Test status quo for Optional support in SpEL expressions

This is a prerequisite for null-safe Optional support.

See gh-20433

Author: sbrannen

Diff for: spring-expression/src/test/java/org/springframework/expression/spel/OptionalNullSafetyTests.java

@@ -0,0 +1,250 @@
+/*
+ * Copyright 2002-2025 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.expression.spel;
+
+import java.util.List;
+import java.util.Optional;
+
+import org.jspecify.annotations.Nullable;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Nested;
+import org.junit.jupiter.api.Test;
+
+import org.springframework.expression.Expression;
+import org.springframework.expression.spel.standard.SpelExpressionParser;
+import org.springframework.expression.spel.support.StandardEvaluationContext;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
+import static org.springframework.expression.spel.SpelMessage.PROPERTY_OR_FIELD_NOT_READABLE;
+import static org.springframework.expression.spel.SpelMessage.PROPERTY_OR_FIELD_NOT_READABLE_ON_NULL;
+
+/**
+ * Tests which verify support for using {@link Optional} with the null-safe and
+ * Elvis operators in SpEL expressions.
+ *
+ * @author Sam Brannen
+ * @since 7.0
+ */
+class OptionalNullSafetyTests {
+
+	private final SpelExpressionParser parser = new SpelExpressionParser();
+
+	private final StandardEvaluationContext context = new StandardEvaluationContext();
+
+
+	@BeforeEach
+	void setUpContext() {
+		context.setVariable("service", new Service());
+	}
+
+
+	/**
+	 * Tests for the status quo when using {@link Optional} in SpEL expressions,
+	 * before explicit null-safe support was added in 7.0.
+	 */
+	@Nested
+	class LegacyOptionalTests {
+
+		@Test
+		void accessPropertyOnNullOptional() {
+			Expression expr = parser.parseExpression("#service.findJediByName(null).empty");
+
+			assertThatExceptionOfType(SpelEvaluationException.class)
+					.isThrownBy(() -> expr.getValue(context))
+					.satisfies(ex -> {
+						assertThat(ex.getMessageCode()).isEqualTo(PROPERTY_OR_FIELD_NOT_READABLE_ON_NULL);
+						assertThat(ex).hasMessageContaining("Property or field 'empty' cannot be found on null");
+					});
+		}
+
+		@Test
+		void accessPropertyOnNullOptionalViaNullSafeOperator() {
+			Expression expr = parser.parseExpression("#service.findJediByName(null)?.empty");
+
+			assertThat(expr.getValue(context)).isNull();
+		}
+
+		@Test
+		void invokeMethodOnNullOptionalViaNullSafeOperator() {
+			Expression expr = parser.parseExpression("#service.findJediByName(null)?.salutation('Master')");
+
+			assertThat(expr.getValue(context)).isNull();
+		}
+
+		@Test
+		void accessIndexOnNullOptionalViaNullSafeOperator() {
+			Expression expr = parser.parseExpression("#service.findFruitsByColor(null)?.[1]");
+
+			assertThat(expr.getValue(context)).isNull();
+		}
+
+		@Test
+		void projectionOnNullOptionalViaNullSafeOperator() {
+			Expression expr = parser.parseExpression("#service.findFruitsByColor(null)?.![#this.length]");
+
+			assertThat(expr.getValue(context)).isNull();
+		}
+
+		@Test
+		void selectAllOnNullOptionalViaNullSafeOperator() {
+			Expression expr = parser.parseExpression("#service.findFruitsByColor(null)?.?[#this.length > 5]");
+
+			assertThat(expr.getValue(context)).isNull();
+		}
+
+		@Test
+		void selectFirstOnNullOptionalViaNullSafeOperator() {
+			Expression expr = parser.parseExpression("#service.findFruitsByColor(null)?.^[#this.length > 5]");
+
+			assertThat(expr.getValue(context)).isNull();
+		}
+
+		@Test
+		void selectLastOnNullOptionalViaNullSafeOperator() {
+			Expression expr = parser.parseExpression("#service.findFruitsByColor(null)?.$[#this.length > 5]");
+
+			assertThat(expr.getValue(context)).isNull();
+		}
+
+		@Test
+		void elvisOperatorOnNullOptional() {
+			Expression expr = parser.parseExpression("#service.findJediByName(null) ?: 'unknown'");
+
