DefaultListableBeanFactory checks for alias circle on registerAlias (avoiding endless loop; SPR-7274)

Author: jhoeller

org.springframework.beans/src/test/java/org/springframework/beans/factory/DefaultListableBeanFactoryTests.java

@@ -723,6 +723,20 @@ private void testSingleTestBean(ListableBeanFactory lbf) {
 		assertTrue("Test bean age is 48", tb.getAge() == 48);
 	}
 
+	@Test
+	public void testAliasCircle() {
+		DefaultListableBeanFactory lbf = new DefaultListableBeanFactory();
+		lbf.registerAlias("test", "test2");
+		lbf.registerAlias("test2", "test3");
+		try {
+			lbf.registerAlias("test3", "test");
+			fail("Should have thrown IllegalStateException");
+		}
+		catch (IllegalStateException ex) {
+			// expected
+		}
+	}
+
 	@Test
 	public void testBeanDefinitionOverriding() {
 		DefaultListableBeanFactory lbf = new DefaultListableBeanFactory();

org.springframework.core/src/main/java/org/springframework/core/SimpleAliasRegistry.java

@@ -55,6 +55,7 @@ public void registerAlias(String name, String alias) {
 							name + "': It is already registered for name '" + registeredName + "'.");
 				}
 			}
+			checkForAliasCircle(name, alias);
 			this.aliasMap.put(alias, name);
 		}
 	}
@@ -128,6 +129,7 @@ else if (!resolvedAlias.equals(alias)) {
 								"') for name '" + resolvedName + "': It is already registered for name '" +
 								registeredName + "'.");
 					}
+					checkForAliasCircle(resolvedName, resolvedAlias);
 					this.aliasMap.remove(alias);
 					this.aliasMap.put(resolvedAlias, resolvedName);
 				}
@@ -157,4 +159,20 @@ public String canonicalName(String name) {
 		return canonicalName;
 	}
 
+	/**
+	 * Check whether the given name points back to given alias as an alias
+	 * in the other direction, catching a circular reference upfront and
+	 * throwing a corresponding IllegalStateException.
+	 * @param name the candidate name
+	 * @param alias the candidate alias
+	 * @see #registerAlias
+	 */
+	protected void checkForAliasCircle(String name, String alias) {
+		if (alias.equals(canonicalName(name))) {
+			throw new IllegalStateException("Cannot register alias '" + alias +
+					"' for name '" + name + "': Circular reference - '" +
+					name + "' is a direct or indirect alias for '" + alias + "' already");
+		}
+	}
+
 }