[SPR-6025] support for recursive property placeholder replacement in system properties

Author: Rob Harrop

org.springframework.core/src/main/java/org/springframework/util/PropertyPlaceholderUtils.java

@@ -17,6 +17,8 @@
 package org.springframework.util;
 
 import java.util.Properties;
+import java.util.Set;
+import java.util.HashSet;
 
 /**
  * Utility class for working with Strings that have placeholder values in them. A placeholder takes the form
@@ -63,29 +65,75 @@ public String resolvePlaceholder(String placeholderName) {
 	 * @return the supplied value with placeholders replaced inline.
 	 */
 	public static String replacePlaceholders(String value, PlaceholderResolver placeholderResolver) {
-		StringBuilder result = new StringBuilder(value);
+		return parseStringValue(value, placeholderResolver, new HashSet<String>());
+	}
+
+	protected static String parseStringValue(String strVal, PlaceholderResolver placeholderResolver, Set<String> visitedPlaceholders) {
+		StringBuilder buf = new StringBuilder(strVal);
 
-		int startIndex = result.indexOf(PLACEHOLDER_PREFIX);
+		int startIndex = strVal.indexOf(PLACEHOLDER_PREFIX);
 		while (startIndex != -1) {
-			int endIndex = result.indexOf(PLACEHOLDER_SUFFIX, startIndex + PLACEHOLDER_PREFIX.length());
+			int endIndex = findPlaceholderEndIndex(buf, startIndex);
 			if (endIndex != -1) {
-				String placeholder = result.substring(startIndex + PLACEHOLDER_PREFIX.length(), endIndex);
-				int nextIndex = endIndex + PLACEHOLDER_SUFFIX.length();
+				String placeholder = buf.substring(startIndex + PLACEHOLDER_PREFIX.length(), endIndex);
+				if (!visitedPlaceholders.add(placeholder)) {
+					throw new IllegalArgumentException(
+							"Circular placeholder reference '" + placeholder + "' in property definitions");
+				}
+				// Recursive invocation, parsing placeholders contained in the placeholder key.
+				placeholder = parseStringValue(placeholder, placeholderResolver, visitedPlaceholders);
 
+				// Now obtain the value for the fully resolved key...
 				String propVal = placeholderResolver.resolvePlaceholder(placeholder);
 				if (propVal != null) {
-					result.replace(startIndex, endIndex + PLACEHOLDER_SUFFIX.length(), propVal);
-					nextIndex = startIndex + propVal.length();
+					// Recursive invocation, parsing placeholders contained in the
+					// previously resolved placeholder value.
+					propVal = parseStringValue(propVal, placeholderResolver, visitedPlaceholders);
+					buf.replace(startIndex, endIndex + PLACEHOLDER_SUFFIX.length(), propVal);
+
+					//if (logger.isTraceEnabled()) {
+					//	logger.trace("Resolved placeholder '" + placeholder + "'");
+					//}
+
+					startIndex = buf.indexOf(PLACEHOLDER_PREFIX, startIndex + propVal.length());
+				}
+				else  {
+					// Proceed with unprocessed value.
+					startIndex = buf.indexOf(PLACEHOLDER_PREFIX, endIndex + PLACEHOLDER_SUFFIX.length());
 				}
 
-				startIndex = result.indexOf(PLACEHOLDER_PREFIX, nextIndex);
+				visitedPlaceholders.remove(placeholder);
 			}
 			else {
 				startIndex = -1;
 			}
 		}
 
-		return result.toString();
+		return buf.toString();
+	}
+
+	private static int findPlaceholderEndIndex(CharSequence buf, int startIndex) {
+		int index = startIndex + PLACEHOLDER_PREFIX.length();
+		int withinNestedPlaceholder = 0;
+		while (index < buf.length()) {
+			if (StringUtils.substringMatch(buf, index, PLACEHOLDER_SUFFIX)) {
+				if (withinNestedPlaceholder > 0) {
+					withinNestedPlaceholder--;
+					index = index + PLACEHOLDER_PREFIX.length() - 1;
+				}
+				else {
+					return index;
+				}
+			}
+			else if (StringUtils.substringMatch(buf, index, PLACEHOLDER_PREFIX)) {
+				withinNestedPlaceholder++;
+				index = index + PLACEHOLDER_PREFIX.length();
+			}
+			else {
+				index++;
+			}
+		}
+		return -1;
 	}
 
 	/**

org.springframework.core/src/main/java/org/springframework/util/SystemPropertyUtils.java

@@ -16,17 +16,19 @@
 
 package org.springframework.util;
 
