android File文件的读写操作

本程序实现两个文本框和两个按钮，其中一个文本框和一个按钮用于读取文件内容、另一个文本框和另一个按钮用于写入。

java代码：

 

package com.example.activity;



import java.io.BufferedReader;

import java.io.File;

import java.io.FileInputStream;

import java.io.FileNotFoundException;

import java.io.IOException;

import java.io.InputStreamReader;

import java.io.RandomAccessFile;



import android.app.Activity;

import android.os.Bundle;

import android.os.Environment;

import android.view.View;

import android.view.View.OnClickListener;

import android.widget.Button;

import android.widget.EditText;



public class FileReadWrite extends Activity implements OnClickListener {

private static final String FILE_NAME = "/zhuhuajie.bin";

private EditText readtext;

private EditText writetext;

private Button read;

private Button write;



	@Override

protected void onCreate(Bundle savedInstanceState) {

	super.onCreate(savedInstanceState);

	setContentView(R.layout.filereadwrite);

	init();

	read.setOnClickListener(this);

	write.setOnClickListener(this);

}

	public void init(){

		readtext=(EditText)findViewById(R.id.readtext);

		writetext=(EditText)findViewById(R.id.writetext);

		read=(Button)findViewById(R.id.read);

		write=(Button)findViewById(R.id.write);

	}



	@Override

	public void onClick(View v) 

	{

		switch(v.getId())

		{

		case R.id.read:

			readtext.setText(read());

			break;

		case R.id.write:

			write(writetext.getText().toString());

			writetext.setText("");

			break;

		}



	}

	private String read(){

		try {

		//如果手机插入了SD卡，而且应用程序具有访问SD的权限

		if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED))

		{

			//获取SD卡对应的存储目录

			File sdCardDir=Environment.getExternalStorageDirectory();

			//获取指定文件对应的输入流

			

				FileInputStream fis=new FileInputStream(sdCardDir.getCanonicalPath()+FILE_NAME);

				//将指定输入流包装成BufferedReader

				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;

	}

	

	private void write(String content)

	{

		try

		{

			if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED))

			{

				File sdCardDir=Environment.getExternalStorageDirectory();

				File targetFile=new File(sdCardDir.getCanonicalPath()+FILE_NAME);

                //以指定文件创建RandomAccessFile对象

				RandomAccessFile raf=new RandomAccessFile(targetFile,"rw");

				//将文件记录指针移动到最后

				raf.seek(targetFile.length());

				//输出文件内容

				raf.write(content.getBytes());

				raf.close();

			}

		}catch(Exception e)

		{

			e.printStackTrace();

		}

	}



}

界面布局文件：

 

 

<?xml version="1.0" encoding="utf-8"?>

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:orientation="vertical" >



    <LinearLayout 

    android:layout_width="wrap_content"

    android:layout_height="wrap_content"

    android:orientation="horizontal">

    <EditText

        android:id="@+id/readtext"

        android:layout_height="wrap_content" 

        android:layout_width="180dip">

    </EditText>



    <Button

        android:id="@+id/read"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="读取" />



    </LinearLayout>

    

     <LinearLayout 

    android:layout_width="wrap_content"

    android:layout_height="wrap_content"

    android:orientation="horizontal">

    <EditText

        android:id="@+id/writetext"

        android:layout_height="wrap_content" 

        android:layout_width="180dip">

    </EditText>



    <Button

        android:id="@+id/write"

        android:layout_width="wrap_content"

        android:layout_height="wrap_content"

        android:text="写入" />



    </LinearLayout>

</LinearLayout>

另外要在AndroidMetifest.xml中加入权限配置文件.

 

 

<uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>

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