CMU 95-702 Distributed Systems - Project 1: Compute Hash
95-702 Distributed Systems
Project 1
This project has five objectives:
First, you are introduced to IntelliJ and TomEE. You already have some practice with these. In this assignment, you'll build several web apps to gain more experience.
Second, you build your first set of distributed systems. These are two small web applications using Servlets and Java Server Pages.
Third, you are introduced to web scraping, API processing, and JSON records.
Fourth, you are introduced to the MVC pattern if you have not used it before.
Fifth, as in all projects this semester, you should reflect on the functional and non-functional characteristics (e.g. security, scalability, failure handling, interoperability) of your solutions. There will be questions on the final exam concerning these characteristics. You should be able to demonstrate a nuanced comprehension of course content and be able to explain the technical aspects in relation to potential real-world applications. For each project task, software documentation is required. The software that you write (Java files and so on) must contain comments that describe what each significant piece of code is intended to accomplish. Points will be deducted if code is not well documented. Read the documentation-related links provided on the course schedule (for class #1) to understand what is expected. Be sure to consult the rubric for details on grading.
and sixth, optionally you may use ChatGPT and Copilot to create some of your code in Task 3. Task 1 and Task 2 must be done on your own. There will be exam questions that ask specifically about the code in all three tasks. While you are allowed to use AI tools to help with Task 3, it is totally optional. There will be questions about this code, too. Also pay attention to the more general issues like, what is MVC and what are the benefits of using it? What does it mean to scrape a web page?.
Deliverables
There are two parts to deliver, all zipped into one file for upload, with the name Project1_andrewID.zip, where "andrewID" is replaced with your actual andrew id:
- one PDF containing relevant screeenshots of all the parts followed by code snippets (which is relative: how much to include is up to you for each part) that produced the result shown in the screenshot. Each section of the PDF must be clearly labeled.
- your three projects, each zipped, with all of the three tasks zipped together.
See the end for more detail, but read the project task descriptions first so that you know what the details are talking about.
Task 1
Use the IntelliJ Project Name: Project1Task1
Create an index.jsp page that asks the user to enter a string of text data, and to make a choice of two hash functions using radio buttons. The hash function choices should be MD5 and SHA-256, with MD5 being the default. When the submit button is pressed a request is sent to a servlet. The servlet must be named ComputeHashes.java. The servlet will compute the requested cryptographic hash value (MD5 or SHA-256) from the text transmitted by the browser. You will need to employ the Java crypto API to compute the hash of the text. The original text will be echoed back to the browser along with the name of the hash, and the hash value. The hash values sent back to the browser should be displayed in two forms: as hexadecimal text and as base 64 notation. We will discuss the use of such hash values later in the course. To compute the MD5 and SHA-256 hashes, use these standard java packages:
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;To print the Base64 encoding, use the following method:
jakarta.xml.bind.DatatypeConverter.printBase64Binary()To print the hexadecimal encoding, use the following method:
jakarta.xml.bind.DatatypeConverter.printHexBinary()To include the DatatypeConverter class into your project, use:
import jakarta.xml.bind.DatatypeConverter;and add these lines to your pom.xml file, then refresh Maven:
<dependency>
<groupId>jakarta.xml.bind</groupId>
<artifactId>jakarta.xml.bind-api</artifactId>
<version>4.0.1</version>
</dependency>Be sure to provide a simple and user friendly interface. If you are unfamiliar with HTML forms, a simple explanation can be found at:
http://www.w3schools.com/html/html_forms.aspBecause Task 1 is fairly simple, you do not have to use MVC for it. Do the simplest thing possible (however, feel free to use MVC if you'd like).
Be sure to create screen shots of your working application and submit them as described in the Submission section at the end of this document.
Task 2
Use the IntelliJ Project Name: Project1Task2
Create a web application that implements a simple desktop and mobile “clicker” for class. Your app should allow users to submit answers to questions posed in class, and should provide a separate URL end point for getting the results of the submitted responses. The welcome page for your app should be similar to Figure 1. You can make it more stylish if you like, but it is not required.
