Java tutorial
/* * 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.avro.compiler.schema; import com.google.common.base.Function; import com.google.common.base.Supplier; import com.google.common.collect.Lists; import java.util.ArrayDeque; import java.util.Arrays; import java.util.Deque; import java.util.IdentityHashMap; import java.util.Iterator; import java.util.Map; import java.util.Set; import org.apache.avro.JsonProperties; import org.apache.avro.LogicalType; import org.apache.avro.Schema; import org.apache.avro.Schema.Field; import org.apache.avro.compiler.specific.SpecificCompiler; /** * Avro Schema utilities, to traverse... */ public final class Schemas { private Schemas() { } public static void copyAliases(final Schema from, final Schema to) { switch (from.getType()) { // only named types. case RECORD: case ENUM: case FIXED: Set<String> aliases = from.getAliases(); for (String alias : aliases) { to.addAlias(alias); } } } public static void copyAliases(final Schema.Field from, final Schema.Field to) { Set<String> aliases = from.aliases(); for (String alias : aliases) { to.addAlias(alias); } } public static void copyLogicalTypes(final Schema from, final Schema to) { LogicalType logicalType = from.getLogicalType(); if (logicalType != null) { logicalType.addToSchema(to); } } public static void copyProperties(final JsonProperties from, final JsonProperties to) { Map<String, Object> objectProps = from.getObjectProps(); for (Map.Entry<String, Object> entry : objectProps.entrySet()) { to.addProp(entry.getKey(), entry.getValue()); } } public static boolean hasGeneratedJavaClass(final Schema schema) { Schema.Type type = schema.getType(); switch (type) { case ENUM: case RECORD: case FIXED: return true; default: return false; } } public static String getJavaClassName(final Schema schema) { String namespace = schema.getNamespace(); if (namespace == null) { return SpecificCompiler.mangle(schema.getName()); } else { return namespace + '.' + SpecificCompiler.mangle(schema.getName()); } } /** * depth first visit. * * @param start * @param visitor */ public static <T> T visit(final Schema start, final SchemaVisitor<T> visitor) { // Set of Visited Schemas IdentityHashMap<Schema, Schema> visited = new IdentityHashMap<>(); // Stack that contains the Schams to process and afterVisitNonTerminal functions. // Deque<Either<Schema, Supplier<SchemaVisitorAction>>> // Using either has a cost which we want to avoid... Deque<Object> dq = new ArrayDeque<>(); dq.addLast(start); Object current; while ((current = dq.pollLast()) != null) { if (current instanceof Supplier) { // we are executing a non terminal post visit. SchemaVisitorAction action = ((Supplier<SchemaVisitorAction>) current).get(); switch (action) { case CONTINUE: break; case SKIP_SUBTREE: throw new UnsupportedOperationException(); case SKIP_SIBLINGS: while (dq.getLast() instanceof Schema) { dq.removeLast(); } break; case TERMINATE: return visitor.get(); default: throw new UnsupportedOperationException("Invalid action " + action); } } else { Schema schema = (Schema) current; boolean terminate; if (!visited.containsKey(schema)) { Schema.Type type = schema.getType(); switch (type) { case ARRAY: terminate = visitNonTerminal(visitor, schema, dq, Arrays.asList(schema.getElementType())); visited.put(schema, schema); break; case RECORD: terminate = visitNonTerminal(visitor, schema, dq, Lists.transform(Lists.reverse(schema.getFields()), new Function<Field, Schema>() { @Override public Schema apply(Field f) { return f.schema(); } })); visited.put(schema, schema); break; case UNION: terminate = visitNonTerminal(visitor, schema, dq, schema.getTypes()); visited.put(schema, schema); break; case MAP: terminate = visitNonTerminal(visitor, schema, dq, Arrays.asList(schema.getValueType())); visited.put(schema, schema); break; case NULL: case BOOLEAN: case BYTES: case DOUBLE: case ENUM: case FIXED: case FLOAT: case INT: case LONG: case STRING: terminate = visitTerminal(visitor, schema, dq); break; default: throw new UnsupportedOperationException("Invalid type " + type); } } else { terminate = visitTerminal(visitor, schema, dq); } if (terminate) { return visitor.get(); } } } return visitor.get(); } private static boolean visitNonTerminal(final SchemaVisitor visitor, final Schema schema, final Deque<Object> dq, final Iterable<Schema> itSupp) { SchemaVisitorAction action = visitor.visitNonTerminal(schema); switch (action) { case CONTINUE: dq.addLast(new Supplier<SchemaVisitorAction>() { @Override public SchemaVisitorAction get() { return visitor.afterVisitNonTerminal(schema); } }); Iterator<Schema> it = itSupp.iterator(); while (it.hasNext()) { Schema child = it.next(); dq.addLast(child); } break; case SKIP_SUBTREE: dq.addLast(new Supplier<SchemaVisitorAction>() { @Override public SchemaVisitorAction get() { return visitor.afterVisitNonTerminal(schema); } }); break; case SKIP_SIBLINGS: while (!dq.isEmpty() && dq.getLast() instanceof Schema) { dq.removeLast(); } break; case TERMINATE: return true; default: throw new UnsupportedOperationException("Invalid action " + action + " for " + schema); } return false; } private static boolean visitTerminal(final SchemaVisitor visitor, final Schema schema, final Deque<Object> dq) { SchemaVisitorAction action = visitor.visitTerminal(schema); switch (action) { case CONTINUE: break; case SKIP_SUBTREE: throw new UnsupportedOperationException("Invalid action " + action + " for " + schema); case SKIP_SIBLINGS: while (!dq.isEmpty() && dq.getLast() instanceof Schema) { dq.removeLast(); } break; case TERMINATE: return true; default: throw new UnsupportedOperationException("Invalid action " + action + " for " + schema); } return false; } }