SD卡操作

package com.wms.file2;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

import android.app.Activity;
import android.os.Bundle;
import android.os.Environment;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

public class SD_Files_RW extends Activity implements OnClickListener{
    
    private String Text_of_input;
    
    private Button button_01,button_02;
    private EditText ed_text;
    private TextView text_view;
    
    private File sdCardDir;
    private File saveFile;
    private FileOutputStream outStream;
    private FileInputStream inStream;


    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        
        sdCardDir = Environment.getExternalStorageDirectory();
        saveFile = new File(sdCardDir,"wms.txt");
        
        
        
        ed_text = (EditText) findViewById(R.id.edit_01);
        text_view = (TextView) findViewById(R.id.text_01);
        
        button_01 = (Button)findViewById(R.id.button_01);
        button_01.setOnClickListener(this);
        
        button_02 = (Button)findViewById(R.id.button_02);
        button_02.setOnClickListener(this);
    }
    
    
    // Button 监听
    @Override
    public void onClick(View v)
    {
        // TODO Auto-generated method stub
        switch(v.getId())
        {
        case R.id.button_01: 
            {
                Toast.makeText(SD_Files_RW.this, "开始写入文件！", Toast.LENGTH_SHORT).show();
                Write_Files();
                //text_view.setText(ed_text.getText().toString());
            }break;
        case R.id.button_02:
            {
                Toast.makeText(SD_Files_RW.this, "开始读出文件！", Toast.LENGTH_SHORT).show();
                Read_Files();
                
            }break;    
        }
        
    }

    private void Write_Files()
    {
        
        //得到用户输入字符
        Text_of_input = ed_text.getText().toString();
        
        
        if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
        
            
        //创建  初始化 流对象
        try{
            
        outStream = new FileOutputStream(saveFile);
        }
        catch (FileNotFoundException e){
            Toast.makeText(this, "文件不存在！", Toast.LENGTH_SHORT).show();
            return ;
        }
        

        try {
            
        //把内容写入文件
        outStream.write(Text_of_input.getBytes());

        } catch (FileNotFoundException e) {
            
        // TODO Auto-generated catch block
            Toast.makeText(this, "文件未发现异常！", Toast.LENGTH_SHORT).show();

        } catch (IOException e) {

        // TODO Auto-generated catch block
            Toast.makeText(this, "文件读写异常！", Toast.LENGTH_SHORT).show();

        } 
        catch (NullPointerException e){
            Toast.makeText(this, "文件读写空指针异常！", Toast.LENGTH_SHORT).show();
          }
        finally {
    
        try {

        //关闭文件输出流


        outStream.close();

        
        } catch (IOException e) {

        // TODO Auto-generated catch block
            Toast.makeText(this, "文件读写异常！", Toast.LENGTH_SHORT).show();            

        }
        
        Toast.makeText(this, "文件写入成功！", Toast.LENGTH_SHORT).show();
        
        }
        
        }else {
            Toast.makeText(this, "内存卡不存在！", Toast.LENGTH_SHORT).show();
            return ;
         }

    }
    
    private void Read_Files()
    {
        
        int len;
        
        //然后创建一个字节数组输出流
        byte[] buffer = new byte[1024];
        
        ByteArrayOutputStream ostream = new ByteArrayOutputStream();

        if(Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)){
                        
            //创建  初始化 流对象
            try{
                
            inStream = new FileInputStream(saveFile);
            Log.v("Instance inStream", "实例化inStream！");
            }
            catch (FileNotFoundException e){
                Toast.makeText(this, "文件不存在！", Toast.LENGTH_SHORT).show();
                return ;
            }
            
            
            try{
                
            Log.v("Read", "读数据！");
                
            while((len=inStream.read(buffer))!=-1){
                ostream.write(buffer, 0, len);

            }
            
            Log.v("Read", "读成功！");
            
            }catch (IOException e){
                Toast.makeText(this, "读 异常！", Toast.LENGTH_SHORT).show();
            }
            
            
            try{
            //最后关闭输入流和输出流
            inStream.close();
            ostream.close();
            
            Log.v("Read", "读成功！");
            
            }catch (IOException e){
                Toast.makeText(this, "读 异常！", Toast.LENGTH_SHORT).show();
            }
            
            String str = new String(ostream.toByteArray());
            
            Log.v("Disp", "文本显示！");
            
            text_view.setText(str);
        
    }else{    
        Toast.makeText(this, "内存卡不存在！", Toast.LENGTH_SHORT).show();
        return ;    
    }
    }

    

}

权限：

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