/*
 * Copyright 2002-2020 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 ${...} placeholders, to be resolved as system properties: e.g. ${user.dir}. Default values can be supplied using the ":" separator between key and value. 
Author:
Juergen Hoeller, Rob Harrop, Dave Syer
See Also:
PLACEHOLDER_PREFIX
PLACEHOLDER_SUFFIX
System.getProperty(String)
Since:
1.2.5/**
 * Helper class for resolving placeholders in texts. Usually applied to file paths.
 *
 * <p>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: "${". /** Prefix for system property placeholders: "${". */
	public static final String PLACEHOLDER_PREFIX = "${";

	
Suffix for system property placeholders: "}". /** Suffix for system property placeholders: "}". */
	public static final String PLACEHOLDER_SUFFIX = "}";

	
Value separator for system property placeholders: ":". /** Value separator for system property placeholders: ":". */
	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 ${...} placeholders in the given text, replacing them with corresponding system property values. 
Params:
text – the String to resolve
Throws:
IllegalArgumentException – if there is an unresolvable placeholder
See Also:
PLACEHOLDER_PREFIX
PLACEHOLDER_SUFFIX
Returns:
the resolved String/**
	 * 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 ${...} 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 true. 
Params:
text – the String to resolve
ignoreUnresolvablePlaceholders – whether unresolved placeholders are to be ignored
Throws:
IllegalArgumentException – if there is an unresolvable placeholder
See Also:
PLACEHOLDER_PREFIX
 and the "ignoreUnresolvablePlaceholders" flag is false
Returns:
the resolved String/**
	 * 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.
/**
	 * 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;
			}
		}
	}

}