Figure 1
When the user makes a choice and hits “submit”, their answer should be stored in your MVC model. The response should be similar to The first line of Figure 2. Notice that it is required to provide feedback to the user regarding the choice that they made (i.e. “D” in this example).
The user should also have the ability to submit another answer as shown in the screenshot.
Figure 2
You can test the application by repeatedly submitting answers and allowing your model to tally the results. Your web app should also have a URL path “/getResults” (shown in Figure 3) for listing the results of user voting.
Figure 3
Requirements for the /getResults path:
- List each answer that has been given, and the number of times a user has submitted that answer.
- You do not have to list options that have been chosen zero times.
- The results should be displayed sorted in alphabetical order.
- /getResults should also clear the stored results so that a new question can be posed.
- If there are no results available, then report this as shown in Figure 4.
Figure 4
Note that requirement 4 does not adhere to the HTTP standard for a GET request. You should understand why this is bad behavior according to the standard, and how you could fix it (It might be on the exam).
The web app should work with a mobile browser. For this project you can use a simple check like the one that was used in InterestingPicture and then use an appropriate mobile doctype. An easy way to check your web app for mobile is to use the Google Chrome DevTools Using the Google Chrome browser.
- Browse to your web application in Chrome
- Access the Chrome DevTools (https://developers.google.com/web/tools/chrome-devtools/?hl=en#access-devtools).
- Toggle device mode to mobile and choose an Android or iPhone device (https://developers.google.com/web/tools/chrome-devtools/iterate/device-mode/?hl=en)
- Reload the page.
- In addition to testing, you use this to produce a screen shot showing your web app working for mobile. If your page looks like the one Figure 4, even after reloading, then the doctype is not being set correctly.
Figure 5 is what the web app should look like for mobile if the doctype is set correctly.
Figure 5
Overall web app requirements:
- You must use MVC to separate concerns.
- Implement only one HttpServlet
Hints:
-
You can have multiple URL patterns in a WebServlet annotation. For example, you can indicate that a servlet can be called by two paths such as: urlPatterns = {"/submit", "/getResults"}
- In order to determine within the servlet which path was actually requested, you can use request.getServletPath();
Produce screen shots of your application:
- With the answer options on desktop
- With the getResults on desktop
- With the answer options on mobile
- With the getResults on mobile
Task 3
Use IntelliJ Project Name: Project1Task3
Task 3 is meant to give you practice with several things: servlet programming, web scraping, API's, JSON, and MVC.
For this assignment, you may optionally use ChatGPT and/or Copilot to help you generate a solution; it's not a requirement and you should be able to do the design and coding without it. Keep in mind that:
- generated code is not always correct
- the more precise your ChatGPT prompt, the better the solution is likely to be
- how you generate the solution should be repeatable and explainable
- you **must** be able to explain fully the solution, generated by AI or by you, if asked
- you **must** document your use of AI tools. Show the prompt(s) you used to generate sections of code and what tools you used. Also note where you edited (if you did) any of the generated code and why you did so.Dogs! App
Create a web app using information about the common breeds of dogs. The information you choose to display is (somewhat) up to you, with the requirements given below.
Your program will present a welcome screen containing a title, a "created by" citation (that's you), a drop-down menu of a limited number of dog breeds, and a Submit button, as shown in Figure 6 and Figure 7. Only the breeds shown in Figure 7 will be used. The Submit button is used to record the user's choice. Note that you will need to learn about HTML drop-down menus on your own. Next, it will show the user some choices for data from the list below.
Figure 6: Welcome screen
The drop-down menu shows the required breeds.
Figure 7: Drop-down menu
Your app must meet these criteria:
- Display an image of a dog of the chosen breed. The image must come from the site https://dog.ceo/dog-api/. API returns JSON data. You'll have to check out their examples to see the query format and the answer format. Choose one image at random from the list of jpg's returned; also display how many images there were and which one you chose (like, "40 images returned, using #7"). Include the web site citation as part of the output; see Figure 8 for an example of a dog picture and credit.
