Use String#isEmpty()

Closes gh-1335

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

 /*
- * 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 @@ public abstract class PropertyMatches {
 	 * @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

 /*
- * 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

 /*
- * 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 @@ final class StringToEnumConverterFactory implements ConverterFactory<String, Enu
 
 		@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

 /*
- * 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 @@ final class StringToNumberConverterFactory implements ConverterFactory<String, N
 
 		@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

 /*
- * 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.
@@ -809,7 +809,7 @@ public class PathMatchingResourcePatternResolver implements ResourcePatternResol
 		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

 /*
- * 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.
@@ -120,7 +120,7 @@ public abstract class Base64Utils {
 		if (src == null) {
 			return null;
 		}
-		if (src.length() == 0) {
+		if (src.isEmpty()) {
 			return new byte[0];
 		}
 		return decode(src.getBytes(DEFAULT_CHARSET));

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

@@ -180,7 +180,7 @@ public abstract class MimeTypeUtils {
 
 		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

@@ -373,7 +373,7 @@ public abstract class StringUtils {
 	 * @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;
@@ -515,7 +515,7 @@ public abstract class StringUtils {
 	}
 
 	private static String changeFirstCharacterCase(String str, boolean capitalize) {
-		if (str == null || str.length() == 0) {
+		if (!hasLength(str)) {
 			return str;
 		}
 		else {

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

 /*
- * 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.
@@ -223,8 +223,8 @@ abstract class AbstractStaxHandler implements ContentHandler, LexicalHandler {
 	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());
 	}
 
 

spring-expression/src/main/java/org/springframework/expression/common/TemplateAwareExpressionParser.java

 /*
- * 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.
@@ -79,7 +79,7 @@ public abstract class TemplateAwareExpressionParser implements ExpressionParser
 
 	private Expression parseTemplate(String expressionString, ParserContext context)
 			throws ParseException {
-		if (expressionString.length() == 0) {
+		if (expressionString.isEmpty()) {
 			return new LiteralExpression("");
 		}
 		Expression[] expressions = parseExpressions(expressionString, context);
@@ -145,7 +145,7 @@ public abstract class TemplateAwareExpressionParser implements ExpressionParser
 						suffixIndex);
 				expr = expr.trim();
 
-				if (expr.length() == 0) {
+				if (expr.isEmpty()) {
 					throw new ParseException(expressionString, prefixIndex,
 							"No expression defined within delimiter '" + prefix + suffix
 									+ "' at character " + prefixIndex);

spring-messaging/src/main/java/org/springframework/messaging/handler/annotation/support/AbstractNamedValueMethodArgumentResolver.java

@@ -142,7 +142,7 @@ public abstract class AbstractNamedValueMethodArgumentResolver implements Handle
 	 */
 	private NamedValueInfo updateNamedValueInfo(MethodParameter parameter, NamedValueInfo info) {
 		String name = info.name;
-		if (info.name.length() == 0) {
+		if (info.name.isEmpty()) {
 			name = parameter.getParameterName();
 			if (name == null) {
 				throw new IllegalArgumentException("Name for argument type [" + parameter.getParameterType().getName() +

spring-web/src/main/java/org/springframework/web/method/annotation/AbstractNamedValueMethodArgumentResolver.java

 /*
- * 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.
@@ -160,7 +160,7 @@ public abstract class AbstractNamedValueMethodArgumentResolver implements Handle
 	 */
 	private NamedValueInfo updateNamedValueInfo(MethodParameter parameter, NamedValueInfo info) {
 		String name = info.name;
-		if (info.name.length() == 0) {
+		if (info.name.isEmpty()) {
 			name = parameter.getParameterName();
 			if (name == null) {
 				throw new IllegalArgumentException(

spring-web/src/main/java/org/springframework/web/util/patterns/PathPattern.java

@@ -21,6 +21,7 @@ import java.util.HashMap;
 import java.util.Map;
 
 import org.springframework.util.PathMatcher;
+import static org.springframework.util.StringUtils.hasLength;
 
