我有一个活动（MyFTPClient）连接到FTP服务器并异步下载文件列表。 MyFTPClient.java
@Override
protected void onPreExecute(){
dialog = ProgressDialog.show(MyFTPClient.this,null,"Please wait...");
}
protected ArrayList<String> doInBackground(String... connection) {
XmlSerializer serializer = Xml.newSerializer();
StringWriter writer = new StringWriter();
Activity context = MyFTPClient.this;
final ConnectivityManager connec = (ConnectivityManager)context.getSystemService(Context.CONNECTIVITY_SERVICE);
if(connec.getNetworkInfo(0).getState() == android.net.NetworkInfo.State.CONNECTED ||
connec.getNetworkInfo(1).getState() == android.net.NetworkInfo.State.CONNECTED)
{
File sdCard = Environment.getExternalStorageDirectory();
File directory = new File(sdCard.getAbsolutePath()+"/FTPClient/FTPCL.xml");
temparrlist=listftpitems("/public_html/");
if(temparrlist!= null){
sizelist = listftpfilesize("/public_html/");
if(sizelist!=null){
try {
//xml file creation
}
}
else{
//dialog.dismiss();
MyFTPClient.this.runOnUiThread(new Runnable() {
@Override
public void run() {
AlertDialog.Builder builder = new AlertDialog.Builder(MyFTPClient.this);
builder.setTitle("Connection problem")
.setMessage("Problem in connecting to server")
.setNegativeButton("OK", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
dialog.cancel();
}
});
AlertDialog alert = builder.create();
alert.show();
}});
}
}
else if(connec.getNetworkInfo(0).getState() == android.net.NetworkInfo.State.CONNECTING ||
connec.getNetworkInfo(0).getState() == android.net.NetworkInfo.State.DISCONNECTED ||
connec.getNetworkInfo(1).getState() == android.net.NetworkInfo.State.CONNECTING ||
connec.getNetworkInfo(1).getState() == android.net.NetworkInfo.State.DISCONNECTED )
{
dialog.dismiss();
MyFTPClient.this.runOnUiThread(new Runnable() {
@Override
public void run() {
AlertDialog.Builder builder = new AlertDialog.Builder(MyFTPClient.this);
builder.setTitle("Connection problem")
.setMessage("Unable connect to host server. Please Check your Internet Connectivity.")
.setNegativeButton("OK", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
dialog.cancel();
}
});
AlertDialog alert = builder.create();
alert.show();
}});
return null;
}
return temparrlist;
}
@Override
protected void onPostExecute(ArrayList<String>result) {
dialog.dismiss();
}
listfile方法是
public ArrayList<String> listftpitems(String dir_path){
ArrayList<String> arrayList = new ArrayList<String>();
try {
mFTPClient = new FTPClient();
mFTPClient.connect("ftp.abcd.com",21);
boolean status = mFTPClient.login("usrname", "pass");
mFTPClient.setFileType(FTP.BINARY_FILE_TYPE);
mFTPClient.enterLocalPassiveMode();
if (status == true) {
Log.d(TAG, "Connection Success");
final FTPFile[] files;
try {
files = mFTPClient.listFiles("/public_html/");
for (FTPFile file : files) {
String details = file.getName();
boolean isFile = file.isFile();
if (isFile) {
Log.d(TAG, details);
arrayList.add(details);
}
}
}catch (IOException e1) {
e1.printStackTrace();
}
}
else {
Log.d(TAG, "Connection failed");
}
} catch (Exception e) {
e.printStackTrace();
Log.d(TAG, "Unable to connect");
dialog.dismiss();
}
return arrayList;
}
因此，当移动设备连接到互联网但没有数据传输时，应用程序就会崩溃。
logcat是
02-17 22:48:43.276: W/System.err(17703): java.net.UnknownHostException: Host is unresolved: ftp.andi.site11.com
02-17 22:48:43.276: W/System.err(17703): at java.net.Socket.connect(Socket.java:855)
02-17 22:48:43.286: W/System.err(17703): at org.apache.commons.net.SocketClient.connect(SocketClient.java:176)
02-17 22:48:43.306: W/System.err(17703): at com.example.ftpclient.MyFTPClient.listftpitems(MyFTPClient.java:258)
02-17 22:48:43.316: W/System.err(17703): at com.example.ftpclient.MyFTPClient$connection_test.doInBackground(MyFTPClient.java:118)
02-17 22:48:43.346: W/System.err(17703): at com.example.ftpclient.MyFTPClient$connection_test.doInBackground(MyFTPClient.java:1)
02-17 22:48:43.346: W/System.err(17703): at android.os.AsyncTask$2.call(AsyncTask.java:264)
02-17 22:48:43.356: W/System.err(17703): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
02-17 22:48:43.356: W/System.err(17703): at java.util.concurrent.FutureTask.run(FutureTask.java:137)
02-17 22:48:43.386: W/System.err(17703): at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:208)
02-17 22:48:43.406: W/System.err(17703): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
02-17 22:48:43.406: W/System.err(17703): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
02-17 22:48:43.416: W/System.err(17703): at java.lang.Thread.run(Thread.java:864)
02-17 22:48:43.416: D/MyFTPClient(17703): Unable to connect
