如何获取 Android 上的电子邮件？

Question

我正在尝试开发一个从非 Google 的 POP3 服务器获取电子邮件的应用程序，但我遇到了很多问题。
我正在使用 JavaMail 库并遵循 TutorialsPoint 教程。他们的 pop3 示例在 Eclipse/desktop 上运行良好，但是当我在 Android 上移动代码时，它永远不会运行，我很沮丧。
在 logcat 中，我得到了所有错误，其中第一个指出

W/System.err﹕ android.os.NetworkOnMainThreadException even though I'm using AsyncTask (probably not correctly).

有什么方法可以让 AsyncTask 正常工作吗？

此外，有没有一种方法可以让我不使用像 K-9 Mail 这样的专业应用程序来做这样的事情？

代码如果有人感兴趣：

 public class FetchPop extends AsyncTask{

    public static void fetch(String pop3Host, String storeType, String user,
                             String password) {
        try {
            // create properties field
            Properties properties = new Properties();
            properties.put("mail.store.protocol", "pop3");
            properties.put("mail.pop3.host", pop3Host);
            properties.put("mail.pop3.port", "995");
            properties.put("mail.pop3.starttls.enable", "true");
            Session emailSession = Session.getDefaultInstance(properties);
            // emailSession.setDebug(true);

            // create the POP3 store object and connect with the pop server
            Store store = emailSession.getStore("pop3s");

            store.connect(pop3Host, user, password);

            // create the folder object and open it
            Folder emailFolder = store.getFolder("INBOX");
            emailFolder.open(Folder.READ_ONLY);

            BufferedReader reader = new BufferedReader(new InputStreamReader(
                    System.in));

            // retrieve the messages from the folder in an array and print it
            Message[] messages = emailFolder.getMessages();
            Log.d("No. messages:", messages.length + ""); //just the number at first


/*for (int i = 0; i < messages.length; i++) {
                Message message = messages[i];
                writePart(message);
                String line = reader.readLine();
                if ("YES".equals(line)) {
                    message.writeTo(System.out);
                } else if ("QUIT".equals(line)) {
                    break;
                }
            }*/
            // close the store and folder objects
            emailFolder.close(false);
            store.close();

        } catch (NoSuchProviderException e) {
            e.printStackTrace();
        } catch (MessagingException e) {
            e.printStackTrace();
        } /*catch (IOException e) {
            e.printStackTrace();
        }*/ catch (Exception e) {
            e.printStackTrace();
        }
    }


        @Override
        protected Object doInBackground(Object[] params) {
            String host = "pop.gmail.com";// I tried google's pop 
            String mailStoreType = "pop3";
            String username =
                    "myusername";// change accordingly
            String password = "notmyrealpass";// change accordingly

            //Call method fetch
            fetch(host, mailStoreType, username, password);
            Log.d("mytag","done!");
            return null;
        }

    public void GO() {
        doInBackground(null);
    }





    /*
    * This method checks for content-type
    * based on which, it processes and
    * fetches the content of the message
    */
    public static void writePart(Part p) throws Exception {
        if (p instanceof Message)
            //Call methos writeEnvelope
            writeEnvelope((Message) p);

       /* System.out.println("----------------------------");
        System.out.println("CONTENT-TYPE: " + p.getContentType());*/

        //check if the content is plain text
        if (p.isMimeType("text/plain")) {
            System.out.println("This is plain text");
            System.out.println("---------------------------");
            System.out.println((String) p.getContent());
        }
        //check if the content has attachment
        else if (p.isMimeType("multipart/*")) {
            System.out.println("This is a Multipart");
            System.out.println("---------------------------");
            Multipart mp = (Multipart) p.getContent();
            int count = mp.getCount();
            for (int i = 0; i < count; i++)
                writePart(mp.getBodyPart(i));
        }
        //check if the content is a nested message
        else if (p.isMimeType("message/rfc822")) {
            System.out.println("This is a Nested Message");
            System.out.println("---------------------------");
            writePart((Part) p.getContent());
        }
        //check if the content is an inline image
        else if (p.isMimeType("image/jpeg")) {
            System.out.println("--------> image/jpeg");
            Object o = p.getContent();

