How to check if @RequestParam is empty

Question

I am wondering how I could check the RequestParams to see if they are empty so I could forward to another html page, right now I am just working around this by checking if each parameter is empty. The problem is I want to forward to another page if the user tries to submit a compeletly empty form and if they do that my program will crash. It will crash because the program tries to convert the int Price to a string becasue that is what is submitted in the empty form. I know I could just make the Int Price a String but I was wondering if there was another soultion.

@Controller
public class HomeController {
    
    @Autowired
    private GlassesList glassesList;

    
    @GetMapping("/")
    public String goHome(Model model) {
        return "index";
    }
    
    @GetMapping("/addGlasses")
    public String addSunglasses(Model model) {
        return "addGlasses";
    }
    
    
    @GetMapping("/searchGlasses")
    public String searchSunglasses() {
        return "searchGlasses";
    }
    
    @GetMapping("/displayGlasses")
    public String displaySunglasses() {
        return "displayGlasses";
    }
    @PostMapping("/formPost")public String processForm (
            Model model,
            @RequestParam String productName,
            @RequestParam String brandName,
            @RequestParam String frameType,
            @RequestParam String color,
            @RequestParam String size,
            @RequestParam String lensType,
            @RequestParam int price
            ) {
if (productName.equals("") && brandName.equals("") && frameType.equals("") && color.equals("") && size.equals("") && lensType.equals("") && price == 0) {
            
            return "displayGlasses";
        }
        else {
        Glasses glasses = new Glasses(productName, brandName,frameType,
       color, size, lensType, price);
        glassesList.getGlassesList().add(glasses); 
        model.addAttribute("glassesList", glassesList);
        System.out.println(model.getAttribute(lensType));
        System.out.print(glassesList.getGlassesList());
        
        
        return "addGlasses";
        
        
        
    }
}

productName.equals("") or required param in the method defintion — Senthil
– Senthil, Commented Oct 2, 2021 at 0:34
Use @ModelAttribute instead, and you could write a clean method on that class. — chrylis -cautiouslyoptimistic-
– chrylis -cautiouslyoptimistic-, Commented Oct 2, 2021 at 0:43
Well what I want is if all my feilds in my form are blank the porgram should forward to the displayGlasses.html automatically and if I implement required param then it will require me to have the form filled. I apologize if I am misunderstanding you answer I am very new to java and spring-boot. — Mathew Boyd
– Mathew Boyd, Commented Oct 2, 2021 at 0:45
Since you parameters are all strings please don’t use “==“ instead of you should use “equals” method from string class to compare values. If all you need to do is redirect, you can keep using these methods or write an utility method which can check all or some of your request parameters. — Rituraj
– Rituraj, Commented Oct 2, 2021 at 1:12

user404 · Accepted Answer · 2021-10-02 05:26:58Z

Instead of handling too many request params, you can use RequestBody and send those params in that request like below: Define a class representing all your request-params:

public class AllParams{
       @NotNull
       @NotEmpty
       private String productName;
       @NotNull
       @NotEmpty
       private String brandName;
       @NotNull
       @NotEmpty 
       private String frameType;
       @NotNull
       @NotEmpty
       private String color;
       @NotNull
       @NotEmpty
       private String size; 
       @NotNull
       @NotEmpty
       private String lensType;
    
       @Min(1)
       private int price;
    
      //getters and setters
    }

Now, use this in your method and bind the errors:

 @PostMapping("/formPost")public String processForm (@Valid @RequestBody AllParams requestParam, BindingResult bindingResult,
            Model model){

     //check if there is any error[based on your annotations]
     if(bindingResult.hasErrors()) {
        return "displayGlasses";
       
     }

//otherwise, write your usual code here
  ....
...
}

About annotations, please refer here: Difference Between @NotNull, @NotEmpty, and @NotBlank Constraints in Bean Validation

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