Upgrade to Spring Framework 6 and Jakarta EE 9

Closes gh-750
Closes gh-748

docs/src/docs/asciidoc/documenting-your-api.adoc

@@ -1252,7 +1252,7 @@ example of such a resource bundle].
 
 Each key in the resource bundle is the fully-qualified name of a constraint plus a
 `.description`. For example, the key for the standard `@NotNull` constraint is
-`javax.validation.constraints.NotNull.description`.
+`jakarta.validation.constraints.NotNull.description`.
 
 You can use a property placeholder referring to a constraint's attributes in its
 description. For example, the default description of the `@Min` constraint,
@@ -1318,7 +1318,7 @@ You can configure which snippets are produced by default. See the
 === Using Parameterized Output Directories
 
 When using MockMvc, REST Assured, or `WebTestClient` you can parameterize the output directory used by
-`document`. Parameterizing output with `WebTestClient` requires Spring Framework 5.3.5 or later.
+`document`.
 
 The following parameters are supported:
 

docs/src/docs/asciidoc/getting-started.adoc

@@ -77,7 +77,7 @@ If you want to jump straight in, a number of sample applications are available:
 Spring REST Docs has the following minimum requirements:
 
 * Java 17
-* Spring Framework 5 (5.0.2 or later)
+* Spring Framework 6
 
 Additionally, the `spring-restdocs-restassured` module requires REST Assured 4 (4.4 or later).
 

docs/src/test/java/com/example/Constraints.java

@@ -18,8 +18,8 @@ package com.example;
 
 import java.util.List;
 
-import javax.validation.constraints.NotNull;
-import javax.validation.constraints.Size;
+import jakarta.validation.constraints.NotNull;
+import jakarta.validation.constraints.Size;
 
 import org.springframework.restdocs.constraints.ConstraintDescriptions;