Efficient checks for empty strings and single character matches

Closes gh-25552
Closes gh-25553

spring-beans/src/main/java/org/springframework/beans/factory/config/ConstructorArgumentValues.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -164,10 +164,10 @@ public ValueHolder getIndexedArgumentValue(int index, @Nullable Class<?> require
 		Assert.isTrue(index >= 0, "Index must not be negative");
 		ValueHolder valueHolder = this.indexedArgumentValues.get(index);
 		if (valueHolder != null &&
-				(valueHolder.getType() == null ||
-						(requiredType != null && ClassUtils.matchesTypeName(requiredType, valueHolder.getType()))) &&
-				(valueHolder.getName() == null || "".equals(requiredName) ||
-						(requiredName != null && requiredName.equals(valueHolder.getName())))) {
+				(valueHolder.getType() == null || (requiredType != null &&
+						ClassUtils.matchesTypeName(requiredType, valueHolder.getType()))) &&
+				(valueHolder.getName() == null || (requiredName != null &&
+						(requiredName.isEmpty() || requiredName.equals(valueHolder.getName()))))) {
 			return valueHolder;
 		}
 		return null;
@@ -277,17 +277,19 @@ public ValueHolder getGenericArgumentValue(Class<?> requiredType, String require
 	 * @return the ValueHolder for the argument, or {@code null} if none found
 	 */
 	@Nullable
-	public ValueHolder getGenericArgumentValue(@Nullable Class<?> requiredType, @Nullable String requiredName, @Nullable Set<ValueHolder> usedValueHolders) {
+	public ValueHolder getGenericArgumentValue(@Nullable Class<?> requiredType, @Nullable String requiredName,
+			@Nullable Set<ValueHolder> usedValueHolders) {
+
 		for (ValueHolder valueHolder : this.genericArgumentValues) {
 			if (usedValueHolders != null && usedValueHolders.contains(valueHolder)) {
 				continue;
 			}
-			if (valueHolder.getName() != null && !"".equals(requiredName) &&
-					(requiredName == null || !valueHolder.getName().equals(requiredName))) {
+			if (valueHolder.getName() != null && (requiredName == null ||
+					(!requiredName.isEmpty() && !requiredName.equals(valueHolder.getName())))) {
 				continue;
 			}
-			if (valueHolder.getType() != null &&
-					(requiredType == null || !ClassUtils.matchesTypeName(requiredType, valueHolder.getType()))) {
+			if (valueHolder.getType() != null && (requiredType == null ||
+					!ClassUtils.matchesTypeName(requiredType, valueHolder.getType()))) {
 				continue;
 			}
 			if (requiredType != null && valueHolder.getType() == null && valueHolder.getName() == null &&

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

@@ -446,8 +446,8 @@ else if (SCOPE_KEY.equals(property)) {
 				else if (SINGLETON_KEY.equals(property)) {
 					// Spring 1.2 style
 					String val = StringUtils.trimWhitespace((String) entry.getValue());
-					scope = ("".equals(val) || TRUE_VALUE.equals(val) ? BeanDefinition.SCOPE_SINGLETON :
-							BeanDefinition.SCOPE_PROTOTYPE);
+					scope = (!StringUtils.hasLength(val) || TRUE_VALUE.equals(val) ?
+							BeanDefinition.SCOPE_SINGLETON : BeanDefinition.SCOPE_PROTOTYPE);
 				}
 				else if (LAZY_INIT_KEY.equals(property)) {
 					String val = StringUtils.trimWhitespace((String) entry.getValue());

spring-beans/src/main/java/org/springframework/beans/factory/xml/BeanDefinitionParserDelegate.java

