https://github.com/spring-projects/spring-framework: Spring Web (Spring IO)
  • Juergen Hoeller 
/*
 * 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.web.util;

import javax.servlet.ServletContext;

import org.springframework.lang.Nullable;
import org.springframework.util.PropertyPlaceholderHelper;
import org.springframework.util.SystemPropertyUtils;


Helper class for resolving placeholders in texts. Usually applied to file paths.

A text may contain ${...} placeholders, to be resolved as servlet context init parameters or system properties: e.g. ${user.dir}. Default values can be supplied using the ":" separator between key and value. 
Author:Juergen Hoeller, Marten Deinum
See Also:
Since:3.2.2
/**
 * Helper class for resolving placeholders in texts. Usually applied to file paths.
 *
 * <p>A text may contain {@code ${...}} placeholders, to be resolved as servlet context
 * init parameters or system properties: e.g. {@code ${user.dir}}. Default values can
 * be supplied using the ":" separator between key and value.
 *
 * @author Juergen Hoeller
 * @author Marten Deinum
 * @since 3.2.2
 * @see SystemPropertyUtils
 * @see ServletContext#getInitParameter(String)
 */
public abstract class ServletContextPropertyUtils {

	private static final PropertyPlaceholderHelper strictHelper =
			new PropertyPlaceholderHelper(SystemPropertyUtils.PLACEHOLDER_PREFIX,
					SystemPropertyUtils.PLACEHOLDER_SUFFIX, SystemPropertyUtils.VALUE_SEPARATOR, false);

	private static final PropertyPlaceholderHelper nonStrictHelper =
			new PropertyPlaceholderHelper(SystemPropertyUtils.PLACEHOLDER_PREFIX,
					SystemPropertyUtils.PLACEHOLDER_SUFFIX, SystemPropertyUtils.VALUE_SEPARATOR, true);


	
Resolve ${...} placeholders in the given text, replacing them with corresponding
servlet context init parameter or system property values.

Params:
  • text – the String to resolve
  • servletContext – the servletContext to use for lookups.
Throws:
See Also:
Returns:the resolved String
/**
	 * Resolve ${...} placeholders in the given text, replacing them with corresponding
	 * servlet context init parameter or system property values.
	 * @param text the String to resolve
	 * @param servletContext the servletContext to use for lookups.
	 * @return the resolved String
	 * @throws IllegalArgumentException if there is an unresolvable placeholder
	 * @see SystemPropertyUtils#PLACEHOLDER_PREFIX
	 * @see SystemPropertyUtils#PLACEHOLDER_SUFFIX
	 * @see SystemPropertyUtils#resolvePlaceholders(String, boolean)
	 */
	public static String resolvePlaceholders(String text, ServletContext servletContext) {
		return resolvePlaceholders(text, servletContext, false);
	}

	
Resolve ${...} placeholders in the given text, replacing them with corresponding
servlet context init parameter or 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
  • servletContext – the servletContext to use for lookups.
  • ignoreUnresolvablePlaceholders – flag to determine is unresolved placeholders are ignored
Throws:
See Also:
Returns:the resolved String
/**
	 * Resolve ${...} placeholders in the given text, replacing them with corresponding
	 * servlet context init parameter or system property values. Unresolvable placeholders
	 * with no default value are ignored and passed through unchanged if the flag is set to true.
	 * @param text the String to resolve
	 * @param servletContext the servletContext to use for lookups.
	 * @param ignoreUnresolvablePlaceholders flag to determine is unresolved placeholders are ignored
	 * @return the resolved String
	 * @throws IllegalArgumentException if there is an unresolvable placeholder and the flag is false
	 * @see SystemPropertyUtils#PLACEHOLDER_PREFIX
	 * @see SystemPropertyUtils#PLACEHOLDER_SUFFIX
	 * @see SystemPropertyUtils#resolvePlaceholders(String, boolean)
	 */
	public static String resolvePlaceholders(
			String text, ServletContext servletContext, boolean ignoreUnresolvablePlaceholders) {

		if (text.isEmpty()) {
			return text;
		}
		PropertyPlaceholderHelper helper = (ignoreUnresolvablePlaceholders ? nonStrictHelper : strictHelper);
		return helper.replacePlaceholders(text, new ServletContextPlaceholderResolver(text, servletContext));
	}


	private static class ServletContextPlaceholderResolver implements PropertyPlaceholderHelper.PlaceholderResolver {

		private final String text;

		private final ServletContext servletContext;

		public ServletContextPlaceholderResolver(String text, ServletContext servletContext) {
			this.text = text;
			this.servletContext = servletContext;
		}

		@Override
		@Nullable
		public String resolvePlaceholder(String placeholderName) {
			try {
				String propVal = this.servletContext.getInitParameter(placeholderName);
				if (propVal == null) {
					// Fall back to system properties.
					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 ServletContext init-parameter or system property: " + ex);
				return null;
			}
		}
	}

}