Fixed GH-3526, Fixed the error in using the Builder in SystemPromptTemplate.

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

@@ -209,17 +209,17 @@ public static Builder builder() {
 		return new Builder();
 	}
 
-	public static final class Builder {
+	public static class Builder {
 
-		private String template;
+		protected String template;
 
-		private Resource resource;
+		protected Resource resource;
 
-		private Map<String, Object> variables = new HashMap<>();
+		protected Map<String, Object> variables = new HashMap<>();
 
-		private TemplateRenderer renderer = DEFAULT_TEMPLATE_RENDERER;
+		protected TemplateRenderer renderer = DEFAULT_TEMPLATE_RENDERER;
 
-		private Builder() {
+		protected Builder() {
 		}
 
 		public Builder template(String template) {

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

@@ -20,7 +20,9 @@
 
 import org.springframework.ai.chat.messages.Message;
 import org.springframework.ai.chat.messages.SystemMessage;
+import org.springframework.ai.template.TemplateRenderer;
 import org.springframework.core.io.Resource;
+import org.springframework.util.Assert;
 
 public class SystemPromptTemplate extends PromptTemplate {
 
@@ -32,6 +34,14 @@ public SystemPromptTemplate(Resource resource) {
 		super(resource);
 	}
 
+	private SystemPromptTemplate(String template, Map<String, Object> variables, TemplateRenderer renderer) {
+		super(template, variables, renderer);
+	}
+
+	private SystemPromptTemplate(Resource resource, Map<String, Object> variables, TemplateRenderer renderer) {
+		super(resource, variables, renderer);
+	}
+
 	@Override
 	public Message createMessage() {
 		return new SystemMessage(render());
@@ -52,4 +62,50 @@ public Prompt create(Map<String, Object> model) {
 		return new Prompt(new SystemMessage(render(model)));
 	}
 
+	public static Builder builder() {
+		return new Builder();
+	}
+
+	public static class Builder extends PromptTemplate.Builder {
+
+		public Builder template(String template) {
+			Assert.hasText(template, "template cannot be null or empty");
+			this.template = template;
+			return this;
+		}
+
+		public Builder resource(Resource resource) {
+			Assert.notNull(resource, "resource cannot be null");
+			this.resource = resource;
+			return this;
+		}
+
+		public Builder variables(Map<String, Object> variables) {
+			Assert.notNull(variables, "variables cannot be null");
+			Assert.noNullElements(variables.keySet(), "variables keys cannot be null");
+			this.variables = variables;
+			return this;
+		}
+
+		public Builder renderer(TemplateRenderer renderer) {
+			Assert.notNull(renderer, "renderer cannot be null");
+			this.renderer = renderer;
+			return this;
+		}
+
+		@Override
+		public SystemPromptTemplate build() {
+			if (this.template != null && this.resource != null) {
+				throw new IllegalArgumentException("Only one of template or resource can be set");
+			}
+			else if (this.resource != null) {
+				return new SystemPromptTemplate(this.resource, this.variables, this.renderer);
+			}
+			else {
+				return new SystemPromptTemplate(this.template, this.variables, this.renderer);
+			}
+		}
+
+	}
+
 }