Introduction

This short recipe covers how to connect to Corporate Memory using a Java program.Such program can connect to Corporate Memory at any time autonomously, independently of whether a user is logged in or not. 

Java example

This example assumes that there is a Corporate Memory instance runnning at http://docker.local, and the programmer has access to its files. The process is very simple:

  1. Obtain a Bearer token.
    1. Go to the file cmem-orchestration/environments/config.env, and get the client secret from variable CMEM_SERVICE_ACCOUNT_CLIENT_SECRET.
    2. With the client secret, connect to to the OpenID endpoint to obtain the Bearer token.
  2. Use the Bearer token to connect to Corporate Memory, and, for example, execute a query.

The following code provides a simple implementation of the process:

JavaCMEMHTTPClient.java

package com.eccenca.cmem.client;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.util.EntityUtils;
import org.json.JSONObject;

public class HTTPClient {

	public static void main(String[] args) throws ClientProtocolException, IOException {
		
		// We assume that the Corporate Memory instance is running at docker.local
		String openidConnectEndpoint="http://docker.local/auth/realms/cmem/protocol/openid-connect/token";
		
		// Get the client secret to obtain the bearer token from file cmem-orchestration/environments/config.env, 
		// variable CMEM_SERVICE_ACCOUNT_CLIENT_SECRET
		String clientSecret="..."; 
		
		// Create an HTTP Client
		CloseableHttpClient client = HttpClientBuilder.create().build();
		
		// POST request to obtain the bearer token for later authorization
		HttpPost httpPostToken = new HttpPost(openidConnectEndpoint);
		httpPostToken.setHeader("Content-type", "application/x-www-form-urlencoded");
		List<NameValuePair> params = new ArrayList<NameValuePair>();
		params.add(new BasicNameValuePair("grant_type", "client_credentials"));
		params.add(new BasicNameValuePair("client_id", "cmem-service-account"));
		params.add(new BasicNameValuePair("client_secret", clientSecret));
		httpPostToken.setEntity(new UrlEncodedFormEntity(params));
		
		// Parse the JSON response to obtain the bearer token
		HttpResponse httpResponseToken = client.execute(httpPostToken);
		HttpEntity httpEntity = httpResponseToken.getEntity();
		String responseBody = EntityUtils.toString(httpEntity);
		JSONObject obj = new JSONObject(responseBody);
		String bearerToken = "Bearer " + obj.getString("access_token");
		
		// POST request to query the default SPARQL endpoint with the bearer token obtained above
		HttpPost httpPostQuery = new HttpPost("http://docker.local/dataplatform/proxy/default/sparql");
		httpPostQuery.setHeader("Accept", "application/sparql-results+json");
		httpPostQuery.setHeader("Content-type", "application/x-www-form-urlencoded");
		httpPostQuery.setHeader("Authorization", bearerToken);
		final ArrayList<NameValuePair> postParameters = new ArrayList<NameValuePair>();
		postParameters.add(new BasicNameValuePair("query", "SELECT * WHERE {?s ?p ?o} LIMIT 10"));
		httpPostQuery.setEntity(new UrlEncodedFormEntity(postParameters));
		
		// The response (variable responseBodyQuery bellow) should have some bindings:
//		{
//			  "head": {
//			    "vars": [ "s" , "p" , "o" ]
//			  } ,
//			  "results": {
//			    "bindings": [
		HttpResponse httpResponseQuery = client.execute(httpPostQuery);
		HttpEntity httpEntityQuery = httpResponseQuery.getEntity();
		String responseBodyQuery = EntityUtils.toString(httpEntityQuery);	
	}
}
JAVA