jw3 commented on a change in pull request #431: URL: https://github.com/apache/incubator-daffodil/pull/431#discussion_r505087452
########## File path: daffodil-lib/src/main/scala/org/apache/daffodil/util/Validators.scala ########## @@ -0,0 +1,71 @@ +/* + * 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.util + +import java.util.ServiceLoader + +import org.apache.daffodil.api.CompiledValidator +import org.apache.daffodil.api.Validator +import org.apache.daffodil.api.Validator.CompilerOps.CheckArgs +import org.apache.daffodil.api.ValidatorNotFoundException + +import scala.collection.JavaConverters._ + +object Validators { + val default: Validator = new DefaultValidatorSPIProvider + def compiler(): ValidatorCompiler = new Compiler + + trait ValidatorCompiler { + def find(name: String): Option[CompiledValidator] + def isRegistered(name: String): Boolean + def compile(name: String, args: Validator.ArgumentList): CompiledValidator + } + + private class Compiler extends ValidatorCompiler { + private var compiled = Map.empty[String, CompiledValidator] + private lazy val impls: Map[String, Validator] = + ServiceLoader + .load(classOf[Validator]) + .iterator() + .asScala + .map(v => v.name() -> v) + .toMap + Review comment: Sure. The primary motivation was to drop validators into binary distributions of daffodil, both for cli and artifacts. The sample application demonstrates the process and has installation instructions in the readme. > I feel like SPI things are useful when you just want to swap different mechanisms without any code/configuration changes, but it seems like that's not really the case here. The clearest way to describe it is as a plugin framework. You can define an interface in your software and at runtime collect all instances of that type that exist on the classpath and use them for whatever. No need for a client to register anything other than providing a text file in META-INF. And also no need for the client to package up Daffodil in their binary distribution. > Swapping different validation mechanisms requires speciying the validation name somewhere (I think) and somehow providing args The name is provided by the implementation, see the Validator trait. The args are provided either programmatically or via the CLI. My primary motivation here was supplementing CLI usage of the binary distribution of Daffodil without recompiling Daffodil, that was what the first implementation was based on, which led to some of the feedback that rightly pointed out CLI concepts were leaking into the API. Definitely want to make it easy to use programmatically, and I think thats still a bit of a WIP that needs some polish yet. > so swapping in a new validation mechamisnm still requires code changes. Only on the client side, Daffodil defines an API, finds things through ServiceLoader, and handles them all abstractly. Take a look at the sample application that went with the original reference impl. Its drifted some as I have tried to adjust to the feedback, but the concepts are still the same. https://github.com/ctc-oss/daffodil-schematron-validator ---------------------------------------------------------------- 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: [email protected]