@@ -1523,7 +1523,7 @@ public boolean nodeNameEquals(Node node, String desiredName) {
 	 * Determine whether the given URI indicates the default namespace.
 	 */
 	public boolean isDefaultNamespace(@Nullable String namespaceUri) {
-		return (!StringUtils.hasLength(namespaceUri) || BEANS_NAMESPACE_URI.equals(namespaceUri));
+		return !StringUtils.hasLength(namespaceUri) || BEANS_NAMESPACE_URI.equals(namespaceUri);
 	}
 
 	/**
@@ -1534,7 +1534,7 @@ public boolean isDefaultNamespace(Node node) {
 	}
 
 	private boolean isDefaultValue(String value) {
-		return (DEFAULT_VALUE.equals(value) || "".equals(value));
+		return !StringUtils.hasLength(value) || DEFAULT_VALUE.equals(value);
 	}
 
 	private boolean isCandidateElement(Node node) {

spring-context/src/main/java/org/springframework/validation/AbstractBindingResult.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -105,7 +105,7 @@ public void reject(String errorCode, @Nullable Object[] errorArgs, @Nullable Str
 	public void rejectValue(@Nullable String field, String errorCode, @Nullable Object[] errorArgs,
 			@Nullable String defaultMessage) {
 
-		if ("".equals(getNestedPath()) && !StringUtils.hasLength(field)) {
+		if (!StringUtils.hasLength(getNestedPath()) && !StringUtils.hasLength(field)) {
 			// We're at the top of the nested object hierarchy,
 			// so the present level is not a field but rather the top object.
 			// The best we can do is register a global error here...

spring-context/src/main/java/org/springframework/validation/beanvalidation/SpringValidatorAdapter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -311,7 +311,7 @@ protected MessageSourceResolvable getResolvableField(String objectName, String f
 	@Nullable
 	protected Object getRejectedValue(String field, ConstraintViolation<Object> violation, BindingResult bindingResult) {
 		Object invalidValue = violation.getInvalidValue();
-		if (!"".equals(field) && !field.contains("[]") &&
+		if (!field.isEmpty() && !field.contains("[]") &&
 				(invalidValue == violation.getLeafBean() || field.contains("[") || field.contains("."))) {
 			// Possibly a bean constraint with property path: retrieve the actual property value.
 			// However, explicitly avoid this for "address[]" style paths that we can't handle.

spring-core/src/main/java/org/springframework/core/io/support/PathMatchingResourcePatternResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -340,7 +340,7 @@ protected Set<Resource> doFindAllClassPathResources(String path) throws IOExcept
 			URL url = resourceUrls.nextElement();
 			result.add(convertClassLoaderURL(url));
 		}
-		if ("".equals(path)) {
+		if (!StringUtils.hasLength(path)) {
 			// The above result is likely to be incomplete, i.e. only containing file system references.
 			// We need to have pointers to each of the jar files on the classpath as well...
 			addAllClassLoaderJarRoots(cl, result);
@@ -639,7 +639,7 @@ protected Set<Resource> doFindPathMatchingJarResources(Resource rootDirResource,
 			if (logger.isTraceEnabled()) {
 				logger.trace("Looking for matching resources in jar file [" + jarFileUrl + "]");
 			}
-			if (!"".equals(rootEntryPath) && !rootEntryPath.endsWith("/")) {
+			if (StringUtils.hasLength(rootEntryPath) && !rootEntryPath.endsWith("/")) {
 				// Root entry path must end with slash to allow for proper matching.
 				// The Sun JRE does not return a slash here, but BEA JRockit does.
 				rootEntryPath = rootEntryPath + "/";

spring-core/src/main/java/org/springframework/util/StringUtils.java

@@ -331,6 +331,16 @@ public static String trimTrailingCharacter(String str, char trailingCharacter) {
 		return sb.toString();
 	}
 
