try {
    FileOutputStream fos = mContext.openFileOutput(mFileName,Context.MODE_PRIVATE);
    fos.write(info.getBytes());
    fos.close();
}catch (Exception e){
    e.printStackTrace();
}

 try {
      FileInputStream fis = mContext.openFileInput(mFileName);
      BufferedReader reader = new BufferedReader(new InputStreamReader(fis));
      String info = reader.readLine();
      fis.close();
      return info;
 }catch (Exception e){
      e.printStackTrace();
 }

 <string name="write_data">写入数据</string>
  <string name="read_data">读取数据</string>
  <string name="file">File</string>

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/file"
    android:layout_gravity="center_horizontal"
    />
  <LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="horizontal"
    android:layout_marginTop="@dimen/fab_margin"
    android:layout_marginBottom="@dimen/fab_margin"
    >

    <Button
      android:id="@+id/file_write"
      android:layout_height="wrap_content"
      android:layout_width="0dp"
      android:layout_weight="1"
      android:text="@string/write_data" />

    <Button
      android:id="@+id/file_read"
      android:layout_height="wrap_content"
      android:layout_width="0dp"
      android:layout_weight="1"
      android:text="@string/read_data" />

  </LinearLayout>

package com.zhangmiao.datastoragedemo;

import android.content.Context;
import android.os.Environment;
import android.util.Log;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStreamReader;
import java.io.ObjectOutputStream;

/**
 * Created by zhangmiao on 2016/12/20.
 */
public class FileDBManager {

  private File mFile;

  private Context mContext;

  private String mFileName = "myfile";

  public FileDBManager(Context context){
    mContext = context;
  }

  public void write(String info){
    try {
      FileOutputStream fos = mContext.openFileOutput(mFileName,Context.MODE_PRIVATE);
      fos.write(info.getBytes());
      fos.close();
    }catch (Exception e){
      e.printStackTrace();
    }
  }

  public String read(){
    try {
      FileInputStream fis = mContext.openFileInput(mFileName);
      BufferedReader reader = new BufferedReader(new InputStreamReader(fis));
      String info = reader.readLine();
      fis.close();
      return info;
    }catch (Exception e){
      e.printStackTrace();
    }
    return "";
  }
}

package com.zhangmiao.datastoragedemo;

import android.content.ContentResolver;
import android.content.ContentValues;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import java.util.ArrayList;
import java.util.List;

public class MainActivity extends AppCompatActivity implements View.OnClickListener {private FileDBManager mFileManager;private TextView mTableInfo;

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    mFileManager = new FileDBManager(this);

    mTableInfo = (TextView) findViewById(R.id.table_info);

    fileWrite.setOnClickListener(this);
    fileRead.setOnClickListener(this);
  }

  @Override
  public void onClick(View v) {
    switch (v.getId()) {
　　　　　　　case R.id.file_write:
        mFileManager.write("hello world!");
        break;
      case R.id.file_read:
        mTableInfo.setText(mFileManager.read());
        break;default:break;
    }
  }
}