001/* 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017package org.apache.commons.configuration2.convert; 018 019import java.util.Collection; 020import java.util.List; 021 022/** 023 * <p> 024 * Definition of an interface that controls the handling of list delimiters in configuration properties. 025 * </p> 026 * <p> 027 * {@link org.apache.commons.configuration2.AbstractConfiguration AbstractConfiguration} supports list delimiters in 028 * property values. If such a delimiter is found, the value actually contains multiple values and has to be split. This 029 * is useful for instance for {@link org.apache.commons.configuration2.PropertiesConfiguration PropertiesConfiguration}: 030 * properties files that have to be compatible with the {@code java.util.Properties} class cannot have multiple 031 * occurrences of a single property key, therefore a different storage scheme for multi-valued properties is needed. A 032 * possible storage scheme could look as follows: 033 * </p> 034 * 035 * <pre> 036 * myProperty=value1,value2,value3 037 * </pre> 038 * 039 * <p> 040 * Here a comma is used as list delimiter. When parsing this property (and using a corresponding 041 * {@code ListDelimiterHandler} implementation) the string value is split, and three values are added for the property 042 * key. 043 * </p> 044 * <p> 045 * A {@code ListDelimiterHandler} knows how to parse and to escape property values. It is called by concrete 046 * {@code Configuration} implementations when they have to deal with properties with multiple values. 047 * </p> 048 * 049 * @since 2.0 050 */ 051public interface ListDelimiterHandler { 052 /** 053 * A specialized {@code ValueTransformer} implementation which does no transformation. The {@code transformValue()} 054 * method just returns the passed in object without changes. This instance can be used by configurations which do not 055 * require additional encoding. 056 */ 057 ValueTransformer NOOP_TRANSFORMER = value -> value; 058 059 /** 060 * Parses the specified value for list delimiters and splits it if necessary. The passed in object can be either a 061 * single value or a complex one, e.g. a collection, an array, or an {@code Iterable}. It is the responsibility of this 062 * method to return an {@code Iterable} which contains all extracted values. 063 * 064 * @param value the value to be parsed 065 * @return an {@code Iterable} allowing access to all extracted values 066 */ 067 Iterable<?> parse(Object value); 068 069 /** 070 * Splits the specified string at the list delimiter and returns a collection with all extracted components. A concrete 071 * implementation also has to deal with escape characters which might mask a list delimiter character at certain 072 * positions. The boolean {@code trim} flag determines whether each extracted component should be trimmed. This 073 * typically makes sense as the list delimiter may be surrounded by whitespace. However, there may be specific use cases 074 * in which automatic trimming is not desired. 075 * 076 * @param s the string to be split 077 * @param trim a flag whether each component of the string is to be trimmed 078 * @return a collection with all components extracted from the string 079 */ 080 Collection<String> split(String s, boolean trim); 081 082 /** 083 * Escapes the specified single value object. This method is called for properties containing only a single value. So 084 * this method can rely on the fact that the passed in object is not a list. An implementation has to check whether the 085 * value contains list delimiter characters and - if so - escape them accordingly. 086 * 087 * @param value the value to be escaped 088 * @param transformer a {@code ValueTransformer} for an additional encoding (must not be <b>null</b>) 089 * @return the escaped value 090 */ 091 Object escape(Object value, ValueTransformer transformer); 092 093 /** 094 * Escapes all values in the given list and concatenates them to a single string. This operation is required by 095 * configurations that have to represent properties with multiple values in a single line in their external 096 * configuration representation. This may require an advanced escaping in some cases. 097 * 098 * @param values the list with all the values to be converted to a single value 099 * @param transformer a {@code ValueTransformer} for an additional encoding (must not be <b>null</b>) 100 * @return the resulting escaped value 101 */ 102 Object escapeList(List<?> values, ValueTransformer transformer); 103}