Deprecate StringUtils.isEmpty(Object) and replace remaining usage

Closes gh-25945

spring-beans/src/main/java/org/springframework/beans/factory/annotation/QualifierAnnotationAutowireCandidateResolver.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.
@@ -40,7 +40,6 @@ import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
 import org.springframework.util.ObjectUtils;
-import org.springframework.util.StringUtils;
 
 /**
  * {@link AutowireCandidateResolver} implementation that matches bean definition qualifiers
@@ -188,7 +187,7 @@ public class QualifierAnnotationAutowireCandidateResolver extends GenericTypeAwa
 						foundMeta = true;
 						// Only accept fallback match if @Qualifier annotation has a value...
 						// Otherwise it is just a marker for a custom qualifier annotation.
-						if ((fallbackToMeta && StringUtils.isEmpty(AnnotationUtils.getValue(metaAnn))) ||
+						if ((fallbackToMeta && ObjectUtils.isEmpty(AnnotationUtils.getValue(metaAnn))) ||
 								!checkQualifier(bdHolder, metaAnn, typeConverter)) {
 							return false;
 						}

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

@@ -128,7 +128,6 @@ public abstract class ObjectUtils {
 	 * @see Optional#isPresent()
 	 * @see ObjectUtils#isEmpty(Object[])
 	 * @see StringUtils#hasLength(CharSequence)
-	 * @see StringUtils#isEmpty(Object)
 	 * @see CollectionUtils#isEmpty(java.util.Collection)
 	 * @see CollectionUtils#isEmpty(java.util.Map)
 	 */

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

@@ -91,9 +91,10 @@ public abstract class StringUtils {
 	 * {@link #hasLength(String)} or {@link #hasText(String)} instead.</b>
 	 * @param str the candidate object (possibly a {@code String})
 	 * @since 3.2.1
-	 * @see #hasLength(String)
-	 * @see #hasText(String)
+	 * @deprecated as of 5.3, in favor of {@link #hasLength(String)} and
+	 * {@link #hasText(String)} (or {@link ObjectUtils#isEmpty(Object)})
 	 */
+	@Deprecated
 	public static boolean isEmpty(@Nullable Object str) {
 		return (str == null || "".equals(str));
 	}

spring-expression/src/main/java/org/springframework/expression/spel/ast/Elvis.java

@@ -24,7 +24,6 @@ import org.springframework.expression.spel.CodeFlow;
 import org.springframework.expression.spel.ExpressionState;
 import org.springframework.util.Assert;
 import org.springframework.util.ObjectUtils;
-import org.springframework.util.StringUtils;
 
 /**
  * Represents the elvis operator ?:. For an expression "a?:b" if a is not null, the value
@@ -52,7 +51,7 @@ public class Elvis extends SpelNodeImpl {
 	public TypedValue getValueInternal(ExpressionState state) throws EvaluationException {
 		TypedValue value = this.children[0].getValueInternal(state);
 		// If this check is changed, the generateCode method will need changing too
-		if (!StringUtils.isEmpty(value.getValue())) {
+		if (value.getValue() != null && !"".equals(value.getValue())) {
 			return value;
 		}
 		else {

spring-messaging/src/main/java/org/springframework/messaging/simp/stomp/DefaultStompSession.java

@@ -45,6 +45,7 @@ import org.springframework.scheduling.TaskScheduler;
 import org.springframework.util.AlternativeJdkIdGenerator;
 import org.springframework.util.Assert;
 import org.springframework.util.IdGenerator;
+import org.springframework.util.ObjectUtils;
 import org.springframework.util.StringUtils;
 import org.springframework.util.concurrent.ListenableFuture;
 import org.springframework.util.concurrent.ListenableFutureCallback;
@@ -263,7 +264,7 @@ public class DefaultStompSession implements ConnectionHandlingStompSession {
 	private Message<byte[]> createMessage(StompHeaderAccessor accessor, @Nullable Object payload) {
 		accessor.updateSimpMessageHeadersFromStompHeaders();
 		Message<byte[]> message;
-		if (StringUtils.isEmpty(payload) || (payload instanceof byte[] && ((byte[]) payload).length == 0)) {
+		if (ObjectUtils.isEmpty(payload)) {
 			message = MessageBuilder.createMessage(EMPTY_PAYLOAD, accessor.getMessageHeaders());
 		}
 		else {

spring-web/src/test/java/org/springframework/http/converter/json/Jackson2ObjectMapperBuilderTests.java

@@ -683,13 +683,12 @@ class Jackson2ObjectMapperBuilderTests {
 
 		@Override
 		public OffsetDateTime deserialize(JsonParser jsonParser, DeserializationContext deserializationContext) throws IOException {
-			final String value = jsonParser.getValueAsString();
-			if (StringUtils.isEmpty(value)) {
+			String value = jsonParser.getValueAsString();
+			if (!StringUtils.hasLength(value)) {
 				return null;
 			}
 			try {
 				return OffsetDateTime.parse(value);
-
 			}
 			catch (DateTimeParseException exception) {
 				return OffsetDateTime.parse(value + CURRENT_ZONE_OFFSET);

spring-webflux/src/main/java/org/springframework/web/reactive/result/method/annotation/RequestPartMethodArgumentResolver.java

@@ -129,10 +129,10 @@ public class RequestPartMethodArgumentResolver extends AbstractMessageReaderArgu
 		if (requestPart != null) {
 			name = requestPart.name();
 		}
-		if (StringUtils.isEmpty(name)) {
+		if (!StringUtils.hasLength(name)) {
 			name = methodParam.getParameterName();
 		}
-		if (StringUtils.isEmpty(name)) {
+		if (!StringUtils.hasLength(name)) {
 			throw new IllegalArgumentException("Request part name for argument type [" +
 					methodParam.getNestedParameterType().getName() +
 					"] not specified, and parameter name information not found in class file either.");

spring-webflux/src/main/java/org/springframework/web/reactive/socket/CloseStatus.java

@@ -200,7 +200,7 @@ public final class CloseStatus {
 	 * @since 5.3
 	 */
 	public static CloseStatus create(int code, @Nullable String reason) {
-		if (StringUtils.isEmpty(reason)) {
+		if (!StringUtils.hasText(reason)) {
 			switch (code) {
 				case 1000:
 					return NORMAL;