 /**
  * Represents a parsed path pattern. Includes a chain of path elements
@@ -132,9 +133,9 @@ public class PathPattern implements Comparable<PathPattern> {
 	 */
 	public boolean matches(String path) {
 		if (head == null) {
-			return (path == null) || (path.length() == 0);
+			return !hasLength(path);
 		}
-		else if (path == null || path.length() == 0) {
+		else if (!hasLength(path)) {
 			if (head instanceof WildcardTheRestPathElement || head instanceof CaptureTheRestPathElement) {
 				path = ""; // Will allow CaptureTheRest to bind the variable to empty
 			}
@@ -152,9 +153,9 @@ public class PathPattern implements Comparable<PathPattern> {
 	 */
 	public boolean matchStart(String path) {
 		if (head == null) {
-			return (path == null || path.length() == 0);
+			return !hasLength(path);
 		}
-		else if (path == null || path.length() == 0) {
+		else if (!hasLength(path)) {
 			return true;
 		}
 		MatchingContext matchingContext = new MatchingContext(path, false);
@@ -172,7 +173,7 @@ public class PathPattern implements Comparable<PathPattern> {
 			return matchingContext.getExtractedVariables();
 		}
 		else {
-			if (path == null || path.length() == 0) {
+			if (!hasLength(path)) {
 				return NO_VARIABLES_MAP;
 			}
 			else {
@@ -434,15 +435,15 @@ public class PathPattern implements Comparable<PathPattern> {
 	 */
 	public String combine(String pattern2string) {
 		// If one of them is empty the result is the other. If both empty the result is ""
-		if (patternString == null || patternString.length() == 0) {
-			if (pattern2string == null || pattern2string.length() == 0) {
+		if (!hasLength(patternString)) {
+			if (!hasLength(pattern2string)) {
 				return "";
 			}
 			else {
 				return pattern2string;
 			}
 		}
-		else if (pattern2string == null || pattern2string.length() == 0) {
+		else if (!hasLength(pattern2string)) {
 			return patternString;
 		}
 
@@ -504,4 +505,4 @@ public class PathPattern implements Comparable<PathPattern> {
 		}
 	}
 
-}
\ No newline at end of file
+}

spring-web/src/test/java/org/springframework/web/multipart/commons/CommonsMultipartResolverTests.java

 /*
- * 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.
@@ -258,13 +258,13 @@ public class CommonsMultipartResolverTests {
 		binder.setBindEmptyMultipartFiles(false);
 		String firstBound = mtb2.getField2();
 		binder.bind(request);
-		assertTrue(mtb2.getField2().length() > 0);
+		assertFalse(mtb2.getField2().isEmpty());
 		assertEquals(firstBound, mtb2.getField2());
 
 		request = resolver.resolveMultipart(originalRequest);
 		binder.setBindEmptyMultipartFiles(true);
 		binder.bind(request);
-		assertTrue(mtb2.getField2().length() == 0);
+		assertTrue(mtb2.getField2().isEmpty());
 	}
 
 	@Test

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

 /*
- * 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.
@@ -132,7 +132,7 @@ public abstract class AbstractNamedValueArgumentResolver implements HandlerMetho
 	 */
 	private NamedValueInfo updateNamedValueInfo(MethodParameter parameter, NamedValueInfo info) {
 		String name = info.name;
-		if (info.name.length() == 0) {
+		if (info.name.isEmpty()) {
 			name = parameter.getParameterName();
 			if (name == null) {
 				String type = parameter.getNestedParameterType().getName();

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/RequestPartMethodArgumentResolver.java

 /*
- * 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 class RequestPartMethodArgumentResolver extends AbstractMessageConverterM
 
 	private String getPartName(MethodParameter methodParam, RequestPart requestPart) {
 		String partName = (requestPart != null ? requestPart.name() : "");
-		if (partName.length() == 0) {
+		if (partName.isEmpty()) {
 			partName = methodParam.getParameterName();
 			if (partName == null) {
 				throw new IllegalArgumentException("Request part name for argument type [" +

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/SseEmitter.java

 /*
- * 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.
@@ -25,6 +25,7 @@ import java.util.Set;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.MediaType;
 import org.springframework.http.server.ServerHttpResponse;
+import org.springframework.util.StringUtils;
 
 /**
  * A specialization of {@link ResponseBodyEmitter} for sending
@@ -234,7 +235,7 @@ public class SseEmitter extends ResponseBodyEmitter {
 
 		@Override
 		public Set<DataWithMediaType> build() {
-			if ((this.sb == null || this.sb.length() == 0) && this.dataToSend.isEmpty()) {
+			if (!StringUtils.hasLength(this.sb) && this.dataToSend.isEmpty()) {
 				return Collections.emptySet();
 			}
 			append("\n");