Thymeleaf templateResolver WebApplicationContext throw nullpointexception - spring-mvc

Question

When I use thymeleaf in SpringMVC,the ServletContext throw nullpointexception ,here my code and trace stack
#Configuration
public class ViewResolverConfig {
#Bean
public ITemplateResolver templateResolver() {
WebApplicationContext webApplicationContext = ContextLoader.getCurrentWebApplicationContext();
ServletContextTemplateResolver templateResolver = new ServletContextTemplateResolver(webApplicationContext.getServletContext());
templateResolver.setPrefix("/WEB-INF/templates/");
templateResolver.setSuffix(".html");
templateResolver.setCharacterEncoding("UTF-8");
templateResolver.setTemplateMode(TemplateMode.HTML);
return templateResolver;
}
#Bean
public SpringTemplateEngine templateEngine(ITemplateResolver templateResolver) {
SpringTemplateEngine templateEngine = new SpringTemplateEngine();
templateEngine.setTemplateResolver(templateResolver);
return templateEngine;
}
#Bean
public ViewResolver viewResolver(SpringTemplateEngine templateEngine) {
ThymeleafViewResolver viewResolver = new ThymeleafViewResolver();
viewResolver.setCharacterEncoding("UTF-8");
viewResolver.setTemplateEngine(templateEngine);
return viewResolver;
}}
here is the buttom error
Caused by: java.lang.NullPointerException: null
at com.lh.config.WebConfig.templateResolver(WebConfig.java:46)
at com.lh.config.WebConfig$$EnhancerBySpringCGLIB$$ede505eb.CGLIB$templateResolver$3()
at com.lh.config.WebConfig$$EnhancerBySpringCGLIB$$ede505eb$$FastClassBySpringCGLIB$$6ff8b31b.invoke()
at org.springframework.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:244)
at org.springframework.context.annotation.ConfigurationClassEnhancer$BeanMethodInterceptor.intercept(ConfigurationClassEnhancer.java:331)
at com.lh.config.WebConfig$$EnhancerBySpringCGLIB$$ede505eb.templateResolver()
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:498)
at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:154)
... 63 common frames omitted
but I dont know why the WebApplicationContext is null