+	/**
+	 * Test if the given {@code String} matches the given single character.
+	 * @param str the {@code String} to check
+	 * @param singleCharacter the character to compare to
+	 * @since 5.2.9
+	 */
+	public static boolean matchesCharacter(@Nullable String str, char singleCharacter) {
+		return (str != null && str.length() == 1 && str.charAt(0) == singleCharacter);
+	}
+
 	/**
 	 * Test if the given {@code String} starts with the specified prefix,
 	 * ignoring upper/lower case.
@@ -713,7 +723,7 @@ else if (TOP_PATH.equals(element)) {
 			pathElements.add(0, TOP_PATH);
 		}
 		// If nothing else left, at least explicitly point to current path.
-		if (pathElements.size() == 1 && "".equals(pathElements.getLast()) && !prefix.endsWith(FOLDER_SEPARATOR)) {
+		if (pathElements.size() == 1 && pathElements.getLast().isEmpty() && !prefix.endsWith(FOLDER_SEPARATOR)) {
 			pathElements.add(0, CURRENT_PATH);
 		}
 

spring-jms/src/main/java/org/springframework/jms/config/AbstractListenerContainerParser.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -255,7 +255,7 @@ else if (DESTINATION_TYPE_DURABLE_TOPIC.equals(destinationType)) {
 		else if (DESTINATION_TYPE_TOPIC.equals(destinationType)) {
 			pubSubDomain = true;
 		}
-		else if ("".equals(destinationType) || DESTINATION_TYPE_QUEUE.equals(destinationType)) {
+		else if (!StringUtils.hasLength(destinationType) || DESTINATION_TYPE_QUEUE.equals(destinationType)) {
 			// the default: queue
 		}
 		else {

spring-jms/src/main/java/org/springframework/jms/config/JmsListenerContainerParser.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -64,10 +64,10 @@ protected RootBeanDefinition createContainerFactory(String factoryId, Element co
 
 		String containerType = containerEle.getAttribute(CONTAINER_TYPE_ATTRIBUTE);
 		String containerClass = containerEle.getAttribute(CONTAINER_CLASS_ATTRIBUTE);
-		if (!"".equals(containerClass)) {
-			return null; // Not supported
+		if (StringUtils.hasLength(containerClass)) {
+			return null;  // not supported
 		}
-		else if ("".equals(containerType) || containerType.startsWith("default")) {
+		else if (!StringUtils.hasLength(containerType) || containerType.startsWith("default")) {
 			factoryDef.setBeanClassName("org.springframework.jms.config.DefaultJmsListenerContainerFactory");
 		}
 		else if (containerType.startsWith("simple")) {
@@ -91,10 +91,10 @@ protected RootBeanDefinition createContainer(Element containerEle, Element liste
 
 		String containerType = containerEle.getAttribute(CONTAINER_TYPE_ATTRIBUTE);
 		String containerClass = containerEle.getAttribute(CONTAINER_CLASS_ATTRIBUTE);
-		if (!"".equals(containerClass)) {
+		if (StringUtils.hasLength(containerClass)) {
 			containerDef.setBeanClassName(containerClass);
 		}
-		else if ("".equals(containerType) || containerType.startsWith("default")) {
+		else if (!StringUtils.hasLength(containerType) || containerType.startsWith("default")) {
 			containerDef.setBeanClassName("org.springframework.jms.listener.DefaultMessageListenerContainer");
 		}
 		else if (containerType.startsWith("simple")) {

spring-test/src/main/java/org/springframework/test/context/jdbc/MergedSqlConfig.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -235,7 +235,7 @@ private static <E extends Enum<?>> E getEnum(AnnotationAttributes attributes, St
 
 	private static String getString(AnnotationAttributes attributes, String attributeName, String defaultValue) {
 		String value = attributes.getString(attributeName);
-		if ("".equals(value)) {
+		if (value.isEmpty()) {
 			value = defaultValue;
 		}
 		return value;

spring-web/src/main/java/org/springframework/http/server/DefaultRequestPath.java

@@ -50,7 +50,7 @@ private DefaultRequestPath(RequestPath requestPath, String contextPath) {
 	}
 
 	private static PathContainer initContextPath(PathContainer path, @Nullable String contextPath) {
-		if (!StringUtils.hasText(contextPath) || "/".equals(contextPath)) {
+		if (!StringUtils.hasText(contextPath) || StringUtils.matchesCharacter(contextPath, '/')) {
 			return PathContainer.parsePath("");
 		}
 
