how to send message with image to slack channel using java
"attachments": [{ "fallback": "The attachement isn't supported.", "title": "VALENTINE'S DAY OFFER", "color": "#9C1A22", "pretext": "Today's list of awesome offers picked for you", "author_name": "Preethi", "author_link": "https://www.hongkiat.com/blog/author/preethi/", "author_icon": "https://assets.hongkiat.com/uploads/author/preethi.jpg", "mrkdwn_in": ["text","fields"], "text": "Just click the site names and start buying. Get *extra reduction with the offer code*, if provided.", "thumb_url": "http://example.com/thumbnail.jpg" }]
