文件操作工具类 内部文件 外部文件

public class FileUtils {    private static final String EXTERNAL_FILE_DIR = "/moliying_dir";    private static final String EXTERNAL_CACHE_DIR = "/moliying_cache";    public static boolean isExternalStorageWritable(){        String state = Environment.getExternalStorageState();        //判断是否存在外部存储设备(可写)        if(Environment.MEDIA_MOUNTED.equals(state)){           return true;        }        return false;    }    public static boolean isExternalStorageReadable() {        String state = Environment.getExternalStorageState();        //判断sdcard是否可读        if (Environment.MEDIA_MOUNTED.equals(state) ||                Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) {            return true;        }        return false;    }    /**     * 获取sdcard的根目录     * @return     */    public static String getSDCardPath(){        return Environment.getExternalStorageDirectory().getPath();    }    /**     * 获取外部存储的私有目录（4.4）     * @param context     * @return     */    public static File getExternalFilesDir(Context context){        File file = context.getExternalFilesDir(null);        if(file==null){            file = new File(Environment.getExternalStorageDirectory()+EXTERNAL_FILE_DIR);        }        return file;    }    /**     * 获取外部存储的私有缓存目录（4.4）     * @param context     * @return     */    public static File getCacheDir(Context context){        File file = context.getExternalCacheDir();        if(file==null){            file = new File(Environment.getExternalStorageDirectory()+EXTERNAL_CACHE_DIR);        }        return file;    }    /**     * 获取sdcard的可用空间大小     * @return     */    public static long getFreeSpace(){        return Environment.getExternalStorageDirectory().getFreeSpace();    }    /**     * 获取sdcard的总空间大小     * @return     */    public static long getTotalSpace(){        return Environment.getExternalStorageDirectory().getTotalSpace();    }}

布局文件中对应的 按钮布局

  <Button        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="写入私有数据"        android:id="@+id/button_write_private"        android:onClick="writeClick"        android:layout_alignParentTop="true"        android:layout_alignParentStart="true" />    <Button        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="读取私有数据"        android:id="@+id/button2_read_private"        android:onClick="readClick"        android:layout_below="@+id/button_write_private"        android:layout_alignParentStart="true" />    <Button        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="读取RAW文件"        android:onClick="readRAWClick"        android:id="@+id/button"        android:layout_below="@+id/button2_read_private"        android:layout_alignParentStart="true" />    <Button        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="assert文件"        android:onClick="assertClick"        android:id="@+id/button2"        android:layout_below="@+id/button"        android:layout_alignParentStart="true" />    <Button        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="内部缓冲文件"        android:onClick="innerCacheClick"        android:id="@+id/button3"        android:layout_below="@+id/button2"        android:layout_alignParentStart="true" />    <Button        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:text="检查sdcard"        android:onClick="checkSdCardClick"        android:id="@+id/button4"        android:layout_below="@+id/button3"        android:layout_alignParentStart="true" /></RelativeLayout>

MainActivity中的代码

public class MainActivity extends AppCompatActivity {    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_main);    }    public void checkSdCardClick(View view){       Log.i("sdcard",FileUtils.isExternalStorageWritable()+"-可写");       Log.i("sdcard",FileUtils.isExternalStorageReadable()+"-可读");        //获取sdcard上指定的目录：        Log.i("dir",Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES)+"");        Log.i("dir",Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_ALARMS)+"");        Log.i("dir",Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DCIM)+"");        Log.i("dir",Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOCUMENTS)+"");        Log.i("dir",Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS)+"");        Log.i("dir",Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_MOVIES)+"");        Log.i("dir",Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_MUSIC)+"");        Log.i("dir",Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_NOTIFICATIONS)+"");        Log.i("dir",Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PODCASTS)+"");        Log.i("dir",Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_RINGTONES)+"");    }    /**     * 内部缓存文件操作     * 系统在内存低的情况下，会自动清除缓存，但通常我们应该自己维护缓存     * 一般大小在1MB     * @param view     */    public void innerCacheClick(View view){        String rootpath = "http://www.baidu.com/image/";        Log.i("cache",getCacheDir().toString());        try {            //创建一个临时文件（前缀，后缀，文件目录）//            File file = File.createTempFile("url","tmp",getCacheDir());//            File file1 = getCacheDir();//            File aa = file1.listFiles();            File file2 = new File(getCacheDir()+"/xxxxxx.tmp");            BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(file2));            bos.write("今天下雨了".getBytes());            bos.close();        } catch (IOException e) {            e.printStackTrace();        }    }    public void assertClick(View v){        //只读        AssetManager am = getAssets();        try {            InputStream in = am.open("my.txt");            BufferedInputStream bis = new BufferedInputStream(in);            StringBuilder buf = new StringBuilder();            byte[] bytes = new byte[1024];            int len = -1;            try {                while ((len = bis.read(bytes)) != -1) {                    buf.append(new String(bytes, 0, len));                }                bis.close();            } catch (IOException e) {                e.printStackTrace();            }            Toast.makeText(MainActivity.this, buf, Toast.LENGTH_SHORT).show();        } catch (IOException e) {            e.printStackTrace();        }    }    /**     * 读取RAW文件(只读)     *     * @param v     */    public void readRAWClick(View v) {        BufferedInputStream in = new BufferedInputStream(getResources().openRawResource(R.raw.my));        StringBuilder buf = new StringBuilder();        byte[] bytes = new byte[1024];        int len = -1;        try {            while ((len = in.read(bytes)) != -1) {                buf.append(new String(bytes, 0, len));            }            in.close();        } catch (IOException e) {            e.printStackTrace();        }        Toast.makeText(MainActivity.this, buf, Toast.LENGTH_SHORT).show();    }    public void writeClick(View view) {        String info = "程序员好帅";        try {            BufferedOutputStream out = new BufferedOutputStream(openFileOutput("mly", Context.MODE_PRIVATE));            out.write(info.getBytes());            out.close();            Toast.makeText(MainActivity.this, "write success", Toast.LENGTH_SHORT).show();        } catch (FileNotFoundException e) {            e.printStackTrace();        } catch (IOException e) {            e.printStackTrace();        }    }    public void readClick(View view) {        try {            BufferedInputStream in = new BufferedInputStream(openFileInput("mly"));            StringBuilder buf = new StringBuilder();            byte[] bytes = new byte[1024 * 100];            int len = -1;            while ((len = in.read(bytes)) != -1) {                buf.append(new String(bytes, 0, len));            }            in.close();            Toast.makeText(MainActivity.this, buf, Toast.LENGTH_SHORT).show();        } catch (FileNotFoundException e) {            e.printStackTrace();        } catch (IOException e) {            e.printStackTrace();        }    }}