+import org.springframework.util.PropertyPlaceholderUtils.PlaceholderResolver;
+
 /**
  * Helper class for resolving placeholders in texts. Usually applied to file paths.
  *
- * <p>A text may contain <code>${...}</code> placeholders, to be resolved as
- * system properties: e.g. <code>${user.dir}</code>.
+ * <p>A text may contain <code>${...}</code> placeholders, to be resolved as system properties: e.g.
+ * <code>${user.dir}</code>.
  *
  * @author Juergen Hoeller
- * @since 1.2.5
  * @see #PLACEHOLDER_PREFIX
  * @see #PLACEHOLDER_SUFFIX
  * @see System#getProperty(String)
+ * @since 1.2.5
  */
 public abstract class SystemPropertyUtils {
 
@@ -36,51 +38,39 @@ public abstract class SystemPropertyUtils {
 	/** Suffix for system property placeholders: "}" */
 	public static final String PLACEHOLDER_SUFFIX = "}";
 
-
 	/**
-	 * Resolve ${...} placeholders in the given text,
-	 * replacing them with corresponding system property values.
+	 * Resolve ${...} placeholders in the given text, replacing them with corresponding system property values.
+	 *
 	 * @param text the String to resolve
 	 * @return the resolved String
 	 * @see #PLACEHOLDER_PREFIX
 	 * @see #PLACEHOLDER_SUFFIX
 	 */
-	public static String resolvePlaceholders(String text) {
-		StringBuilder result = new StringBuilder(text);
+	public static String resolvePlaceholders(final String text) {
+		return PropertyPlaceholderUtils.replacePlaceholders(text, new PlaceholderResolver() {
 
-		int startIndex = result.indexOf(PLACEHOLDER_PREFIX);
-		while (startIndex != -1) {
-			int endIndex = result.indexOf(PLACEHOLDER_SUFFIX, startIndex + PLACEHOLDER_PREFIX.length());
-			if (endIndex != -1) {
-				String placeholder = result.substring(startIndex + PLACEHOLDER_PREFIX.length(), endIndex);
-				int nextIndex = endIndex + PLACEHOLDER_SUFFIX.length();
+			public String resolvePlaceholder(String placeholderName) {
+				String propVal = null;
 				try {
-					String propVal = System.getProperty(placeholder);
+					propVal = System.getProperty(placeholderName);
 					if (propVal == null) {
 						// Fall back to searching the system environment.
-						propVal = System.getenv(placeholder);
-					}
-					if (propVal != null) {
-						result.replace(startIndex, endIndex + PLACEHOLDER_SUFFIX.length(), propVal);
-						nextIndex = startIndex + propVal.length();
+						propVal = System.getenv(placeholderName);
 					}
-					else {
-						System.err.println("Could not resolve placeholder '" + placeholder + "' in [" + text +
+
+					if (propVal == null) {
+						System.err.println("Could not resolve placeholder '" + placeholderName + "' in [" + text +
 								"] as system property: neither system property nor environment variable found");
 					}
 				}
 				catch (Throwable ex) {
-					System.err.println("Could not resolve placeholder '" + placeholder + "' in [" + text +
+					System.err.println("Could not resolve placeholder '" + placeholderName + "' in [" + text +
 							"] as system property: " + ex);
+
 				}
-				startIndex = result.indexOf(PLACEHOLDER_PREFIX, nextIndex);
+				return propVal;
 			}
-			else {
-				startIndex = -1;
-			}
-		}
-
-		return result.toString();
+		});
 	}
 
 }

org.springframework.core/src/test/java/org/springframework/util/PropertyPlaceholderUtilsTests.java

@@ -43,6 +43,26 @@ public void testWithMultipleProperties() {
 		assertEquals("foo=bar,bar=baz", PropertyPlaceholderUtils.replacePlaceholders(text, props));
 	}
 
+	@Test
+	public void testRecurseInProperty() {
+		String text = "foo=${bar}";
+		Properties props = new Properties();
+		props.setProperty("bar", "${baz}");
+		props.setProperty("baz", "bar");
+
+		assertEquals("foo=bar", PropertyPlaceholderUtils.replacePlaceholders(text, props));
+	}
+
+	@Test
+	public void testRecurseInPlaceholder() {
+		String text = "foo=${b${inner}}";
+		Properties props = new Properties();
+		props.setProperty("bar", "bar");
+		props.setProperty("inner", "ar");
+
+		assertEquals("foo=bar", PropertyPlaceholderUtils.replacePlaceholders(text, props));
+	}
+
 	@Test
 	public void testWithResolver() {
 		String text = "foo=${foo}";

org.springframework.core/src/test/java/org/springframework/util/SystemPropertyUtilsTests.java

@@ -31,6 +31,14 @@ public void testReplaceFromSystemProperty() {
 		assertEquals("bar", resolved);
 	}
 
+	@Test
+	public void testRecursiveFromSystemProperty() {
+		System.setProperty("test.prop", "foo=${bar}");
+		System.setProperty("bar", "baz");
+		String resolved = SystemPropertyUtils.resolvePlaceholders("${test.prop}");
+		assertEquals("foo=baz", resolved);
+	}
+
 	@Test
 	public void testReplaceFromEnv() {
 		Map<String,String> env = System.getenv();