1. Overview

In this second article of the series, we'll build some simple functionality to post on Reddit from our application, via their API.

2. Necessary Security

First – let's get the security aspect out of the way.

In order to Submit a Link to Reddit, we need to define an OAuth protected Resource with the scope of “submit“:

@Bean
public OAuth2ProtectedResourceDetails reddit() {
    AuthorizationCodeResourceDetails details = new AuthorizationCodeResourceDetails();
    details.setId("reddit");
    details.setClientId(clientID);
    details.setClientSecret(clientSecret);
    details.setAccessTokenUri(accessTokenUri);
    details.setUserAuthorizationUri(userAuthorizationUri);
    details.setTokenName("oauth_token");
    details.setScope(Arrays.asList("identity", "submit"));
    details.setGrantType("authorization_code");
    return details;
}

Note that we're also specifying the scopeidentity” because we also need access the user account information.

3. Is Captcha Needed?

Users that are new to Reddit have to fill in a Captcha in order to submit; that is before they pass a certain karma threshold within Reddit.

For these users, we first need to check if the Captcha is needed:

private String needsCaptcha() {
    String result = redditRestTemplate.getForObject(
      "https://oauth.reddit.com/api/needs_captcha.json", String.class);
    return result;
}

private String getNewCaptcha() {
    HttpHeaders headers = new HttpHeaders();
    headers.setContentType(MediaType.APPLICATION_JSON);
    HttpEntity req = new HttpEntity(headers);

    Map<String, String> param = new HashMap<String, String>();
    param.put("api_type", "json");

    ResponseEntity<String> result = redditRestTemplate.postForEntity(
      "https://oauth.reddit.com/api/new_captcha", req, String.class, param);
    String[] split = result.getBody().split("""); 
    return split[split.length - 2];
}

4. The “Submit Post” Form

Next, let's create the main form for submitting new posts to Reddit. Submitting a Link requires the following details:

  • title – the title of the article
  • url – the URL of the article
  • subreddit – the sub-reddit to submit the link to

So let's see how we can display this simple submission page:

@RequestMapping("/post")
public String showSubmissionForm(Model model) throws JsonProcessingException, IOException {
    String needsCaptchaResult = needsCaptcha();
    if (needsCaptchaResult.equalsIgnoreCase("true")) {
        String iden = getNewCaptcha();
        model.addAttribute("iden", iden);
    }
    return "submissionForm";
}

And of course the basic submissionForm.html:

<form>
    <input name="title"/>
    <input name="url" />
    <input name="sr"/>
    <input  type="checkbox" name="sendReplies" value="true"/>

    <div th:if="${iden != null}">
        <input type="hidden" name="iden" value="${iden}"/>
        <input name="captcha"/>
        <img src="http://www.reddit.com/captcha/${iden}" alt="captcha" width="200"/>
    </div>
    <button type="submit" onclick="submitPost()">Post</button>
</form>

<script>
function submitPost(){
    var data = {};
    $('form').serializeArray().map(function(x){data[x.name] = x.value;});
    $.ajax({
        url: "api/posts",
        data: JSON.stringify(data),
        type: 'POST',
        contentType:'application/json'
    }).done(function(data) {
        if(data.length < 2){ alert(data[0]);}
        else{
            window.location.href="submissionResponse?msg="+
              data[0]+"&url="+data[1];
        }
    }).fail(function(error) { alert(error.responseText); }); 
}
</script>

5. Submit a Link to Reddit

Now – let's take a look at the final step – submitting the actual link via the Reddit API.

We'll POST a submit request to Reddit using the parameters from our submissionForm:

@Controller
@RequestMapping(value = "/api/posts")
public class RedditPostRestController {

    @Autowired
    private RedditService service;

    @RequestMapping(method = RequestMethod.POST)
    @ResponseBody
    public List<String> submit(@Valid @RequestBody PostDto postDto) {
        return service.submitPost(postDto);
    }
}

Here's the actual method implementation:

public List<String> submitPost(PostDto postDto) {
    MultiValueMap<String, String> param1 = constructParams(postDto);
    JsonNode node = redditTemplate.submitPost(param1);
    return parseResponse(node);
}

private MultiValueMap<String, String> constructParams(PostDto postDto) {
    MultiValueMap<String, String> param = new LinkedMultiValueMap<String, String>();
    param.add("title", postDto.getTitle());
    param.add("sr", postDto.getSubreddit());
    param.add("url", postDto.getUrl());
    param.add("iden", postDto.getIden());
    param.add("captcha", postDto.getCaptcha());
    if (postDto.isSendReplies()) {
        param.add("sendReplies", "true");
    }

    param.add("api_type", "json");
    param.add("kind", "link");
    param.add("resubmit", "true");
    param.add("then", "comments");
    return param;
}

And the simple parsing logic, handling the response from the Reddit API:

private List<String> parseResponse(JsonNode node) {
    String result = "";
    JsonNode errorNode = node.get("json").get("errors").get(0);
    if (errorNode != null) {
        for (JsonNode child : errorNode) {
            result = result + child.toString().replaceAll("\"|null", "") + "<br>";
        }
        return Arrays.asList(result);
    } else {
        if ((node.get("json").get("data") != null) && 
            (node.get("json").get("data").get("url") != null)) {
            return Arrays.asList("Post submitted successfully", 
              node.get("json").get("data").get("url").asText());
        } else {
            return Arrays.asList("Error Occurred while parsing Response");
        }
    }
}

All of this is working with a basic DTO:

public class PostDto {
    @NotNull
    private String title;

    @NotNull
    private String url;

    @NotNull
    private String subreddit;

    private boolean sendReplies;

    private String iden;
    private String captcha;
}

Finally – the submissionResponse.html:

<html>
<body>
    <h1 th:text="${msg}">Hello</h1>
    <h1 th:if="${param.containsKey('msg')}" th:text="${param.msg[0]}">Hello</h1>
    <h2 th:if="${param.containsKey('url')}"><a th:href="${param.url[0]}">Here</a></h2>
</body>
</html>

6. Conclusion

In this quick tutorial we implemented some basic Submit to Reddit functionality – simplistic but fully functional.

In the next part of this case study, we'll implement a Schedule Post for Later functionality into our app.

The full implementation of this tutorial can be found in the github project – this is an Eclipse based project, so it should be easy to import and run as it is.

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