+			assertThat(expr.getValue(context)).isEqualTo("unknown");
+		}
+
+		@Test
+		void accessNonexistentPropertyOnEmptyOptional() {
+			assertPropertyNotReadable("#service.findJediByName('').name");
+		}
+
+		@Test
+		void accessNonexistentPropertyOnNonEmptyOptional() {
+			assertPropertyNotReadable("#service.findJediByName('Yoda').name");
+		}
+
+		@Test
+		void accessOptionalPropertyOnEmptyOptional() {
+			Expression expr = parser.parseExpression("#service.findJediByName('').present");
+
+			assertThat(expr.getValue(context, Boolean.class)).isFalse();
+		}
+
+		@Test
+		void accessOptionalPropertyOnEmptyOptionalViaNullSafeOperator() {
+			Expression expr = parser.parseExpression("#service.findJediByName('')?.present");
+
+			// Invoke multiple times to ensure there are no caching issues.
+			assertThat(expr.getValue(context, Boolean.class)).isFalse();
+			assertThat(expr.getValue(context, Boolean.class)).isFalse();
+		}
+
+		@Test
+		void accessOptionalPropertyOnNonEmptyOptional() {
+			Expression expr = parser.parseExpression("#service.findJediByName('Yoda').present");
+
+			assertThat(expr.getValue(context, Boolean.class)).isTrue();
+		}
+
+		@Test
+		void accessOptionalPropertyOnNonEmptyOptionalViaNullSafeOperator() {
+			Expression expr = parser.parseExpression("#service.findJediByName('Yoda')?.present");
+
+			// Invoke multiple times to ensure there are no caching issues.
+			assertThat(expr.getValue(context, Boolean.class)).isTrue();
+			assertThat(expr.getValue(context, Boolean.class)).isTrue();
+		}
+
+		@Test
+		void invokeOptionalMethodOnEmptyOptional() {
+			Expression expr = parser.parseExpression("#service.findJediByName('').orElse('Luke')");
+
+			assertThat(expr.getValue(context)).isEqualTo("Luke");
+		}
+
+		@Test
+		void invokeOptionalMethodOnEmptyOptionalViaNullSafeOperator() {
+			Expression expr = parser.parseExpression("#service.findJediByName('')?.orElse('Luke')");
+
+			// Invoke multiple times to ensure there are no caching issues.
+			assertThat(expr.getValue(context)).isEqualTo("Luke");
+			assertThat(expr.getValue(context)).isEqualTo("Luke");
+		}
+
+		@Test
+		void invokeOptionalMethodOnNonEmptyOptional() {
+			Expression expr = parser.parseExpression("#service.findJediByName('Yoda').orElse('Luke')");
+
+			assertThat(expr.getValue(context)).isEqualTo(new Jedi("Yoda"));
+		}
+
+		@Test
+		void invokeOptionalMethodOnNonEmptyOptionalViaNullSafeOperator() {
+			Expression expr = parser.parseExpression("#service.findJediByName('Yoda')?.orElse('Luke')");
+
+			// Invoke multiple times to ensure there are no caching issues.
+			assertThat(expr.getValue(context)).isEqualTo(new Jedi("Yoda"));
+			assertThat(expr.getValue(context)).isEqualTo(new Jedi("Yoda"));
+		}
+
+		private void assertPropertyNotReadable(String expression) {
+			Expression expr = parser.parseExpression(expression);
+
+			assertThatExceptionOfType(SpelEvaluationException.class)
+					.isThrownBy(() -> expr.getValue(context))
+					.satisfies(ex -> {
+						assertThat(ex.getMessageCode()).isEqualTo(PROPERTY_OR_FIELD_NOT_READABLE);
+						assertThat(ex).hasMessageContaining("Property or field 'name' cannot be found on object of type 'java.util.Optional'");
+					});
+		}
+
+	}
+
+
+	record Jedi(String name) {
+
+		public String salutation(String salutation) {
+			return salutation + " " + this.name;
+		}
+	}
+
+	static class Service {
+
+		public Optional<Jedi> findJediByName(@Nullable String name) {
+			if (name == null) {
+				return null;
+			}
+			if (name.isEmpty()) {
+				return Optional.empty();
+			}
+			return Optional.of(new Jedi(name));
+		}
+
+		public Optional<List<String>> findFruitsByColor(@Nullable String color) {
+			if (color == null) {
+				return null;
+			}
+			if (color.isEmpty()) {
+				return Optional.empty();
+			}
+			return Optional.of(List.of("banana", "lemon", "mango", "pineapple"));
+		}
+
+	}
+
+}