Migration to Wicket 8.0

Environment

Wicket 8.0 requires at least Java 8

Wicket 8.0 requires Servlet 3.1

API changes

Deprecate org.apache.wicket.util.IProvider WICKET-6060

Replace it with standard Java 8 java.util.function.Supplier<T> which is virtually identical.

IGenericComponent's setter methods now return the current instance for method chaining

All specialization classes return their type.

AjaxFallback** components now use java.util.Optional WICKET-6104

All AjaxFallback** components and the containers which use internally AjaxFallback** components, like AjaxTabbedPanel, RatingPanel and TableTree, have been reworked to pass Optional<AjaxRequestTarget> instead of just AjaxRequestTarget to their onXyz() callback methods. This way the application developer should not forget to check that the AjaxRequestTarget is not null.

Behavior changes

FormComponentPanel delegates the call to #clearInput to its FormComponent children WICKET-6114

FormComponent#clearInput() has been made non-final, so that now containers like FormComponentPanel could override this method and call #clearInput() on its children of type FormComponent.

Removals

Drop Jetty 7.x and 9.0.x modules for Wicket Native WebSocket WICKET-5990

Since Wicket 8.x requires Servlet 3.1 the modules for native websocket support for Jetty 7.x/9.0.x have been dropped.

Users are advised to use wicket-native-websocket-javax module with Jetty 9.2+, Apache Tomcat 7/8, JBoss WildFly.

Improvements

IModel uses Java 8 default interface method for IDetachable#detach() WICKET-6115

For convenience IModel class provides a do-nothing implementation of IDetachable#detach() method, so custom implementations are not required to implement it when not needed.

ResourceStreamResource now receives Attributes as a parameter to its #getResourceStream() method WICKET-6113

For access to the response, the request and its parameters now ResourceStreamResource#getResourceStream() receives an instance of org.apache.wicket.request.resource.IResource.Attributes.

Provide serializable versions of java.util.function.(Supplier|Consumer|Function) WICKET-5991

java.util.function.Consumer and other classes are not serializable and this makes them unusable in stateful Wicket pages. For this reason Wicket provides org.apache.wicket.model.lambda.WicketSupplier, org.apache.wicket.model.lambda.WicketConsumer and org.apache.wicket.model.lambda.WicketFunction. Those interfaces should be used in method signatures where Java 8 lambdas or method references could be used. At the call site there is nothing specific to be done, i.e. just use lambdas and method references without any casting.

Provide IModel implementations which make use of Java 8 lambdas and method references WICKET-5991

Wicket provides three new implementations of IModel which use Java 8 consumers and suppliers, i.e. may be used with lambda or method references.

org.apache.wicket.model.lambda.LambdaModel.

LambdaModel

Person person = ...;
IModel<String> personNameModel = new LambdaModel<>(
      () -> person.getName(),
      (name) -> person.setName(name));

org.apache.wicket.model.lambda.SupplierModel. It is similar to org.apache.wicket.model.AbstractReadOnlyModel.
SupplierModel Expand source
```
Person person = ...;
IModel<String> personNameModel = new SupplierModel<>(person::getName);
```
org.apache.wicket.model.lambda.SupplierCachingModel. It is similar to org.apache.wicket.model.LoadableDetachableModel
SupplierCachingModel Expand source
```
Person person = ...;
IModel<String> personNameModel = new SupplierCachingModel<>(person::getName);
```

IGenericComponent is a mixin/trait interface WICKET-6117

IGenericComponent uses Java 8 default methods to implement #setModel(IModel<T>), #getModel(), #setModelObject(T) and #getModelObject() by delegating to the respective get/setDefaultModel[Object] methods.

This way it could be easily used by any Component by just implementing it.

Dependency updates

All libraries on which Wicket modules depend are updated to their latest stable versions.
The most notable ones are:

Spring Framework 4.2.x
Jetty 9.3.x (used in the Quickstart application archetype and for internal Wicket testing)

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