Use StringBuilder.append(char) where possible

To slightly improve performance, this commit switches to
StringBuilder.append(char) instead of StringBuilder.append(String)
whenever we append a single character to a StringBuilder.

Closes spring-projectsgh-27098

spring-aop/src/main/java/org/springframework/aop/aspectj/AspectJAdviceParameterNameDiscoverer.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.
@@ -625,7 +625,7 @@ private PointcutBody getPointcutBody(String[] tokens, int startIndex) {
 			StringBuilder sb = new StringBuilder();
 			if (bodyStart >= 0 && bodyStart != (currentToken.length() - 1)) {
 				sb.append(currentToken.substring(bodyStart + 1));
-				sb.append(" ");
+				sb.append(' ');
 			}
 			numTokensConsumed++;
 			int currentIndex = startIndex + numTokensConsumed;
@@ -645,7 +645,7 @@ private PointcutBody getPointcutBody(String[] tokens, int startIndex) {
 					toAppend = toAppend.substring(1);
 				}
 				sb.append(toAppend);
-				sb.append(" ");
+				sb.append(' ');
 				currentIndex++;
 				numTokensConsumed++;
 			}

spring-aop/src/main/java/org/springframework/aop/aspectj/AspectJExpressionPointcut.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 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.
@@ -547,7 +547,7 @@ public String toString() {
 		StringBuilder sb = new StringBuilder("AspectJExpressionPointcut: (");
 		for (int i = 0; i < this.pointcutParameterTypes.length; i++) {
 			sb.append(this.pointcutParameterTypes[i].getName());
-			sb.append(" ");
+			sb.append(' ');
 			sb.append(this.pointcutParameterNames[i]);
 			if ((i+1) < this.pointcutParameterTypes.length) {
 				sb.append(", ");

spring-aop/src/main/java/org/springframework/aop/aspectj/MethodInvocationProceedingJoinPoint.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.
@@ -255,19 +255,19 @@ private String toString(boolean includeModifier, boolean includeReturnTypeAndArg
 			StringBuilder sb = new StringBuilder();
 			if (includeModifier) {
 				sb.append(Modifier.toString(getModifiers()));
-				sb.append(" ");
+				sb.append(' ');
 			}
 			if (includeReturnTypeAndArgs) {
 				appendType(sb, getReturnType(), useLongReturnAndArgumentTypeName);
-				sb.append(" ");
+				sb.append(' ');
 			}
 			appendType(sb, getDeclaringType(), useLongTypeName);
-			sb.append(".");
+			sb.append('.');
 			sb.append(getMethod().getName());
-			sb.append("(");
+			sb.append('(');
 			Class<?>[] parametersTypes = getParameterTypes();
 			appendTypes(sb, parametersTypes, includeReturnTypeAndArgs, useLongReturnAndArgumentTypeName);
-			sb.append(")");
+			sb.append(')');
 			return sb.toString();
 		}
 
@@ -278,7 +278,7 @@ private void appendTypes(StringBuilder sb, Class<?>[] types, boolean includeArgs
 				for (int size = types.length, i = 0; i < size; i++) {
 					appendType(sb, types[i], useLongReturnAndArgumentTypeName);
 					if (i < size - 1) {
-						sb.append(",");
+						sb.append(',');
 					}
 				}
 			}

spring-aop/src/main/java/org/springframework/aop/support/AbstractBeanFactoryPointcutAdvisor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 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.
@@ -137,7 +137,7 @@ public String toString() {
 		StringBuilder sb = new StringBuilder(getClass().getName());
 		sb.append(": advice ");
 		if (this.adviceBeanName != null) {
-			sb.append("bean '").append(this.adviceBeanName).append("'");
+			sb.append("bean '").append(this.adviceBeanName).append('\'');
 		}
 		else {
 			sb.append(this.advice);

spring-aop/src/main/java/org/springframework/aop/target/AbstractBeanFactoryBasedTargetSource.java

@@ -191,9 +191,9 @@ public int hashCode() {
 	@Override
 	public String toString() {
 		StringBuilder sb = new StringBuilder(getClass().getSimpleName());
-		sb.append(" for target bean '").append(this.targetBeanName).append("'");
+		sb.append(" for target bean '").append(this.targetBeanName).append('\'');
 		if (this.targetClass != null) {
-			sb.append(" of type [").append(this.targetClass.getName()).append("]");
+			sb.append(" of type [").append(this.targetClass.getName()).append(']');
 		}
 		return sb.toString();
 	}

spring-aop/src/test/java/org/springframework/aop/aspectj/AspectJAdviceParameterNameDiscovererTests.java

