[英]Android JavaMail Detect If Server Goes Offline
我目前正在開發帶有后台服務和JavaMail Idle功能一起使用的電子郵件應用程序。 后台服務通過每29分鍾發出一次檢查來保持空閑功能正常工作(因為正在使用的服務器(Exchange服務器))有時在連接30分鍾后會斷開連接。
盡管這可以正常運行,但如果Exchange服務器處於脫機狀態,則應用程序將繼續嘗試無限期地重新連接到IMAP文件夾。 我注意到3AM和6AM(典型的Exchange更新時間)之間的數據使用量激增。
為了避免增加數據使用量,我正在尋求實現一些功能,使應用程序應嘗試三遍重新連接到IMAP文件夾,然后向用戶顯示警告,表明服務器處於脫機狀態,並且將在30分鍾內重試一次新的連接。
為了實現此目的,如果應用程序無法連接到IMAP文件夾,我將如何檢測Exchange服務器是否實際上處於脫機/更新狀態,並且會引發任何異常? 好像會引發異常,那么我可以保存一個本地int變量,並在每次引發異常時將其遞增1,然后在第三次向用戶顯示警報。
我當前的代碼實現如下所示:
public void checkInboxEmail(final String host, final String user, final String password) {
Log.d(TAG, "checkEmail");
this.host = host;
this.user = user;
this.password = password;
new Thread(new Runnable() {
@Override
public void run() {
try {
Log.d(TAG, "checkEmail - run()");
long databaseRecords;
//create properties field
Properties properties = new Properties();
properties.put("mail.store.protocol", "imaps");
properties.put("mail.imaps.ssl.trust", "*");
properties.put("mail.debug", "true");
emailSession = Session.getInstance(properties, new Authenticator() {
protected PasswordAuthentication getPasswordAuthentication() {
return new PasswordAuthentication(user, password);
}
});
IMAPStore imapStore = (IMAPStore) emailSession.getStore("imaps");
// imapStore.connect();
imapStore.connect(host, user, password);
if (imapStore.isConnected()) {
Log.d("MailPush", "Successfully connected to IMAP");
} else {
Log.d("MailPush", "Not connected to IMAP");
}
final IMAPFolder folder = (IMAPFolder) imapStore.getFolder("Inbox");
folder.open(IMAPFolder.READ_WRITE);
databaseRecords = dbManager.getReceivedEmailRecordsCount();
if (databaseRecords < folder.getMessageCount()) {
Log.d(TAG, "Receiving Mail...");
receiveMail(folder.getMessages());
} else {
Log.d(TAG, "Records match.");
}
Folder[] fdr = imapStore.getDefaultFolder().list();
for (Folder fd : fdr)
System.out.println(">> " + fd.getName());
folder.addMessageCountListener(new MessageCountListener() {
public void messagesAdded(MessageCountEvent e) {
System.out.println("Message Added Event Fired");
Log.d(TAG, "MESSAGE TYPE: " + e.getType());
//ADDED = 1 & REMOVED = 2
try {
Message[] messages = e.getMessages();
System.out.println("messages.length---" + messages.length);
for (Message message : messages) {
if (!message.getFlags().contains(Flags.Flag.SEEN)) {
//Message is new (hasn't been seen) > Message Details
System.out.println("---------------------------------");
System.out.println("Email Number " + (message.getMessageNumber()));
System.out.println("Subject: " + message.getSubject());
System.out.println("From: " + message.getFrom()[0]);
System.out.println("Text: " + message.getContent().toString());
String from = message.getFrom()[0].toString();
String cc = InternetAddress.toString(message.getRecipients(Message.RecipientType.CC));
Log.d(TAG, "CC 1: " + cc);
Address[] recipients = message.getRecipients(Message.RecipientType.CC);
cc = InternetAddress.toString(recipients);
Log.d(TAG, "CC 2: " + cc);
//Check Encryption Details > Add SEEN Flag > Add to database
checkEncryption((MimeMessage) message, from, cc);
}
}
} catch (Exception ex) {
ex.printStackTrace();
}
}
public void messagesRemoved(MessageCountEvent e) {
System.out.println("Message Removed Event fired");
}
});
folder.addMessageChangedListener(new MessageChangedListener() {
public void messageChanged(MessageChangedEvent e) {
System.out.println("Message Changed Event fired");
}
});
startListening(folder);
//close the store and folder objects
// emailFolder.close(false);
// store.close();
} catch (NoSuchProviderException e) {
e.printStackTrace();
} catch (MessagingException e) {
e.printStackTrace();
} catch (Exception e) {
e.printStackTrace();
}
}
}).start();
}
private void startListening(IMAPFolder imapFolder) {
Log.d(TAG, "startListening");
// We need to create a new thread to keep alive the connection
Thread t = new Thread(
new KeepAliveRunnable(imapFolder), "IdleConnectionKeepAlive"
);
t.start();
while (!Thread.interrupted()) {
Log.d(TAG, "Starting IDLE");
try {
Log.d(TAG, "Setting IDLE");
imapFolder.idle();
} catch (FolderClosedException fex) {
//Server closes connection.
