Java 控制器不工作，在白标签错误中显示错误

我正在观看如何在春季创建REST控制器的视频教程。 但是，当我创建一个TopicController，如视频课程中所示时，我得到了一个Whitelabel错误页面的错误。我无法解决它

这是我的主题控制器

package spring.boot.topic;

import java.util.Arrays;
import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class TopicController {

    @Autowired
    private TopicService topicService;

    @RequestMapping("/topic")
    public List<Topic> getAllTopics() {
        return topicService.getAllTopics();
    }
}

pom.xml文件

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.demo</groupId>
  <artifactId>spring-boot-api</artifactId>
  <version>0.0.1-SNAPSHOT</version>

<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.2.2.RELEASE</version>
</parent>
  <dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
  </dependencies>  
</project>

当我在Eclipse中运行程序并在浏览器中导航到localhost:8080/topic时，我得到一个错误

Whitelabel Error Page
This application has no explicit mapping for /error, so you are seeing this as a fallback.

Sat May 09 16:45:04 IST 2020
There was an unexpected error (type=Not Found, status=404).
No message available

---

你的代码运行良好。请先尝试通过命令mvn clean install重新生成项目，然后重新运行应用程序。

由于您使用的是Rest服务，因此无法期望收到html文件作为响应。将

@RestController

更改为

@Controller

并返回视图模型对象。

请发布出现的错误

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.demo</groupId>
  <artifactId>spring-boot-api</artifactId>
  <version>0.0.1-SNAPSHOT</version>

<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.2.2.RELEASE</version>
</parent>
  <dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
  </dependencies>  
</project>

:: Spring Boot ::        (v2.2.2.RELEASE)

2020-05-09 16:09:24.519  INFO 8256 --- [           main] spring.boot.api.CourseApiApp             : Starting CourseApiApp on DESKTOP-JBQF1EV with PID 8256 (C:\Users\spars\eclipse-workspace\spring-boot-api\target\classes started by spars in C:\Users\spars\eclipse-workspace\spring-boot-api)
2020-05-09 16:09:24.528  INFO 8256 --- [           main] spring.boot.api.CourseApiApp             : No active profile set, falling back to default profiles: default
2020-05-09 16:09:28.549  INFO 8256 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2020-05-09 16:09:28.579  INFO 8256 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2020-05-09 16:09:28.579  INFO 8256 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet engine: [Apache Tomcat/9.0.29]
2020-05-09 16:09:28.761  INFO 8256 --- [           main] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2020-05-09 16:09:28.761  INFO 8256 --- [           main] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 3908 ms
2020-05-09 16:09:29.039  INFO 8256 --- [           main] o.s.s.concurrent.ThreadPoolTaskExecutor  : Initializing ExecutorService 'applicationTaskExecutor'
2020-05-09 16:09:29.620  INFO 8256 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2020-05-09 16:09:29.623  INFO 8256 --- [           main] spring.boot.api.CourseApiApp             : Started CourseApiApp in 6.686 seconds (JVM running for 7.891)
2020-05-09 16:09:54.896  INFO 8256 --- [nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring DispatcherServlet 'dispatcherServlet'
2020-05-09 16:09:54.897  INFO 8256 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : Initializing Servlet 'dispatcherServlet'
2020-05-09 16:09:54.922  INFO 8256 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : Completed initialization in 24 ms

Whitelabel Error Page
This application has no explicit mapping for /error, so you are seeing this as a fallback.

Sat May 09 16:45:04 IST 2020
There was an unexpected error (type=Not Found, status=404).
No message available