@@ -276,14 +276,14 @@ protected void assertException(Method method, String pointcut, String returning,
 
 	private static String format(String[] names) {
 		StringBuilder sb = new StringBuilder();
-		sb.append("(");
+		sb.append('(');
 		for (int i = 0; i < names.length; i++) {
 			sb.append(names[i]);
 			if ((i + 1) < names.length) {
-				sb.append(",");
+				sb.append(',');
 			}
 		}
-		sb.append(")");
+		sb.append(')');
 		return sb.toString();
 	}
 

spring-beans/src/main/java/org/springframework/beans/TypeConverterDelegate.java

@@ -247,14 +247,14 @@ else if (conversionService != null && typeDescriptor != null) {
 				// Definitely doesn't match: throw IllegalArgumentException/IllegalStateException
 				StringBuilder msg = new StringBuilder();
 				msg.append("Cannot convert value of type '").append(ClassUtils.getDescriptiveType(newValue));
-				msg.append("' to required type '").append(ClassUtils.getQualifiedName(requiredType)).append("'");
+				msg.append("' to required type '").append(ClassUtils.getQualifiedName(requiredType)).append('\'');
 				if (propertyName != null) {
-					msg.append(" for property '").append(propertyName).append("'");
+					msg.append(" for property '").append(propertyName).append('\'');
 				}
 				if (editor != null) {
 					msg.append(": PropertyEditor [").append(editor.getClass().getName()).append(
 							"] returned inappropriate value of type '").append(
-							ClassUtils.getDescriptiveType(convertedValue)).append("'");
+							ClassUtils.getDescriptiveType(convertedValue)).append('\'');
 					throw new IllegalArgumentException(msg.toString());
 				}
 				else {

spring-beans/src/main/java/org/springframework/beans/factory/annotation/RequiredAnnotationBeanPostProcessor.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.
@@ -217,13 +217,13 @@ private String buildExceptionMessage(List<String> invalidProperties, String bean
 					sb.append(" and");
 				}
 				else {
-					sb.append(",");
+					sb.append(',');
 				}
 			}
-			sb.append(" '").append(propertyName).append("'");
+			sb.append(" '").append(propertyName).append('\'');
 		}
 		sb.append(size == 1 ? " is" : " are");
-		sb.append(" required for bean '").append(beanName).append("'");
+		sb.append(" required for bean '").append(beanName).append('\'');
 		return sb.toString();
 	}
 

spring-beans/src/main/java/org/springframework/beans/factory/support/AbstractBeanDefinition.java

@@ -1241,7 +1241,7 @@ public int hashCode() {
 	@Override
 	public String toString() {
 		StringBuilder sb = new StringBuilder("class [");
-		sb.append(getBeanClassName()).append("]");
+		sb.append(getBeanClassName()).append(']');
 		sb.append("; scope=").append(this.scope);
 		sb.append("; abstract=").append(this.abstractFlag);
 		sb.append("; lazyInit=").append(this.lazyInit);

spring-context-support/src/main/java/org/springframework/cache/jcache/interceptor/AbstractJCacheOperation.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 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.
@@ -138,7 +138,7 @@ protected ExceptionTypeFilter createExceptionTypeFilter(
 
 	@Override
 	public String toString() {
-		return getOperationDescription().append("]").toString();
+		return getOperationDescription().append(']').toString();
 	}
 
 	/**
@@ -148,7 +148,7 @@ public String toString() {
 	protected StringBuilder getOperationDescription() {
 		StringBuilder result = new StringBuilder();
 		result.append(getClass().getSimpleName());
-		result.append("[");
+		result.append('[');
 		result.append(this.methodDetails);
 		return result;
 	}

spring-context/src/main/java/org/springframework/cache/interceptor/CacheEvictOperation.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 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.
@@ -71,9 +71,9 @@ public void setBeforeInvocation(boolean beforeInvocation) {
 		@Override
 		protected StringBuilder getOperationDescription() {
 			StringBuilder sb = super.getOperationDescription();
-			sb.append(",");
+			sb.append(',');
 			sb.append(this.cacheWide);
-			sb.append(",");
+			sb.append(',');
 			sb.append(this.beforeInvocation);
 			return sb;
 		}

spring-context/src/main/java/org/springframework/cache/interceptor/CacheOperation.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 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.
@@ -216,13 +216,13 @@ public void setCondition(String condition) {
 		 */
 		protected StringBuilder getOperationDescription() {
 			StringBuilder result = new StringBuilder(getClass().getSimpleName());
-			result.append("[").append(this.name);
+			result.append('[').append(this.name);
 			result.append("] caches=").append(this.cacheNames);
 			result.append(" | key='").append(this.key);
 			result.append("' | keyGenerator='").append(this.keyGenerator);
 			result.append("' | cacheManager='").append(this.cacheManager);
 			result.append("' | cacheResolver='").append(this.cacheResolver);
-			result.append("' | condition='").append(this.condition).append("'");
+			result.append("' | condition='").append(this.condition).append('\'');
 			return result;
 		}
 

spring-context/src/main/java/org/springframework/cache/interceptor/CachePutOperation.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 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.
@@ -66,7 +66,7 @@ protected StringBuilder getOperationDescription() {
 			StringBuilder sb = super.getOperationDescription();
 			sb.append(" | unless='");
 			sb.append(this.unless);
-			sb.append("'");
+			sb.append('\'');
 			return sb;
 		}
 

