一、保存文件到手机内存

/**
     * 保存数据到手机rom的文件里面.
     * @param context 应用程序的上下文 提供环境
     * @param name 用户名
     * @param password 密码
     * @throws Exception
     */
public static void saveToRom(Context context, String name , String password) throws Exception{
        //File file = new File("/data/data/com.itheima.login/files/info.txt");
        File file = new File(context.getFilesDir(),"info.txt");//该文件在data下的files文件夹下getCacheDir()在cache文件夹下 文件大小不要超过1Mb
        FileOutputStream fos = new FileOutputStream(file);
        String txt = name+":"+password;
        fos.write(txt.getBytes());
        fos.flush();
        fos.close();
    }





/**
     * 获取保存的数据
     * @param context
     * @return
     */
public static Map<String,String> getUserInfo(Context context) {
        File file = new File(context.getFilesDir(),"info.txt");
        try {
            FileInputStream fis = new FileInputStream(file);
           //也可直接读取文件String result = StreamTools.readFromStream(fis);
            BufferedReader br = new BufferedReader(new InputStreamReader(fis));
            String str = br.readLine();
            String[] infos = str.split(":");
            Map<String,String> map = new HashMap<String, String>();
            map.put("username", infos[0]);
            map.put("password", infos[1]);
            return map;
        } catch(Exception e) {
            
            e.printStackTrace();
            return null;
        }
        
    }
//最后可以直接调用上面的方法读取信息
Map<String, String> map = getUserInfo(this);
If(map!=null){
Textview.setText(map.get(“username”));
}

二、保存文件到SD卡

获取手机sd空间的大小：

File path = Environment.getExternalStorageDirectory();
        StatFs stat = new StatFs(path.getPath());
        long blockSize = stat.getBlockSize();
        long totalBlocks = stat.getBlockCount();
        long availableBlocks = stat.getAvailableBlocks();
        long totalSize = blockSize*totalBlocks;
        long availSize = blockSize * availableBlocks;
        
        String totalStr = Formatter.formatFileSize(this,totalSize);
        String availStr = Formatter.formatFileSize(this, availSize);
        tv.setText("总空间"+totalStr+"\n"+"可用空间"+availStr);

加入写外部存储的权限：

<uses-permission android:name=”android.permission.WRITE_EXTERNAL_STORAGE”/>

public static void save(String name ,String password) throws Exception{
if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
File file = new File(Environment.getExternalStorageDirectory(),"info.txt");
//也可直接写/sdcard/info.txt 先判断sd卡是否存在
        FileOutputStream fos = new FileOutputStream(file);
        String txt = name+":"+password;
        fos.write(txt.getBytes());
        fos.flush();
        fos.close();
// 使用RandomAccessFile像文件追加内容FileOutputStream会把原有的文件内容清空
//RandomAccessFile raf = new RandomAccessFile(file,"rw");
//raf.seek(file.length());  将文件指针移动到最后
//raf.write(name.getBytes()+password.getBytes());
//raf.close();
    }
}



//读取文件 加入读取权限
public static String read(){
            try {
                if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
                    File sdcardDir = Environment.getExternalStorageDirectory();
                    FileInputStream fis = new FileInputStream(sdcardDir.getCanonicalPath() + "info.txt");
                    BufferedReader br = new BufferedReader(new InputStreamReader(fis));
                    StringBuilder sb = new StringBuilder("");
                    String line = null;
                    while ((line = br.readLine())!= null){
                        sb.append(line);
                    }
                    return sb.toString();
                }
            }  catch (Exception e) {
                
                e.printStackTrace();
            }
            return null;
        }

三、Sharedpreferences的使用

SharedPreference是开发中常用的一种存储方式，主要存储一些系统不变的参数如是否是第一次进入应用程序等，通过键值对的方式进行存储

可以存储的类型：booleans, floats, ints, longs,strings.

• getSharedPreferences() – 存储多个参数
• getPreferences() – 仅存储一个参数并且不需要指定名字（key）

写入的步骤：

1. SharedPreferences调用edit（）得到一个Editor对象
2. 使用 putBoolean() and putString()添加值
3. 提交事务完成存储

读取时：只需要调用SharedPreferences的getBoolean() and getString()

下面是示例代码：

public class MySharedPreference {
    private Context context;
    private SharedPreferences sp ;
    private Editor edit;
    public MySharedPreference(Context context){
        this.context = context;
    }
    public boolean saveMessage(String name,String pwd){
        boolean flag = false;
         sp = context.getSharedPreferences("userInfo",Context.MODE_PRIVATE);
         //MODE定义了访问的权限现在是本应用可以访问
        edit = sp.edit();
        edit.putString("name", name);
        edit.putString("pwd", pwd);
        flag = edit.commit();//提交事务将数据持久化到存储器中
        return flag;
        
    }
    public Map<String,Object> getMessage(){
        Map<String,Object> map = new HashMap<String, Object>();
        sp = context.getSharedPreferences("userInfo", Context.MODE_PRIVATE);
        String name = sp.getString("name", "");
        String pwd = sp.getString("pwd", "");
        map.put("name", name);
        map.put("pwd",pwd);
        return map;
        
    }

}