Thymleaf how to take an input and then redirect to another page - html

Question

I'm learning Spring boot. I have a list of products with unique ids, and I want to implement a "lookup by id" functionality, but I don't know how to do it, I searched but got totally different stuff.
I already have a #Getmapping method like this:
#Getmapping(/products/{id})
If I manually type in the id in the url I'll get what I what. But I want to have an input box in the HTML page like:
<form>
Look up by id: <input/>
</form>
and after I submit the form it'll redirect to that page. For example, if I enter input of 1, it'll go to localhost:8080/products/1
I've been searching but all I got was stuff about #Postmapping.

Answer 1

Add a #PostMapping to your controller:
#Controller
#RequestMapping("/products")
public class ProductController {
#GetMapping //Controller method for showing the empty form
public String index(Model model) {
model.addAttribute("formData", new SearchFormData()); // Create an empty form data object so Thymeleaf can bind to it
return "index";
}
#PostMapping
public String searchById(SearchFormData formData) {
return "redirect:/products/" + formData.getId(); //Use the value the user entered in the form to do the redirect
}
#GetMapping("/{id}")
public String showProduct(#PathVariable("id") long id) {
...
}
}
With SearchFormData representing the form fields (there is only 1 field in this case):
public class SearchFormData {
private long id;
// getters and setters
And update Thymeleaf template like this:
<form th:action="#{/products}" th:method="post" th:object="${formData}">
<input th:field="*{id}" type="number">
<button type="submit">Search</button>
</form>
Note that the value of th:object needs to match with the name used to add the SearchFormData instance to the model.
See Form handling with Thymeleaf for more info.

Answer 2

The following simple code will direct you to a URL that is generated from a concatenation of the base address of the <form>'s action attribute and the value of its first <input>:
document.querySelector("form").addEventListener("submit",function(ev){
ev.preventDefault();
this.action="/product/"+this.querySelector("input").value;
console.log(this.action);
// in real code: uncomment next line!
// this.submit()
})
<form>
Look up by id: <input type="text" value="123" />
</form>
In the real code you will delete the console.log() und uncomment the following line: this.submit().
Alternatively you could also do:
document.querySelector("form").addEventListener("submit",function(ev){
ev.preventDefault();
location = "/product/"+this.querySelector("input").value;
})
This will redirect you to the page without actually submitting the form.