Add `spring.thymeleaf.check-template` property

This commit adds a new `spring.thymeleaf.check-template` property which
is only used for Thymeleaf 3.0+.

Since thymeleaf/thymeleaf#419, the Thymeleaf template resolver
implementations can implement the `setCheckExistence` method - this
enables the template existence verification at **resolution** time,
which means the resolver can return null as a `TemplateResolution`
and let other template resolvers in the chain try.

This new property is set to `true` by default and can be disabled if the
application only has a single resolver and the template existence check
is considered as a performance penalty with the configured resolver.

Fixes gh-6500

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/thymeleaf/AbstractTemplateResolverConfiguration.java

@@ -37,7 +37,7 @@ abstract class AbstractTemplateResolverConfiguration {
 	private static final Log logger = LogFactory
 			.getLog(AbstractTemplateResolverConfiguration.class);
 
-	private final ThymeleafProperties properties;
+	protected final ThymeleafProperties properties;
 
 	private final ApplicationContext applicationContext;
 

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/thymeleaf/ThymeleafAutoConfiguration.java

@@ -29,6 +29,7 @@ import org.thymeleaf.extras.java8time.dialect.Java8TimeDialect;
 import org.thymeleaf.extras.springsecurity4.dialect.SpringSecurityDialect;
 import org.thymeleaf.spring4.SpringTemplateEngine;
 import org.thymeleaf.spring4.resourceresolver.SpringResourceResourceResolver;
+import org.thymeleaf.spring4.templateresolver.SpringResourceTemplateResolver;
 import org.thymeleaf.spring4.view.ThymeleafViewResolver;
 import org.thymeleaf.templateresolver.ITemplateResolver;
 
@@ -132,6 +133,16 @@ public class ThymeleafAutoConfiguration {
 				super(properties, applicationContext);
 			}
 
+			@Bean
+			@Override
+			public SpringResourceTemplateResolver defaultTemplateResolver() {
+				SpringResourceTemplateResolver resolver = super.defaultTemplateResolver();
+				Method setCheckExistence = ReflectionUtils
+						.findMethod(resolver.getClass(), "setCheckExistence", boolean.class);
+				ReflectionUtils.invokeMethod(setCheckExistence, resolver, this.properties.isCheckTemplate());
+				return resolver;
+			}
+
 		}
 
 		@Configuration

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/thymeleaf/ThymeleafProperties.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2015 the original author or authors.
+ * Copyright 2012-2016 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.
@@ -38,6 +38,11 @@ public class ThymeleafProperties {
 
 	public static final String DEFAULT_SUFFIX = ".html";
 
+	/**
+	 * Check that the template exists before rendering it (Thymeleaf 3+).
+	 */
+	private boolean checkTemplate = true;
+
 	/**
 	 * Check that the templates location exists.
 	 */
@@ -103,6 +108,14 @@ public class ThymeleafProperties {
 		this.enabled = enabled;
 	}
 
+	public boolean isCheckTemplate() {
+		return checkTemplate;
+	}
+
+	public void setCheckTemplate(boolean checkTemplate) {
+		this.checkTemplate = checkTemplate;
+	}
+
 	public boolean isCheckTemplateLocation() {
 		return this.checkTemplateLocation;
 	}

spring-boot-docs/src/main/asciidoc/appendix-application-properties.adoc

@@ -394,6 +394,7 @@ content into your application; rather pick only the properties that you need.
 
 	# THYMELEAF ({sc-spring-boot-autoconfigure}/thymeleaf/ThymeleafAutoConfiguration.{sc-ext}[ThymeleafAutoConfiguration])
 	spring.thymeleaf.cache=true # Enable template caching.
+	spring.thymeleaf.check-template=true # Check that the template exists before rendering it.
 	spring.thymeleaf.check-template-location=true # Check that the templates location exists.
 	spring.thymeleaf.content-type=text/html # Content-Type value.
 	spring.thymeleaf.enabled=true # Enable MVC Thymeleaf view resolution.