Android开发中，文件下载时必须的，在此总结一下。
Android文件下载需要的准备工作：1、联网和读写SD卡的权限设置；2、HttpURLConnection的使用知识；3、流式操作读写文件的知识。
以下是我自己写的示例代码，用以理解Android文件下载。
1、AndroidMainfest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.downloader"
android:versionCode="1"
android:versionName="1.0" >
<uses-sdk
android:minSdkVersion="8"
android:targetSdkVersion="18" />
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name="com.example.downloader.MainActivity"
android:label="@string/app_name" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
</manifest>
2、activity_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"
>
<TextView
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="你好"
/>
<Button
android:id="@+id/buttontxt"
android:layout_width="300dp"
android:layout_height="wrap_content"
android:text="单击下载txt文件"
/>
<Button
android:id="@+id/buttonmp3"
android:layout_width="300dp"
android:layout_height="wrap_content"
android:text="单击下载mp3文件"
/>
</LinearLayout>
3、MainActivity.java
package com.example.downloader;
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 {
private Button buttontxt;
private Button buttonmp3;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
buttontxt=(Button)findViewById(R.id.buttontxt);
//为buttontxt添加单击事件监听器
buttontxt.setOnClickListener(new OnClickListener(){
/* (non-Javadoc)
* @see android.view.View.OnClickListener#onClick(android.view.View)
*/
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
//创建一个匿名线程用于下载文件
new Thread()
{
public void run()
{
HttpDownloader httpDownloader=new HttpDownloader();
//调用httpDownloader对象的重载方法download下载txt文件
String txt=httpDownloader.download("http://192.168.1.84:8080/Android/1.txt");
System.out.println(txt);
}
}.start();
}
});
buttonmp3=(Button)findViewById(R.id.buttonmp3);
//为buttonmp3添加单击事件监听器
buttonmp3.setOnClickListener(new OnClickListener()
{
/* (non-Javadoc)
* @see android.view.View.OnClickListener#onClick(android.view.View)
*/
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
new Thread()
{
public void run()
{
try
{
HttpDownloader httpDownloader=new HttpDownloader();
//调用httpDownloader对象的重载方法download下载mp3文件
int result=httpDownloader.download("http://192.168.1.84:8080/Android/1.mp3","Android/","music.mp3");
System.out.println(result);
}
catch(Exception e)
{
e.printStackTrace();
}
}
}.start();
}
});
}
}
4、HttpDownloader.java
package com.example.downloader;
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.URL;
public class HttpDownloader {
private URL url=null;
public String download(String urlStr)
{
StringBuffer stringbuffer=new StringBuffer();
String line;
BufferedReader bufferReader=null;
try
{
//创建一个URL对象
url=new URL(urlStr);
//得到一个HttpURLConnection对象
HttpURLConnection httpUrlConnection=(HttpURLConnection) url.openConnection();
// 得到IO流，使用IO流读取数据
bufferReader=new BufferedReader(new InputStreamReader(httpUrlConnection.getInputStream()));
while((line=bufferReader.readLine())!=null)
{
stringbuffer.append(line);
}
}
catch(Exception e)
{
e.printStackTrace();
}
return stringbuffer.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 download(String urlStr,String path,String fileName)
{
InputStream inputstream=null;
FileUtils fileUtils=new FileUtils();
if(fileUtils.isExist(path+fileName))
return 1;
else
{
try {
inputstream=getFromUrl(urlStr);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
File file=fileUtils.writeToSDPATHFromInput(path, fileName, inputstream);
if(file!=null)
return 0;
else
return -1;
}
}
//根据url字符串得到输入流
public InputStream getFromUrl(String urlStr) throws IOException
{
url=new URL(urlStr);
HttpURLConnection httpUrlConnection=(HttpURLConnection) url.openConnection();
InputStream input=httpUrlConnection.getInputStream();
return input;
}
}
5、FileUtils.java
package com.example.downloader;
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 = null;
public String getSDPATH() {
return SDPATH;
}
public FileUtils() {
// 获得当前外部存储设备SD卡的目录
SDPATH = Environment.getExternalStorageDirectory() + "/";
}
// 创建文件
public File createFile(String fileName) throws IOException {
File file = new File(SDPATH + fileName);
file.createNewFile();
return file;
}
// 创建目录
public File createDir(String fileName) throws IOException {
File dir = new File(SDPATH + fileName);
dir.mkdir();
return dir;
}
// 判断文件是否存在
public boolean isExist(String fileName) {
File file = new File(SDPATH + fileName);
return file.exists();
}
public File writeToSDPATHFromInput(String path, String fileName, InputStream inputstream) {
File file = null;
OutputStream outputstream = null;
try {
createDir(path);
file = createFile(path + fileName);
outputstream = new FileOutputStream(file);
byte buffer[] = new byte[128];
// 将输入流中的内容先输入到buffer中缓存，然后用输出流写到文件中
do {
int length = (inputstream.read(buffer));
if (length != -1) {
outputstream.write(buffer, 0, length);
} else {
break;
}
} while (true);
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
outputstream.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
return file;
}
}
注意：AndroidMainfest.xml中声明了联网权限和读写文件权限；activity_main.xml中布局了两个按钮，分别绑定下载txt文件盒下载mp3文件的事件；HttpDownloader.java里面封装了从网络地址获取流的方法；FileUtils.java实现从流将数据写入文件。写文件的时候，随时注意buffer大小，否则会导致文件为空或者写失败。
Android开发之下载文件
时间： 2024-03-10 03:04:57