what is the real use case scenario for spring conversion service

I was reading this questions

ConversionService in Spring

But i still dont get it under what scenarios we need to do conversion.

Can someone give me example of what can be rea开发者_JAVA技巧l life example of using conversion service in web apllicationj

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Spring Webflow utilizes spring's conversion service. Webflow does not offer the availability of an InitBinder type method/annotation. So you tell Spring about all the conversions you want to be done for all flows. If the ConversionService was not available the binding support wouldn't be as available.

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The Conversion Service can be used to directly convert between the UI and business objects.

Let's say that I have a webapp with a dropdown of Products. It's straightforward to define a ProductConversionService that converts from the value of the dropdown (say, id 4) to a Product. Now in my code (controller, API, etc) I just refer to a Product, and everything happens automatically.

In older UIs, I have seen lots of lots of code devoted to this conversion. I'll give a deliberately crude example:

String productIdParam = request.getParameter("productId");
// Validate that the param exists, is numeric, etc.....
Long productId        = Long.valueOf(productIdParam);
Product product       = productManager.findProduct(productId);

This code is also more difficult to test, since I have to create a mock request, give it a productIdParameter and so forth. Also I need to have the productManager available everywhere that this is needed.

With ConversionService, I can just put this in a JSP:

<form:select path="mystuff.product">
  <option value="1">Nook</option>
  <option value="2">Cranny</option>
</form:select>

When my Spring MVC controller gets the request, mystuff.getProduct() has the selected product. Clean and simple. And I can use this outside the web tier as well.