Add indirection to avoid runtime dependency on MVC in templates

Velocity and Freemarker share some common properties so the base class for
configuring their properties makes some sense. Unfortunately the implementation
pulls in Spring MVC at runtime because of the signature of one method (that
would never be called). We can fix that in a number of ways, but the least
disruptive is probably to change the signature of that method and only refer
to the concrete template view resolver type if the method is called.

Fixes gh-1437

spring-boot-samples/spring-boot-sample-velocity/src/main/java/sample/velocity/SampleVelocityApplication.java

@@ -0,0 +1,57 @@
+/*
+ * Copyright 2012-2014 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package sample.velocity;
+
+import java.util.Date;
+import java.util.HashMap;
+import java.util.Map;
+
+import org.apache.velocity.app.VelocityEngine;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.boot.CommandLineRunner;
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
+import org.springframework.context.annotation.ComponentScan;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.ui.velocity.VelocityEngineUtils;
+
+@Configuration
+@EnableAutoConfiguration
+@ComponentScan
+public class SampleVelocityApplication implements CommandLineRunner {
+
+	@Value("${application.message}")
+	private String message;
+
+	@Autowired
+	private VelocityEngine engine;
+
+	@Override
+	public void run(String... args) throws Exception {
+		Map<String, Object> model = new HashMap<String, Object>();
+		model.put("time", new Date());
+		model.put("message", this.message);
+		System.out.println(VelocityEngineUtils.mergeTemplateIntoString(this.engine,
+				"welcome.vm", "UTF-8", model));
+	}
+
+	public static void main(String[] args) throws Exception {
+		SpringApplication.run(SampleVelocityApplication.class, args);
+	}
+
+}