RedditClient.java

import java.io.IOException;
import java.net.MalformedURLException;

import com.gargoylesoftware.htmlunit.BrowserVersion;
import com.gargoylesoftware.htmlunit.FailingHttpStatusCodeException;
import com.gargoylesoftware.htmlunit.WebClient;
import com.gargoylesoftware.htmlunit.html.HtmlForm;
import com.gargoylesoftware.htmlunit.html.HtmlPage;

public class RedditClient {
	//Create a new WebClient with any BrowserVersion. WebClient belongs to the
	//HtmlUnit library.
	private final WebClient WEB_CLIENT = new WebClient(BrowserVersion.CHROME);
	
	//This is pretty self explanatory, this is your Reddit credentials.
	private final String username;
	private final String password;
	
	//Our constructor. Sets our username and password and does some client config.
	RedditClient(String username, String password){
		this.username = username;
		this.password = password;
		
		//Retreives our WebClient's cookie manager and enables cookies.
		//This is what allows us to view pages that require login.
		//If this were set to false, the login wouldn't persist.
		WEB_CLIENT.getCookieManager().setCookiesEnabled(true);
	}
	
	public void login(){
		//This is where we log in, easy.
		String loginURL = "https://www.reddit.com/login";		
		try {
			
			//Okay, bare with me here. This part is simple but it can be tricky
			//to understand at first. Reference the login form above and follow
			//along.
			
			//Create an HtmlPage and get the login page.
			HtmlPage loginPage = WEB_CLIENT.getPage(loginURL);
			
			//Create an HtmlForm by locating the form that pertains to logging in.
			//"//form[@id='login-form']" means "Hey, look for a <form> tag with the
			//id attribute 'login-form'" Sound familiar?
			//<form id="login-form" method="post" ...
			HtmlForm loginForm = loginPage.getFirstByXPath("//form[@id='login-form']");
			
			//This is where we modify the form. The getInputByName method looks
			//for an <input> tag with some name attribute. For example, user or passwd.
			//If we take a look at the form, it all makes sense.
			//<input value="" name="user" id="user_login" ...
			//After we locate the input tag, we set the value to what belongs.
			//So we're saying, "Find the <input> tags with the names "user" and "passwd"
			//and throw in our usernames in the text field.
			loginForm.getInputByName("user").setValueAttribute(username);
			loginForm.getInputByName("passwd").setValueAttribute(password);
			
			//<button type="submit" class="c-btn c-btn-primary c-pull-right" ...
			//Okay, you may have noticed the button has no name. What the line
			//below does is locate all of the <button>s in the login form and
			//clicks the first and only one. (.get(0)) This is something that
			//you can do if you come across inputs without names, ids, etc.
			loginForm.getElementsByTagName("button").get(0).click();
			
		} catch (FailingHttpStatusCodeException e) {
			e.printStackTrace();
		} catch (MalformedURLException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		}
	}
	
	public String get(String URL){
		try {
			//All this method does is return the HTML response for some URL.
			//We'll call this after we log in!
			return WEB_CLIENT.getPage(URL).getWebResponse().getContentAsString();
		} catch (FailingHttpStatusCodeException e) {
			e.printStackTrace();
		} catch (MalformedURLException e) {
			e.printStackTrace();
		} catch (IOException e) {
			e.printStackTrace();
		}
		return null;
	}
}