Figure 8: Output screen. Who's a good boy?
See the section below about using JSON and setting up the correct Maven dependency. You must use the gson library to handle JSON records.
-
Provide other information about the dog breed. This must include at least three facts about the breed. You must web scrape this data. And you cannot use Flickr for the web scraping. You must use an HTML CheckBox for this; it allows the user to select one or more of the options; you'll have to figure out how these are used. Include reference citations for each fact (they might come from different sites or the same site).
-
Include at least one other image about dogs, obtained either by scraping or some API. This image cannot be static - that is, do not use the same image on each iteration on breeds or on each execution of the program. You may not use either Flickr or dog.ceo (the site in #1) for this.
Because parts 2 and 3 are up to you, there's no sample output shown here. Beware of using exactly the same output as another student; you are not allowed to share code!
-
Be coded primarily in Java and JSP. If you use something else, give a brief but convincing argument why this was necessary and not just a convenience (like you copied the code from github, or you got ChatGPT to generate it, are not good reasons).
-
Use one page for input and at least two web pages for your output - one for the dog image and one for the three (or more) facts displayed.
-
Use the Model-View-Contorller (MVC) pattern and good separation of concerns.
-
Handle error conditions in a "reasonable" way.
-
Be well documented - the code, the usage of the app, and the structure/design of the app, any AI-related things as described above.
What sites you use for state is up to you (except for the required dog picture)- but be careful of copying other students' ideas; this must be your own work. The overall design of the web app is up to you (subject to the criteria above). If you have questions about sites, citations, or output, ASK.
Again, you MUST use the MVC pattern for Task 3.
Notes and hints
Screen Scraping
Screen scraping is programmatically processing the HTML that typically is displayed by a browser and can be a useful tool when your data source does not have an API that provides structured data. Instead, you can search or parse the HTML to find and extract the data that you need. For more information, see
Your application should work similarly to InterestingPicture, but instead of searching Flickr, it will use the sites mentioned above.
-
You are allowed to and encouraged to build your solution based on the InterestingPicture code you have been given in class. You MUST refactor it, however, so that it has project, variable, and class names that make sense for your application. For example, you will lose points if your class is still named InterestingPictureServlet.
-
You do not need to, but you are welcome to, use jsoup (https://jsoup.org/) which is a Java HTML Parser, to do the scraping. It is the Java version of Beautiful Soup, which you may have used in Python. The downsides of using jsoup are you will first need to understand the Document Object Model (DOM) and CSS Selectors. These are both useful to know. The upside of using jsoup is that it makes it much easier to find and select content from HTML (i.e. screen scrape). Refer to the JSON Maven notes below; adding jsoup will require a similar process.
HTML
Refer to http://www.w3schools.com for good help on the basic HTML you need for this task. This has examples of drop-down boxes.
JSON and gson
JSON records are text records containing tag-value pairs, where the tag is the field name - think of it as a dictionary or map with nesting. It is much shorter than XML. In order to find what you need, use the JSON library GSON. To use GSON, download the gson v.2.11.0 jar file to a place you'll remember. To add it to your project, go to File->Project Structure->Modules, choose the Dependencies tab, click the + icon at the bottom choose Jars or Directories, navigate to where you put the jar file, click that, then Apply and OK. It should show up in your pom.xml file as the last entry in
<dependency>
<groupId>com.google.code.gson</groupId>
<artifactId>gson</artifactId>
<version>2.11.0</version>
</dependency>If this does not appear, add the above lines manually to pom.xml.
Finally, reload the Maven dependencies to have this new dependency take effect - an icon will probably appear in the pom.xml window, but if you don't see it, got to the Project View window, find the pom.xml entry (it should be near the bottom of the tree), right click it, choose Maven -> Reload Project. (FYI, Maven is a build management tool, different from the usual Gradle build; Maven uses the Project Object Model (pom) file to keep track of properties and dependencies.)
Please use gson and not some other JSON library.
