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https://issues.apache.org/jira/browse/FLINK-2017?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14745233#comment-14745233
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ASF GitHub Bot commented on FLINK-2017:
---------------------------------------

Github user fhueske commented on a diff in the pull request:

    https://github.com/apache/flink/pull/1097#discussion_r39496768
  
    --- Diff: 
flink-java/src/main/java/org/apache/flink/api/java/utils/RequiredParameter.java 
---
    @@ -0,0 +1,124 @@
    +/*
    + * 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.flink.api.java.utils;
    +
    +import java.util.HashMap;
    +import java.util.Map;
    +import java.util.Objects;
    +
    +/**
    + * Facility to manage required parameters in user defined functions.
    + */
    +public class RequiredParameter {
    +
    +   private static final String HELP_TEXT_PARAM_DELIMITER = "\t";
    +   private static final String HELP_TEXT_LINE_DELIMITER = "\n";
    +
    +   private HashMap<String, Option> data;
    +
    +   public RequiredParameter() {
    +           this.data = new HashMap<>();
    +   }
    +
    +   public void add(Option option) {
    +           this.data.put(option.getName(), option);
    +   }
    +
    +   /**
    +    * Check if all parameters defined as required have been supplied.
    +    *
    +    * @param parameterTool - parameters supplied by user.
    +    */
    +   public void check(ParameterTool parameterTool) throws 
RequiredParameterException {
    +           for (Option o : data.values()) {
    +                   // if the parameter is not present or its value is 
undefined, throw a RuntimeException.
    +                   if (!parameterTool.data.containsKey(o.getName()) || 
keyIsUndefined(o.getName(), parameterTool.data)) {
    --- End diff --
    
    The RequiredParameter tool should check for each Option that:
    - the ParameterTool contains a value for either the full or short key (if 
short key is defined)
    - the ParameterTool does not contain values for both full and short key (if 
short key is defined)
    - if the value is set on the short key, it should be copied to the full key
    
    The checkAndPopulate method should only add the default value to the full 
key
    
    That way, the value can be retrieved using the full key.
    
    What do you think?


> Add predefined required parameters to ParameterTool
> ---------------------------------------------------
>
>                 Key: FLINK-2017
>                 URL: https://issues.apache.org/jira/browse/FLINK-2017
>             Project: Flink
>          Issue Type: Improvement
>    Affects Versions: 0.9
>            Reporter: Robert Metzger
>              Labels: starter
>
> In FLINK-1525 we've added the {{ParameterTool}}.
> During the PR review, there was a request for required parameters.
> This issue is about implementing a facility to define required parameters. 
> The tool should also be able to print a help menu with a list of all 
> parameters.
> This test case shows my initial ideas how to design the API
> {code}
>       @Test
>       public void requiredParameters() {
>               RequiredParameters required = new RequiredParameters();
>               Option input = required.add("input").alt("i").help("Path to 
> input file or directory"); // parameter with long and short variant
>               required.add("output"); // parameter only with long variant
>               Option parallelism = 
> required.add("parallelism").alt("p").type(Integer.class); // parameter with 
> type
>               Option spOption = 
> required.add("sourceParallelism").alt("sp").defaultValue(12).help("Number 
> specifying the number of parallel data source instances"); // parameter with 
> default value, specifying the type.
>               Option executionType = 
> required.add("executionType").alt("et").defaultValue("pipelined").choices("pipelined",
>  "batch");
>               ParameterUtil parameter = ParameterUtil.fromArgs(new 
> String[]{"-i", "someinput", "--output", "someout", "-p", "15"});
>               required.check(parameter);
>               required.printHelp();
>               required.checkAndPopulate(parameter);
>               String inputString = input.get();
>               int par = parallelism.getInteger();
>               String output = parameter.get("output");
>               int sourcePar = parameter.getInteger(spOption.getName());
>       }
> {code}



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