Spring boot web starter cannot find jsp

The file structure:

app
  -build.gradle
  -src/
    -main/
      -java
        {source code}
      -resources
        -application.properties
      -webapp
        -WEB-INF
          -jsp
            -index.jsp

Here is the core code segments:
build.gradle:

buildscript {
    ext {
        springBootVersion = '1.2.3.RELEASE'
    }
    repositories {
        maven { url "http://repo.spring.io/libs-snapshot" }
        mavenLocal()
    }
    dependencies {
        classpath("org.springframework.boot:spring-boot-gradle-plugin:1.2.3.RELEASE")
    }
}

apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'idea'
apply plugin: 'spring-boot'
apply plugin: 'war'
apply plugin: 'application'

repositories {
    mavenCentral()
    maven { url "http://repo.spring.io/libs-snapshot" }
    maven { url "http://maven.springframework.org/milestone" }
}

dependencies {
    compile("org.springframework.boot:spring-boot-starter-web:${springBootVersion}")
    compile("org.springframework.boot:spring-boot-starter-tomcat:${springBootVersion}")
    compile("org.springframework.boot:spring-boot-starter-test:${springBootVersion}")
    compile("org.springframework.boot:spring-boot-starter-data-jpa:${springBootVersion}")
    compile("org.springframework.data:spring-data-rest-webmvc")
    compile("org.hsqldb:hsqldb")

compile("com.google.guava:guava:17.0")
compile("org.apache.httpcomponents:httpclient:4.3.4")
compile("com.squareup.retrofit:retrofit:1.6.0")
compile("commons-io:commons-io:2.4")
compile("org.apache.commons:commons-lang3:3.4")

testCompile("junit:junit")

}

sourceCompatibility = 1.7
targetCompatibility = 1.7

war {
    baseName = 'gs-convert-jar-to-war'
    version =  '0.1.0'
}

task wrapper(type: Wrapper) {
    gradleVersion = '2.3'
}

Application.java at package root:

@SpringBootApplication
@EnableWebMvc
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

}

ViewController.java:

@Controller
public class ViewController {

    @RequestMapping("/")
    public String welcome(Map<String, Object> model) {
        model.put("time", new Date());
        model.put("message", "hellop");
        return "index";
    }
}

application.properties:

spring.view.prefix: /WEB-INF/jsp/
spring.view.suffix: .jsp

However when I go to http://localhost:8080 on browser I got 500 error:

javax.servlet.ServletException: Could not resolve view with name 'index' in servlet with name 'dispatcherServlet'
    at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1227)
    at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1027)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:971)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:966)
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:857)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:622)
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:842)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:85)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:668)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1521)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1478)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:745)

I found on spring documentation that there are some limitations to use jsp: http://docs.spring.io/spring-boot/docs/1.1.x/reference/html/boot-features-developing-web-applications.html#boot-features-jsp-limitations

However I am really not sure if this is the reason and how to resolve them. Any suggestions will be appreciated. Thanks in advance.