codeconsole opened a new pull request, #15732:
URL: https://github.com/apache/grails-core/pull/15732
## Summary
Follow-up to #15715. The named converters (`string`, `int`, `boolean`, …)
cover scalar attribute values, but attributes frequently hold richer objects —
a security principal, a domain instance, a CSRF token — where today the only
statically-compilable read is a cast at every call site:
```groovy
CsrfToken token = (CsrfToken) session.getAttribute('_csrf')
UserDetails user = request.getAttribute(USER_ATTRIBUTE) as UserDetails
```
This adds a `Class`-typed overload of `getAttribute` (plus a default-value
variant) to `session`, `request` and `servletContext`:
```groovy
CsrfToken token = session.getAttribute('_csrf', CsrfToken)
UserDetails user = request.getAttribute('apiUser', UserDetails)
Theme theme = session.getAttribute('theme', Theme, Theme.DEFAULT)
```
The generic signature (`static <T> T getAttribute(holder, String name,
Class<T> type)`) lets the static compiler infer the return type from the class
literal, so the read compiles under `@CompileStatic` / `@GrailsCompileStatic`
with no cast.
## Design
- **Typed read, not coercion.** The attribute is returned only when it is an
instance of the requested type; absent and wrong-typed attributes read as
`null` (so the default-value overload also applies on a type mismatch). No
`TypeConverters` delegation — the named converters remain the coercing API, the
`Class` overload is the type-safe retrieval API. Two simple contracts instead
of one mixed one.
- **Overloads `getAttribute` rather than introducing a new verb.** Mirrors
`grails.config.Config.getProperty(String key, Class<T> targetType, T
defaultValue)` (and Spring's `Environment.getProperty(key, type, default)`),
and shows up in IDE completion right next to the raw `getAttribute(String)`.
- **Scope: the three attribute holders only.** `flash` is skipped — it is a
`Map`, and Groovy's DGM `Map.get(key, default)` (which *inserts* the default)
makes a two-arg sibling on flash a semantic trap. `params` is skipped — its
values are Strings, where a non-coercing typed read is not useful.
## Tests & docs
- `HttpSessionExtensionSpec`, `HttpServletRequestExtensionSpec`,
`ServletContextExtensionSpec` each gain two features: instance-match /
supertype-match / absent / wrong-type-reads-as-null semantics, default-value
behavior, and a `@CompileStatic` static-resolution guard (the guard fails test
compilation without the new extension methods).
- New "Typed Reads of Attributes" subsection in the controllers guide,
following the "Type Conversion of Attributes" section from #15715.
`:grails-web-core:test` passes in full.
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