SD卡操作

一.手机内存图

2.SD卡介绍：

1.一般手机文件管理 根路径 /storage/emulated/0/或者/mnt/shell/emulated/0

2.重要代码：
(1)Environment.getExternalStorageState();// 判断SD卡是否
(2)Environment.getExternalStorageDirectory(); 获取SD卡的根目录
(3)Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES); 获取SD卡公开目录pictures文件夹
3.必须要添加读写SD卡的权限

三.代码

(1)添加读写SD卡的 权限
(2)FileUtils.java:四个方法：实现向SD卡中读写Bitmap图片和json字符串

 public class FileUtils {
    //方法1：向SD卡中写json串
    public static void write_json(String json)  {
        //判断是否挂载
        if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
            //获取SD卡根路径：mnt/shell/emulated/0
            File file=Environment.getExternalStorageDirectory();
            FileOutputStream out=null;
            try {
                //创建输出流
                out= new FileOutputStream(new File(file,"json.txt"));
                out.write(json.getBytes());
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }finally{
                if(out!=null){
                    try {
                        out.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            }

        }
    }
    //方法2：从SD卡中读取json串
    public static String read_json() {
        if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
            File file = Environment.getExternalStorageDirectory();
            FileInputStream inputStream = null;
            StringBuffer sb=new StringBuffer();
            try {
                inputStream=new FileInputStream(new File(file,"json.txt"));
                byte[] b=new byte[1024];
                int len=0;
                while((len=inputStream.read(b))!=-1){
                    sb.append(new String(b,0,len));
                }
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }finally{
                if(inputStream!=null){
                    try {
                        inputStream.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            }
            return  sb.toString();
        }else{
            return "";
        }
    }

    //方法3:从SD卡中读取一张图片
    public  static  Bitmap read_bitmap(String filename) {//filename图片名字
        Bitmap bitmap=null;
        if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
            File file=Environment.getExternalStorageDirectory();
            File file1 = new File(file, filename);
            //BitmapFactory可以直接根据SD卡图片路径转成一个bitmap对象
             bitmap= BitmapFactory.decodeFile(file1.getAbsolutePath());
        }
        return bitmap;
    }
    //方法4：网络下载一张图片存储到SD卡中
    public  static  void write_bitmap(String url) {//网址
       new MyTask().execute(url);
    }
    static class MyTask extends AsyncTask<String,String,String> {
        @Override
        protected String doInBackground(String... strings) {
            FileOutputStream out=null;
            InputStream inputStream=null;//网络连接的输入流
            HttpURLConnection connection=null;//向SD卡写的输出流
            try {
                URL url= new URL(strings[0]);
                connection= (HttpURLConnection) url.openConnection();
                connection.setConnectTimeout(5*1000);
                connection.setReadTimeout(5*1000);
                if (connection.getResponseCode()==200){
                    inputStream = connection.getInputStream();
                    //TODO 获取SD卡的路径
                    if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {//是否挂载
                        File file = Environment.getExternalStorageDirectory();
                        out = new FileOutputStream(new File(file,"xiaoyueyue.jpg"));
                        byte[] bytes=new byte[1024];
                        int len=0;
                        while((len=inputStream.read(bytes))!=-1){
                            out.write(bytes,0,len);
                        }
                    }
                }
            } catch (MalformedURLException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }finally {
                //关流
                if(out!=null){
                    try {
                        out.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
                if(inputStream!=null){
                    try {
                        inputStream.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
                if(connection!=null){
                    connection.disconnect();
                }
            }
            return null;
        }
    }
}