文件下载

文件下载步骤:

·创建一个HttpURLConnection对象HttpURLConnection urlConn = (HttpURLConnection)url.openConnection();

·获得一个InputStream对象urlConn.getInputStream()

·访问网络的权限android.permission.INTERNET

访问SDCARD:

得到当前设备的SD卡目录：

Environment.getExternalStorageDirectory()

访问SD卡的权限：

android.permissin.WRITE_EXTERNAL_STORAGE

Manifest文件中需要添加:

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

main.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<Button  
    android:id="@+id/downloadTxt"
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:text="下载文本文件"
    />
<Button  
    android:id="@+id/downloadMp3"
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    android:text="下载MP3文件 "
    />
</LinearLayout>

　FileUtils.java：

package mars.utils;

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import android.os.Environment;

public class FileUtils {
	private String SDPATH;

	public String getSDPATH() {
		return SDPATH;
	}
	public FileUtils() {
		//得到当前外部存储设备的目录
		// /SDCARD
		SDPATH = Environment.getExternalStorageDirectory() + "/";
	}
	/**
	 * 在SD卡上创建文件
	 * 
	 * @throws IOException
	 */
	public File creatSDFile(String fileName) throws IOException {
		File file = new File(SDPATH + fileName);
		file.createNewFile();
		return file;
	}
	
	/**
	 * 在SD卡上创建目录
	 * 
	 * @param dirName
	 */
	public File creatSDDir(String dirName) {
		File dir = new File(SDPATH + dirName);
		dir.mkdirs();
		return dir;
	}

	/**
	 * 判断SD卡上的文件夹是否存在
	 */
	public boolean isFileExist(String fileName){
		File file = new File(SDPATH + fileName);
		return file.exists();
	}
	
	/**
	 * 将一个InputStream里面的数据写入到SD卡中
	 */
	public File write2SDFromInput(String path,String fileName,InputStream input){
		File file = null;
		OutputStream output = null;
		try{
			creatSDDir(path);
			file = creatSDFile(path + fileName);
			output = new FileOutputStream(file);
			byte buffer [] = new byte[4 * 1024];
			while((input.read(buffer)) != -1){
				output.write(buffer);
			}
			output.flush();
		}
		catch(Exception e){
			e.printStackTrace();
		}
		finally{
			try{
				output.close();
			}
			catch(Exception e){
				e.printStackTrace();
			}
		}
		return file;
	}

}

 HttpDownloader.java:

package mars.utils;

import java.io.BufferedReader;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;


public class HttpDownloader {
	private URL url = null;
	/**
	 * 根据URL下载文件，前提是这个文件当中的内容是文本，函数的返回值就是文件当中的内容
	 * 1.创建一个URL对象
	 * 2.通过URL对象，创建一个HttpURLConnection对象
	 * 3.得到InputStram
	 * 4.从InputStream当中读取数据
	 * @param urlStr
	 * @return
	 */
	public String download(String urlStr) {
		StringBuffer sb = new StringBuffer();
		String line = null;
		BufferedReader buffer = null;
		try {
			// 创建一个URL对象
			url = new URL(urlStr);
			// 创建一个Http连接
			HttpURLConnection urlConn = (HttpURLConnection) url
					.openConnection();
			// 使用IO流读取数据
			buffer = new BufferedReader(new InputStreamReader(urlConn
					.getInputStream()));     //urlConn.getInputStream得到的是字节流，new InputStreamReader()将它转化为字符流，
                                                                 //然后转化为BufferedReader,就可以使用BufferedReader的readLine()方法
			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();
	}

	/**
	 * 该函数返回整形 -1：代表下载文件出错 0：代表下载文件成功 1：代表文件已经存在
	 */
	public int downFile(String urlStr, String path, String fileName) {
		InputStream inputStream = null;
		try {
			FileUtils fileUtils = new FileUtils();
			
			if (fileUtils.isFileExist(path + fileName)) {
				return 1;
			} else {
				inputStream = getInputStreamFromUrl(urlStr);
				File resultFile = fileUtils.write2SDFromInput(path,fileName, inputStream);
				if (resultFile == null) {
					return -1;
				}
			}
		} catch (Exception e) {
			e.printStackTrace();
			return -1;
		} finally {
			try {
				inputStream.close();
			} catch (Exception e) {
				e.printStackTrace();
			}
		}
		return 0;
	}

	/**
	 * 根据URL得到输入流
	 * 
	 * @param urlStr
	 * @return
	 * @throws MalformedURLException
	 * @throws IOException
	 */
	public InputStream getInputStreamFromUrl(String urlStr)
			throws MalformedURLException, IOException {
		url = new URL(urlStr);
		HttpURLConnection urlConn = (HttpURLConnection) url.openConnection();
		InputStream inputStream = urlConn.getInputStream();
		return inputStream;
	}
}

 DownLoad.java:

package mars.download;

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

public class Download extends Activity {
    /** Called when the activity is first created. */
    private Button downloadTxtButton;
    private Button downloadMp3Button;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        downloadTxtButton = (Button)findViewById(R.id.downloadTxt);
        downloadTxtButton.setOnClickListener(new DownloadTxtListener());
        downloadMp3Button = (Button)findViewById(R.id.downloadMp3);
        downloadMp3Button.setOnClickListener(new DownloadMp3Listener());
    }
    
    class DownloadTxtListener implements OnClickListener{

		@Override
		public void onClick(View v) {
			HttpDownloader httpDownloader = new HttpDownloader();
			String lrc = httpDownloader.download("http://192.168.1.107:8080/voa1500/a1.lrc");
			System.out.println(lrc);
		}
    	
    }
    class DownloadMp3Listener implements OnClickListener{

		@Override
		public void onClick(View v) {
			// TODO Auto-generated method stub
			HttpDownloader httpDownloader = new HttpDownloader();
			int result = httpDownloader.downFile("http://192.168.1.107:8080/voa1500/a1.mp3", "voa/", "a1.mp3");
			System.out.println(result);
		}
    	
    }
    
}