Log.d(TAG, "FolderClosedException. Server potentially dropped connection. Retrying connection...");
fex.printStackTrace();
if (!isServiceRunning(MyService.class)) {
Log.d(TAG, "Service isn't running. Starting service...");
//Start service
Intent intent = new Intent(context, MyService.class);
intent.putExtra("host", host);
intent.putExtra("email", user);
intent.putExtra("password", password);
context.startService(intent);
} else {
Log.d(TAG, "Service is already running. Checking email...");
checkInboxEmail(host, user, password);
}
} catch (MessagingException e) {
//Idle isn't supported by server.
Log.d(TAG, "Messaging exception during IDLE: ");
e.printStackTrace();
}
}
// Shutdown keep alive thread
if (t.isAlive()) {
Log.d(TAG, "Interrupting thread");
t.interrupt();
}
}
private static class KeepAliveRunnable implements Runnable {
private final String TAG = getClass().getName();
private static final long KEEP_ALIVE_FREQ = 60000 * 29; // 29 minutes (Exchange connection drops after 20-30 minutes)
private IMAPFolder folder;
KeepAliveRunnable(IMAPFolder folder) {
this.folder = folder;
}
@Override
public void run() {
while (!Thread.interrupted()) {
try {
Thread.sleep(KEEP_ALIVE_FREQ);
// Perform a messageCount check just to keep alive the connection
Log.d(TAG, "Performing a messageCount check to keep the connection alive");
folder.getMessageCount();
} catch (InterruptedException e) {
// Ignore, just aborting the thread...
Log.d(TAG, "Interrupted...");
e.printStackTrace();
} catch (MessagingException e) {
// Shouldn't really happen...
Log.d(TAG, "Unexpected exception while keeping alive the IDLE connection");
e.printStackTrace();
}
}
}
}
private void receiveMail(Message[] messages) {
try {
System.out.println("messages.length---" + messages.length);
for (Message message : messages) {
if (!message.getFlags().contains(Flags.Flag.SEEN)) {
//Message is new (hasn't been seen) > Message Details
System.out.println("---------------------------------");
System.out.println("Email Number " + (message.getMessageNumber()));
System.out.println("Subject: " + message.getSubject());
System.out.println("From: " + message.getFrom()[0]);
System.out.println("Text: " + message.getContent().toString());
String from = message.getFrom()[0].toString();
String cc = InternetAddress.toString(message.getRecipients(Message.RecipientType.CC));
//Check Encryption Details > Add SEEN Flag > Add to database
checkEncryption((MimeMessage) message, from, cc);
}
}
} catch (Exception ex) {
ex.printStackTrace();
}
}
如果服務器已啟動但不接受連接,則連接將立即失敗(例外)。 如果服務器已關閉,並且您設置了連接超時,則超時后連接將失敗(例外)。
為了闡明@BillShannon的答案,如果服務器主機已啟動,但Exchange不接受連接,則連接將立即失敗,並顯示ConnectException: connection refused
。 如果服務器主機已關閉,則連接將在超時后失敗,並顯示ConnectException: connect timeout
(或可能是SocketTimeoutException
), 無論您是否設置了連接超時,因為平台始終都有一個連接超時。
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