SSLHandshakeException
Most modern sites require you to make https, not http requests. When you do so from your Java program, you will hit an SSLHandshakeException. We will be covering SSL and related topics in a few weeks. In the meantime, you will have to deal with this exception.
If you use jsoup, you should use validateTLSCertificates(false). (Refer to the jsoup API to understand this when you need it.)
If you do not use jsoup, here is a code to replace the fetch method in InterestingPictureModel to ignore the exception. The parameter "certType" should be set to the string "TLSV1.3".
private String fetch(String searchURL, String certType) {
try {
// Create trust manager, which lets you ignore SSLHandshakeExceptions
createTrustManager(certType);
} catch (KeyManagementException ex) {
System.out.println("Shouldn't come here: ");
ex.printStackTrace();
} catch (NoSuchAlgorithmException ex) {
System.out.println("Shouldn't come here: ");
ex.printStackTrace();
}
String response = "";
try {
URL url = new URL(searchURL);
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
// Read all the text returned by the server
BufferedReader in = new BufferedReader(new InputStreamReader(connection.getInputStream(), "UTF-8"));
String str;
// Read each line of "in" until done, adding each to "response"
while ((str = in.readLine()) != null) {
// str is one line of text readLine() strips newline characters
response += str;
}
in.close();
} catch (IOException e) {
System.err.println("Something wrong with URL");
return null;
}
return response;
}
private void createTrustManager(String certType) throws KeyManagementException, NoSuchAlgorithmException{
/**
* Annoying SSLHandShakeException. After trying several methods, finally this
* seemed to work.
* Taken from: http://www.nakov.com/blog/2009/07/16/disable-certificate-validation-in-java-ssl-connections/
*/
// Create a trust manager that does not validate certificate chains
TrustManager[] trustAllCerts = new TrustManager[] {new X509TrustManager() {
public X509Certificate[] getAcceptedIssuers() {
return null;
}
public void checkClientTrusted(X509Certificate[] certs, String authType) {
}
public void checkServerTrusted(X509Certificate[] certs, String authType) {
}
}
};
// Install the all-trusting trust manager
SSLContext sc = SSLContext.getInstance(certType);
sc.init(null, trustAllCerts, new java.security.SecureRandom());
HttpsURLConnection.setDefaultSSLSocketFactory(sc.getSocketFactory());
// Create all-trusting host name verifier
HostnameVerifier allHostsValid = new HostnameVerifier() {
public boolean verify(String hostname, SSLSession session) {
return true;
}
};
// Install the all-trusting host verifier
HttpsURLConnection.setDefaultHostnameVerifier(allHostsValid);
}
Questions:
If you have questions, you can post them to the class Piazza and tag them as “Project1”. Track Piazza for additional hints and answers to questions.
Summary & Submission:
Be sure to review the Rubric linked on the course schedule for the first day. Please remember to document your code! Points will be deducted if you don't have enough.
Submit one PDF naned Project1_andrewID.zip, where "andrewID" is replaced with your actual andrew id, containing the following; each part should begin with the headers shown (that is, "Task 1") and subheaders for the subparts. "Code snippet" means a copy of the relevant code, not all of the .java or .jsp file.
Task 1:
- Screen shots of input, MD5 and SHA-256 output, both in hex and base 64
- Code snippets of computation of each hash
Task 2:
- Screen shots of input page(s) and output page(s).
- Code snippets for producing clicker output.
Task 3:
- Screen shots of two uses of the input page (two different choices of breed) and the corresponding output pages.
- Code snippets from the Java code that screen scrapes, queries the API, and produces output.
Code:
Create three zip files, each one of which is the zip of your WHOLE project for task 1, 2 and 3. For each project, zip the whole project, you need to use "File->Export Project->To Zip" in IDEA.
LLM Self-Reporting
If you used ChatGPT, Copilot, or some other LLM in Task 3 (remember: this is only allowed in Task 3), say so (it should be part of your documentation, too, but we just want some note of it here).
Finally:
Zip the one PDF and the three project zip files into one big zip file for submission.
