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Update docs on how a `@ModelAttribute` is sourced 

Closes gh-26873
This commit is contained in:
Rossen Stoyanchev 2021-05-07 21:30:24 +01:00
parent 355d394d7f
commit 29790d5bb1
1 changed files with 25 additions and 17 deletions
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42
src/docs/asciidoc/web/webmvc.adoc
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@ -2622,33 +2622,41 @@ query parameters and form fields. The following example shows how to do so:
.Java
----
@PostMapping("/owners/{ownerId}/pets/{petId}/edit")
public String processSubmit(@ModelAttribute Pet pet) { } <1>
public String processSubmit(@ModelAttribute Pet pet) {
// method logic...
}
----
<1> Bind an instance of `Pet`.
[source,kotlin,indent=0,subs="verbatim,quotes",role="secondary"]
.Kotlin
----
@PostMapping("/owners/{ownerId}/pets/{petId}/edit")
fun processSubmit(@ModelAttribute pet: Pet): String { } // <1>
fun processSubmit(@ModelAttribute pet: Pet): String {
// method logic...
}
----
<1> Bind an instance of `Pet`.
The `Pet` instance above is resolved as follows:
The `Pet` instance above is sourced in one of the following ways:
* From the model if already added by using <<mvc-ann-modelattrib-methods>>.
* From the HTTP session by using <<mvc-ann-sessionattributes>>.
* From a URI path variable passed through a `Converter` (see the next example).
* From the invocation of a default constructor.
* From the invocation of a "`primary constructor`" with arguments that match to Servlet
request parameters. Argument names are determined through JavaBeans
`@ConstructorProperties` or through runtime-retained parameter names in the bytecode.
* Retrieved from the model where it may have been added by a
<<mvc-ann-modelattrib-methods,@ModelAttribute method>>.
* Retrieved from the HTTP session if the model attribute was listed in
the class-level <<mvc-ann-sessionattributes>> annotation.
* Obtained through a `Converter` where the model attribute name matches the name of a
request value such as a path variable or a request parameter (see next example).
* Instantiated using its default constructor.
* Instantiated through a "`primary constructor`" with arguments that match to Servlet
request parameters. Argument names are determined through JavaBeans
`@ConstructorProperties` or through runtime-retained parameter names in the bytecode.
While it is common to use a <<mvc-ann-modelattrib-methods>> to populate the model with
attributes, one other alternative is to rely on a `Converter<String, T>` in combination
with a URI path variable convention. In the following example, the model attribute name,
`account`, matches the URI path variable, `account`, and the `Account` is loaded by passing
the `String` account number through a registered `Converter<String, Account>`:
One alternative to using a <<mvc-ann-modelattrib-methods,@ModelAttribute method>> to
supply it or relying on the framework to create the model attribute, is to have a
`Converter<String, T>` to provide the instance. This is applied when the model attribute
name matches to the name of a request value such as a path variable or a request
parameter, and there is a `Converter` from `String` to the model attribute type.
In the following example, the model attribute name is `account` which matches the URI
path variable `account`, and there is a registered `Converter<String, Account>` which
could load the `Account` from a data store:
[source,java,indent=0,subs="verbatim,quotes",role="primary"]
.Java