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/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");
+        }
+    }
+
+}