Introduce getValueType(ValueEvaluationContext) to ValueExpression.

Closes #3169

Author: mp911de

src/main/java/org/springframework/data/expression/CompositeValueExpression.java

@@ -72,4 +72,10 @@ public String evaluate(ValueEvaluationContext context) {
 
 		return builder.toString();
 	}
+
+	@Override
+	public Class<?> getValueType(ValueEvaluationContext context) {
+		return String.class;
+	}
+
 }

src/main/java/org/springframework/data/expression/ExpressionExpression.java

@@ -47,9 +47,14 @@ public boolean isLiteral() {
 	public Object evaluate(ValueEvaluationContext context) {
 
 		EvaluationContext evaluationContext = context.getEvaluationContext();
-		if (evaluationContext != null) {
-			return expression.getValue(evaluationContext);
-		}
-		return expression.getValue();
+		return evaluationContext != null ? expression.getValue(evaluationContext) : expression.getValue();
 	}
+
+	@Override
+	public Class<?> getValueType(ValueEvaluationContext context) {
+
+		EvaluationContext evaluationContext = context.getEvaluationContext();
+		return evaluationContext != null ? expression.getValueType(evaluationContext) : expression.getValueType();
+	}
+
 }

src/main/java/org/springframework/data/expression/LiteralValueExpression.java

@@ -39,4 +39,9 @@ public String evaluate(ValueEvaluationContext context) {
 		return expression;
 	}
 
+	@Override
+	public Class<?> getValueType(ValueEvaluationContext context) {
+		return String.class;
+	}
+
 }

src/main/java/org/springframework/data/expression/PlaceholderExpression.java

@@ -38,7 +38,7 @@ public boolean isLiteral() {
 	}
 
 	@Override
-	public Object evaluate(ValueEvaluationContext context) {
+	public String evaluate(ValueEvaluationContext context) {
 
 		Environment environment = context.getEnvironment();
 		if (environment != null) {
@@ -51,4 +51,9 @@ public Object evaluate(ValueEvaluationContext context) {
 		return expression;
 	}
 
+	@Override
+	public Class<?> getValueType(ValueEvaluationContext context) {
+		return String.class;
+	}
+
 }

src/main/java/org/springframework/data/expression/ValueExpression.java

@@ -62,4 +62,15 @@ default ExpressionDependencies getExpressionDependencies() {
 	@Nullable
 	Object evaluate(ValueEvaluationContext context) throws EvaluationException;
 
+	/**
+	 * Return the most general type that the expression would use as return type for the given context.
+	 *
+	 * @param context the context in which to evaluate the expression.
+	 * @return the most general type of value.
+	 * @throws EvaluationException if there is a problem determining the type
+	 * @since 3.4
+	 */
+	@Nullable
+	Class<?> getValueType(ValueEvaluationContext context) throws EvaluationException;
+
 }

src/test/java/org/springframework/data/expression/ValueEvaluationUnitTests.java

@@ -19,6 +19,7 @@
 
 import java.util.Map;
 
+import org.jetbrains.annotations.Nullable;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
@@ -38,6 +39,7 @@
  */
 public class ValueEvaluationUnitTests {
 
+	private ValueExpressionParser parser = ValueExpressionParser.create();
 	private ValueEvaluationContext evaluationContext;
 
 	@BeforeEach
@@ -47,6 +49,10 @@ void setUp() {
 		StandardEnvironment environment = new StandardEnvironment();
 		environment.getPropertySources().addFirst(propertySource);
 
+		record MyRecord(String foo, @org.springframework.lang.Nullable String bar) {
+
+		}
+
 		this.evaluationContext = new ValueEvaluationContext() {
 			@Override
 			public Environment getEnvironment() {
@@ -57,6 +63,8 @@ public Environment getEnvironment() {
 			public EvaluationContext getEvaluationContext() {
 				StandardEvaluationContext context = new StandardEvaluationContext();
 				context.setVariable("contextVar", "contextVal");
+				context.setVariable("nullVar", null);
+				context.setVariable("someRecord", new MyRecord("foo", null));
 
 				return context;
 			}
@@ -82,6 +90,20 @@ void shouldParseAndEvaluateExpressions() {
 				.withMessageContaining("Could not resolve placeholder 'env.does.not.exist'");
 	}
 
+	@Test // GH-3169
+	void shouldReturnValueType() {
+
+		assertThat(getValueType("foo")).isEqualTo(String.class);
+		assertThat(getValueType("${env.key.one}")).isEqualTo(String.class);
+		assertThat(getValueType("#{'foo'}")).isEqualTo(String.class);
+		assertThat(getValueType("#{1+1}")).isEqualTo(Integer.class);
+		assertThat(getValueType("#{null}")).isNull();
+		assertThat(getValueType("#{#contextVar}")).isEqualTo(String.class);
+		assertThat(getValueType("#{#nullVar}")).isNull();
+		assertThat(getValueType("#{#someRecord.foo}")).isEqualTo(String.class);
+		assertThat(getValueType("#{#someRecord.bar}")).isEqualTo(String.class);
+	}
+
 	@Test // GH-2369
 	void shouldParseLiteral() {
 
@@ -128,10 +150,14 @@ void shouldParseQuoted() {
 		assertThat(eval("#{(1+1) + \"-foo'}\" + '-bar}'}")).isEqualTo("2-foo'}-bar}");
 	}
 
+	@SuppressWarnings("DataFlowIssue")
 	private String eval(String expressionString) {
-
-		ValueExpressionParser parser = ValueExpressionParser.create();
 		return (String) parser.parse(expressionString).evaluate(evaluationContext);
 	}
 
+	@Nullable
+	private Class<?> getValueType(String expressionString) {
+		return parser.parse(expressionString).getValueType(evaluationContext);
+	}
+
 }