Reuse parsed expression instead of reparsing it on every invocation.

Signed-off-by: Dominique Villard <[email protected]>

Author: doumdoum

spring-boot-project/spring-boot-observation/src/main/java/org/springframework/boot/observation/autoconfigure/SpelValueExpressionResolver.java

@@ -16,10 +16,12 @@
 
 package org.springframework.boot.observation.autoconfigure;
 
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
 import io.micrometer.common.annotation.ValueExpressionResolver;
 
 import org.springframework.expression.Expression;
-import org.springframework.expression.ExpressionParser;
 import org.springframework.expression.spel.standard.SpelExpressionParser;
 import org.springframework.expression.spel.support.SimpleEvaluationContext;
 
@@ -30,17 +32,23 @@
  */
 class SpelValueExpressionResolver implements ValueExpressionResolver {
 
+	private final Map<String, Expression> expressionMap = new ConcurrentHashMap<>();
+
 	@Override
 	public String resolve(String expression, Object parameter) {
 		try {
 			SimpleEvaluationContext context = SimpleEvaluationContext.forReadOnlyDataBinding().build();
-			ExpressionParser expressionParser = new SpelExpressionParser();
-			Expression expressionToEvaluate = expressionParser.parseExpression(expression);
-			return expressionToEvaluate.getValue(context, parameter, String.class);
+			Expression parsedExpression = this.expressionMap.computeIfAbsent(expression,
+					SpelValueExpressionResolver::parseExpression);
+			return parsedExpression.getValue(context, parameter, String.class);
 		}
 		catch (Exception ex) {
 			throw new IllegalStateException("Unable to evaluate SpEL expression '%s'".formatted(expression), ex);
 		}
 	}
 
+	private static Expression parseExpression(String expression) {
+		return new SpelExpressionParser().parseExpression(expression);
+	}
+
 }

spring-boot-project/spring-boot-observation/src/test/java/org/springframework/boot/observation/autoconfigure/SpelValueExpressionResolverTests.java

@@ -20,6 +20,8 @@
 
 import org.junit.jupiter.api.Test;
 
+import org.springframework.test.util.ReflectionTestUtils;
+
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatIllegalStateException;
 
@@ -44,6 +46,19 @@ void checkInvalidExpression() {
 		assertThatIllegalStateException().isThrownBy(() -> this.resolver.resolve("['bar'].first", value));
 	}
 
+	@Test
+	void checkParserReuse() {
+		var map = (Map<?, ?>) ReflectionTestUtils.getField(this.resolver, "expressionMap");
+
+		this.resolver.resolve("length", "foo");
+		this.resolver.resolve("length", "bar");
+
+		assertThat(map).hasSize(1);
+
+		this.resolver.resolve("isEmpty", "foo");
+		assertThat(map).hasSize(2);
+	}
+
 	record Pair(int first, int second) {
 
 		static Pair of(int first, int second) {