org.springframework.web.util.ServletContextPropertyUtils.java Source code

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Here is the source code for org.springframework.web.util.ServletContextPropertyUtils.java

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/*
 * Copyright 2002-2018 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.
 *
 * <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.
     * @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.
     * @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) {

        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;
            }
        }
    }

}