[FIXED] Getting error "Whitelabel Error Page" while running localhost:8080

Issue

I started learning Spring Framework and get this kind of error while running localhost:8080

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

Controller.java

package com.springFramework.helloGame.controller;

import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class Controller {

    @GetMapping("/sum")
    public long displaySum(){
        return 100;
    }

}

HelloGameApplication.java

package com.springFramework.helloGame;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.ComponentScan;

@SpringBootApplication
public class HelloGameApplication {

    public static void main(String[] args) {
        ConfigurableApplicationContext context =
                SpringApplication.run(HelloGameApplication.class, args);
    }

}

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<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>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.5.4</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.springFramework</groupId>
    <artifactId>helloGame</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>helloGame</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>11</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

my project structure looks fine, but don't know why I got error! Please help me!

Solution

The Whitelabel page is a spring error handling method and it tries to hint to you that you do have a mapping for /error. Now coming to the issue you need to write @RequestMapping("/") above your get mapping in the controller so that the spring knows the base URI. It's an entry point for the spring application for the browser.

Now you have written /sum get URI and in the browser, you are trying for http://localhost:8080 So for the above Uri to work you need to provide @RequestMapping("/")

or you can use http://localhost:8080/sum with you current code.

Answered By - Ankit Dhar