Chess Server Implementation Tips

CS – Advanced Programming Concepts

Server Class Structure

What do Web API handlers do?

• If the web API requires an auth token, the handler can validate the auth token
• Might put this logic in a handler base class so it can be shared by multiple handlers or in a Service class that can be shared by multiple services
• Deserialize JSON request body to Java request object
• Call service class to perform the requested function, passing it the Java request object
• Receive Java response object from service
• Serialize Java response object to JSON
• Send HTTP response back to client with appropriate status code and response body

Example Web API handler logic

…

…

LoginRequest request = (LoginRequest)gson.fromJson(reqData, LoginRequest.class);

​

LoginService service = new LoginService();

LoginResult result = service.login(request);

​

return gson.toJson(result);

…

…

Best to create a separate class with fromJson and toJson methods instead of calling Gson directly from handlers

How are Handlers Created and Invoked?

post("/user", context ->

(new RegisterHandler()).handleRequest(context));�

​

Note: There are multiple ways to avoid creating a new handler instance for every request:

1. Create and keep them in instance variables of your Server class
2. Use a static method (will make it difficult to avoid code duplication across handlers)
3. Use the singleton pattern: Create a static getInstance() method that always returns the same instance

Tip – Avoid code duplication

• Areas of potential code duplication
• HTTP Handler classes
• Service classes
• Request/Result classes
• DAO classes
• Use inheritance to avoid this kind of code duplication
• Put common code in bases classes that can be inherited

JSON Tips

• Make sure that the field (variable) names in your Request and Response classes match exactly the names used in the specification (including capitalization)
• Not doing this will cause bugs

​

• GSON does not serialize null fields (they will be missing in the JSON)
• This is helpful when generating Success and Failure JSON responses

class Response {

String message;

}

​

class LoginResponse extends Response {

String authtoken;

String username;

}

​

Generating an Auth Token

• There are multiple ways. Here’s a simple way:

​

UUID.randomUUID().toString()

Server Implementation Approach

• Review class structure diagram
• Create Java packages in your project to contain your server classes
• Create your Server class and get static file handling to work so you can see the test page (see the Server Web API lecture for details)
• Pick one Web API and get it working end-to-end, and test it with the test Web page or curl (e.g., register)
• As you go, write JUnit test cases for Service classes you create
• Repeat for the other Web APIs until you have written all 7 and are passing all of the passoff tests