port in JMPS module-compatible form of ServiceSelector

nb-annotations/src/main/java/io/nosqlbench/nb/annotations/ServiceSelector.java

@@ -0,0 +1,103 @@
+/*
+ * Copyright (c) 2022 nosqlbench
+ *
+ * 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 io.nosqlbench.nb.annotations;
+
+import java.util.List;
+import java.util.Optional;
+import java.util.ServiceLoader;
+import java.util.function.Predicate;
+import java.util.stream.Collectors;
+
+/**
+ * A service loader filter which works with {@link io.nosqlbench.nb.annotations.Service} to load a named service.
+ * This version requires the caller to provide the service loader instance, since it is now caller sensitive.
+ *
+ * Use it like this:<pre>{@code
+ *       ResultValueFilterType filterType =
+ *           SelectorFilter.of("core", ServiceLoader.load(ResultValueFilterType.class)).get();
+ * }</pre>
+ *
+ * @param <T> The service type
+ */
+public class ServiceSelector<T> implements Predicate<ServiceLoader.Provider<? extends T>> {
+    private final String name;
+    private final ServiceLoader<? extends T> loader;
+
+    public ServiceSelector(String name, ServiceLoader<? extends T> loader) {
+        this.name = name;
+        this.loader = loader;
+    }
+
+    public static <T> ServiceSelector<T> of(String name, ServiceLoader<? extends T> loader) {
+        return new ServiceSelector<>(name, loader);
+    }
+
+    public static <T> boolean matches(String name, ServiceLoader.Provider<? extends T> provider) {
+        Service annotation = provider.type().getAnnotation(Service.class);
+        if (annotation == null) {
+            return false;
+        }
+        return (annotation.selector().equals(name));
+    }
+
+    @Override
+    public boolean test(ServiceLoader.Provider<? extends T> provider) {
+        return false;
+    }
+
+    public T getOne() {
+        List<? extends T> services = getAll();
+        if (services.size() == 0) {
+            throw new RuntimeException("You requested exactly one instance of a service by name '" + name + "', but got " +
+                (services.stream().map(s -> s.getClass().getSimpleName())).collect(Collectors.joining(",")) + " (" + services.stream().count() + ")");
+        }
+        return services.get(0);
+    }
+
+    public List<? extends T> getAll() {
+        List<? extends T> services = loader
+            .stream()
+            .peek(l -> {
+                    if (l.type().getAnnotation(Service.class) == null) {
+                        throw new RuntimeException(
+                            "Annotator services must be annotated with distinct selectors\n" +
+                                "such as @Selector(\"myimpl42\")"
+                        );
+                    }
+                }
+            )
+            .filter(l -> l.type().getAnnotation(Service.class) != null)
+            .filter(l -> l.type().getAnnotation(Service.class).selector().equals(name))
+            .map(ServiceLoader.Provider::get)
+            .toList();
+        return services;
+    }
+
+    public Optional<? extends T> get() {
+        List<? extends T> services = getAll();
+        if (services.size() == 1) {
+            return Optional.of(services.get(0));
+        }
+        if (services.size()==0) {
+            throw new RuntimeException("No services were found for '" + name + "'.");
+        }
+        throw new RuntimeException("You requested exactly one instance of a service by name '" + name + "', but got " +
+            (services.stream().map(s -> s.getClass().getSimpleName())).collect(Collectors.joining(",")) + " (" + services.stream().count() + ")");
+
+
+    }
+}