What is wrong with this POST request implementation?

Question

I have been working around Google OAuth 2.0 with java and got struck with some unknown error during implementation.
The following CURL for POST request works fine:

curl -v -k --header "Content-Type: application/x-www-form-urlencoded" --data "code=4%2FnKVGy9V3LfVJF7gRwkuhS3jbte-5.Arzr67Ksf-cSgrKXntQAax0iz1cDegI&client_id=[my_client_id]&client_secret=[my_client_secret]&redirect_uri=[my_redirect_uri]&grant_type=authorization_code" https://accounts.google.com/o/oauth2/token

And produces the required result.
But the following implementation of above POST request in java causes some error and the response in "invalid_request"
Check the following code and point whats going wrong here:(made use of Apache http-components)

HttpPost post = new HttpPost("https://accounts.google.com/o/oauth2/token");
HttpParams params = new BasicHttpParams();
params.setParameter("code", code);
params.setParameter("client_id", client_id);
params.setParameter("client_secret", client_secret);
params.setParameter("redirect_uri", redirect_uri);
params.setParameter("grant_type", grant_type);
post.addHeader("Content-Type", "application/x-www-form-urlencoded");
post.setParams(params);
DefaultHttpClient httpClient = new DefaultHttpClient();
HttpResponse response = httpClient.execute(post);

Tried with URLEncoder.encode( param , "UTF-8") for each parameter but that too doesn't work.
What might be the cause?

Answer 1

You should be using UrlEncodedFormEntity not setParameter on the post. It handles the Content-Type: application/x-www-form-urlencoded header for you too.

HttpPost post = new HttpPost("https://accounts.google.com/o/oauth2/token");
List <NameValuePair> nvps = new ArrayList <NameValuePair>();
nvps.add(new BasicNameValuePair("code", code));
nvps.add(new BasicNameValuePair("client_id", client_id));
nvps.add(new BasicNameValuePair("client_secret", client_secret));
nvps.add(new BasicNameValuePair("redirect_uri", redirect_uri));
nvps.add(new BasicNameValuePair("grant_type", grant_type));

post.setEntity(new UrlEncodedFormEntity(nvps, HTTP.UTF_8));

DefaultHttpClient httpClient = new DefaultHttpClient();
HttpResponse response = httpClient.execute(post);

Answer 2

A bit more generic and unified method for sending UrlEncoded request:

  @SneakyThrows
  public String postUrlEncoded(String context, Map<String, String> body) {
    List<NameValuePair> nameValuePairs = body.entrySet()
          .stream()
          .map(entry -> new BasicNameValuePair(entry.getKey(), entry.getValue()))
          .collect(Collectors.toList());
    HttpResponse response = Request.Post(baseUrl + context)
          .bodyForm(nameValuePairs)
          .execute().returnResponse();

    return EntityUtils.toString(response.getEntity());
  }

Ps: it requires fluent Apache HTTP client. Pom dependency:

<dependency>
        <groupId>org.apache.httpcomponents</groupId>
        <artifactId>fluent-hc</artifactId>
        <version>${fluent-hc.version}</version>
</dependency>