Use String#isEmpty()

Closes gh-1335
(cherry picked from commit 7d062df)

Author: stonio

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 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.
@@ -150,10 +150,10 @@ else if (i == this.possibleMatches.length - 2) {
 	 * @return the distance value
 	 */
 	private static int calculateStringDistance(String s1, String s2) {
-		if (s1.length() == 0) {
+		if (s1.isEmpty()) {
 			return s2.length();
 		}
-		if (s2.length() == 0) {
+		if (s2.isEmpty()) {
 			return s1.length();
 		}
 		int d[][] = new int[s1.length() + 1][s2.length() + 1];

spring-core/src/main/java/org/springframework/core/convert/support/StringToCharacterConverter.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2017 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.
@@ -28,7 +28,7 @@ final class StringToCharacterConverter implements Converter<String, Character> {
 
 	@Override
 	public Character convert(String source) {
-		if (source.length() == 0) {
+		if (source.isEmpty()) {
 			return null;
 		}
 		if (source.length() > 1) {

spring-core/src/main/java/org/springframework/core/convert/support/StringToEnumConverterFactory.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 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.
@@ -45,7 +45,7 @@ public StringToEnum(Class<T> enumType) {
 
 		@Override
 		public T convert(String source) {
-			if (source.length() == 0) {
+			if (source.isEmpty()) {
 				// It's an empty enum identifier: reset the enum value to null.
 				return null;
 			}

spring-core/src/main/java/org/springframework/core/convert/support/StringToNumberConverterFactory.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 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.
@@ -56,7 +56,7 @@ public StringToNumber(Class<T> targetType) {
 
 		@Override
 		public T convert(String source) {
-			if (source.length() == 0) {
+			if (source.isEmpty()) {
 				return null;
 			}
 			return NumberUtils.parseNumber(source, this.targetType);

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 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.
@@ -833,7 +833,7 @@ private static class PatternVirtualFileVisitor implements InvocationHandler {
 		public PatternVirtualFileVisitor(String rootPath, String subPattern, PathMatcher pathMatcher) {
 			this.subPattern = subPattern;
 			this.pathMatcher = pathMatcher;
-			this.rootPath = (rootPath.length() == 0 || rootPath.endsWith("/") ? rootPath : rootPath + "/");
+			this.rootPath = (rootPath.isEmpty() || rootPath.endsWith("/") ? rootPath : rootPath + "/");
 		}
 
 		@Override

spring-core/src/main/java/org/springframework/util/Base64Utils.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2017 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.
@@ -159,7 +159,7 @@ public static byte[] decodeFromString(String src) {
 		if (src == null) {
 			return null;
 		}
-		if (src.length() == 0) {
+		if (src.isEmpty()) {
 			return new byte[0];
 		}
 

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

@@ -243,7 +243,7 @@ public static MimeType parseMimeType(String mimeType) {
 
 		int index = mimeType.indexOf(';');
 		String fullType = (index >= 0 ? mimeType.substring(0, index) : mimeType).trim();
-		if (fullType.length() == 0) {
+		if (fullType.isEmpty()) {
 			throw new InvalidMimeTypeException(mimeType, "'mimeType' must not be empty");
 		}
 

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

@@ -371,7 +371,7 @@ public static boolean substringMatch(CharSequence str, int index, CharSequence s
 	 * @param sub string to search for. Return 0 if this is {@code null}.
 	 */
 	public static int countOccurrencesOf(String str, String sub) {
-		if (str == null || sub == null || str.length() == 0 || sub.length() == 0) {
+		if (!hasLength(str) || !hasLength(sub)) {
 			return 0;
 		}
 		int count = 0;
@@ -513,25 +513,23 @@ public static String uncapitalize(String str) {
 	}
 
 	private static String changeFirstCharacterCase(String str, boolean capitalize) {
-		if (str == null || str.length() == 0) {
+		if (!hasLength(str)) {
 			return str;
 		}
+		char baseChar = str.charAt(0);
+		char updatedChar;
+		if (capitalize) {
+			updatedChar = Character.toUpperCase(baseChar);
+		}
 		else {
-			char baseChar = str.charAt(0);
-			char updatedChar;
-			if (capitalize) {
-				updatedChar = Character.toUpperCase(baseChar);
-			}
-			else {
-				updatedChar = Character.toLowerCase(baseChar);
-			}
-			if (baseChar == updatedChar) {
-				return str;
-			}
-			char[] chars = str.toCharArray();
-			chars[0] = updatedChar;
-			return new String(chars, 0, chars.length);
+			updatedChar = Character.toLowerCase(baseChar);
+		}
+		if (baseChar == updatedChar) {
+			return str;
 		}
+		char[] chars = str.toCharArray();
+		chars[0] = updatedChar;
+		return new String(chars, 0, chars.length);
 	}
 
 	/**

spring-core/src/main/java/org/springframework/util/xml/AbstractStaxHandler.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2014 the original author or authors.
+ * Copyright 2002-2017 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.
@@ -223,8 +223,8 @@ protected QName toQName(String namespaceUri, String qualifiedName) {
 	protected boolean isNamespaceDeclaration(QName qName) {
 		String prefix = qName.getPrefix();
 		String localPart = qName.getLocalPart();
-		return (XMLConstants.XMLNS_ATTRIBUTE.equals(localPart) && prefix.length() == 0) ||
-				(XMLConstants.XMLNS_ATTRIBUTE.equals(prefix) && localPart.length() != 0);
+		return (XMLConstants.XMLNS_ATTRIBUTE.equals(localPart) && prefix.isEmpty()) ||
+				(XMLConstants.XMLNS_ATTRIBUTE.equals(prefix) && !localPart.isEmpty());
 	}