            InputStream x = (InputStream) o;
            // Construct the required byte array
            int i;
            byte[] bArray = new byte[0];
            System.out.println("x.length = " + x.available());
            while ((i = (int) ((InputStream) x).available()) > 0) {
                int result = (int) (((InputStream) x).read(bArray));
                if (result == -1)
                    i=0;
                bArray = new byte[x.available()];

                break;
            }
            FileOutputStream f2 = new FileOutputStream("/tmp/image.jpg");
            f2.write(bArray);
        }
        else if (p.getContentType().contains("image/")) {
            System.out.println("content type" + p.getContentType());
            File f = new File("image" + new Date().getTime() + ".jpg");
            DataOutputStream output = new DataOutputStream(
                    new BufferedOutputStream(new FileOutputStream(f)));
            com.sun.mail.util.BASE64DecoderStream test =
                    (com.sun.mail.util.BASE64DecoderStream) p
                            .getContent();
            byte[] buffer = new byte[1024];
            int bytesRead;
            while ((bytesRead = test.read(buffer)) != -1) {
                output.write(buffer, 0, bytesRead);
            }
        }
        else {
            Object o = p.getContent();
            if (o instanceof String) {
                System.out.println("This is a string");
                System.out.println("---------------------------");
                System.out.println((String) o);
            }
            else if (o instanceof InputStream) {
                System.out.println("This is just an input stream");
                System.out.println("---------------------------");
                InputStream is = (InputStream) o;
                is = (InputStream) o;
                int c;
                while ((c = is.read()) != -1)
                    System.out.write(c);
            }
            else {
                System.out.println("This is an unknown type");
                System.out.println("---------------------------");
                System.out.println(o.toString());
            }
        }

    }
    /*
    * This method would print FROM,TO and SUBJECT of the message
    */
    public static void writeEnvelope(Message m) throws Exception {
        System.out.println("This is the message envelope");
        System.out.println("---------------------------");
        Address[] a;

        // FROM
        if ((a = m.getFrom()) != null) {
            for (int j = 0; j < a.length; j++)
                System.out.println("FROM: " + a[j].toString());
        }

        // TO
        if ((a = m.getRecipients(Message.RecipientType.TO)) != null) {
            for (int j = 0; j < a.length; j++)
                System.out.println("TO: " + a[j].toString());
        }

        // SUBJECT
        if (m.getSubject() != null)
            System.out.println("SUBJECT: " + m.getSubject());

    }

}

Answer 1

试试这个库 https://code.google.com/p/javamail-android/。

不知道库的确切状态，但他们在这个博客中有一个很好的例子 (http://www.jondev.net/articles/Sending_Emails_without_User_Intervention_%28no_Intents%29_in_Android)，他们说

"this is a special version of the JavaMail API, which was written specifically for Android."

Answer 2

看起来您没有正确使用 AsyncTask，尤其是看到您有一个直接调用 doInBackground() 的 GO() 方法。去掉GO()方法，不需要了

执行 AsyncTask 的正确方法是使用 execute() 方法，该方法调用 doInBackground() 并在工作线程上运行它，这将消除 NetworkOnMainThreadException 运行时错误你现在得到。

因此，除了使用特定于 Android 的库之外，修复您的 AsyncTask 以便它实际上在工作线程而不是主线程中运行 doInBackground() 方法 UI 线程。

一般来说，更好的做法是使用泛型和可变参数，而不是让 doInBackground() 将 Object[] 作为参数。每次执行 AsyncTask 时都能够传递用户名和密码也很有用，因此让它采用 String varargs 参数。

public class FetchPop extends AsyncTask<String, Void, Void> {

    @Override
    protected Void doInBackground(String... params) {
        String host = "pop.gmail.com";// I tried google's pop 
        String mailStoreType = "pop3";

        String username = params[0]; //passed in through the execute() method      
        String password = params[1]; //passed in through the execute() method

        //Call method fetch
        fetch(host, mailStoreType, username, password);
        Log.d("mytag", "done!");
        return null;
    }
}

然后，要正确执行AsyncTask，使用execute()方法，并传入用户名和密码：

 //First get the username and password from the user through the UI
 String user =  "myusername"; // change accordingly
 String pass = "notmyrealpass"; // change accordingly
 new FetchPop().execute(user, pass);

此外，请注意任何 UI 相关代码都需要放在 onPostExecute() 中，因为所有 UI 任务都需要在主 UI 线程上执行在 Android.

有关 AsyncTasks 的更多一般信息，this question and the answers posted

中有很多有用的信息

如何获取 Android 上的电子邮件？

How can I fetch emails on Android?

java

email

android

jakarta-mail