Howto access Flags.Flag value in javax.mail?

Dear all,

I am stuck finding a solution for the following problem:

Problem description:

I want to download all unseen mails from a mailaccount using the JavaMail package in MATLAB. I am able to setup, connect and open the folder I want to get the mails from. For finding all messages that are unseen, I want to use the function IMAPFolder.search(SearchTerm term). For this SearchTerm, a Flags.Flag is required which is defined in a nested public static final class in javax.mail.Flags. The problem is now how to get the values of this class.

JavaMail Documentation

What I tried and what errors I get:

I already tried several ways to access fields in a nested java class, here is a list:

For the following link below, the first solution does not work for me because I am not able to change the Java library. Also the second solution does not work because it is a static class.

https://www.mathworks.com/matlabcentral/answers/98620-how-do-i-create-an-instance-of-a-java-public-static-nested-class-from-inside-matlab-7-13-r2011b

In the following solution https://www.mathworks.com/matlabcentral/answers/15711-how-do-i-access-a-java-inner-class-from-matlab it says:

SEEN = javaMethod('valueOf', 'javax.mail.Flags$Flag', 'SEEN')

And this is the error I get:

Error using javaMethod
No method valueOf exists in Java class javax.mail.Flags$Flag

I also found another question about this topic here:

https://www.mathworks.com/matlabcentral/answers/48021-in-matlab-how-can-i-delete-an-email-using-javamail-api-s-flags

My most recent code:

config = load('myconfig.mat');
props = java.util.Properties;
props.put('mail.imap.port', config.MAIL.port);
props.put('mail.imap.timeout', config.MAIL.imap_timeout);
props.put('mail.imaps.connectiontimeout', config.MAIL.imaps_connection_timeout);
session = javax.mail.Session.getInstance(props);
imapstore = session.getStore('imaps');
imapstore.connect( ...
      config.MAIL.server, ...
      config.MAIL.port, ...
      config.MAIL.username, ...
      config.MAIL.password ...
  );
folder = imapstore.getFolder('Inbox');
folder.open(folder.READ_ONLY);
% everything works fine up to this point
search_flags = javax.mail.Flags;
flags_class = search_flags.getClass;
nested_classes = flags_class.getClasses;
flag_class = nested_classes(1);
% how do I access the static fields now?

Can someone help me? My Matlab version is R2016a.

EDIT1:

I also tried creating the FlagTerm using

cl = flags_class.getClassLoader;
rt = java.lang.Class.forName('javax.mail.Flags$Flag', false, cl);
search_flags.add(rt.getField('SEEN'));

as seen in http://de.mathworks.com/matlabcentral/newsreader/view_thread/125420 but it resulted in the following error:

No method 'add' with matching signature found for class 'javax.mail.Flags'.

Answer 1

[Lewin Probst]

Hi all,

i found the solution by myself. See http://undocumentedmatlab.com/blog/accessing-internal-java-class-members, the last paragraph is about how to solve this problem.

Quote:

>> channel = java.io.FileInputStream('234.jpg').getChannel
channel =
sun.nio.ch.FileChannelImpl@1c7a5d3    <= which extends FileChannel

>> innerClasses = channel.getClass.getSuperclass.getDeclaredClasses;
>> innerClasses(1)
ans =
class java.nio.channels.FileChannel$MapMode

>> read_only_const = innerClasses(1).getField('READ_ONLY').get(1)
read_only_const = 
READ_ONLY    <= a java.nio.channels.FileChannel$MapMode object

>> fields = innerClasses(1).getFields;
>> read_only_const = fields(1).get(1);    % an alternative

>> buffer = channel.map(read_only_const, 0, channel.size);