正在尝试创建一个应用程序来下载SD卡上的文件，这是我的代码。：
public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
new Thread(new Runnable() {
public void run() {
Log.i("step0","it starts here");
URLConnection urlConnection = null;
// TODO Auto-generated method stub
try {
//fetching the URL
Log.i("step 1.1","getting the url");
URL url = new URL("http://people.opera.com/howcome/2005/ala/sample.pdf");
Log.i("step 1.2","captured the url");
urlConnection = url.openConnection();
Log.i("step 1.3","captured the url");
urlConnection.connect();
Log.i("step 1","fetching the URL");
//specifying path and file name
File sdcard = Environment.getExternalStorageDirectory();
File file = new File(sdcard, "filename.pdf");
Log.i("step 2","specifying path and file name");
//Preparing for download
FileOutputStream fileOutput = new FileOutputStream(file);
InputStream inputStream = urlConnection.getInputStream();
byte[] buffer = new byte[1024];
int bufferLength = 0;
Log.i("step 3","Preparing for download");
//Downloading
while ( (bufferLength = inputStream.read(buffer)) > 0 ) {
fileOutput.write(buffer, 0, bufferLength);
}
fileOutput.close();
Log.i("step 4","Downloading");
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}).start();
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
清单文件中的权限：
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.WRITE_SYNC_SETTINGS"/>
<uses-permission android:name="android.permission.INTERNET"/>
我的日志文件：
09-11 16:27:27.835: D/jdwp(5892): sendBufferedRequest : len=0x47
09-11 16:27:27.865: W/asset(5892): AssetManager-->addDefaultAssets CIP path not exsit!
09-11 16:27:27.920: V/PhoneWindow(5892): DecorView setVisiblity: visibility = 4
09-11 16:27:27.921: I/step0(5892): it starts here
09-11 16:27:27.922: I/step 1.1(5892): getting the url
09-11 16:27:27.923: I/step 1.2(5892): captured the url
09-11 16:27:27.924: I/step 1.3(5892): captured the url
09-11 16:27:27.935: D/libc-netbsd(5892): getaddrinfo: people.opera.com NO result from proxy
09-11 16:27:27.937: I/System.out(5892): [CDS][DNS]Unable to resolve host "people.opera.com": No address associated with hostname
09-11 16:27:27.937: W/System.err(5892): java.net.UnknownHostException: Unable to resolve host "people.opera.com": No address associated with hostname
09-11 16:27:27.938: W/System.err(5892): at java.net.InetAddress.lookupHostByName(InetAddress.java:439)
09-11 16:27:27.938: W/System.err(5892): at java.net.InetAddress.getAllByNameImpl(InetAddress.java:236)
09-11 16:27:27.938: W/System.err(5892): at java.net.InetAddress.getAllByName(InetAddress.java:214)
09-11 16:27:27.938: W/System.err(5892): at libcore.net.http.HttpConnection.<init>(HttpConnection.java:70)
09-11 16:27:27.939: W/System.err(5892): at libcore.net.http.HttpConnection.<init>(HttpConnection.java:50)
09-11 16:27:27.939: W/System.err(5892): at libcore.net.http.HttpConnection$Address.connect(HttpConnection.java:340)
09-11 16:27:27.939: W/System.err(5892): at libcore.net.http.HttpConnectionPool.get(HttpConnectionPool.java:87)
09-11 16:27:27.939: W/System.err(5892): at libcore.net.http.HttpConnection.connect(HttpConnection.java:128)
09-11 16:27:27.939: W/System.err(5892): at libcore.net.http.HttpEngine.openSocketConnection(HttpEngine.java:316)
09-11 16:27:27.939: W/System.err(5892): at libcore.net.http.HttpEngine.connect(HttpEngine.java:311)
09-11 16:27:27.939: W/System.err(5892): at libcore.net.http.HttpEngine.sendSocketRequest(HttpEngine.java:290)
09-11 16:27:27.939: W/System.err(5892): at libcore.net.http.HttpEngine.sendRequest(HttpEngine.java:240)
09-11 16:27:27.939: W/System.err(5892): at libcore.net.http.HttpURLConnectionImpl.connect(HttpURLConnectionImpl.java:81)
09-11 16:27:27.940: W/System.err(5892): at com.android.installapp.MainActivity$1.run(MainActivity.java:53)
09-11 16:27:27.940: W/System.err(5892): at java.lang.Thread.run(Thread.java:838)
09-11 16:27:27.940: W/System.err(5892): Caused by: libcore.io.GaiException: getaddrinfo failed: EAI_NODATA (No address associated with hostname)
09-11 16:27:27.941: W/System.err(5892): at libcore.io.Posix.getaddrinfo(Native Method)
09-11 16:27:27.941: W/System.err(5892): at libcore.io.ForwardingOs.getaddrinfo(ForwardingOs.java:59)
