Support ScriptEngine#eval(String, Bindings) in ScriptTemplateView

Supporting ScriptEngine#eval(String, Bindings) when no render function
is specified allows to support use cases where script templates are
simply evaluating a script expression with an even more simplified
configuration.

This improvement also makes it possible to use script engines that
do not implement Invocable.

Issue: SPR-15115

spring-webmvc/src/main/java/org/springframework/web/servlet/view/script/ScriptTemplateConfig.java

@@ -17,6 +17,8 @@
 package org.springframework.web.servlet.view.script;
 
 import java.nio.charset.Charset;
+
+import javax.script.Bindings;
 import javax.script.ScriptEngine;
 
 import org.springframework.lang.Nullable;
@@ -63,7 +65,8 @@ public interface ScriptTemplateConfig {
 	String getRenderObject();
 
 	/**
-	 * Return the render function name (mandatory).
+	 * Return the render function name (optional). If not specified, the script templates
+	 * will be evaluated with {@link ScriptEngine#eval(String, Bindings)}.
 	 */
 	@Nullable
 	String getRenderFunction();

spring-webmvc/src/main/java/org/springframework/web/servlet/view/script/ScriptTemplateConfigurer.java

@@ -17,6 +17,8 @@
 package org.springframework.web.servlet.view.script;
 
 import java.nio.charset.Charset;
+
+import javax.script.Bindings;
 import javax.script.ScriptEngine;
 
 /**
@@ -65,9 +67,23 @@ public class ScriptTemplateConfigurer implements ScriptTemplateConfig {
 	private String resourceLoaderPath;
 
 
+	/**
+	 * Default constructor.
+	 */
+	public ScriptTemplateConfigurer() {
+	}
+
+	/**
+	 * Create a new ScriptTemplateConfigurer using the given engine name.
+	 */
+	public ScriptTemplateConfigurer(String engineName) {
+		this.engineName = engineName;
+	}
+
+
 	/**
 	 * Set the {@link ScriptEngine} to use by the view.
-	 * The script engine must implement {@code Invocable}.
+	 * If {@code renderFunction} is specified, the script engine must implement {@code Invocable}.
 	 * You must define {@code engine} or {@code engineName}, not both.
 	 * <p>When the {@code sharedEngine} flag is set to {@code false}, you should not specify
 	 * the script engine with this setter, but with the {@link #setEngineName(String)}
@@ -85,7 +101,7 @@ public class ScriptTemplateConfigurer implements ScriptTemplateConfig {
 
 	/**
 	 * Set the engine name that will be used to instantiate the {@link ScriptEngine}.
-	 * The script engine must implement {@code Invocable}.
+	 * If {@code renderFunction} is specified, the script engine must implement {@code Invocable}.
 	 * You must define {@code engine} or {@code engineName}, not both.
 	 * @see #setEngine(ScriptEngine)
 	 */
@@ -155,13 +171,15 @@ public class ScriptTemplateConfigurer implements ScriptTemplateConfig {
 	}
 
 	/**
-	 * Set the render function name (mandatory).
+	 * Set the render function name (optional). If not specified, the script templates
+	 * will be evaluated with {@link ScriptEngine#eval(String, Bindings)}.
 	 * <p>This function will be called with the following parameters:
 	 * <ol>
 	 * <li>{@code String template}: the template content</li>
 	 * <li>{@code Map model}: the view model</li>
-	 * <li>{@code String url}: the template url (since 4.2.2)</li>
+	 * <li>{@code RenderingContext context}: the rendering context (since 5.0)</li>
 	 * </ol>
+	 * @see RenderingContext
 	 */
 	public void setRenderFunction(String renderFunction) {
 		this.renderFunction = renderFunction;

spring-webmvc/src/main/java/org/springframework/web/servlet/view/script/ScriptTemplateView.java

@@ -29,6 +29,7 @@ import javax.script.Invocable;
 import javax.script.ScriptEngine;
 import javax.script.ScriptEngineManager;
 import javax.script.ScriptException;
+import javax.script.SimpleBindings;
 import javax.servlet.ServletException;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
@@ -126,7 +127,6 @@ public class ScriptTemplateView extends AbstractUrlBasedView {
 	 * See {@link ScriptTemplateConfigurer#setEngine(ScriptEngine)} documentation.
 	 */
 	public void setEngine(ScriptEngine engine) {
-		Assert.isInstanceOf(Invocable.class, engine, "ScriptEngine must implement Invocable");
 		this.engine = engine;
 	}
 
@@ -260,7 +260,9 @@ public class ScriptTemplateView extends AbstractUrlBasedView {
 			setEngine(createEngineFromName());
 		}
 
-		Assert.isTrue(this.renderFunction != null, "The 'renderFunction' property must be defined.");
+		if (this.renderFunction != null && this.engine != null) {
+			Assert.isInstanceOf(Invocable.class, this.engine, "ScriptEngine must implement Invocable when 'renderFunction' is specified.");
+		}
 	}
 
 	protected ScriptEngine getEngine() {
@@ -357,7 +359,6 @@ public class ScriptTemplateView extends AbstractUrlBasedView {
 
 		try {
 			ScriptEngine engine = getEngine();
-			Invocable invocable = (Invocable) engine;
 			String url = getUrl();
 			Assert.state(url != null, "'url' not set");
 			String template = getTemplate(url);
@@ -372,12 +373,18 @@ public class ScriptTemplateView extends AbstractUrlBasedView {
 			RenderingContext context = new RenderingContext(obtainApplicationContext(), this.locale, templateLoader, url);
 
 			Object html;
-			if (this.renderObject != null) {
+			if (this.renderFunction == null) {
+				SimpleBindings bindings = new SimpleBindings();
+				bindings.putAll(model);
+				model.put("renderingContext", context);
+				html = engine.eval(template, bindings);
+			}
+			else if (this.renderObject != null) {
 				Object thiz = engine.eval(this.renderObject);
-				html = invocable.invokeMethod(thiz, this.renderFunction, template, model, context);
+				html = ((Invocable)engine).invokeMethod(thiz, this.renderFunction, template, model, context);
 			}
 			else {
-				html = invocable.invokeFunction(this.renderFunction, template, model, context);
+				html = ((Invocable)engine).invokeFunction(this.renderFunction, template, model, context);
 			}
 
 			response.getWriter().write(String.valueOf(html));