PromptTemplate: Parameterized render(Map) fails to handle Resource in this.variables (inconsistent with no-arg render)

Signed-off-by: lance <leehaut@gmail.com>

Author: leehaut

spring-ai-model/src/main/java/org/springframework/ai/chat/prompt/PromptTemplate.java

@@ -111,8 +111,8 @@ public String render() {
 		// Process internal variables to handle Resources before rendering
 		Map<String, Object> processedVariables = new HashMap<>();
 		for (Entry<String, Object> entry : this.variables.entrySet()) {
-			if (entry.getValue() instanceof Resource) {
-				processedVariables.put(entry.getKey(), renderResource((Resource) entry.getValue()));
+			if (entry.getValue() instanceof Resource resource) {
+				processedVariables.put(entry.getKey(), renderResource(resource));
 			}
 			else {
 				processedVariables.put(entry.getKey(), entry.getValue());
@@ -123,11 +123,16 @@ public String render() {
 
 	@Override
 	public String render(Map<String, Object> additionalVariables) {
-		Map<String, Object> combinedVariables = new HashMap<>(this.variables);
+		Map<String, Object> combinedVariables = new HashMap<>();
+		Map<String, Object> mergedVariables = new HashMap<>(this.variables);
+		// variables + additionalVariables => mergedVariables
+		if (additionalVariables != null && !additionalVariables.isEmpty()) {
+			mergedVariables.putAll(additionalVariables);
+		}
 
-		for (Entry<String, Object> entry : additionalVariables.entrySet()) {
-			if (entry.getValue() instanceof Resource) {
-				combinedVariables.put(entry.getKey(), renderResource((Resource) entry.getValue()));
+		for (Entry<String, Object> entry : mergedVariables.entrySet()) {
+			if (entry.getValue() instanceof Resource resource) {
+				combinedVariables.put(entry.getKey(), renderResource(resource));
 			}
 			else {
 				combinedVariables.put(entry.getKey(), entry.getValue());

spring-ai-model/src/test/java/org/springframework/ai/chat/prompt/PromptTemplateTests.java

@@ -26,6 +26,7 @@
 import org.springframework.ai.template.NoOpTemplateRenderer;
 import org.springframework.ai.template.TemplateRenderer;
 import org.springframework.core.io.ByteArrayResource;
+import org.springframework.core.io.ClassPathResource;
 import org.springframework.core.io.Resource;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -306,6 +307,19 @@ void resource_Builder() {
 		assertThat(promptTemplate.render()).isEqualTo("Hello Builder from Resource!");
 	}
 
+	@Test
+	void renderWithResourceFile() {
+		Resource resource = new ClassPathResource("prompt-user.txt");
+
+		// Build PromptTemplate: bind the Resource to "name" in this.variables
+		PromptTemplate promptTemplate = PromptTemplate.builder()
+			.template("How {name}")
+			.variables(Map.of("name", resource))
+			.build();
+
+		assertThat(promptTemplate.render(Map.of())).isEqualTo("How Hello, world!");
+	}
+
 	// Helper Custom Renderer for testing
 	private static class CustomTestRenderer implements TemplateRenderer {