Simple example to access Gmail by Java

To show the folders and their message counts:

        Properties props = System.getProperties();
        props.setProperty("mail.pop3.port", prop.getProperty("995"));
        Session session = Session.getInstance(props, null);
 
        Store store = session.getStore("imaps");
 
        store.connect("pop.gmail.com", "name", "password");
 
        javax.mail.Folder[] dfolders = store.getDefaultFolder().list("*");
        for (Folder f : dfolders) {
            System.out.println(f.getFullName());
        
            if ((f.getType() & javax.mail.Folder.HOLDS_MESSAGES) != 0) {
                System.out.println(f.getMessageCount());
            }
   
        }

On github

The output:

INBOX
25
[Gmail]
[Gmail]/All Mail
69
[Gmail]/Drafts
0
[Gmail]/Important
1
[Gmail]/Sent Mail
6
[Gmail]/Spam
4761
[Gmail]/Starred
0
[Gmail]/Trash
121

Open folder and delete the messages

IMAPFolder folder = null;
        String[] folders = new String[]{"INBOX", "[Gmail]/Spam"};

        for (String fname : folders) {

            folder = (IMAPFolder) store.getFolder(fname);
            folder.open(Folder.READ_WRITE);
            int c = folder.getMessageCount();
            System.out.println(c);

            Map map = new HashMap<>();
            for (int i = c; i > 0; i--) {

                Enumeration
 headers = message.getAllHeaders();

                while (headers.hasMoreElements()) {
                    Header h = headers.nextElement();
                    //h.getName()
                    //h.getValue()

                 }

                if (message.isSet(Flags.Flag.SEEN)) {
                message.setFlag(Flags.Flag.DELETED, true); //mark this message as deleted
                }

            }
        }
        folder.expunge(); //
        folder.close(true);

on Github