Application.java

package com.example.hellodemo;


import org.apache.http.HttpEntity;
import org.apache.http.NameValuePair;
import org.apache.http.client.entity.UrlEncodedFormEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.message.BasicNameValuePair;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
import java.util.stream.Collectors;

public class Application {
    public static void main(String[] args) throws IOException {
        OAuth oAuth = new OAuth();
        oAuth.getCode();
        oAuth.getAccessToken();
    }
}

class OAuth {
    final private String authorizationUri = "https://sandbox.api.service.nhs.uk/oauth2/authorize";  // Authorization code endpoint
    final private String redirectUri = "http://localhost:5000/callback";  // Callback endpoint
    final private String tokenUri = "https://sandbox.api.service.nhs.uk/oauth2/token";  // Get tokens endpoint
    final private String clientId= "your-client-id";  // change to your Client_ID
    final private String clientSecret = "your-client-secret";  // change to your client_secret
    final private String state = "random";

    public void getCode() {
        System.out.println("Open the link below in your browser");
        System.out.println(authorizationUri +
                "?client_id=" + clientId +
                "&redirect_uri=" + redirectUri +
                "&response_type=code" +
                "&state=" + state);
    }

    public void getAccessToken() throws IOException {
        Scanner in = new Scanner(System.in);
        System.out.println("Enter code:");
        String code = in.nextLine();

        HttpPost httpPost = new HttpPost(tokenUri);
        List<NameValuePair> params = new ArrayList<>();
        params.add(new BasicNameValuePair("grant_type", "authorization_code"));
        params.add(new BasicNameValuePair("client_id", clientId));
        params.add(new BasicNameValuePair("client_secret", clientSecret));
        params.add(new BasicNameValuePair("redirect_uri", redirectUri));
        params.add(new BasicNameValuePair("code", code));

        httpPost.setEntity(new UrlEncodedFormEntity(params));

        CloseableHttpClient client = HttpClients.createDefault();
        CloseableHttpResponse response = client.execute(httpPost);
        HttpEntity entity = response.getEntity();

        if (entity != null) {
            InputStream instream = entity.getContent();
            String text = new BufferedReader(
                    new InputStreamReader(instream, StandardCharsets.UTF_8)).lines()
                    .collect(Collectors.joining("\n"));
            System.out.println(text);
            instream.close();
        }

        client.close();
    }
}

build.gradle

apply plugin: 'java'
apply plugin: 'application'

mainClassName = 'com.example.hellodemo.Application'

group = 'com.example'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = '1.8'

repositories {
	mavenCentral()
}

dependencies {
	compile 'org.apache.httpcomponents:httpclient:4.5.13'
}

jar {
	manifest {
		attributes('Main-Class': mainClassName)
	}
	from {
		configurations.compile.collect { it.isDirectory() ? it : zipTree(it) }
	}
}