GH-4251 Add the capability to parse required variables from templates to TemplateRenderer

spring-ai-commons/src/main/java/org/springframework/ai/template/NoOpTemplateRenderer.java

@@ -17,6 +17,7 @@
 package org.springframework.ai.template;
 
 import java.util.Map;
+import java.util.Set;
 
 import org.springframework.util.Assert;
 
@@ -36,4 +37,9 @@ public String apply(String template, Map<String, Object> variables) {
 		return template;
 	}
 
+	@Override
+	public Set<String> getRequiredVariables(String template) {
+		return Set.of();
+	}
+
 }

spring-ai-commons/src/main/java/org/springframework/ai/template/TemplateRenderer.java

@@ -17,17 +17,21 @@
 package org.springframework.ai.template;
 
 import java.util.Map;
+import java.util.Set;
 import java.util.function.BiFunction;
 
 /**
  * Renders a template using a given strategy.
  *
  * @author Thomas Vitale
+ * @author Sun Yuhan
  * @since 1.0.0
  */
 public interface TemplateRenderer extends BiFunction<String, Map<String, Object>, String> {
 
 	@Override
 	String apply(String template, Map<String, Object> variables);
 
+	Set<String> getRequiredVariables(String template);
+
 }

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

@@ -18,6 +18,7 @@
 
 import java.util.HashMap;
 import java.util.Map;
+import java.util.Set;
 
 import org.junit.jupiter.api.Test;
 
@@ -316,6 +317,11 @@ public String apply(String template, Map<String, Object> model) {
 			return template + " (Rendered by Custom)";
 		}
 
+		@Override
+		public Set<String> getRequiredVariables(String template) {
+			return Set.of();
+		}
+
 	}
 
 }

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

@@ -18,6 +18,7 @@
 
 import java.util.HashMap;
 import java.util.Map;
+import java.util.Set;
 
 import org.junit.jupiter.api.Test;
 
@@ -325,6 +326,11 @@ public String apply(String template, Map<String, Object> model) {
 			return template + " (Rendered by Custom)";
 		}
 
+		@Override
+		public Set<String> getRequiredVariables(String template) {
+			return Set.of();
+		}
+
 	}
 
 }

spring-ai-template-st/src/main/java/org/springframework/ai/template/st/StTemplateRenderer.java

@@ -49,6 +49,7 @@
  * is shared between threads.
  *
  * @author Thomas Vitale
+ * @author Sun Yuhan
  * @since 1.0.0
  */
 public class StTemplateRenderer implements TemplateRenderer {
@@ -110,6 +111,11 @@ public String apply(String template, Map<String, Object> variables) {
 		return st.render();
 	}
 
+	@Override
+	public Set<String> getRequiredVariables(String template) {
+		return getInputVariables(createST(template));
+	}
+
 	private ST createST(String template) {
 		try {
 			return new ST(template, this.startDelimiterToken, this.endDelimiterToken);

spring-ai-template-st/src/test/java/org/springframework/ai/template/st/StTemplateRendererTests.java

@@ -18,6 +18,7 @@
 
 import java.util.HashMap;
 import java.util.Map;
+import java.util.Set;
 
 import org.junit.jupiter.api.Test;
 
@@ -31,6 +32,7 @@
  * Unit tests for {@link StTemplateRenderer}.
  *
  * @author Thomas Vitale
+ * @author Sun Yuhan
  */
 class StTemplateRendererTests {
 
@@ -297,4 +299,16 @@ void shouldRenderTemplateWithBuiltInFunctions() {
 		assertThat(result).isEqualTo("Hello!");
 	}
 
+	/**
+	 * Test whether the required variables can be correctly extracted from the template.
+	 */
+	@Test
+	void shouldCorrectlyExtractedRequiredVariables() {
+		StTemplateRenderer renderer = StTemplateRenderer.builder().build();
+		String template = "Person: {name}, Age: {age}";
+		Set<String> requiredVariables = renderer.getRequiredVariables(template);
+
+		assertThat(requiredVariables).contains("name", "age");
+	}
+
 }