读写SD卡上的文件有几个步骤

1.调用Environment的getExternalStorageState()　方法判断手机上是否插入了SD卡，并且应用程序具有读写权限

　　如使用如下代码

       //如果手机已插入SD卡,且应用程序具有读写SD卡的能力,下面语句返回true

       Environment.getExternalstorageState().equals(Environment.MEDIA_MOUNTED)

2.调用Environment的getExternalStorageDirectory()方法来获取外部存储器,也就是SD卡的目录

3.使用FileInputStream,FileOutputStream,FileReader或FileWriter读，写SD卡里的文件

此外必须向AndroidManifest.xml添加SD卡的读写权限

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

下面是一个示例，用来读写SD卡里的文件

package WangLi.IO.SDCardTest;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
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 SDCardTest extends Activity {
	final String FILE_NAME = "/sdcardtest.txt";
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        //获取两个按钮
        Button read = (Button)findViewById(R.id.read);
        Button write = (Button)findViewById(R.id.write);
        //获取两个文本框
        final EditText edit1 = (EditText)findViewById(R.id.edit1);
        final EditText edit2 = (EditText)findViewById(R.id.edit2);
        //为write按钮绑定事件监听器
        write.setOnClickListener(new OnClickListener(){
        	public void onClick(View source)
        	{
        		write(edit1.getText().toString());
        		edit1.setText("");
        	}
        });
        //为read按钮绑定事件监听器
        read.setOnClickListener(new OnClickListener(){
        	public void onClick(View source)
        	{
        		//读取指定文件中的内容并显示出来
        		edit2.setText(read());
        	}
        });
    }
    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
    	{
    		//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卡根目录
    			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();
    	}
    }
}

上面有两个按钮，两个文本框，和上一篇一样，一个用来读，一个用来写

写入后，可以在DMSS里面找到刚刚写入的文件