Consistent use of StringUtils.hasLength(String) vs isEmpty(Object)

Author: jhoeller

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

@@ -75,15 +75,20 @@ public abstract class StringUtils {
 	//---------------------------------------------------------------------
 
 	/**
-	 * Check whether the given {@code String} is empty.
+	 * Check whether the given object (possibly a {@code String}) is empty.
+	 * This is effectly a shortcut for {@code !hasLength(String)}.
 	 * <p>This method accepts any Object as an argument, comparing it to
 	 * {@code null} and the empty String. As a consequence, this method
 	 * will never return {@code true} for a non-null non-String object.
 	 * <p>The Object signature is useful for general attribute handling code
 	 * that commonly deals with Strings but generally has to iterate over
 	 * Objects since attributes may e.g. be primitive value objects as well.
-	 * @param str the candidate String
+	 * <p><b>Note: If the object is typed to {@code String} upfront, prefer
+	 * {@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)
 	 */
 	public static boolean isEmpty(@Nullable Object str) {
 		return (str == null || "".equals(str));
@@ -102,7 +107,8 @@ public static boolean isEmpty(@Nullable Object str) {
 	 * </pre>
 	 * @param str the {@code CharSequence} to check (may be {@code null})
 	 * @return {@code true} if the {@code CharSequence} is not {@code null} and has length
-	 * @see #hasText(String)
+	 * @see #hasLength(String)
+	 * @see #hasText(CharSequence)
 	 */
 	public static boolean hasLength(@Nullable CharSequence str) {
 		return (str != null && str.length() > 0);
@@ -136,6 +142,8 @@ public static boolean hasLength(@Nullable String str) {
 	 * @param str the {@code CharSequence} to check (may be {@code null})
 	 * @return {@code true} if the {@code CharSequence} is not {@code null},
 	 * its length is greater than 0, and it does not contain whitespace only
+	 * @see #hasText(String)
+	 * @see #hasLength(CharSequence)
 	 * @see Character#isWhitespace
 	 */
 	public static boolean hasText(@Nullable CharSequence str) {
@@ -151,6 +159,8 @@ public static boolean hasText(@Nullable CharSequence str) {
 	 * @return {@code true} if the {@code String} is not {@code null}, its
 	 * length is greater than 0, and it does not contain whitespace only
 	 * @see #hasText(CharSequence)
+	 * @see #hasLength(String)
+	 * @see Character#isWhitespace
 	 */
 	public static boolean hasText(@Nullable String str) {
 		return (str != null && !str.isEmpty() && containsText(str));

spring-jdbc/src/main/java/org/springframework/jdbc/core/JdbcTemplate.java

@@ -576,7 +576,7 @@ public int[] doInStatement(Statement stmt) throws SQLException, DataAccessExcept
 			}
 
 			private String appendSql(@Nullable String sql, String statement) {
-				return (StringUtils.isEmpty(sql) ? statement : sql + "; " + statement);
+				return (StringUtils.hasLength(sql) ? sql + "; " + statement : statement);
 			}
 
 			@Override

spring-web/src/main/java/org/springframework/http/HttpHeaders.java

@@ -699,7 +699,7 @@ public void setAllow(Set<HttpMethod> allowedMethods) {
 	 */
 	public Set<HttpMethod> getAllow() {
 		String value = getFirst(ALLOW);
-		if (!StringUtils.isEmpty(value)) {
+		if (StringUtils.hasLength(value)) {
 			String[] tokens = StringUtils.tokenizeToStringArray(value, ",");
 			List<HttpMethod> result = new ArrayList<>(tokens.length);
 			for (String token : tokens) {

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

@@ -74,7 +74,7 @@ private static URI initUri(HttpServerExchange exchange) throws URISyntaxExceptio
 		Assert.notNull(exchange, "HttpServerExchange is required.");
 		String requestURL = exchange.getRequestURL();
 		String query = exchange.getQueryString();
-		String requestUriAndQuery = StringUtils.isEmpty(query) ? requestURL : requestURL + "?" + query;
+		String requestUriAndQuery = (StringUtils.hasLength(query) ? requestURL + "?" + query : requestURL);
 		return new URI(requestUriAndQuery);
 	}
 

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 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.
@@ -213,8 +213,8 @@ public void contributeMethodArgument(MethodParameter parameter, @Nullable Object
 		}
 
 		RequestParam requestParam = parameter.getParameterAnnotation(RequestParam.class);
-		String name = (requestParam == null || StringUtils.isEmpty(requestParam.name()) ?
-				parameter.getParameterName() : requestParam.name());
+		String name = (requestParam != null && StringUtils.hasLength(requestParam.name()) ?
+				requestParam.name() : parameter.getParameterName());
 		Assert.state(name != null, "Unresolvable parameter name");
 
 		if (value == null) {

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 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.
@@ -33,7 +33,6 @@
  * <p>Provides options to create {@link UriBuilder} instances with a common
  * base URI, alternative encoding mode strategies, among others.
  *
- *
  * @author Rossen Stoyanchev
  * @since 5.0
  * @see UriComponentsBuilder
@@ -222,31 +221,27 @@ private class DefaultUriBuilder implements UriBuilder {
 
 		private final UriComponentsBuilder uriComponentsBuilder;
 
