android学习笔记之文件下载

文件下载步骤:

1、创建一个HttpURLConnection对象：HttpURLConnection urlConn = (HttpURLConnection)url.openConnection();

2、获得一个InputStream对象:urlConn.getInputStream();

3、添加程序访问网络的权限：在AndroidManifest.xml文件中添加android.permission.INTERNET

下载文本文件：

public String download(String urlStr)

{

StringBuffer sb = new StringBuffer();

String line = null;

BufferedReader buffer = null;

URL url = null;

try{

url = new URL(urlStr); //urlstr为下载的文本文件的地址

HttpURLConnection urlConn = (HttpURLConnection)url.openConnection();

buffer = new BufferedReader(new InputStreamReader(urlConn.getInputStream()));

转化为容易读取的 转化为字符读取 得到二进制流

while((line = buffer.readLine()) != null){

sb.append(line);

}

}catch(Exception e){

e.printStackTrace();

}finally{

try{

buffer.close();

}catch(Exception e){

e.printStackTrace();

}

}

return sb.toString();

}

访问SDCARD的步骤

1、得到当前设备SD卡的目录：Environment.getExternalStorageDirectory();

2、设置访问SD卡的权限： android.permission.WRITE_EXTERNAL_STORAGE

String SDPATH = Environment.getExternalStorageDirectory() + "/"; 得到SD卡的目录，一般为/sdcard/

File file = new File(SDPATH + filename);

file.createNewFile(); //在SD卡上创建新文件

File dir = new File(SDPATH + dirname);

file.mkdir(); //在SD卡上创建目录

在SD卡创建了要下载的文件后，就可以通过

url = new URL(urlStr); //urlstr为下载的文本文件的地址

HttpURLConnection urlConn = (HttpURLConnection)url.openConnection();

urlConn.getInputStream();

得到InputStream对象，通过SD卡上创建的Filefile对象来写入

OutputStream output = new FileOutputStream(file);

byte buffer[] = new byte[4*1024];

while((input.read(buffer)) != -1){

output.write(buffer);

}

output.flush();

output.close();