Java 如何在Android上获取电子邮件？

我正在尝试开发一个应用程序，从不是谷歌的POP3服务器获取电子邮件，我面临着许多问题。
我正在使用JavaMail库和下面的教程Point教程。他们的pop3示例在Eclipse/desktop上运行得很好，但当我在Android上移动代码时，它就不起作用了，我很沮丧。
在logcat中，我得到了所有的错误堆，其中首先声明

W/System.err﹕ android.os.NetworkOnMainThreadException，即使我使用的是AsyncTask（可能不正确）

有没有一种方法可以使AsyncTask正常工作

还有，有没有一种方法可以让我不用像K-9 Mail这样的专业应用程序来做类似的事情

如果有人感兴趣，请输入代码：

 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());

    }

}

公共类FetchPop扩展异步任务{
publicstaticvoidfetch（字符串pop3Host、字符串storeType、字符串user、，
字符串（密码）{
试一试{
//创建属性字段
属性=新属性（）；
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”）；
会话emailSession=Session.getDefaultInstance（属性）；
//emailSession.setDebug（true）；
//创建POP3存储对象并连接pop服务器
Store Store=emailSession.getStore（“pop3s”）；
store.connect（pop3Host、用户、密码）；
//创建文件夹对象并将其打开
文件夹emailFolder=store.getFolder（“收件箱”）；
emailFolder.open（文件夹只读）；
BufferedReader reader=新的BufferedReader（新的InputStreamReader(
系统(in),；
//从数组中的文件夹中检索邮件并打印
Message[]messages=emailFolder.getMessages（）；
Log.d（“No.messages:，messages.length+”）；//只需输入第一个数字
/*for（int i=0；iimage/jpeg”）；
对象o=p.getContent（）；
输入流x=（输入流）o；
//构造所需的字节数组
int i；
字节[]bArray=新字节[0]；
System.out.println（“x.length=“+x.available（））；
而（（i=（int）（（InputStream）x）.available（））>0）{
int结果=（int）（（InputStream）x.read（bArray））；
如果（结果==-1）
i=0；
bArray=新字节[x.available（）]；
打破
}
FileOutputStream f2=新的FileOutputStream（“/tmp/image.jpg”）；
f2.写入（bArray）；
}
else if（p.getContentType（）.contains（“image/”））{
System.out.println（“内容类型”+p.getContentType（））；
文件f=新文件（“图像”+新日期（）.getTime（）+”.jpg”）；
DataOutputStream输出=新的DataOutputStream(
新的BufferedOutputStream（新的FileOutputStream（f））；
com.s
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;
    }
}

 //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);