxDirectory = new File(Environment.getExternalStorageDirectory().getPath() + "/DATA/EXAMPLE/");

            File lxFile = new File(lxDirectory, (fileName);

            FileInputStream mFileInputStream = new FileInputStream(lxFile);

            mFileInputStream.read(binaryDataBuffer, pos, len);
         }  
        catch (Exception e) {
            Log.d("Exception", e.getMessage());             
        }
    }  

So, if I call this method first time and read and save 5 bytes for example, will be on next call of the method read out bytes from 5th byte? I don't close file after reading.

Answer 1

When you create an InputStream (because a FileInputStream is an InputStream ), the stream is created anew each time, and starts at the beginning of the stream (therefore the file).

If you want to read from where you left off the last time, you need to retain the offset and seek -- or retain the initial input stream you have opened.

While you can seek into a stream (using .skip() ), it is in any event NOT recommended to reopen each time, it is costly; also, when you are done with a stream, you should close it:

// with Java 7: in automatically closed
try (InputStream in = ...;) {
    // do stuff
} catch (WhateverException e) {
    // handle exception
}

// with Java 6
InputStream in = ...;
try {
    // do stuff
} catch (WhateverException e) {
    // handle exception
} finally {
    in.close();
}

Answer 2

Try this code:

public String getStringFromFile (String filePath) throws Exception {    
    File fl = new File(filePath);
    FileInputStream fin = new FileInputStream(fl);
    BufferedReader reader = new BufferedReader(new InputStreamReader(fin));
    StringBuilder sb = new StringBuilder();

    String line = null;
    while ((line = reader.readLine()) != null) {
        sb.append(line).append("\n");
    }
    String ret = sb.toString();

    //Make sure you close all streams.
    fin.close();  
    reader.close();

    return ret;
}

Answer 3

我找到RandomAccessFile，它具有我需要的偏移量。