一、推断是否有sdcard卡

//推断是否有SD卡
//ture:有SD卡
//false:没有SD卡
public boolean avaiableMedia(){
    String status=Environment.getExternalStorageState();
         
    if(status.equals(Environment.MEDIA_MOUNTED)){
        return true;
    }
    else {
        return false;
    }
}

二、下载文件至sdcard卡

if(avaiableMedia()){
    HttpClient client = new DefaultHttpClient();
    HttpGet get = new HttpGet(url);
    HttpResponse response;
    try {
        response = client.execute(get);
        HttpEntity entity = response.getEntity();
        long length = entity.getContentLength();
        InputStream is = entity.getContent();
        FileOutputStream fileOutputStream = null;
        if (is != null) {
            File file = new File(Environment.getExternalStorageDirectory(),"test.apk");                         fileOutputStream = new FileOutputStream(file);
                             
            byte[] buf = new byte[1024];
            int ch = -1;
            int count = 0;
            while ((ch = is.read(buf)) != -1) {
                fileOutputStream.write(buf, 0, ch);
                count += ch;
            }
     
        }
        fileOutputStream.flush();
        if (fileOutputStream != null) {
            fileOutputStream.close();
        }
        if (is != null) {
            is.close();
        }  
    } catch (ClientProtocolException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

三、下载文件至本应用程序的数据目录

else{
    try {
    FileOutputStream outStream = this.openFileOutput("test.apk" , Context.MODE_WORLD_READABLE);
                   
    HttpClient client = new DefaultHttpClient();
        HttpGet get = new HttpGet(url);
        HttpResponse response;
                      
        response = client.execute(get);
        HttpEntity entity = response.getEntity();
        long length = entity.getContentLength();
        InputStream is = entity.getContent();
        int count = 0;
        if (is != null) {
            byte[] buf = new byte[1024];
            int ch = -1;
             
            while ((ch = is.read(buf)) >0) {
                outStream.write(buf,0,ch);
                count += ch;
                Toast.makeText(getApplicationContext(),"正在下载升级包...",Toast.LENGTH_SHORT).show();
        }
    }
                 
        outStream.flush();
        if (outStream != null) {
            outStream.close();
        }
        if (is != null) {
            is.close();
        } 
} catch (ClientProtocolException e) {
    e.printStackTrace();
} catch (IOException e) {
    e.printStackTrace();
}
}