Log4jWebConfigurer supports resolving placeholders against ServletContext init-parameters as well

Introducing a ServletContextPropertyUtils helper (analogous to SystemPropertyUtils) along the way.

Issue: SPR-10284

spring-web/src/main/java/org/springframework/web/util/Log4jWebConfigurer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2013 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.
@@ -17,12 +17,10 @@
 package org.springframework.web.util;
 
 import java.io.FileNotFoundException;
-
 import javax.servlet.ServletContext;
 
 import org.springframework.util.Log4jConfigurer;
 import org.springframework.util.ResourceUtils;
-import org.springframework.util.SystemPropertyUtils;
 
 /**
  * Convenience class that performs custom log4j initialization for web environments,
@@ -90,6 +88,7 @@ import org.springframework.util.SystemPropertyUtils;
  * context-param at all) without worrying.
  *
  * @author Juergen Hoeller
+ * @author Marten Deinum
  * @since 12.08.2003
  * @see org.springframework.util.Log4jConfigurer
  * @see Log4jConfigListener
@@ -122,9 +121,8 @@ public abstract class Log4jWebConfigurer {
 		if (location != null) {
 			// Perform actual log4j initialization; else rely on log4j's default initialization.
 			try {
-				// Resolve system property placeholders before potentially
-				// resolving a real path.
-				location = SystemPropertyUtils.resolvePlaceholders(location);
+				// Resolve property placeholders before potentially resolving a real path.
+				location = ServletContextPropertyUtils.resolvePlaceholders(location, servletContext);
 
 				// Leave a URL (e.g. "classpath:" or "file:") as-is.
 				if (!ResourceUtils.isUrl(location)) {

spring-web/src/main/java/org/springframework/web/util/ServletContextPropertyUtils.java

@@ -0,0 +1,113 @@
+/*
+ * Copyright 2002-2013 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
+ *
+ *      http://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.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
+	 * @see SystemPropertyUtils#PLACEHOLDER_PREFIX
+	 * @see SystemPropertyUtils#PLACEHOLDER_SUFFIX
+     * @see SystemPropertyUtils#resolvePlaceholders(String, boolean)
+	 * @throws IllegalArgumentException if there is an unresolvable placeholder
+	 */
+	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
+	 * @see SystemPropertyUtils#PLACEHOLDER_PREFIX
+	 * @see SystemPropertyUtils#PLACEHOLDER_SUFFIX
+     * @see SystemPropertyUtils#resolvePlaceholders(String, boolean)
+	 * @throws IllegalArgumentException if there is an unresolvable placeholder and the flag is false
+	 */
+	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;
+        }
+
+        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;
+            }
+        }
+    }
+
+}

spring-web/src/test/java/org/springframework/web/util/ServletContextPropertyUtilsTests.java

@@ -0,0 +1,50 @@
+/*
+ * Copyright 2002-2013 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
+ *
+ *      http://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 org.junit.Test;
+
+import org.springframework.mock.web.test.MockServletContext;
+
+import static org.junit.Assert.*;
+
+/**
+ * @author Marten Deinum
+ * @since 3.2.2
+ */
+public class ServletContextPropertyUtilsTests {
+
+    @Test
+    public void resolveAsServletContextInitParameter() {
+        MockServletContext servletContext = new MockServletContext();
+        servletContext.setInitParameter("test.prop", "bar");
+        String resolved = ServletContextPropertyUtils.resolvePlaceholders("${test.prop:foo}", servletContext);
+        assertEquals(resolved, "bar");
+    }
+
+    @Test
+    public void fallbackToSystemProperties() {
+        MockServletContext servletContext = new MockServletContext();
+        System.setProperty("test.prop", "bar");
+        try {
+            String resolved = ServletContextPropertyUtils.resolvePlaceholders("${test.prop:foo}", servletContext);
+            assertEquals(resolved, "bar");
+        }
+		finally {
+            System.clearProperty("test.prop");
+        }
+    }
+
+}