02-17 22:48:43.426: D/memalloc(17703): /dev/pmem: Unmapping buffer base:0x54333000 size:6574080 offset:6266880
02-17 22:48:43.426: D/memalloc(17703): /dev/pmem: Unmapping buffer base:0x56187000 size:6881280 offset:6574080
02-17 22:48:43.426: D/memalloc(17703): /dev/pmem: Unmapping buffer base:0x58114000 size:7188480 offset:6881280
02-17 22:48:43.576: W/dalvikvm(17703): threadid=11: thread exiting with uncaught exception (group=0x40a7d228)
02-17 22:48:43.626: E/AndroidRuntime(17703): FATAL EXCEPTION: AsyncTask #1
02-17 22:48:43.626: E/AndroidRuntime(17703): java.lang.RuntimeException: An error occured while executing doInBackground()
02-17 22:48:43.626: E/AndroidRuntime(17703): at android.os.AsyncTask$3.done(AsyncTask.java:278)
02-17 22:48:43.626: E/AndroidRuntime(17703): at java.util.concurrent.FutureTask$Sync.innerSetException(FutureTask.java:273)
02-17 22:48:43.626: E/AndroidRuntime(17703): at java.util.concurrent.FutureTask.setException(FutureTask.java:124)
02-17 22:48:43.626: E/AndroidRuntime(17703): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:307)
02-17 22:48:43.626: E/AndroidRuntime(17703): at java.util.concurrent.FutureTask.run(FutureTask.java:137)
02-17 22:48:43.626: E/AndroidRuntime(17703): at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:208)
02-17 22:48:43.626: E/AndroidRuntime(17703): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
02-17 22:48:43.626: E/AndroidRuntime(17703): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
02-17 22:48:43.626: E/AndroidRuntime(17703): at java.lang.Thread.run(Thread.java:864)
02-17 22:48:43.626: E/AndroidRuntime(17703): Caused by: java.lang.NullPointerException
02-17 22:48:43.626: E/AndroidRuntime(17703): at org.apache.commons.net.ftp.FTP.sendCommand(FTP.java:471)
02-17 22:48:43.626: E/AndroidRuntime(17703): at org.apache.commons.net.ftp.FTP.sendCommand(FTP.java:534)
02-17 22:48:43.626: E/AndroidRuntime(17703): at org.apache.commons.net.ftp.FTP.sendCommand(FTP.java:583)
02-17 22:48:43.626: E/AndroidRuntime(17703): at org.apache.commons.net.ftp.FTP.syst(FTP.java:1393)
02-17 22:48:43.626: E/AndroidRuntime(17703): at org.apache.commons.net.ftp.FTPClient.getSystemName(FTPClient.java:1849)
02-17 22:48:43.626: E/AndroidRuntime(17703): at org.apache.commons.net.ftp.FTPClient.initiateListParsing(FTPClient.java:2263)
02-17 22:48:43.626: E/AndroidRuntime(17703): at org.apache.commons.net.ftp.FTPClient.listFiles(FTPClient.java:2046)
02-17 22:48:43.626: E/AndroidRuntime(17703): at com.example.ftpclient.MyFTPClient.listftpfilesize(MyFTPClient.java:326)
02-17 22:48:43.626: E/AndroidRuntime(17703): at com.example.ftpclient.MyFTPClient.access$0(MyFTPClient.java:322)
02-17 22:48:43.626: E/AndroidRuntime(17703): at com.example.ftpclient.MyFTPClient$connection_test.doInBackground(MyFTPClient.java:122)
02-17 22:48:43.626: E/AndroidRuntime(17703): at com.example.ftpclient.MyFTPClient$connection_test.doInBackground(MyFTPClient.java:1)
02-17 22:48:43.626: E/AndroidRuntime(17703): at android.os.AsyncTask$2.call(AsyncTask.java:264)
02-17 22:48:43.626: E/AndroidRuntime(17703): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
02-17 22:48:43.626: E/AndroidRuntime(17703): ... 5 more
listftpitem和listftpfilesize
public ArrayList<String> listftpitems(String dir_path){
ArrayList<String> arrayList = new ArrayList<String>();
try {
mFTPClient = new FTPClient();
mFTPClient.setConnectTimeout(5000);
//mFTPClient.setDefaultTimeout(10*1000);
mFTPClient.connect("ftp.andi.site11.com",21);
boolean status = mFTPClient.login("a7078185", "hack@44");
mFTPClient.setFileType(FTP.BINARY_FILE_TYPE);
mFTPClient.enterLocalPassiveMode();
if (status == true) {
Log.d(TAG, "Connection Success");
final FTPFile[] files;
try {
files = mFTPClient.listFiles("/public_html/");
for (FTPFile file : files) {
String details = file.getName();
boolean isFile = file.isFile();
if (isFile) {
Log.d(TAG, details);
arrayList.add(details);
}
}
}catch (IOException e1) {
e1.printStackTrace();
}
}
else {
Log.d(TAG, "Connection failed");
}
} catch (Exception e) {
e.printStackTrace();
Log.d(TAG, "Unable to connect");
}
return arrayList;
}
private ArrayList<Integer> listftpfilesize(String string) {
ArrayList<Integer> sizeList = new ArrayList<Integer>();
final FTPFile[] filesz;
try {
filesz = mFTPClient.listFiles("/public_html/");
for (FTPFile file : filesz) {
long details = file.getSize();
long size = details/1024;
boolean isFile = file.isFile();
if (isFile) {
Log.d(TAG, String.format("EAN-8: %d",size ));
sizeList.add((int) size);
}
}
}catch (IOException e1) {
e1.printStackTrace();
}
return sizeList;
}
我无法修复错误。谢谢。