HTTP/1.1 401 Unauthorized error when calling HttpGet with OAuthConsumer client

Question

I am getting 401 Unauthorized error when i use Http GET call with OAuthConsumer client.

I have all the required parameters for Oauth 1.0 authorization.

Consumer Key = "XXX"
Consumer Secret = "YYY"
oauth_signature_method = "HMAC-SHA1"
oauth_timestamp = "calculated timestamp"
oauth_nonce = "calculated nonce"
oauth_version = 1.0
oauth_signature = "calculated signature"

The same Ouath 1.0 code in python is working well for me just by using consumer key, secret and signature_type='auth_header' and by calling requests.get(). Here's my python code below :

import requests
from requests_oauthlib import OAuth1

url = "XXX"
header_auth = OAuth1('consumer_key','consumer_secret', signature_type='auth_header')
response = requests.get(url, auth=header_auth)
print(response.status_code)
print(response.content)

Here is my code snippet in Java. Could you please suggest where I am going wrong?

public class OauthConsumerClient {

@SuppressWarnings("deprecation")
public static void main(String[] args) {

        String url = "XXX";

        DefaultHttpClient httpClient = new DefaultHttpClient();
        httpClient.getParams().setParameter("http.protocol.content-charset", "UTF-8");      
        HttpRequestBase httpRequest = null;
        URI uri = null;
        HttpResponse httpResponse = null;
        OAuthConsumer oAuthConsumer = new CommonsHttpOAuthConsumer("consumer_key", "consumer_secret");
        oAuthConsumer.setSigningStrategy(new AuthorizationHeaderSigningStrategy());

        try {
            uri = new URI(url);
            httpRequest = new HttpGet(uri);
            httpRequest.setHeader("Content-Type", "application/json");
            oAuthConsumer.sign(httpRequest);
            HttpHost target = new HttpHost(uri.getHost(), -1, uri.getScheme());
            httpResponse = httpClient.execute(target, httpRequest);
            System.out.println("Connection status : " + httpResponse.getStatusLine());
            System.out.println("Connection status code : " + httpResponse.getStatusLine().getStatusCode());

        } catch (Exception e) {
            System.out.println("Exception occured");
        }
        InputStream inputStraem = httpResponse.getEntity().getContent();
        StringWriter writer = new StringWriter();
        IOUtils.copy(inputStraem, writer, "UTF-8");
        String output = writer.toString();
        System.out.println("Connection response : " + output);
}

}

Output 
-------------------------------------------------------------------------

16:13:43.064 [main] DEBUG o.a.h.impl.client.DefaultHttpClient - Authentication required
16:13:43.064 [main] DEBUG o.a.h.impl.client.DefaultHttpClient - "URL" requested authentication
16:13:43.064 [main] DEBUG o.a.h.i.c.TargetAuthenticationStrategy - Authentication schemes in the order of preference: [Negotiate, Kerberos, NTLM, Digest, Basic]
16:13:43.064 [main] DEBUG o.a.h.i.c.TargetAuthenticationStrategy - Challenge for Negotiate authentication scheme not available
16:13:43.064 [main] DEBUG o.a.h.i.c.TargetAuthenticationStrategy - Challenge for Kerberos authentication scheme not available
16:13:43.064 [main] DEBUG o.a.h.i.c.TargetAuthenticationStrategy - Challenge for NTLM authentication scheme not available
16:13:43.064 [main] DEBUG o.a.h.i.c.TargetAuthenticationStrategy - Challenge for Digest authentication scheme not available
16:13:43.064 [main] DEBUG o.a.h.i.c.TargetAuthenticationStrategy - Challenge for Basic authentication scheme not available
Connection status : HTTP/1.1 401 Unauthorized
Connection status code : 401
16:13:43.076 [main] DEBUG org.apache.http.wire -  << "  ["The request must be signed"]"
16:13:43.076 [main] DEBUG o.a.h.i.c.BasicClientConnectionManager - Releasing connection org.apache.http.impl.conn.ManagedClientConnectionImpl@78691363
16:13:43.076 [main] DEBUG o.a.h.i.c.BasicClientConnectionManager - Connection can be kept alive indefinitely
Connection response :   ["The request must be signed"]

NOTE : When i hit the same URL in postman with Oauth 1.0 authorization type. I am getting response code 200 OK with the body.

Let me know if you need additional information. Thank you so much for your help !!!