Android持久化技术之文件的读取与写入实例详解

package com.example.testfilestore;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.Menu;
import android.widget.EditText;
/**
 * 文件存储：写入与读取
 * @author yy
 *
 */
public class MainActivity extends Activity {
  private EditText editText;
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    //获取editText对象
    editText = (EditText) findViewById(R.id.editText1);
    //首先加载上次输入的内容
    String inputCOntent= readFromFile();
    if(!TextUtils.isEmpty(inputContent)){
      //如果上次输入的内容不为空，则加载进来
      editText.setText(inputContent);
      //设置光标位置，使之位于文本末尾，默认是在文本头部
      editText.setSelection(inputContent.length());
    }
  }
  /**
   * 当活动销毁时，保存输入的内容
   */
  @Override
  protected void onDestroy() {
    super.onDestroy();
    //获取输入的内容
    String data = editText.getText().toString();
    //写入文件
    writeToFile(data);
  }
  /**
   * 输入的内容写入文件
   */
  public void writeToFile(String data){
    FileOutputStream fileOutputStream = null;
    BufferedWriter bufferedWriter = null;
    try {
      //Context中的方法，用于存储数据
      //第一个参数是文件名
      //第二个参数是写入模式，表示覆盖写入，如果原来有内容，则会覆盖
      fileOutputStream = openFileOutput("first",Context.MODE_PRIVATE);
      bufferedWriter = new BufferedWriter(new OutputStreamWriter(fileOutputStream));
      bufferedWriter.write(data);
    } catch (FileNotFoundException e) {
      e.printStackTrace();
    } catch (IOException e) {
      e.printStackTrace();
    }finally{
        //关闭流
        try {
          if(bufferedWriter!=null){
            bufferedWriter.close();
          }
        } catch (IOException e) {
          e.printStackTrace();
        }
    }
  }
  /**
   * 从文件中读取数据
   * @return
   */
  public String readFromFile(){
    FileInputStream fileInputStream = null;
    BufferedReader bufferedReader = null;
    StringBuffer stringBuffer = new StringBuffer();
    try {
      fileInputStream = openFileInput("first");
      bufferedReader = new BufferedReader(new InputStreamReader(fileInputStream));
      String line = "";
      while((line = bufferedReader.readLine())!=null){
        stringBuffer.append(line);
      }
    } catch (FileNotFoundException e) {
      e.printStackTrace();
    } catch (IOException e) {
      e.printStackTrace();
    }finally{
      //关闭流
      try {
        if (bufferedReader != null) {
          bufferedReader.close();
        }
      } catch (IOException e) {
        e.printStackTrace();
      }
    }
    //返回
    return stringBuffer.toString();
  }
  @Override
  public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
  }
}