Send a slack message to a channel. This provides a demo code to use the slack api and use json to design slack message.

slack-message-java.java

package com.armaandhir.slack_integration.util;

import com.mashape.unirest.http.HttpResponse;
import com.mashape.unirest.http.Unirest;
import com.mashape.unirest.http.exceptions.UnirestException;
import org.json.JSONArray;
import org.json.JSONObject;

/**
 *  Send slack messages using java.
 *
 *  It can be used like:
 *      url = "https://slack.com/api";
 *      slackToken = "xxop-somethinglikethis-verylong";
 *      SlackIntegration slackIntegration = new SlackIntegration(url, slackToken);
 *		slackIntegration.sendSlackNotification("YourChannelName", text.trim());
 */
public class SlackIntegration
{
    private final String slackApiUrl;
    private final String token;
    private final String postMessageUrl;
    
    public SlackIntegration(String slackApiUrl, String token)
    {
        this.slackApiUrl = slackApiUrl;
        this.token = token;

        postMessageUrl = "/chat.postMessage";
    }

    /**
     * Method to send Slack Notifications regrading unlinked line items.
     * @param channel   name of the channel
     * @param message
     */
    public void sendSlackNotification(String channel, String message) throws UnirestException
    {
        log.info("Sending slack notification to {}: {}", channel, message);

        JSONArray json = new JSONArray();
        JSONObject lineOne = new JSONObject();
        lineOne.put("color", "warning");
        lineOne.put("title", "Warning! Warning Items heading");
        lineOne.put("text", "<!here> The following items are causing problems.");
        JSONObject lineTwo = new JSONObject();
        lineTwo.put("text", message.trim());
        JSONArray markdownArray = new JSONArray();
        markdownArray.put("text");
        lineTwo.put("mrkdwn_in", markdownArray);
        json.put(lineOne);
        json.put(lineTwo);
		
        HttpResponse<String> httpResponse = Unirest.post(slackApiUrl + postMessageUrl)
                .header("Content-Type", "application/x-www-form-urlencoded")
                .queryString("token", token)
                .queryString("channel", channel)
                //.queryString("text", message)
                .queryString("as_user", "false")
                .queryString("username", "Test User")
                .queryString("attachments", json.toString())
                .asString();
        // find a better way to print toString the json response
        log.info("Slack notification sent");
        log.info("Response: {}", httpResponse.getBody().trim());
    }

} // end of class