001/* 002 * Copyright 2002-2020 the original author or authors. 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); 005 * you may not use this file except in compliance with the License. 006 * You may obtain a copy of the License at 007 * 008 * https://www.apache.org/licenses/LICENSE-2.0 009 * 010 * Unless required by applicable law or agreed to in writing, software 011 * distributed under the License is distributed on an "AS IS" BASIS, 012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 013 * See the License for the specific language governing permissions and 014 * limitations under the License. 015 */ 016 017package org.springframework.util; 018 019import org.springframework.lang.Nullable; 020 021/** 022 * Helper class for resolving placeholders in texts. Usually applied to file paths. 023 * 024 * <p>A text may contain {@code ${...}} placeholders, to be resolved as system properties: 025 * e.g. {@code ${user.dir}}. Default values can be supplied using the ":" separator 026 * between key and value. 027 * 028 * @author Juergen Hoeller 029 * @author Rob Harrop 030 * @author Dave Syer 031 * @since 1.2.5 032 * @see #PLACEHOLDER_PREFIX 033 * @see #PLACEHOLDER_SUFFIX 034 * @see System#getProperty(String) 035 */ 036public abstract class SystemPropertyUtils { 037 038 /** Prefix for system property placeholders: "${". */ 039 public static final String PLACEHOLDER_PREFIX = "${"; 040 041 /** Suffix for system property placeholders: "}". */ 042 public static final String PLACEHOLDER_SUFFIX = "}"; 043 044 /** Value separator for system property placeholders: ":". */ 045 public static final String VALUE_SEPARATOR = ":"; 046 047 048 private static final PropertyPlaceholderHelper strictHelper = 049 new PropertyPlaceholderHelper(PLACEHOLDER_PREFIX, PLACEHOLDER_SUFFIX, VALUE_SEPARATOR, false); 050 051 private static final PropertyPlaceholderHelper nonStrictHelper = 052 new PropertyPlaceholderHelper(PLACEHOLDER_PREFIX, PLACEHOLDER_SUFFIX, VALUE_SEPARATOR, true); 053 054 055 /** 056 * Resolve {@code ${...}} placeholders in the given text, replacing them with 057 * corresponding system property values. 058 * @param text the String to resolve 059 * @return the resolved String 060 * @throws IllegalArgumentException if there is an unresolvable placeholder 061 * @see #PLACEHOLDER_PREFIX 062 * @see #PLACEHOLDER_SUFFIX 063 */ 064 public static String resolvePlaceholders(String text) { 065 return resolvePlaceholders(text, false); 066 } 067 068 /** 069 * Resolve {@code ${...}} placeholders in the given text, replacing them with 070 * corresponding system property values. Unresolvable placeholders with no default 071 * value are ignored and passed through unchanged if the flag is set to {@code true}. 072 * @param text the String to resolve 073 * @param ignoreUnresolvablePlaceholders whether unresolved placeholders are to be ignored 074 * @return the resolved String 075 * @throws IllegalArgumentException if there is an unresolvable placeholder 076 * @see #PLACEHOLDER_PREFIX 077 * @see #PLACEHOLDER_SUFFIX 078 * and the "ignoreUnresolvablePlaceholders" flag is {@code false} 079 */ 080 public static String resolvePlaceholders(String text, boolean ignoreUnresolvablePlaceholders) { 081 if (text.isEmpty()) { 082 return text; 083 } 084 PropertyPlaceholderHelper helper = (ignoreUnresolvablePlaceholders ? nonStrictHelper : strictHelper); 085 return helper.replacePlaceholders(text, new SystemPropertyPlaceholderResolver(text)); 086 } 087 088 089 /** 090 * PlaceholderResolver implementation that resolves against system properties 091 * and system environment variables. 092 */ 093 private static class SystemPropertyPlaceholderResolver implements PropertyPlaceholderHelper.PlaceholderResolver { 094 095 private final String text; 096 097 public SystemPropertyPlaceholderResolver(String text) { 098 this.text = text; 099 } 100 101 @Override 102 @Nullable 103 public String resolvePlaceholder(String placeholderName) { 104 try { 105 String propVal = System.getProperty(placeholderName); 106 if (propVal == null) { 107 // Fall back to searching the system environment. 108 propVal = System.getenv(placeholderName); 109 } 110 return propVal; 111 } 112 catch (Throwable ex) { 113 System.err.println("Could not resolve placeholder '" + placeholderName + "' in [" + 114 this.text + "] as system property: " + ex); 115 return null; 116 } 117 } 118 } 119 120}