Improve startup times

Improve startup times (although not by much) by adding more background
pre-initializers and lazily evaluating the whitelabel SpEL view.

See gh-6177

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/BackgroundPreinitializer.java

@@ -24,6 +24,8 @@ import org.springframework.boot.context.event.ApplicationEnvironmentPreparedEven
 import org.springframework.boot.logging.LoggingApplicationListener;
 import org.springframework.context.ApplicationListener;
 import org.springframework.core.annotation.Order;
+import org.springframework.format.support.DefaultFormattingConversionService;
+import org.springframework.http.converter.json.Jackson2ObjectMapperBuilder;
 import org.springframework.http.converter.support.AllEncompassingFormHttpMessageConverter;
 
 /**
@@ -48,6 +50,8 @@ public class BackgroundPreinitializer
 					runSafely(new MessageConverterInitializer());
 					runSafely(new MBeanFactoryInitializer());
 					runSafely(new ValidationInitializer());
+					runSafely(new JacksonInitializer());
+					runSafely(new ConverstionServiceInitializer());
 				}
 
 				public void runSafely(Runnable runnable) {
@@ -105,4 +109,28 @@ public class BackgroundPreinitializer
 
 	}
 
+	/**
+	 * Early initializer for Jackson.
+	 */
+	private static class JacksonInitializer implements Runnable {
+
+		@Override
+		public void run() {
+			Jackson2ObjectMapperBuilder.json().build();
+		}
+
+	}
+
+	/**
+	 * Early initializer for Spring's ConverstionService.
+	 */
+	private static class ConverstionServiceInitializer implements Runnable {
+
+		@Override
+		public void run() {
+			new DefaultFormattingConversionService();
+		}
+
+	}
+
 }

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/web/ErrorMvcAutoConfiguration.java

@@ -189,14 +189,11 @@ public class ErrorMvcAutoConfiguration {
 
 		private final String template;
 
-		private final Map<String, Expression> expressions;
+		private volatile Map<String, Expression> expressions;
 
 		SpelView(String template) {
 			this.helper = new NonRecursivePropertyPlaceholderHelper("${", "}");
 			this.template = template;
-			ExpressionCollector expressionCollector = new ExpressionCollector();
-			this.helper.replacePlaceholders(this.template, expressionCollector);
-			this.expressions = expressionCollector.getExpressions();
 		}
 
 		@Override
@@ -212,11 +209,22 @@ public class ErrorMvcAutoConfiguration {
 			}
 			Map<String, Object> map = new HashMap<String, Object>(model);
 			map.put("path", request.getContextPath());
-			PlaceholderResolver resolver = new ExpressionResolver(this.expressions, map);
+			PlaceholderResolver resolver = new ExpressionResolver(getExpressions(), map);
 			String result = this.helper.replacePlaceholders(this.template, resolver);
 			response.getWriter().append(result);
 		}
 
+		private Map<String, Expression> getExpressions() {
+			if (this.expressions == null) {
+				synchronized (this) {
+					ExpressionCollector expressionCollector = new ExpressionCollector();
+					this.helper.replacePlaceholders(this.template, expressionCollector);
+					this.expressions = expressionCollector.getExpressions();
+				}
+			}
+			return this.expressions;
+		}
+
 	}
 
 	/**