android-File保存数据

从内部私有存储器读取数据。使得存储器为私有的方法是对 openFileOutput() 使用MODE_PRIVATE。

 

 

public void writeInternalStoragePrivate(
        String filename, byte[] content) {
    try {
        //MODE_PRIVATE creates/replaces a file and makes 
        //  it private to your application. Other modes:
        //    MODE_WORLD_WRITEABLE
        //    MODE_WORLD_READABLE
        //    MODE_APPEND
        FileOutputStream fos = openFileOutput(filename, Context.MODE_PRIVATE);
        fos.write(content);
        fos.close();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

上述方法方法保存文件到/data/data/<package name>/files目录中了
mode取值： 
MODE_APPEND 私有（只有创建此文件的程序能够使用，其他应用程序不能访问），在原有内容基础上增加数据 
MODE_PRIVATE 私有，每次打开文件都会覆盖原来的内容 
MODE_WORLD_READABLE 可以被其他应用程序读取 
MODE_WORLD_WRITEABLE 可以被其他应用程序写入

Activity还提供了getCacheDir()和getFilesDir()方法： 
getCacheDir()方法用于获取/data/data/<package name>/cache目录 
getFilesDir()方法用于获取/data/data/<package name>/files目录

读取数据

    
/**
 * Reads a file from internal storage
 * @param filename the file to read from
 * @return the file content
 */
public byte[] readInternalStoragePrivate(String filename) {
    int len = 1024;
    byte[] buffer = new byte[len];
    try {
        FileInputStream fis = openFileInput(filename);
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        int nrb = fis.read(buffer, 0, len); // read up to len bytes
        while (nrb != -1) {
            baos.write(buffer, 0, nrb);
            nrb = fis.read(buffer, 0, len);
        }
        buffer = baos.toByteArray();
        fis.close();
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
    return buffer;
}

写到外部内存

public void writeToExternalStoragePublic(String filename, InputStream input) {

    if (isExternalStorageAvailable() && 
       !isExternalStorageReadOnly()) {
        try {
            File file = new File(path, filename);
            file.mkdirs();
            FileOutputStream ouput = new FileOutputStream(file);

            byte buffer [] = new byte[4 * 1024];
            int temp ;
            while((temp = input.read(buffer)) != -1){
                    output.write(buffer,0,temp);
               }
            output.flush();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

从外存读取

public byte[] readExternallStoragePublic(String filename) {
    int len = 1024;

    byte[] buffer = new byte[len];
    if (!isExternalStorageReadOnly()) {     
        try {
            File file = new File(path, filename);            
            FileInputStream fis = new FileInputStream(file);
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            int nrb = fis.read(buffer, 0, len); //read up to len bytes
            while (nrb != -1) {
                baos.write(buffer, 0, nrb);
                nrb = fis.read(buffer, 0, len);
            }
            buffer = baos.toByteArray();
            fis.close();
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    return buffer;
}