[SLING-12359] Sling Models: Support constructor injection for Java Record classes

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: Models Implementation 1.6.4
• Fix Version/s: Models Implementation 1.7.0
• Component/s: Sling Models
• Labels: Sling-13-Release-Notes
• Assignee: Stefan Seifert
• Reporter: Herman Ciechanowiec
• Created: 24/Jun/24 08:56
• Updated: 3 hours ago
• Resolved: 25/Jun/24 11:23

Description

Java 14 introduced support for record classes, and Apache Sling 12 by default runs with Java 17, allowing the use of records.

Although Apache Sling 12 supports record classes, the current latest version of Apache Sling Models Implementation does not fully support injection in relation to records. Specifically, for records, the Apache Sling Models Implementation does support constructor injection similarly to a usual class if there is an explicit constructor annotated with `javax.inject.Inject`:

@Model(
        adaptables = {Resource.class, SlingHttpServletRequest.class},
        defaultInjectionStrategy = DefaultInjectionStrategy.REQUIRED
)
public record StudentModel(String name, int age) {

    @Inject
    public StudentModel(
            @ValueMapValue(name = "name") @Default(values = "unknown")
            String name, 
            @ValueMapValue(name = "age") @Default(intValues = 0)
            int age
    ) {
        this.name = name;
        this.age = age;
    }
}

However, for records, Apache Sling Models Implementation does not support constructor injection if there is an implicit constructor. Such a constructor cannot be annotated with `javax.inject.Inject` and will not be picked up during injection. Therefore, such a Sling Model will not be instantiated at all:

@Model(
        adaptables = {Resource.class, SlingHttpServletRequest.class},
        defaultInjectionStrategy = DefaultInjectionStrategy.REQUIRED
)
public record StudentModel(
        @ValueMapValue(name = "name") @Default(values = "unknown")
        String name,
        @ValueMapValue(name = "age") @Default(intValues = 0)
        int age
) {}

The above issue should be addressed by introducing support for injection in records' implicit constructors.

Note:

1. For records, only constructor injection is supported since records cannot have instance fields (code with such fields will not compile).
2. Apache Sling Models Implementation is currently based on Java 8 and may also be executed in a Java 8 environment. Therefore, the records check should be introduced via dynamic loading of the `java.lang.Record` class.

Issue Links

• is related to: SLING-12483 Improve performance of constructor-based instantiation on Java11
• links to: GitHub Pull Request #51