編輯：關於Android編程
Android 文件下載，在Android開發中很長用到，經常需要在應用程序中下載所需要的文件比如電子書，MP3格式的音樂文件，電影等。我在這裡總結了一下，以後要用時可以直接拷貝，
代碼分析：
有兩個工具類，HttpDownloader.java類中定義兩個下載方法，download(String urlstr)下載純文本文件，downfile(String urlStr,String path,String fileName)下載字節文件類。FileUtils.java類定義了寫入sd卡的操作。Download.java類為主線程類，兩個按鈕，監聽下載事件。
注意：
在AndroidManifest.xml中添加網絡訪問權限
<uses-permission android:name="android.permission.INTERNET"/>
在AndroidManifest.xml中加入訪問SDCard的權限
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
代碼：
main.xml
[java] <?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="Android_hello word"
/>
<Button
android:id="@+id/buttontxt"
android:layout_width="300dp"
android:layout_height="wrap_content"
android:text="單擊下載txt文件"
/>
<Button
android:id="@+id/buttonmp3"
android:layout_width="300dp"
android:layout_height="wrap_content"
android:text="單擊下載mp3文件"
/>
</LinearLayout>
<?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="Android_hello word"
/>
<Button
android:id="@+id/buttontxt"
android:layout_width="300dp"
android:layout_height="wrap_content"
android:text="單擊下載txt文件"
/>
<Button
android:id="@+id/buttonmp3"
android:layout_width="300dp"
android:layout_height="wrap_content"
android:text="單擊下載mp3文件"
/>
</LinearLayout>
Download.java
[java] package com.example.download;
import android.os.Bundle;
import android.app.Activity;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
public class Download extends Activity {
private Button buttontxt;
private Button buttonmp3;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_download);
buttontxt = (Button) findViewById(R.id.buttontxt);
buttontxt.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
// TODO Auto-generated method stub
// TODO Auto-generated method stub
// 創建一個匿名線程用於下載文件
new Thread() {
public void run() {
HttpDownloader httpDownloader = new HttpDownloader();
// 調用httpDownloader對象的重載方法download下載txt文件
String txt = httpDownloader
.download("http://www.baidu.com/");
System.out.println(txt);
}
}.start();
}
});
buttonmp3 = (Button) findViewById(R.id.buttonmp3);
// 為buttonmp3添加單擊事件監聽器
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();
// 調用httpDownloader對象的重載方法download下載mp3文件
int result = httpDownloader
.downfile(
"http://sjrjy.apkzz.net/201011/291354164ea84578066309.jpg",
"Android/", "9.jpg");
System.out.println(result);
} catch (Exception e) {
e.printStackTrace();
}
}
}.start();
}
});
}
}
package com.example.download;
import android.os.Bundle;
import android.app.Activity;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
public class Download extends Activity {
private Button buttontxt;
private Button buttonmp3;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_download);
buttontxt = (Button) findViewById(R.id.buttontxt);
buttontxt.setOnClickListener(new OnClickListener() {
public void onClick(View v) {
// TODO Auto-generated method stub
// TODO Auto-generated method stub
// 創建一個匿名線程用於下載文件
new Thread() {
public void run() {
HttpDownloader httpDownloader = new HttpDownloader();
// 調用httpDownloader對象的重載方法download下載txt文件
String txt = httpDownloader
.download("http://www.baidu.com/");
System.out.println(txt);
}
}.start();
}
});
buttonmp3 = (Button) findViewById(R.id.buttonmp3);
// 為buttonmp3添加單擊事件監聽器
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();
// 調用httpDownloader對象的重載方法download下載mp3文件
int result = httpDownloader
.downfile(
"http://sjrjy.apkzz.net/201011/291354164ea84578066309.jpg",
"Android/", "9.jpg");
System.out.println(result);
} catch (Exception e) {
e.printStackTrace();
}
}
}.start();
}
});
}
}
HttpDownloader.java
[java] package com.example.download;
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 bufferedReader=null;
try {
//創建一個URL對象
url=new URL(urlstr);
//得到一個HttpURLConnection對象
HttpURLConnection httpsURLConnection=(HttpURLConnection) url.openConnection();
