Hello, fellow coders and tech enthusiasts! Today, we’re going to dive deep into a common coding conundrum that has left many scratching their heads – transferring data from a Thymeleaf view to a controller, particularly when the data is expected as a HashMap. Trust me, this topic isn’t as complex as it sounds, so let’s dive in!
A Quick Overview of the Problem
Our point of concern revolves around a POJO (Plain Old Java Object) class named DTDays. This class serves as a wrapper for our HashMap data. Here’s what it looks like:
public class DTDays {
private Map driversDays = new HashMap<>();
public Map getDriversDays() {
return driversDays;
}
public void setDriversDays(Map driversDays) {
this.driversDays = driversDays;
}
}
The controller method, in this case, takes DTDays as a model attribute parameter:
@RequestMapping(value = “/go”, method = RequestMethod.POST)
public String advanced(@ModelAttribute DTDays dtDays,
@RequestParam(name = “tourId”) Long tourId, Model model){
// make some business logic with provided data
return “redirect:/tours/advanced”;
}
So, what’s the issue here? When debugging, we find that dtDays is not null, but the map property is empty, even though the tourId is working as expected. That’s the problem we’re trying to solve!
Dealing with the View
Our view looks something like this:
Add tour interval for drivers
<body> <div style=”margin-left: 20px;”> <h1 th:text=”${tour.tittle}”></h1> <p>Add tour interval for drivers</p> <!– Form Code Here –> </div> </body>
The question is – how should we structure our view to submit data properly? How can we make sure the Driver is the key of the map and the data entered in the related input field is the value of the map?
The Hunt for a Solution
After extensive research and going through numerous resources, including Thymeleaf documentation and various forum discussions, it turns out that the answer lies in using a wrapper correctly and understanding the correct syntax for mapping data in the view.
The Ultimate Solution
Finally, the view will look like this:
<form th:action=”@{/save}” th:object=”${form}” method=”post”> <h1>Welcome</h1> <div th:each=”property : ${form.properties.entrySet()}”> <div class=”form-group”> <label th:for=”*{properties[‘__${property.key}__’] }” th:text=”${property.key}”>Property</label> <input type=”text” class=”form-control” th:field=”*{properties[‘__${property.key}__’] }” /> </div> </div> <button type=”submit”>send to controller</button> </form>
And the controller:
@PostMapping("/save")
public ModelAndView save(@ModelAttribute(name = "form") MapWrapper form){
var mav = new ModelAndView();
mav.setViewName("index");
mav.addObject("mapWrapper", form);
var map = form.getProperties();
System.out.println("Size of map = "+map.size());
for (Long id : map.keySet()) {
System.out.println("Key: "+id+"; Value: "+map.get(id));
}
return mav;
}
Et voila! The problem is solved.
Coding isn’t just about algorithms and logic; it’s also about perseverance. The most seemingly unsolvable problems often have simple solutions; it’s just a matter of finding the right approach. Remember, there’s no problem that can’t be solved with a fresh perspective and a bit of coffee!
Wrapping It Up
A key takeaway here is that the Map object keys can be pre-populated in our scenario, and the user’s input for each driver serves as the key value. This effective solution was discovered after navigating through numerous resources and understanding the syntax of Thymeleaf forms. This valuable insight can be used in many similar scenarios involving data submission to a controller, and it demonstrates the power of persistence and research in problem-solving.
If you’ve been stuck on this issue for a while, you’re not alone. I hope this blog post has been helpful in demystifying this complex issue, showing you that even the most daunting problems have solutions. Remember, no matter how insurmountable a coding challenge may seem, you can always find a solution if you’re determined and willing to keep learning.
Keep Going
It’s not unusual for us coders to spend hours, days, or even weeks stuck on a problem. But there’s something incredibly satisfying about finally finding a solution, isn’t there? It’s a sweet victory that makes all the frustration worthwhile. After all, it’s through these challenges that we grow and improve as developers.
So, next time you’re faced with a problem that seems impossible, don’t give up. Keep researching, keep trying new things, and most importantly, keep coding. You might surprise yourself with what you can accomplish.
