I'm following this scheme in a Spring application.
I asked in this other question what was the best way to prepare the object before populate the params of the request. The answer was that the best way was to use a conversion service instead of doing it in a @ModelAtribute annotated method or with an editor in the initBinder.
So I have tried to use a converter, but I haven't found a similar example and I'm a little stuck. I have written a code like the one below: In the init binder I register the conversion service. So before populating the values on the User object convert() method is invoked to load the object from the database. The problem is that this configuration doen't work because it is converting the id (username field) of the Object User into an Object user, but then it tries to make a setUsername() with the object so I get a "java.lang.IllegalArgumentException: argument type mismatch".
Can anyone give me a clue or an example of the way of using the ConversionService to get the desired behaviour?
Thanks.
@Autowired
private ConversionService conversionService;
@InitBinder("user")
public void initBinder(@RequestParam("username")String username, WebDataBinder binder){
binder.setConversionService(conversionService);
}
@RequestMapping(value="/user/save", method=RequestMethod.POST)
public String save(@ModelAttribute("user") User user, Model model) {
...
}
with something like:
@Component
public class UserConversionService implements ConversionService{
...
@Override
public Object convert(Object name, TypeDescriptor arg1, TypeDescriptor arg2) {
return userService.find((String)name);
}
}
A converter converts a source object of type S to a target of type T . Implementations of this interface are thread-safe and can be shared.
Spring provides out-of-the-box various converters for built-in types; this means converting to/from basic types like String, Integer, Boolean and a number of other types.
Spring Formatters come into picture to format the data according to the display where it is rendered. Examples may include formatting date/timestamp values according to locales etc.
Spring 3.0 introduces a simple Converter interface that you can implement and reuse anywhere in Spring. You can use them in Spring MVC to convert request String values to Controller method parameter values of any Object type that you can write a Converter for.
You're trying to implement a ConversionService
to do the conversion between Strings and User objects. However, it's Converter
implementations that do this part. What you want to do is:
Your converter would be something like:
final class UserConverter implements Converter<String, User> { ... public User convert(String username) { return userService.find(username); } }
You then need to register that converter. You can either write your own ConversionServiceFactoryBean or override the default:
<bean id="conversionService" class="org.springframework.context.support.ConversionServiceFactoryBean"> <property name="converters"> <list> <bean class="example.UserConverter"/> </list> </property> </bean>
If you want to use the ConversionService explicitly, as you have, just leave it as something that can be autowired. Spring and that factorybean definition will take care of the rest.
If, however, you're already using the <mvc:annotation-driven>
tag in your context, you can use its conversion-service
attribute to reference your ConversionServiceFactoryBean. You then don't need to have InitBinder or ConversionService in your class at all: by simply having a parameter of a @RequestMapping have your target type, User, the conversion will take place without you having to intervene.
I did exactly what Gary is saying above and it worked:
I want to add some more information to the solution. As per the Spring documentation here a URI template variable gets translated to the target object using the Converter/ConversionService. I tried to use a @RequestParam("id") @ModelAttribute("contact") Contact contact
, but I was getting an IllegalStateException: Neither BindingResult nor plain target object for bean name 'contact' available as request attribute
for not having the model object contact
in my view edit.jsp. This can be easily resolved by declaring a Model model
and model.addAttribute(contact);
. However, there is an even better way; using the URI template variable. It's strange why @RequestParam
did not work.
DID NOT WORK
@RequestMapping("edit") //Passing id as .. edit?id=1 public String editWithConverter(@RequestParam("id") @ModelAttribute("contact") Contact contact){ logger.info("edit with converter"); return "contact/edit"; }
WHAT WORKED
@RequestMapping("edit/{contact}") //Passing id as .. edit/1 public String editWithConverter(@PathVariable("contact") @ModelAttribute("contact") Contact contact){ // STS gave a warning for using {contact} without @PathVariable logger.info("edit with converter"); return "contact/edit"; }
So what does this thing do .. a link like ...edit/1
implicitly invokes the converter for String '1' to Contact of id '1' conversion, and brings this contact object to the view. No need for @InitBinder
and since its a Converter
registered with the ConversionService
I can use this anywhere I want - implicitly or explicitly.
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With