Github user squito commented on a diff in the pull request:
https://github.com/apache/spark/pull/17902#discussion_r119409655
--- Diff:
common/kvstore/src/main/java/org/apache/spark/kvstore/KVTypeInfo.java ---
@@ -0,0 +1,154 @@
+/*
+ * 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.spark.kvstore;
+
+import java.lang.reflect.Field;
+import java.lang.reflect.Method;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.stream.Stream;
+
+import com.google.common.base.Preconditions;
+
+/**
+ * Wrapper around types managed in a KVStore, providing easy access to
their indexed fields.
+ */
+public class KVTypeInfo {
+
+ private final Class<?> type;
+ private final Map<String, KVIndex> indices;
+ private final Map<String, Accessor> accessors;
+
+ public KVTypeInfo(Class<?> type) throws Exception {
+ this.type = type;
+ this.accessors = new HashMap<>();
+ this.indices = new HashMap<>();
+
+ for (Field f : type.getFields()) {
+ KVIndex idx = f.getAnnotation(KVIndex.class);
+ if (idx != null) {
+ checkIndex(idx, indices);
+ indices.put(idx.value(), idx);
+ accessors.put(idx.value(), new FieldAccessor(f));
+ }
+ }
+
+ for (Method m : type.getMethods()) {
+ KVIndex idx = m.getAnnotation(KVIndex.class);
+ if (idx != null) {
+ checkIndex(idx, indices);
+ Preconditions.checkArgument(m.getParameterTypes().length == 0,
+ "Annotated method %s::%s should not have any parameters.",
type.getName(), m.getName());
+ indices.put(idx.value(), idx);
+ accessors.put(idx.value(), new MethodAccessor(m));
+ }
+ }
+
+
Preconditions.checkArgument(indices.containsKey(KVIndex.NATURAL_INDEX_NAME),
+ "No natural index defined for type %s.", type.getName());
+
Preconditions.checkArgument(indices.get(KVIndex.NATURAL_INDEX_NAME).parent().isEmpty(),
+ "Natural index of %s cannot have a parent.", type.getName());
+
+ for (KVIndex idx : indices.values()) {
+ if (!idx.parent().isEmpty()) {
+ KVIndex parent = indices.get(idx.parent());
+ Preconditions.checkArgument(parent != null,
+ "Cannot find parent %s of index %s.", idx.parent(), idx.value());
+ Preconditions.checkArgument(parent.parent().isEmpty(),
+ "Parent index %s of index %s cannot be itself a child index.",
idx.parent(), idx.value());
+ }
+ }
+ }
+
+ private void checkIndex(KVIndex idx, Map<String, KVIndex> indices) {
+ Preconditions.checkArgument(idx.value() != null &&
!idx.value().isEmpty(),
+ "No name provided for index in type %s.", type.getName());
+ Preconditions.checkArgument(
+ !idx.value().startsWith("_") ||
idx.value().equals(KVIndex.NATURAL_INDEX_NAME),
+ "Index name %s (in type %s) is not allowed.", idx.value(),
type.getName());
+ Preconditions.checkArgument(idx.parent().isEmpty() ||
!idx.parent().equals(idx.value()),
+ "Index %s cannot be parent of itself.", idx.value());
+ Preconditions.checkArgument(!indices.containsKey(idx.value()),
+ "Duplicate index %s for type %s.", idx.value(), type.getName());
+ }
+
+ public Class<?> getType() {
+ return type;
+ }
+
+ public Object getIndexValue(String indexName, Object instance) throws
Exception {
+ return getAccessor(indexName).get(instance);
+ }
+
+ public Stream<KVIndex> indices() {
+ return indices.values().stream();
+ }
+
+ Accessor getAccessor(String indexName) {
+ Accessor a = accessors.get(indexName);
+ Preconditions.checkArgument(a != null, "No index %s.", indexName);
+ return a;
+ }
+
+ Accessor getParentAccessor(String indexName) {
+ KVIndex index = indices.get(indexName);
+ return index.parent().isEmpty() ? null : getAccessor(index.parent());
+ }
+
+ /**
+ * Abstracts the difference between invoking a Field and a Method.
+ */
+ interface Accessor {
+
+ Object get(Object instance) throws Exception;
+
+ }
+
+ private class FieldAccessor implements Accessor {
+
+ private final Field field;
+
+ FieldAccessor(Field field) {
+ this.field = field;
+ }
+
+ @Override
+ public Object get(Object instance) throws Exception {
+ return field.get(instance);
--- End diff --
this requires the fields & methods to be public, right? That shoudl go in
the doc for `@KVIndex`, or you can call `setAccessible(true)` in the
constructor.
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