Android 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{
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
HttpDownloader 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{
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
String 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1
if(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.java
File 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;
}
}
