How to send attachment in Slack channel using Restful Webservice

Slack : What comes to your mind when you hear word Slack ? It is probably one of best collaboration tool available in the market. Now a days Slack is also widely used across multiple organization of all level. [Big, mid or small] 


Now since everyone is active on Slack , it is of extreme importance to send messages to slack channels. This is when the need arise to send automated notifications. Slack provides a lot of rest api's to accomplish this task. 

In this post, We will cover how to send attachments in Slack channels using Slack endpoint with Java. 

Prerequisite: 

• You should have slack authentication token generated. 
• Name of the slack channel where the message will be delivered. 

package com.dht.test;

import java.io.File;

import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.mime.MultipartEntityBuilder;
import org.apache.http.impl.client.HttpClientBuilder;

public class SlackChannelAttachmentUtil{

 public static void main(String[] args) {
  try {
   String url = "https://slack.com/api/files.upload";
   HttpClient httpclient = HttpClientBuilder.create().disableContentCompression().build();
   HttpPost httppost = new HttpPost(url);
   MultipartEntityBuilder reqEntity = MultipartEntityBuilder.create();
   reqEntity.addBinaryBody("file", new File("C:\\dht.properties"));
   reqEntity.addTextBody("channels", "attachment-testing");
   reqEntity.addTextBody("token","xoxp-4735837518-xxxxxx");
   reqEntity.addTextBody("media", "file");
   reqEntity.addTextBody("initial_comment", "Hello This is from code");

   httppost.setEntity(reqEntity.build());
   HttpResponse execute = httpclient.execute(httppost);
   System.out.println(execute.getStatusLine().getReasonPhrase());
   System.out.println(execute.getStatusLine().getStatusCode());
  } catch (Exception e) {
   System.out.println(e);
  }

 }

}

The above code will send dht.properties file to attachment-testing slack channel. You will also see Message "Hello This is from code" along with attachment.