CollectionUtils.lastElement for common Set/List extraction

Issue: SPR-16374

Author: jhoeller

spring-context/src/main/java/org/springframework/context/annotation/ConfigurationClassParser.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -712,8 +712,7 @@ public void registerImport(AnnotationMetadata importingClass, String importedCla
 		@Override
 		@Nullable
 		public AnnotationMetadata getImportingClassFor(String importedClass) {
-			List<AnnotationMetadata> list = this.imports.get(importedClass);
-			return (!CollectionUtils.isEmpty(list) ? list.get(list.size() - 1) : null);
+			return CollectionUtils.lastElement(this.imports.get(importedClass));
 		}
 
 		@Override

spring-core/src/main/java/org/springframework/core/env/JOptCommandLinePropertySource.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -24,6 +24,8 @@
 import joptsimple.OptionSpec;
 
 import org.springframework.lang.Nullable;
+import org.springframework.util.CollectionUtils;
+import org.springframework.util.StringUtils;
 
 /**
  * {@link CommandLinePropertySource} implementation backed by a JOpt {@link OptionSet}.
@@ -86,13 +88,13 @@ protected boolean containsOption(String name) {
 	public String[] getPropertyNames() {
 		List<String> names = new ArrayList<>();
 		for (OptionSpec<?> spec : this.source.specs()) {
-			List<String> aliases = new ArrayList<>(spec.options());
-			if (!aliases.isEmpty()) {
+			String lastOption = CollectionUtils.lastElement(spec.options());
+			if (lastOption != null) {
 				// Only the longest name is used for enumerating
-				names.add(aliases.get(aliases.size() - 1));
+				names.add(lastOption);
 			}
 		}
-		return names.toArray(new String[names.size()]);
+		return StringUtils.toStringArray(names);
 	}
 
 	@Override

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -29,6 +29,7 @@
 import java.util.Map;
 import java.util.Properties;
 import java.util.Set;
+import java.util.SortedSet;
 
 import org.springframework.lang.Nullable;
 
@@ -312,6 +313,48 @@ else if (candidate != val.getClass()) {
 		return candidate;
 	}
 
+	/**
+	 * Retrieve the last element of the given Set, using {@link SortedSet#last()}
+	 * or otherwise iterating over all elements (assuming a linked set).
+	 * @param set the Set to check (may be {@code null} or empty)
+	 * @return the last element, or {@code null} if none
+	 * @since 5.0.3
+	 * @see SortedSet
+	 * @see LinkedHashMap#keySet()
+	 * @see java.util.LinkedHashSet
+	 */
+	@Nullable
+	public static <T> T lastElement(@Nullable Set<T> set) {
+		if (isEmpty(set)) {
+			return null;
+		}
+		if (set instanceof SortedSet) {
+			return ((SortedSet<T>) set).last();
+		}
+
+		// Full iteration necessary...
+		Iterator<T> it = set.iterator();
+		T last = null;
+		while (it.hasNext()) {
+			last = it.next();
+		}
+		return last;
+	}
+
+	/**
+	 * Retrieve the last element of the given List, accessing the highest index.
+	 * @param list the List to check (may be {@code null} or empty)
+	 * @return the last element, or {@code null} if none
+	 * @since 5.0.3
+	 */
+	@Nullable
+	public static <T> T lastElement(@Nullable List<T> list) {
+		if (isEmpty(list)) {
+			return null;
+		}
+		return list.get(list.size() - 1);
+	}
+
 	/**
 	 * Marshal the elements from the given enumeration into an array of the given type.
 	 * Enumeration elements must be assignable to the type of the given array. The array

spring-expression/src/main/java/org/springframework/expression/spel/CodeFlow.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -26,6 +26,7 @@
 import org.springframework.asm.MethodVisitor;
 import org.springframework.asm.Opcodes;
 import org.springframework.lang.Nullable;
+import org.springframework.util.CollectionUtils;
 
 /**
  * Manages the class being generated by the compilation process.
@@ -153,10 +154,7 @@ public void exitCompilationScope() {
 	 */
 	@Nullable
 	public String lastDescriptor() {
-		if (this.compilationScopes.peek().isEmpty()) {
-			return null;
-		}
-		return this.compilationScopes.peek().get(this.compilationScopes.peek().size() - 1);
+		return CollectionUtils.lastElement(this.compilationScopes.peek());
 	}
 
