<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:tools="http://schemas.android.com/tools"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:orientation="vertical" >

  <TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="文件名称" />
  <EditText 
    android:id="@+id/et_filename"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:hint="file name"
    />
  <TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="文件内容" />
  <EditText 
    android:id="@+id/et_filecontent"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:lines="7"
    android:hint="file content"
    />
  <Button 
    android:id="@+id/btn_save"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:onClick="toSave"
    android:text="Save"
    />
  <Button 
    android:id="@+id/btn_get"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:onClick="getFile"
    android:text="Get"
    />


</LinearLayout>

package com.mark.storage;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import com.mark.service.FileService;


public class MainActivity extends Activity {

  private EditText mEt_filename,mEt_filecontent;
  private Button mBtn_save;

  private void init(){
    mEt_filecontent = (EditText) findViewById(R.id.et_filecontent);
    mEt_filename = (EditText) findViewById(R.id.et_filename);
    mBtn_save = (Button) findViewById(R.id.btn_save);
  }

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

  /**
   * 保存数据到一个文件中
   * @param view
   */
  public void toSave(View view) {
    String fileName = mEt_filename.getText().toString();
    String fileContent = mEt_filecontent.getText().toString();
    FileService service = new FileService(getApplicationContext());
    boolean isSucceed = service.save(fileName, fileContent);
    if(isSucceed){
      Toast.makeText(getApplicationContext(), "恭喜您保存文件成功！", Toast.LENGTH_SHORT).show();
    }else{
      Toast.makeText(getApplicationContext(), "对不起，您保存文件失败！", Toast.LENGTH_SHORT).show();
    }
  }

  public void getFile(View view){
    String fileName = mEt_filename.getText().toString();

    FileService service = new FileService(getApplicationContext());
    String fileContent = service.getFile(fileName);
    if(fileContent!=null || !fileContent.equals("")) {
      mEt_filecontent.setText(fileContent);
    }else{
      Toast.makeText(getApplicationContext(), "对不起，读取文件失败！", Toast.LENGTH_SHORT).show();
    }


  }


}

package com.mark.service;

import java.io.ByteArrayOutputStream;
import java.io.FileInputStream;
import java.io.FileOutputStream;

import android.content.Context;

public class FileService {

  //android自带的可以快速获得文件输出流的一个类，注意参数不能是路径，只能是文件名称
  private Context mContext;

  public FileService(Context context) {
    this.mContext = context;
  }

  /**
   * 保存文件的一个方法
   * @param fileName
   * @param fileContent
   * @return
   */
  public boolean save(String fileName, String fileContent) {
    try {
      //采用Context.MODE_PRIVATE模式的话，只允许本应用访问此文件，并且熟覆盖式的添加数据
      FileOutputStream fos = mContext.openFileOutput(fileName, Context.MODE_PRIVATE);
      fos.write(fileContent.getBytes());
      fos.close();
      return true;
    } catch (Exception e) {
      e.printStackTrace();
      return false;
    }

  }

  /**
   * 获得之前保存过的文件的详细的信息
   * @param fileName
   * @return
   */
  public String getFile(String fileName) {
    String fileContent = "";
    try{

      FileInputStream fis = mContext.openFileInput(fileName);
      byte[] buf = new byte[1024];
      int len;
      ByteArrayOutputStream bais = new ByteArrayOutputStream();
      while((len = fis.read(buf))!= -1){
        bais.write(buf, 0, len);
      }
      byte[] data = bais.toByteArray();
      fileContent = new String(data);
      fis.close();
      return fileContent;
    }catch(Exception e){
      e.printStackTrace();
      return "对不起，读取文件失败！";
    }

  }


}