/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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 org.apache.beam.sdk.coders;
import com.google.auto.service.AutoService;
import com.google.common.collect.ImmutableList;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.List;
import org.apache.beam.sdk.values.PCollection;
import org.apache.beam.sdk.values.TypeDescriptor;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
/**
* The {@link DefaultCoder} annotation specifies a {@link Coder} class to handle encoding and
* decoding instances of the annotated class.
*
* <p>The specified {@link Coder} must have the following method:
* <pre>
* {@code public static CoderProvider getCoderProvider()}.
* </pre>
*
* <p>Coders specified explicitly via {@link PCollection#setCoder} take precedence, followed by
* Coders found at runtime via {@link CoderRegistry#getCoder}.
* See {@link CoderRegistry} for a more detailed discussion of the precedence rules.
*/
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@SuppressWarnings("rawtypes")
public @interface DefaultCoder {
Class<? extends Coder> value();
/**
* A {@link CoderProviderRegistrar} that registers a {@link CoderProvider} which can use
* the {@code @DefaultCoder} annotation to provide {@link CoderProvider coder providers} that
* creates {@link Coder}s.
*/
@AutoService(CoderProviderRegistrar.class)
class DefaultCoderProviderRegistrar implements CoderProviderRegistrar {
@Override
public List<CoderProvider> getCoderProviders() {
return ImmutableList.<CoderProvider>of(new DefaultCoderProvider());
}
/**
* A {@link CoderProvider} that uses the {@code @DefaultCoder} annotation to provide
* {@link CoderProvider coder providers} that create {@link Coder}s.
*/
static class DefaultCoderProvider extends CoderProvider {
private static final Logger LOG = LoggerFactory.getLogger(DefaultCoderProvider.class);
/**
* Returns the {@link Coder} returned according to the {@link CoderProvider} from any
* {@link DefaultCoder} annotation on the given class.
*/
@Override
public <T> Coder<T> coderFor(TypeDescriptor<T> typeDescriptor,
List<? extends Coder<?>> componentCoders) throws CannotProvideCoderException {
Class<?> clazz = typeDescriptor.getRawType();
DefaultCoder defaultAnnotation = clazz.getAnnotation(DefaultCoder.class);
if (defaultAnnotation == null) {
throw new CannotProvideCoderException(
String.format("Class %s does not have a @DefaultCoder annotation.",
clazz.getName()));
}
if (defaultAnnotation.value() == null) {
throw new CannotProvideCoderException(
String.format("Class %s has a @DefaultCoder annotation with a null value.",
clazz.getName()));
}
LOG.debug("DefaultCoder annotation found for {} with value {}",
clazz, defaultAnnotation.value());
Method coderProviderMethod;
try {
coderProviderMethod = defaultAnnotation.value().getMethod("getCoderProvider");
} catch (NoSuchMethodException e) {
throw new CannotProvideCoderException(String.format(
"Unable to find 'public static CoderProvider getCoderProvider()' on %s",
defaultAnnotation.value()),
e);
}
CoderProvider coderProvider;
try {
coderProvider = (CoderProvider) coderProviderMethod.invoke(null);
} catch (IllegalAccessException
| IllegalArgumentException
| InvocationTargetException
| NullPointerException
| ExceptionInInitializerError e) {
throw new CannotProvideCoderException(String.format(
"Unable to invoke 'public static CoderProvider getCoderProvider()' on %s",
defaultAnnotation.value()),
e);
}
return coderProvider.coderFor(typeDescriptor, componentCoders);
}
}
}
}