// 得到IO流，使用IO流讀取數據
bufferedReader=new BufferedReader(new InputStreamReader(httpsURLConnection.getInputStream()));
while((line=bufferedReader.readLine())!=null){//一行一行的讀
stringBuffer.append(line);
}
} catch (Exception e) {
e.printStackTrace();
}
return stringBuffer.toString();
}
// 該函數返回整形 -1：代表下載文件出錯 ;0：代表下載文件成功; 1：代表文件已經存在
public int downfile(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) {
e.printStackTrace();
}
File file=fileUtils.writeToSDPATHFromInput(path, fileName, inputstream);
if(file!=null)
return 0;
else
return -1;
}
}
//根據url字符串得到輸入流
public InputStream getFromUrl(String urlStr) throws IOException
{
url=new URL(urlStr);
HttpURLConnection httpUrlConnection=(HttpURLConnection) url.openConnection();
InputStream input=httpUrlConnection.getInputStream();
return input;
}
}
package com.example.download;
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 bufferedReader=null;
try {
//創建一個URL對象
url=new URL(urlstr);
//得到一個HttpURLConnection對象
HttpURLConnection httpsURLConnection=(HttpURLConnection) url.openConnection();
// 得到IO流，使用IO流讀取數據
bufferedReader=new BufferedReader(new InputStreamReader(httpsURLConnection.getInputStream()));
while((line=bufferedReader.readLine())!=null){//一行一行的讀
stringBuffer.append(line);
}
} catch (Exception e) {
e.printStackTrace();
}
return stringBuffer.toString();
}
// 該函數返回整形 -1：代表下載文件出錯 ;0：代表下載文件成功; 1：代表文件已經存在
public int downfile(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) {
e.printStackTrace();
}
File file=fileUtils.writeToSDPATHFromInput(path, fileName, inputstream);
if(file!=null)
return 0;
else
return -1;
}
}
//根據url字符串得到輸入流
public InputStream getFromUrl(String urlStr) throws IOException
{
url=new URL(urlStr);
HttpURLConnection httpUrlConnection=(HttpURLConnection) url.openConnection();
InputStream input=httpUrlConnection.getInputStream();
return input;
}
}
FileUtils.java
[java] package com.example.download;
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() {
// 獲得當前外部存儲設備SD卡的目錄
SDPATH = Environment.getExternalStorageDirectory() + "/";
}
// 創建文件
public File createFile(String fileName) throws IOException {
File file = new File(SDPATH + fileName);
file.createNewFile();
return file;
}
// 創建目錄
public File createDir(String fileName) throws IOException {
File dir = new File(SDPATH + fileName);
dir.mkdir();
return dir;
}
// 判斷文件是否存在
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[1024];
// 將輸入流中的內容先輸入到buffer中緩存，然後用輸出流寫到文件中, /*真機測試，這段可能有問題
/*while ((inputstream.read(buffer)) != -1) {
outputstream.write(buffer);
}*/
//用這段
int length;
while((length=(inputstream.read(buffer))) >0){
outputstream.write(buffer,0,length);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
inputstream.close();
outputstream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
return file;
}
}
package com.example.download;
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() {
// 獲得當前外部存儲設備SD卡的目錄
SDPATH = Environment.getExternalStorageDirectory() + "/";
}
// 創建文件
public File createFile(String fileName) throws IOException {
File file = new File(SDPATH + fileName);
file.createNewFile();
return file;
}
// 創建目錄
public File createDir(String fileName) throws IOException {
File dir = new File(SDPATH + fileName);
dir.mkdir();
return dir;
}
// 判斷文件是否存在
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[1024];
// 將輸入流中的內容先輸入到buffer中緩存，然後用輸出流寫到文件中, /*真機測試，這段可能有問題
/*while ((inputstream.read(buffer)) != -1) {
outputstream.write(buffer);
}*/
//用這段
int length;
while((length=(inputstream.read(buffer))) >0){
outputstream.write(buffer,0,length);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
inputstream.close();
outputstream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
return file;
}
}
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