-
 		public DefaultUriBuilder(String uriTemplate) {
 			this.uriComponentsBuilder = initUriComponentsBuilder(uriTemplate);
 		}
 
 		private UriComponentsBuilder initUriComponentsBuilder(String uriTemplate) {
 			UriComponentsBuilder result;
-			if (StringUtils.isEmpty(uriTemplate)) {
-				result = baseUri != null ? baseUri.cloneBuilder() : UriComponentsBuilder.newInstance();
+			if (!StringUtils.hasLength(uriTemplate)) {
+				result = (baseUri != null ? baseUri.cloneBuilder() : UriComponentsBuilder.newInstance());
 			}
 			else if (baseUri != null) {
 				UriComponentsBuilder builder = UriComponentsBuilder.fromUriString(uriTemplate);
 				UriComponents uri = builder.build();
-				result = uri.getHost() == null ? baseUri.cloneBuilder().uriComponents(uri) : builder;
+				result = (uri.getHost() == null ? baseUri.cloneBuilder().uriComponents(uri) : builder);
 			}
 			else {
 				result = UriComponentsBuilder.fromUriString(uriTemplate);
 			}
-
 			if (encodingMode.equals(EncodingMode.TEMPLATE_AND_VALUES)) {
 				result.encode();
 			}
-
 			parsePathIfNecessary(result);
-
 			return result;
 		}
 

spring-webflux/src/main/java/org/springframework/web/reactive/resource/VersionResourceResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 the original author or authors.
+ * Copyright 2002-2019 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.
@@ -172,7 +172,7 @@ private Mono<Resource> resolveVersionedResource(@Nullable ServerWebExchange exch
 		}
 
 		String candidate = versionStrategy.extractVersion(requestPath);
-		if (StringUtils.isEmpty(candidate)) {
+		if (!StringUtils.hasLength(candidate)) {
 			return Mono.empty();
 		}
 

spring-webflux/src/main/java/org/springframework/web/reactive/result/view/RedirectView.java

@@ -309,7 +309,7 @@ protected boolean isRemoteHost(String targetUrl) {
 			return false;
 		}
 		String targetHost = UriComponentsBuilder.fromUriString(targetUrl).build().getHost();
-		if (StringUtils.isEmpty(targetHost)) {
+		if (!StringUtils.hasLength(targetHost)) {
 			return false;
 		}
 		for (String host : this.hosts) {

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

@@ -963,11 +963,12 @@ private void logRequest(HttpServletRequest request) {
 				params = (request.getParameterMap().isEmpty() ? "" : "masked");
 			}
 
-			String query = StringUtils.isEmpty(request.getQueryString()) ? "" : "?" + request.getQueryString();
+			String queryString = request.getQueryString();
+			String queryClause = (StringUtils.hasLength(queryString) ? "?" + queryString : "");
 			String dispatchType = (!request.getDispatcherType().equals(DispatcherType.REQUEST) ?
 					"\"" + request.getDispatcherType().name() + "\" dispatch for " : "");
 			String message = (dispatchType + request.getMethod() + " \"" + getRequestUri(request) +
-					query + "\", parameters={" + params + "}");
+					queryClause + "\", parameters={" + params + "}");
 
 			if (traceOn) {
 				List<String> values = Collections.list(request.getHeaderNames());

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

@@ -100,16 +100,17 @@ public void setMappedHandlerClasses(Class<?>... mappedHandlerClasses) {
 	/**
 	 * Set the log category for warn logging. The name will be passed to the underlying logger
 	 * implementation through Commons Logging, getting interpreted as a log category according
-	 * to the logger's configuration. If {@code null} is passed, warn logging is turned off.
-	 * <p>By default there is no warn logging although sub-classes like
+	 * to the logger's configuration. If {@code null} or empty String is passed, warn logging
+	 * is turned off.
+	 * <p>By default there is no warn logging although subclasses like
 	 * {@link org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver}
 	 * can change that default. Specify this setting to activate warn logging into a specific
 	 * category. Alternatively, override the {@link #logException} method for custom logging.
 	 * @see org.apache.commons.logging.LogFactory#getLog(String)
 	 * @see java.util.logging.Logger#getLogger(String)
 	 */
 	public void setWarnLogCategory(String loggerName) {
-		this.warnLogger = (!StringUtils.isEmpty(loggerName) ? LogFactory.getLog(loggerName) : null);
+		this.warnLogger = (StringUtils.hasLength(loggerName) ? LogFactory.getLog(loggerName) : null);
 	}
 
 	/**