android:文件下载

1 . 使用 http 协议下载文件

A ) : 创建一个 HttpURLConection 对象
HttpURLConnection urlConn = (HttpURLConnection)url.openConnection();
B ) : 获取一个 InputStream
urlConn.getInputStream();
C ) : 访问网络的权限
android.permission.INTERNET

1 . 声明控件对象 ( 略 )
2 . 获得控件对象 ( 略 )
3 . 绑定事件 ( 略 )
4 . 创建监听器对象

// 封装方法 httpDownloader

public class DownloadHelper {
	private URL url = null;
	
	public String download(String newUrl){
		StringBuffer sb = new StringBuffer();
		String line = null;
		BufferedReader br = null;
		
		//创建一个url对象；
		try {
			url = new URL(newUrl);
			//创建一个http连接
			HttpURLConnection urlConn  = (HttpURLConnection)url.openConnection();
			br = new BufferedReader(new InputStreamReader(urlConn.getInputStream()));
			while((line = br.readLine())!=null){
				sb.append(line);
				System.out.println(sb.toString());
			}
			
		} catch (Exception e) {
			e.printStackTrace();
		} finally{
			try{
				br.close();
			}catch (Exception e) {
				e.printStackTrace();
			}
		}
		return sb.toString();
	}
	
	//返回-1下载文件出错，返回0下载成功，返回1文件已经存在
	public int downFile(String urlStr,String path,String fileName){
		try {
			InputStream is = null;
			FileUtils fileUtils = new FileUtils();
			if(fileUtils.existSDFile(path+fileName)){
				return 1;
			}else{
				//inputStream = 上个从网络上获得的输入流
				is = getInputStreamFromUrl(urlStr);
				File resultFile = fileUtils.write2SDCARDFromInputSteam(path, fileName, is);
				if(resultFile==null)return -1;
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
		return 0;
	}
	
	public InputStream getInputStreamFromUrl(String newUrl){
		URL url = null;
		HttpURLConnection httpURLConnection = null;
		InputStream is = null;
		try {
			url = new URL(newUrl);
			httpURLConnection = (HttpURLConnection)url.openConnection();
			is = httpURLConnection.getInputStream();
			
		} catch (MalformedURLException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		}
		return is;
	}
}

2 . 将下载的文件写入 SDCARD
访问 SDCARD
// 得到当前设备 sdka 的目录
Environment.getExternalStorageDirectory();
// 访问 SD 卡的权限
Android.permission.WRITE_EXTERNAL_STORAGE
例 : // 一个完整的访问封装类

public class FileUtils {
	private String SDCARD = null;

	public FileUtils() {
		SDCARD = Environment.getExternalStorageDirectory() + "/";
	}

	// 创建一个目录
	public File createSDDir(String dirName) {
		File fileDir = new File(SDCARD + dirName);
		fileDir.mkdir();
		return fileDir;
	}

	// 创建一个文件；
	public File createSDFile(String fileName) throws IOException {
		File file = new File(SDCARD+fileName);   //注意在这里一定要加上主目录 SDCARD中，才可以，不然会找不到目录 。
		file.createNewFile();
		return file;
	}

	// 判断SD卡上的文件是不是存在；
	public boolean existSDFile(String fileName) {
		File file = new File(SDCARD + fileName);
		return file.exists();
	}

	// 将一个流对象写入SDCARD
	public File write2SDCARDFromInputSteam(String path, String fileName,
			InputStream is) {
		File file = null;
		OutputStream os = null;
		try {
			createSDDir(path);
			file = createSDFile(path + fileName);
			os = new FileOutputStream(file);
			byte[] buffer = new byte[4 * 1024];
			while (is.read(buffer) != -1) {
				os.write(buffer);
			}
			os.flush();
		} catch (FileNotFoundException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		} finally {
			try {
				os.close();
				is.close();
			} catch (IOException e) {
				e.printStackTrace();
			}
		}

		return file;
	}
}

最后在 AndroidManifest,xml 中加入标签
<user-permission android:name="android.permission. WRITE_EXTERNAL_STORAGE" />

DownloadActivity.java

package com.example.android.apis;

import com.example.android.download.DownloadHelper;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class DownloadActivity extends Activity {
    /** Called when the activity is first created. */
	Button down_txt = null;
	Button down_mp3 = null;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        down_txt = (Button)findViewById(R.id.download_txt);
        down_mp3 = (Button)findViewById(R.id.download_mp3);
        
        down_txt.setOnClickListener(new MyDownload_txt());
        down_mp3.setOnClickListener(new MyDownload_mp3());
    }
    
    class MyDownload_txt implements OnClickListener{

		@Override
		public void onClick(View v) {
			DownloadHelper downloadHelper = new DownloadHelper();
			downloadHelper.download("http://192.168.137.3:8080/test.lrc");
		}
    	
    }
    
    class MyDownload_mp3 implements OnClickListener{

		@Override
		public void onClick(View v) {
			DownloadHelper downloadHelper = new DownloadHelper();
			downloadHelper.downFile("http://192.168.137.3:8080/test.lrc", "test/","test.mp3");
		}
    	
    }
}