09-11 16:27:27.941: W/System.err(5892): at java.net.InetAddress.lookupHostByName(InetAddress.java:405)
09-11 16:27:27.941: W/System.err(5892): ... 14 more
09-11 16:27:27.941: W/System.err(5892): Caused by: libcore.io.ErrnoException: getaddrinfo failed: ENETUNREACH (Network is unreachable)
09-11 16:27:27.942: W/System.err(5892): ... 17 more
09-11 16:27:27.960: V/PhoneWindow(5892): DecorView setVisiblity: visibility = 0
09-11 16:27:28.064: D/libEGL(5892): loaded /system/lib/egl/libEGL_mali.so
09-11 16:27:28.072: D/libEGL(5892): loaded /system/lib/egl/libGLESv1_CM_mali.so
09-11 16:27:28.079: D/libEGL(5892): loaded /system/lib/egl/libGLESv2_mali.so
09-11 16:27:28.183: D/OpenGLRenderer(5892): Enabling debug mode 0
09-11 16:27:28.186: V/InputMethodManager(5892): onWindowFocus: null softInputMode=32 first=true flags=#1810100
09-11 16:27:28.187: V/InputMethodManager(5892): START INPUT: com.android.internal.policy.impl.PhoneWindow$DecorView{413fb9c0 V.E..... R.....ID 0,0-480,854} ic=null tba=android.view.inputmethod.EditorInfo@4141e938 controlFlags=#104
09-11 16:27:28.282: V/InputMethodManager(5892): Starting input: Bind result=InputBindResult{null com.android.inputmethod.latin/.LatinIME #47}
09-11 16:27:28.286: V/InputMethodManager(5892): onWindowFocus: null softInputMode=32 first=false flags=#1810100
09-11 16:27:28.290: V/PhoneWindow(5892): DecorView setVisiblity: visibility = 0
09-11 16:27:28.401: W/IInputConnectionWrapper(5892): showStatusIcon on inactive InputConnection
我尝试在互联网上搜索，但我无法解决这个问题。它没有下载文件。 有人可以帮忙吗？
答案 0 :(得分：11)
try {
//set the download URL, a url that points to a file on the internet
//this is the file to be downloaded
URL url = new URL("http://somewhere.com/some/webhosted/file");
//create the new connection
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
//set up some things on the connection
urlConnection.setRequestMethod("GET");
urlConnection.setDoOutput(true);
//and connect!
urlConnection.connect();
//set the path where we want to save the file
//in this case, going to save it on the root directory of the
//sd card.
File SDCardRoot = Environment.getExternalStorageDirectory();
//create a new file, specifying the path, and the filename
//which we want to save the file as.
File file = new File(SDCardRoot,"somefile.ext");
//this will be used to write the downloaded data into the file we created
FileOutputStream fileOutput = new FileOutputStream(file);
//this will be used in reading the data from the internet
InputStream inputStream = urlConnection.getInputStream();
//this is the total size of the file
int totalSize = urlConnection.getContentLength();
//variable to store total downloaded bytes
int downloadedSize = 0;
//create a buffer...
byte[] buffer = new byte[1024];
int bufferLength = 0; //used to store a temporary size of the buffer
//now, read through the input buffer and write the contents to the file
while ( (bufferLength = inputStream.read(buffer)) > 0 ) {
//add the data in the buffer to the file in the file output stream (the file on the sd card
fileOutput.write(buffer, 0, bufferLength);
//add up the size so we know how much is downloaded
downloadedSize += bufferLength;
//this is where you would do something to report the prgress, like this maybe
updateProgress(downloadedSize, totalSize);
}
//close the output stream when done
fileOutput.close();
//catch some possible errors...
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
答案 1 :(得分：2)
如果您从URL下载文件，请尝试下面带有文件夹名称和文件名的代码
public void DownloadFile(String strUrl, String folderName, String fileName) {
try {
File dir = new File(Environment.getExternalStorageDirectory() + "/"
+ folderName);
if (dir.exists() == false) {
dir.mkdirs();
}
URL url = new URL(strUrl);
File file = new File(dir, fileName);
URLConnection ucon = url.openConnection();
InputStream is = ucon.getInputStream();
BufferedInputStream bis = new BufferedInputStream(is);
ByteArrayBuffer baf = new ByteArrayBuffer(20000);
int current = 0;
while ((current = bis.read()) != -1) {
baf.append((byte) current);
}
FileOutputStream fos = new FileOutputStream(file);
fos.write(baf.toByteArray());
fos.flush();
fos.close();
} catch (IOException e) {
e.printStackTrace();
}
}