@@ -59,7 +59,7 @@ private static PathContainer initContextPath(PathContainer path, @Nullable Strin
 		int length = contextPath.length();
 		int counter = 0;
 
-		for (int i=0; i < path.elements().size(); i++) {
+		for (int i = 0; i < path.elements().size(); i++) {
 			PathContainer.Element element = path.elements().get(i);
 			counter += element.value().length();
 			if (length == counter) {

spring-web/src/main/java/org/springframework/web/util/UrlPathHelper.java

@@ -170,7 +170,7 @@ public String getLookupPathForRequest(HttpServletRequest request) {
 		}
 		// Else, use path within current servlet mapping if applicable
 		String rest = getPathWithinServletMapping(request);
-		if (!"".equals(rest)) {
+		if (StringUtils.hasLength(rest)) {
 			return rest;
 		}
 		else {
@@ -362,7 +362,7 @@ public String getContextPath(HttpServletRequest request) {
 		if (contextPath == null) {
 			contextPath = request.getContextPath();
 		}
-		if ("/".equals(contextPath)) {
+		if (StringUtils.matchesCharacter(contextPath, '/')) {
 			// Invalid case, but happens for includes on Jetty: silently adapt it.
 			contextPath = "";
 		}

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

@@ -31,6 +31,7 @@
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.CollectionUtils;
+import org.springframework.util.StringUtils;
 import org.springframework.web.servlet.HandlerExecutionChain;
 
 /**
@@ -127,7 +128,7 @@ protected Object getHandlerInternal(HttpServletRequest request) throws Exception
 			// We need to care for the default handler directly, since we need to
 			// expose the PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE for it as well.
 			Object rawHandler = null;
-			if ("/".equals(lookupPath)) {
+			if (StringUtils.matchesCharacter(lookupPath, '/')) {
 				rawHandler = getRootHandler();
 			}
 			if (rawHandler == null) {

spring-webmvc/src/main/java/org/springframework/web/servlet/resource/ResourceUrlEncodingFilter.java

@@ -31,6 +31,7 @@
 import org.apache.commons.logging.LogFactory;
 
 import org.springframework.lang.Nullable;
+import org.springframework.util.StringUtils;
 import org.springframework.web.filter.GenericFilterBean;
 import org.springframework.web.util.UrlPathHelper;
 
@@ -100,7 +101,7 @@ private void initLookupPath(ResourceUrlProvider urlProvider) {
 					throw new LookupPathIndexException(lookupPath, requestUri);
 				}
 				this.prefixLookupPath = requestUri.substring(0, this.indexLookupPath);
-				if ("/".equals(lookupPath) && !"/".equals(requestUri)) {
+				if (StringUtils.matchesCharacter(lookupPath, '/') && !StringUtils.matchesCharacter(requestUri, '/')) {
 					String contextPath = pathHelper.getContextPath(this);
 					if (requestUri.equals(contextPath)) {
 						this.indexLookupPath = requestUri.length();

spring-webmvc/src/main/java/org/springframework/web/servlet/tags/form/ErrorsTag.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -260,7 +260,7 @@ public String getDelimiter() {
 	@Override
 	protected String autogenerateId() throws JspException {
 		String path = getPropertyPath();
-		if ("".equals(path) || "*".equals(path)) {
+		if (!StringUtils.hasLength(path) || "*".equals(path)) {
 			path = (String) this.pageContext.getAttribute(
 					FormTag.MODEL_ATTRIBUTE_VARIABLE_NAME, PageContext.REQUEST_SCOPE);
 		}