What's the advantage of using package-info.json vs. Export-Packages to define models to export Models?

[Preston]

Recently I encountered a project with a complex model package structure and looked into how best to support this. I found documentation at WCM.io that indicated this. 

<!-- Export all non-internal packages by default --> 
Export-Package: !*.impl.*,!*.internal.*,\ io.wcm.samples.*

Replace io.wcm.samples.* with the topmost package from your project.

That got me wondering what the advantage was of using syntax like this vs. simply dropping package-info.json files into all of the folders that contained models. 

Additionally in the WCM.io documentation it mentions that for bnd plugin implementations Sling-Model-Packages should be moved into bnd configuration. 

<configuration>
   <bnd>
      Sling-Initial-Content: SLING-INF/app-root;overwrite:=true;ignoreImportProviders:=xml;path:=/apps/wcm-io/wcm/commons
      Sling-Model-Packages: io.wcm.wcm.commons
      Sling-Namespaces: wcmio=http://wcm.io/ns
      Import-Package: \
     <!-- For build compatibility with Java 11 -->\
     javax.annotation;version="[0.0,2)",\
     *
   </bnd>
</configuration>

Similarly why use this syntax vs just using the ModelScanner? 

[gkalyan]

@Preston Interesting, I tried searching for this but didn't find a solid answer. I will look into this.

Please let us know if you find an answer for this.

[HrishikeshKa · Accepted solution]

Hi @Preston ,

Using package-info.json versus Export-Package for defining models to export in OSGi bundles offers different approaches with varying advantages. Let's explore each and also delve into the usage of Sling-Model-Packages versus ModelScanner.

Advantages of package-info.json:

1. Granular Control:

   • With package-info.json, you have fine-grained control over which packages contain models and should be exported.

2. Explicit Declaration:

   • It explicitly defines the packages containing models, making it easier to understand and maintain the export configuration.

3. Modularity:

   • You can distribute model definitions across different packages, promoting modularity and organization in complex projects.

Advantages of Export-Package:

1. Simplicity:

   • Export-Package offers a simpler syntax for specifying which packages to export, especially for straightforward projects with fewer model packages.

2. Coarse-Grained Control:

   • It's suitable for exporting entire packages or excluding certain patterns, providing flexibility in export configurations.

3. Convention-Based:

   • It follows OSGi conventions, making it easier for developers familiar with OSGi to understand and work with.

Advantages of Sling-Model-Packages:

1. Explicit Configuration:

   • Sling-Model-Packages explicitly declares the packages containing Sling models, ensuring clarity and precision in the setup.

2. Performance Optimization:

   • It helps in optimizing performance by specifying only the relevant packages to scan for Sling models.

3. Compatibility:

   • Aligns well with Sling's architecture and best practices, ensuring compatibility and smooth integration with Sling-based projects.

Advantages of ModelScanner:

1. Automatic Registration:

   • ModelScanner automatically detects and registers models based on conventions or annotations, reducing manual configuration efforts.

2. Dynamic Discovery:

   • It enables dynamic discovery of models during runtime, facilitating flexibility and extensibility in larger projects.

3. Simplicity:

   • It simplifies the setup process by handling model registration automatically, suitable for projects where explicit configuration is not required.

Example Java Code:

Here's a simple example demonstrating how you can use ModelScanner in Java code:

import org.apache.sling.models.annotations.Model;
import org.apache.sling.models.annotations.injectorspecific.Inject;

@Model(adaptables = Resource.class)
public class MyModel {

    @Inject
    private String title;

    public String getTitle() {
        return title;
    }
}

In this example, MyModel is annotated with @Model, indicating that it's a Sling model. The ModelScanner will automatically detect and register this model based on the annotations and adaptability defined.