ratpack.render.RendererSupport Maven / Gradle / Ivy
/*
* Copyright 2013 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package ratpack.render;
import com.google.common.base.Predicates;
import com.google.common.collect.Iterables;
import com.google.common.reflect.TypeToken;
import ratpack.handling.Context;
import ratpack.util.Types;
import ratpack.util.internal.InternalRatpackError;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.Arrays;
/**
* A {@link Renderer} super class that provides a {@link #getType()} implementation based on the generic type of the impl.
*
* Implementations need only to declare the type they render as the value for type variable {@code T} and implement {@link #render(ratpack.handling.Context, Object)}.
*
{@code
* import ratpack.handling.Context;
* import ratpack.render.RendererSupport;
* import ratpack.test.embed.EmbeddedApp;
*
* import static org.junit.Assert.assertEquals;
*
* public class Example {
*
* // A type of thing to be rendered
* static class Thing {
* private final String name;
*
* public Thing(String name) {
* this.name = name;
* }
*
* public String getName() {
* return this.name;
* }
* }
*
* // Renderer implementation
* public static class ThingRenderer extends RendererSupport {
* public void render(Context context, Thing thing) {
* context.render("Thing: " + thing.getName());
* }
* }
*
* public static void main(String... args) throws Exception {
* EmbeddedApp.fromHandlers(c -> c
* .register(r -> r.add(new ThingRenderer()))
* .handler(ctx -> ctx.render(new Thing("foo")))
* ).test(httpClient -> {
* assertEquals("Thing: foo", httpClient.getText());
* });
* }
* }
* }
*
* An alternative to implementing a render is to make the type to be rendered implement {@link Renderable}.
*
* @param The type of object this renderer renders
*/
public abstract class RendererSupport implements Renderer {
private final Class type;
protected RendererSupport() {
TypeToken typeToken = new TypeToken(getClass()) {
};
Type type = typeToken.getType();
if (type instanceof Class) {
@SuppressWarnings("unchecked") Class rawType = (Class) typeToken.getRawType();
this.type = rawType;
} else if (type instanceof ParameterizedType) {
Iterable typeArgs = Arrays.asList(((ParameterizedType) type).getActualTypeArguments());
if (Iterables.any(typeArgs, Predicates.not((t) -> t.getTypeName().equals("?")))) {
throw new IllegalArgumentException("Invalid renderable type " + type + ": due to type erasure, type parameter T of RendererSupport must be a Class or a parameterized type with '?' for all type variables (e.g. List)");
}
this.type = Types.cast(typeToken.getRawType());
} else {
throw new InternalRatpackError("Unhandled type for renderer support: " + type.getClass());
}
}
/**
* The type of object that this renderer can render (the type for {@code T}).
*
* @return The type of object that this renderer can render.
*/
@Override
public Class getType() {
return type;
}
/**
* {@inheritDoc}
*/
abstract public void render(Context context, T t) throws Exception;
}