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"/>