Check that PathPatternParser is not set too late

This commit ensures the PathPatternParser cannot be set after request mappings
have been initialized when it is too late.

See gh-26427

spring-webmvc/src/main/java/org/springframework/web/servlet/handler/AbstractHandlerMethodMapping.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2021 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.
@@ -48,6 +48,7 @@ import org.springframework.web.cors.CorsConfiguration;
 import org.springframework.web.cors.CorsUtils;
 import org.springframework.web.method.HandlerMethod;
 import org.springframework.web.servlet.HandlerMapping;
+import org.springframework.web.util.pattern.PathPatternParser;
 
 /**
  * Abstract base class for {@link HandlerMapping} implementations that define
@@ -99,6 +100,14 @@ public abstract class AbstractHandlerMethodMapping<T> extends AbstractHandlerMap
 	private final MappingRegistry mappingRegistry = new MappingRegistry();
 
 
+	@Override
+	public void setPatternParser(PathPatternParser patternParser) {
+		Assert.state(this.mappingRegistry.getRegistrations().isEmpty(),
+				"PathPatternParser must be set before the initialization of " +
+						"request mappings through InitializingBean#afterPropertiesSet.");
+		super.setPatternParser(patternParser);
+	}
+
 	/**
 	 * Whether to detect handler methods in beans in ancestor ApplicationContexts.
 	 * <p>Default is "false": Only beans in the current ApplicationContext are

spring-webmvc/src/main/java/org/springframework/web/servlet/handler/AbstractUrlHandlerMapping.java

@@ -41,6 +41,7 @@ import org.springframework.web.servlet.HandlerMapping;
 import org.springframework.web.util.ServletRequestPathUtils;
 import org.springframework.web.util.UrlPathHelper;
 import org.springframework.web.util.pattern.PathPattern;
+import org.springframework.web.util.pattern.PathPatternParser;
 
 /**
  * Abstract base class for URL-mapped {@link HandlerMapping} implementations.
@@ -74,6 +75,14 @@ public abstract class AbstractUrlHandlerMapping extends AbstractHandlerMapping i
 	private final Map<PathPattern, Object> pathPatternHandlerMap = new LinkedHashMap<>();
 
 
+	@Override
+	public void setPatternParser(PathPatternParser patternParser) {
+		Assert.state(this.handlerMap.isEmpty(),
+				"PathPatternParser must be set before the initialization of " +
+						"the handler map via ApplicationContextAware#setApplicationContext.");
+		super.setPatternParser(patternParser);
+	}
+
 	/**
 	 * Set the root handler for this handler mapping, that is,
 	 * the handler to be registered for the root path ("/").