android_文件下载

android 在网络上下载文件

步骤 : 

1.使用HTTP协议下载文件

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

- 获取一个InputStream对象 : urlConn.getInputStream()

- 访问网络的权限 : android.permission.INTERNET

2.将下载的文件写入SDCARD

- 得到当前设备SD卡的目录 : Environment.getExternalStrageDirectory()

- 访问SD卡的权限 : android.permission.WRITE_EXTERNAL_STORAGE

代码 :  

activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <Button
        android:id="@+id/btn_txt"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="download lrc" />
    
    <Button
        android:id="@+id/btn_mp3"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/btn_txt"
        android:text="download mp3" />

</RelativeLayout>

package com.chay.download;

import com.chay.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 MainActivity extends Activity {
	
	String urlStr_txt = "http://192.168.56.1:8080/mp3/wan.lrc";
	String urlStr_mp3 = "http://192.168.56.1:8080/mp3/wan.mp3";
	String path = "mp3/";
	String fileName = "wan.mp3";
	private Button downloadTxtButton;
	private Button downloadMp3Button;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		downloadTxtButton = (Button) findViewById(R.id.btn_txt);
		downloadTxtButton.setOnClickListener(new DownloadTxtListener());
		downloadMp3Button = (Button) findViewById(R.id.btn_mp3);
		downloadMp3Button.setOnClickListener(new DownloadMp3Listener());
	}

	//下载歌词文件按钮监听器
	class DownloadTxtListener implements OnClickListener {
		@Override
		public void onClick(View v) {
			Thread t = new DownloadTxtThread();  
            t.start();
            System.out.println("txt--->");
		}
	}
	//下载歌词文件线程
	class DownloadTxtThread extends Thread{
		@Override
		public void run() {
			HttpDownloader httpDownloader = new HttpDownloader();
			String lrc = httpDownloader.download(urlStr_txt);
			System.out.println(lrc);
		}
	}
	//下载MP3文件按钮监听器
	class DownloadMp3Listener implements OnClickListener {
		@Override
		public void onClick(View v) {
			Thread h = new DownMp3Thread();
			h.start();
			System.out.println("mp3--->");
		}
	}
	//下载MP3文件线程
	class DownMp3Thread extends Thread{
		@Override
		public void run() {
			HttpDownloader httpDownloader = new HttpDownloader();
			int result = httpDownloader.downFile(urlStr_mp3, path, fileName);
			System.out.println(result);
		}
	}	
}

package com.chay.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()));
			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;
	}
}

package com.chay.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;
	}
}