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>

MainActivity.java

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;@Overrideprotected 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 {@Overridepublic 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{@Overridepublic 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 {@Overridepublic 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{@Overridepublic void run() {HttpDownloader httpDownloader = new HttpDownloader();int result = httpDownloader.downFile(urlStr_mp3, path, fileName);System.out.println(result);}}}

工具类:
HttpDownloader.java

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;}}

FileUtils.java

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// /SDCARDSDPATH = 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;}}

 --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- ---

如果不能下载，请先将windows防火墙关闭。

欢迎交流 http://blog.csdn.net/ycwol/article/details/44546337