 	/**

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -31,6 +31,7 @@
 import org.springframework.expression.spel.SpelMessage;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
+import org.springframework.util.CollectionUtils;
 import org.springframework.util.ObjectUtils;
 
 /**
@@ -160,7 +161,7 @@ protected ValueRef getValueRef(ExpressionState state) throws EvaluationException
 			}
 
 			if (this.variant == LAST) {
-				return new ValueRef.TypedValueHolderValueRef(new TypedValue(result.get(result.size() - 1)), this);
+				return new ValueRef.TypedValueHolderValueRef(new TypedValue(CollectionUtils.lastElement(result)), this);
 			}
 
 			if (operand instanceof Iterable) {

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -16,12 +16,11 @@
 
 package org.springframework.web.method.annotation;
 
-import java.util.ArrayList;
-
 import org.springframework.core.MethodParameter;
 import org.springframework.lang.Nullable;
 import org.springframework.ui.ModelMap;
 import org.springframework.util.Assert;
+import org.springframework.util.CollectionUtils;
 import org.springframework.validation.BindingResult;
 import org.springframework.validation.Errors;
 import org.springframework.web.bind.support.WebDataBinderFactory;
@@ -38,6 +37,7 @@
  * {@link BindingResult}.
  *
  * @author Rossen Stoyanchev
+ * @author Juergen Hoeller
  * @since 3.1
  */
 public class ErrorsMethodArgumentResolver implements HandlerMethodArgumentResolver {
@@ -58,18 +58,15 @@ public Object resolveArgument(MethodParameter parameter,
 				"Errors/BindingResult argument only supported on regular handler methods");
 
 		ModelMap model = mavContainer.getModel();
-		if (model.size() > 0) {
-			int lastIndex = model.size()-1;
-			String lastKey = new ArrayList<>(model.keySet()).get(lastIndex);
-			if (lastKey.startsWith(BindingResult.MODEL_KEY_PREFIX)) {
-				return model.get(lastKey);
-			}
+		String lastKey = CollectionUtils.lastElement(model.keySet());
+		if (lastKey != null && lastKey.startsWith(BindingResult.MODEL_KEY_PREFIX)) {
+			return model.get(lastKey);
 		}
 
 		throw new IllegalStateException(
 				"An Errors/BindingResult argument is expected to be declared immediately after " +
-						"the model attribute, the @RequestBody or the @RequestPart arguments " +
-						"to which they apply: " + parameter.getMethod());
+				"the model attribute, the @RequestBody or the @RequestPart arguments " +
+				"to which they apply: " + parameter.getMethod());
 	}
 
 }

spring-web/src/test/java/org/springframework/web/method/annotation/ErrorsMethodHandlerArgumentResolverTests.java renamed to spring-web/src/test/java/org/springframework/web/method/annotation/ErrorsMethodArgumentResolverTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -35,7 +35,7 @@
  *
  * @author Rossen Stoyanchev
  */
-public class ErrorsMethodHandlerArgumentResolverTests {
+public class ErrorsMethodArgumentResolverTests {
 
 	private final ErrorsMethodArgumentResolver resolver = new ErrorsMethodArgumentResolver();
 
@@ -45,15 +45,17 @@ public class ErrorsMethodHandlerArgumentResolverTests {
 
 	private NativeWebRequest webRequest;
 
+
 	@Before
-	public void setUp() throws Exception {
+	public void setup() throws Exception {
 		paramErrors = new MethodParameter(getClass().getDeclaredMethod("handle", Errors.class), 0);
 		bindingResult = new WebDataBinder(new Object(), "attr").getBindingResult();
 		webRequest = new ServletWebRequest(new MockHttpServletRequest());
 	}
 
+
 	@Test
-	public void supports() throws Exception {
+	public void supports() {
 		resolver.supportsParameter(paramErrors);
 	}
 
@@ -68,7 +70,6 @@ public void bindingResult() throws Exception {
 		mavContainer.addAllAttributes(bindingResult.getModel());
 
 		Object actual = resolver.resolveArgument(paramErrors, mavContainer, webRequest, null);
-
 		assertSame(actual, bindingResult);
 	}
 
@@ -86,8 +87,9 @@ public void noBindingResult() throws Exception {
 		resolver.resolveArgument(paramErrors, new ModelAndViewContainer(), webRequest, null);
 	}
 
+
 	@SuppressWarnings("unused")
 	private void handle(Errors errors) {
 	}
 
-}
+}