mbeckerle commented on a change in pull request #394: URL: https://github.com/apache/incubator-daffodil/pull/394#discussion_r453010086
########## File path: daffodil-core/src/main/scala/org/apache/daffodil/dsom/walker/AbstractDSOMWalker.scala ########## @@ -0,0 +1,217 @@ +/* + * 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.daffodil.dsom.walker + +import java.io.File + +import org.apache.daffodil.compiler.Compiler +import org.apache.daffodil.dsom.{Choice, ComplexTypeBase, ElementBase, GroupRef, ModelGroup, Root, Sequence, SimpleTypeBase, Term} + +/** + * A class designed to walk the internal representation of a DFDL Schema File. + * + * There are numerous internal event handlers to be defined by the implementing class; each + * corresponds to "encountering" a particular element type in the DFDL Schema file. + * + * Though recursion is used here to define the walk, it is not advised to use recursion between + * these event handlers. Instead, consider a stack-like structure, as the DFDL Schema structure + * as well as the recursive method call structure can be represented by trees. + * @param schemaFile an input DFDL Schema file to parse + * @tparam T the return type of walkDSOMSchema and onWalkEnd. This should be a class used to + * represent the structure of the Schema. You could always make it Unit if you don't + * want these methods to return anything. + */ +abstract class AbstractDSOMWalker[T](schemaFile: File) { + /** + * The root element of the DFDL Schema. This will be the starting point for the traversal + */ + private final val schemaSetRoot: Root = Compiler().compileFile(schemaFile).sset.root + + /** + * Auxiliary constructor to initialize this class with a path to a schema File rather than + * a File object directly + * @param pathToSchemaFile path to the DFDL Schema file desired to be parsed + */ + def this(pathToSchemaFile: String) = this(new File(pathToSchemaFile)) + + /** + * Method to be called on the beginning of the traversal. It is recommended to add some + * sort of wrapper element to a stack if you're doing a typical stack-based traversal. + * @param root the root element of the DFDL Schema + */ + protected def onWalkBegin(root: Root): Unit + + /** + * Method to be called when the traversal concludes. It is recommended to put any post-processing + * and anything to tidy up the stack or the result here. + * @param root the root element of the DFDL Schema + * @return the result of the traversal + */ + protected def onWalkEnd(root: Root): T + + /** + * Method to be called when a *sequence* element is encountered. + * This is not really your array type; the typical "array" you'll see in an infoset + * is a special kind of Element, so it will be encountered + * in onElementBegin + * @param sequenceElement the sequence element + */ + protected def onSequenceBegin(sequenceElement: Sequence): Unit Review comment: There needs to be a way to "register" a walker. I.e., a Daffodil API call where the walker is passed to Daffodil, so that it can be invoked. Or if the control pattern is that the walker takes control, it's really just a hook where daffodil informs the walker that the DSOM tree is ready to be walked. This should allow for many external walkers to be registered, not just one. They should be called in turn. Then all the NiFi-specific logic, tests, etc. all goes into distinct separate code that is not part of Daffodil. It becomes an application of Daffodil's libraries within NiFi code. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org
