How to Bind a List from HttpServletRequest Parameters Using @RequestParam?

How can I bind a list of parameters from a form submission using @RequestParam in a Spring controller?

public String controllerMethod(@RequestParam(value="myParam") List<String> myParams) { ... }

In Spring MVC, binding parameters to a list or an array is a common requirement, especially when dealing with form submissions. However, correctly configuring the `@RequestParam` annotation is crucial to achieve this.

public String controllerMethod(@RequestParam List<String> myParam) { // access elements using myParam.get(index) or myParam[index] }

Causes

• Incorrect parameter name in the @RequestParam annotation.
• Missing the required index notation in the parameters sent by the HTTP request.
• Using incompatible types (e.g., mixing parameter types) in the controller method.

Solutions

• Ensure that your request parameters are correctly named and match the expected binding. For an array or a list, you can use `myParam[]` for array binding or just `myParam` to bind directly to a list.
• Use the correct method signature in your controller to match the incoming parameter format. For instance, accessing list elements should be through square brackets in the front-end if you are binding directly to List<String> from myParam: `myParam[0]`, `myParam[1]`, etc.

Mistake: Using the wrong name in the @RequestParam annotation.

Solution: Ensure that the name in the @RequestParam matches exactly with the keys in the HTTP request.

Mistake: Not using the correct array or list syntax in the frontend.

Solution: When sending form data, make sure to index your list values as in `myParam[0]=value1`, `myParam[1]=value2`.

Mistake: Trying to directly bind to other data structures without using a list.

Solution: Use a simple List or an array for indexed parameters instead of creating complex structures.