Customize Thymeleaf default template resolver order

Currently, the default TemplateResolver had no specific order. Thymeleaf
handles that with a "always first" strategy (that can be confusing if
several TemplateResolver have a "null" order.

While it is a fine default (and changing it could lead to weird side
effects), it has to be changed as soon as another TemplateResolver bean
is defined in the project.

The `spring.thymeleaf.template-resolver-order` property has been added to
control  the order of the default TemplateResolver.

Closes gh-3575

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

@@ -101,6 +101,10 @@ public class ThymeleafAutoConfiguration {
 				resolver.setCharacterEncoding(this.properties.getEncoding().name());
 			}
 			resolver.setCacheable(this.properties.isCache());
+			Integer order = this.properties.getTemplateResolverOrder();
+			if (order != null) {
+				resolver.setOrder(order);
+			}
 			return resolver;
 		}
 

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

@@ -73,6 +73,13 @@ public class ThymeleafProperties {
 	 */
 	private boolean cache = true;
 
+	/**
+	 * Order of the template resolver in the chain. By default, the template resolver
+	 * is first in the chain. Order start at 1 and should only be set if you have
+	 * defined additional "TemplateResolver" beans.
+	 */
+	private Integer templateResolverOrder;
+
 	/**
 	 * Comma-separated list of view names that can be resolved.
 	 */
@@ -152,6 +159,14 @@ public class ThymeleafProperties {
 		this.cache = cache;
 	}
 
+	public Integer getTemplateResolverOrder() {
+		return templateResolverOrder;
+	}
+
+	public void setTemplateResolverOrder(Integer templateResolverOrder) {
+		this.templateResolverOrder = templateResolverOrder;
+	}
+
 	public String[] getExcludedViewNames() {
 		return this.excludedViewNames;
 	}

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/thymeleaf/ThymeleafAutoConfigurationTests.java

@@ -51,6 +51,7 @@ import static org.junit.Assert.assertTrue;
  * Tests for {@link ThymeleafAutoConfiguration}.
  *
  * @author Dave Syer
+ * @author Stephane Nicoll
  */
 public class ThymeleafAutoConfigurationTests {
 
@@ -92,6 +93,18 @@ public class ThymeleafAutoConfigurationTests {
 		assertEquals("text/html;charset=UTF-16", views.getContentType());
 	}
 
+	@Test
+	public void overrideTemplateResolverOrder() throws Exception {
+		EnvironmentTestUtils.addEnvironment(this.context,
+				"spring.thymeleaf.templateResolverOrder:25");
+		this.context.register(ThymeleafAutoConfiguration.class,
+				PropertyPlaceholderAutoConfiguration.class);
+		this.context.refresh();
+		this.context.getBean(TemplateEngine.class).initialize();
+		ITemplateResolver resolver = this.context.getBean(ITemplateResolver.class);
+		assertEquals(Integer.valueOf(25), resolver.getOrder());
+	}
+
 	@Test
 	public void overrideViewNames() throws Exception {
 		EnvironmentTestUtils.addEnvironment(this.context,

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

@@ -194,6 +194,7 @@ content into your application; rather pick only the properties that you need.
 	spring.thymeleaf.encoding=UTF-8
 	spring.thymeleaf.content-type=text/html # ;charset=<encoding> is added
 	spring.thymeleaf.cache=true # set to false for hot refresh
+	spring.thymeleaf.template-resolver-order= #  order of the template resolver in the chain
 
 	# FREEMARKER ({sc-spring-boot-autoconfigure}/freemarker/FreeMarkerAutoConfiguration.{sc-ext}[FreeMarkerAutoConfiguration])
 	spring.freemarker.allow-request-override=false