Stage 3: read two query parameters and return their sum

Move from serving a file to calculating an answer in Java. The browser sends two numbers after the question mark in the URL.

Download spring-request-params.zip

GET /add?a=10&b=20 -> add(10, 20) -> return 30 -> browser displays 30

@RequestParam("a") reads the query parameter named a and converts it to int. The Java variable first receives that number. The same happens for b and second. @ResponseBody sends the returned number directly as response data. No HTML result page or template engine is used in this stage.

Try and verify: Open /add?a=10&b=20 and expect 30. Try /add?a=7&b=5 and expect 12. A missing or nonnumeric required value produces HTTP 400.

package com.edupoly.hello;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.ResponseBody;

@Controller
public class CalculatorController {
    @GetMapping("/add")
    @ResponseBody
    public int add(@RequestParam("a") int first,
                   @RequestParam("b") int second) {
        return first + second;
    }
}

The ZIP contains every setup file and a README.html with instructions. You can run the supplied project directly.