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/*
* Copyright 2002-2023 the original author or authors.
*
* Licensed 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
*
* https://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.springframework.util;
import org.springframework.lang.Nullable;
/**
* Helper class for resolving placeholders in texts. Usually applied to file paths.
*
* A text may contain {@code ${...}} placeholders, to be resolved as system properties:
* e.g. {@code ${user.dir}}. Default values can be supplied using the ":" separator
* between key and value.
*
* @author Juergen Hoeller
* @author Rob Harrop
* @author Dave Syer
* @since 1.2.5
* @see #PLACEHOLDER_PREFIX
* @see #PLACEHOLDER_SUFFIX
* @see System#getProperty(String)
*/
public abstract class SystemPropertyUtils {
/** Prefix for system property placeholders: {@value}. */
public static final String PLACEHOLDER_PREFIX = "${";
/** Suffix for system property placeholders: {@value}. */
public static final String PLACEHOLDER_SUFFIX = "}";
/** Value separator for system property placeholders: {@value}. */
public static final String VALUE_SEPARATOR = ":";
private static final PropertyPlaceholderHelper strictHelper =
new PropertyPlaceholderHelper(PLACEHOLDER_PREFIX, PLACEHOLDER_SUFFIX, VALUE_SEPARATOR, false);
private static final PropertyPlaceholderHelper nonStrictHelper =
new PropertyPlaceholderHelper(PLACEHOLDER_PREFIX, PLACEHOLDER_SUFFIX, VALUE_SEPARATOR, true);
/**
* Resolve {@code ${...}} placeholders in the given text, replacing them with
* corresponding system property values.
* @param text the String to resolve
* @return the resolved String
* @throws IllegalArgumentException if there is an unresolvable placeholder
* @see #PLACEHOLDER_PREFIX
* @see #PLACEHOLDER_SUFFIX
*/
public static String resolvePlaceholders(String text) {
return resolvePlaceholders(text, false);
}
/**
* Resolve {@code ${...}} placeholders in the given text, replacing them with
* corresponding system property values. Unresolvable placeholders with no default
* value are ignored and passed through unchanged if the flag is set to {@code true}.
* @param text the String to resolve
* @param ignoreUnresolvablePlaceholders whether unresolved placeholders are to be ignored
* @return the resolved String
* @throws IllegalArgumentException if there is an unresolvable placeholder
* @see #PLACEHOLDER_PREFIX
* @see #PLACEHOLDER_SUFFIX
* and the "ignoreUnresolvablePlaceholders" flag is {@code false}
*/
public static String resolvePlaceholders(String text, boolean ignoreUnresolvablePlaceholders) {
if (text.isEmpty()) {
return text;
}
PropertyPlaceholderHelper helper = (ignoreUnresolvablePlaceholders ? nonStrictHelper : strictHelper);
return helper.replacePlaceholders(text, new SystemPropertyPlaceholderResolver(text));
}
/**
* PlaceholderResolver implementation that resolves against system properties
* and system environment variables.
*/
private static class SystemPropertyPlaceholderResolver implements PropertyPlaceholderHelper.PlaceholderResolver {
private final String text;
public SystemPropertyPlaceholderResolver(String text) {
this.text = text;
}
@Override
@Nullable
public String resolvePlaceholder(String placeholderName) {
try {
String propVal = System.getProperty(placeholderName);
if (propVal == null) {
// Fall back to searching the system environment.
propVal = System.getenv(placeholderName);
}
return propVal;
}
catch (Throwable ex) {
System.err.println("Could not resolve placeholder '" + placeholderName + "' in [" +
this.text + "] as system property: " + ex);
return null;
}
}
}
}