Android(安卓)应用软件开发（十一）文件下载

使用Http协议下载文件，写入SD卡中

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.getInoutStream()

3、设置网络访问权限(manifest文件中设置)

android.permission.INTERNET

访问SD卡：

1. 得到SD卡的目录

Environment.getExternalStorageDirectory()

2. 访问SD卡的权限：

android.permission.WRITE_EXTERNAL_STORAGE

注意：一定不要忘记设置权限

Manifest.xml文件：

<?xml version="1.0" encoding="utf-8"?><manifest xmlns:android="http://schemas.android.com/apk/res/android"    package="mars.download"    android:versionCode="1"    android:versionName="1.0" >    <uses-sdk android:minSdkVersion="4" />    <application        android:icon="@drawable/ic_launcher"        android:label="@string/app_name" >        <activity            android:label="@string/app_name"            android:name=".DownloadActivity" >            <intent-filter >                <action android:name="android.intent.action.MAIN" />                <category android:name="android.intent.category.LAUNCHER" />            </intent-filter>        </activity>    </application>    <!-- 设置网络下载权限和SD卡写入权限 -->    <uses-permission android:name="android.permission.INTERNET"/>    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/></manifest>

DownloadActivity.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 DownloadActivity 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);        downloadMp3Button = (Button)findViewById(R.id.downloadMp3);        downloadTxtButton.setOnClickListener(new DownLoadTxtListener());        downloadMp3Button.setOnClickListener(new DownLoadMp3Listener());    }class DownLoadTxtListener implements OnClickListener{@Overridepublic void onClick(View v) {// TODO Auto-generated method stubHttpDownloader httpDownloader = new HttpDownloader();String str = httpDownloader.download("http://ishare.sina.cn/download.php?action=loading&id=13912266&cid=05_14&p=1");System.out.println("Download");System.out.println(str);}}class DownLoadMp3Listener implements OnClickListener{@Overridepublic void onClick(View v) {// TODO Auto-generated method stubString urlStr = "http://ishare.sina.cn/download.php?action=loading&id=13912266&cid=05_14&p=1";HttpDownloader httpDownloader = new HttpDownloader();int state = httpDownloader.downFile(urlStr, "voa/", "myFile");System.out.println(state);}}}

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 * 1. 创建一个URL对象 * 2. 通过URL对象，创建一个HttpURLConnection对象 * 3. 得到InputStream * 4. 从InputStream当中读取数据 *///文本文件的下载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/** * urlConn.getInputStream()得到的是字节流 * 套一层InputStreamReader得到的是字符流 * 在套一层BufferedReader得到的字符流就可以使用readLine按行读取数据了 */buffer = new BufferedReader(new InputStreamReader(urlConn.getInputStream()));while((line = buffer.readLine())!=null){sb.append(line);}}catch(Exception e){System.out.println("Error");e.printStackTrace();}finally{try{buffer.close();}catch(Exception e){e.printStackTrace();}}return sb.toString();}//下载文件并写入到SD卡中//参数：url地址，文件存储目录绝对路径，存储的文件名public int downFile(String urlStr,String path,String fileName){InputStream inputStream = null;try{FileUtils fileUtils = new FileUtils();//如果文件已经存在则返回1if(fileUtils.isFileExist(path+fileName)){return 1;}else{//根据url地址得到文件输入流inputStream = getInputStreamFromUrl(urlStr);//将输入流写入SD卡，具体过程见FileUtils.javaFile resultFile = fileUtils.writeSDFromInput(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地址得到文件输入流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 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;/** * 此类是操作SD卡文件的封装 * 包括判断文件（夹）是否存在，创建文件（夹），将文件流写入文件 *  * @author Administrator * */public class FileUtils {//SD卡的路径名private String SDPATH;public String getSDPATH(){return SDPATH;}public FileUtils(){//得到当前外部存储设备的目录SDPATH = Environment.getExternalStorageDirectory()+"/";}/** * 在SD卡上创建文件 *  */public File createSDFile(String fileName)throws IOException{//根据文件的全路径名得到文件对象File file = new File(SDPATH + fileName);//创建文件file.createNewFile();return file;}/** * 在SD卡上创建目录 */public File createSDDir(String dirName){File dir = new File(SDPATH + dirName);dir.mkdir();return dir;}/** * 判断文件夹是否存在 */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 *///参数：文件存放路径（绝对目录路径），文件名，输入流public File writeSDFromInput(String path,String fileName,InputStream input){File file = null;OutputStream output = null;try{//创建文件存储目录createSDDir(path);//创建文件file = createSDFile(path+fileName);//获取新建文件的输出流output = new FileOutputStream(file);//缓冲区byte buffer [] = new byte[4 * 1024];//从输入流中依次读入数据并输出到文件中，每次4个字节while((input.read(buffer))!= -1){output.write(buffer);}//清空缓存output.flush();}catch(Exception e){e.printStackTrace();}finally{try{//关闭输出流output.close();}catch(Exception e){e.printStackTrace();}}return file;}}

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