What is the difference between @Inject and @ValueMapValue in simple words.

[sachinarora]

Please refer below example to get property value when Model is created using SlingHttpServletRequest as an Adaptable and we have to add @Via to get property from current resource.

@Model(adaptables=SlingHttpServletRequest.class)
public interface MyModel {
 //will return request.getResource().getValueMap().get("propertyName", String.class)
    @Inject @Via("resource")
    String getPropertyName();
} 

whereas if you use @ValueMapValue it will be done automatically and you have to write less code. Refer this snippet from Sling Document :
@ValueMapValue : Injects a ValueMap value. If via is not set, it will automatically take resource if the adaptable is the SlingHttpServletRequest. If name is not set the name is derived from the method/field name.

Link : https://sling.apache.org/documentation/bundles/models.html

[HeenaMadan · Accepted solution]

The injected fields are normally the properties of a component (which the content authors normally set via component dialog). 

@inject:

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

    @Inject
    private String propertyName;
}

In this case, a property named "propertyName" will be looked up from the Resource (after first adapting it to a ValueMap) and it is injected.

Avoid @Inject. Value injection happens at runtime. If you use @inject then you are making the framework do extra guesswork. It would be good if we use  injector annotations like @ValueMapValue, @childResource

Value Map (name=”valuemap”) Injector

Gets a property from a ValueMap by name; If @Via is not set, it will automatically take resource if the adaptable is the SlingHttpServletRequest. If name is not set the name is derived from the method/field name.

@Model(adaptables = SlingHttpServletRequest.class,
    defaultInjectionStrategy = DefaultInjectionStrategy.OPTIONAL)
public class ExampleComponent {

    // @Inject @Source("valuemap") @Named("jcr:title")
    @ValueMapValue(name = "jcr:title")
    private String titleText;

    // @Inject @Source("valuemap")
    @ValueMapValue
    private String titleDescription;

It means if we use @@ValueMapValue it will be done automatically an we have to write less code.

Refer here-https://sling.apache.org/documentation/bundles/models.html

https://sourcedcode.com/blog/aem/aem-sling-model-injectors-annotations-cheat-sheet-reference-guide#V...

[DEBAL_DAS]

@Inject: This annotation is used to inject a property, resource, request, OSGi service.

               This is a generic annotation

@ValueMapValue: Injects a ValueMap value. If via is not set, it will automatically take resource if the adaptable is the SlingHttpServletRequest. If name is not set the name is derived from the method/field name.