spring-context/src/main/java/org/springframework/cache/interceptor/CacheableOperation.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 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.
@@ -79,10 +79,10 @@ protected StringBuilder getOperationDescription() {
 			StringBuilder sb = super.getOperationDescription();
 			sb.append(" | unless='");
 			sb.append(this.unless);
-			sb.append("'");
+			sb.append('\'');
 			sb.append(" | sync='");
 			sb.append(this.sync);
-			sb.append("'");
+			sb.append('\'');
 			return sb;
 		}
 

spring-context/src/main/java/org/springframework/context/event/ApplicationListenerMethodAdapter.java

@@ -396,7 +396,7 @@ protected String getCondition() {
 	 * @param message error message to append the HandlerMethod details to
 	 */
 	protected String getDetailedErrorMessage(Object bean, String message) {
-		StringBuilder sb = new StringBuilder(message).append("\n");
+		StringBuilder sb = new StringBuilder(message).append('\n');
 		sb.append("HandlerMethod details: \n");
 		sb.append("Bean [").append(bean.getClass().getName()).append("]\n");
 		sb.append("Method [").append(this.method.toGenericString()).append("]\n");
@@ -426,7 +426,7 @@ private String getInvocationErrorMessage(Object bean, String message, Object[] r
 		StringBuilder sb = new StringBuilder(getDetailedErrorMessage(bean, message));
 		sb.append("Resolved arguments: \n");
 		for (int i = 0; i < resolvedArgs.length; i++) {
-			sb.append("[").append(i).append("] ");
+			sb.append('[').append(i).append("] ");
 			if (resolvedArgs[i] == null) {
 				sb.append("[null] \n");
 			}

spring-context/src/main/java/org/springframework/context/support/LiveBeansView.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.
@@ -205,12 +205,12 @@ protected String generateJson(Set<ConfigurableApplicationContext> contexts) {
 				}
 			}
 			result.append("]\n");
-			result.append("}");
+			result.append('}');
 			if (it.hasNext()) {
 				result.append(",\n");
 			}
 		}
-		result.append("]");
+		result.append(']');
 		return result.toString();
 	}
 

spring-core/src/main/java/org/springframework/core/Constants.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 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.
@@ -324,7 +324,7 @@ public String propertyToConstantNamePrefix(String propertyName) {
 		for (int i = 0; i < propertyName.length(); i++) {
 			char c = propertyName.charAt(i);
 			if (Character.isUpperCase(c)) {
-				parsedPrefix.append("_");
+				parsedPrefix.append('_');
 				parsedPrefix.append(c);
 			}
 			else {

spring-core/src/main/java/org/springframework/core/annotation/AnnotationAttributes.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 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.
@@ -394,9 +394,11 @@ public String toString() {
 			sb.append(entry.getKey());
 			sb.append('=');
 			sb.append(valueToString(entry.getValue()));
-			sb.append(entries.hasNext() ? ", " : "");
+			if (entries.hasNext()) {
+				sb.append(", ");
+			}
 		}
-		sb.append("}");
+		sb.append('}');
 		return sb.toString();
 	}
 

spring-core/src/main/java/org/springframework/core/annotation/SynthesizedMergedAnnotationInvocationHandler.java

@@ -177,17 +177,17 @@ private int getValueHashCode(Object value) {
 	private String annotationToString() {
 		String string = this.string;
 		if (string == null) {
-			StringBuilder builder = new StringBuilder("@").append(this.type.getName()).append("(");
+			StringBuilder builder = new StringBuilder("@").append(this.type.getName()).append('(');
 			for (int i = 0; i < this.attributes.size(); i++) {
 				Method attribute = this.attributes.get(i);
 				if (i > 0) {
 					builder.append(", ");
 				}
 				builder.append(attribute.getName());
-				builder.append("=");
+				builder.append('=');
 				builder.append(toString(getAttributeValue(attribute)));
 			}
-			builder.append(")");
+			builder.append(')');
 			string = builder.toString();
 			this.string = string;
 		}
@@ -206,7 +206,7 @@ private String toString(Object value) {
 				}
 				builder.append(toString(Array.get(value, i)));
 			}
-			builder.append("]");
+			builder.append(']');
 			return builder.toString();
 		}
 		return String.valueOf(value);

spring-core/src/main/java/org/springframework/core/convert/TypeDescriptor.java

@@ -513,7 +513,7 @@ public int hashCode() {
 	public String toString() {
 		StringBuilder builder = new StringBuilder();
 		for (Annotation ann : getAnnotations()) {
-			builder.append("@").append(ann.annotationType().getName()).append(' ');
+			builder.append('@').append(ann.annotationType().getName()).append(' ');
 		}
 		builder.append(getResolvableType());
 		return builder.toString();