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Simple Spring Boot Project is giving 404 Error

I am learning Spring Boot but I am not able to execute the basic "Hello World" program. I have built the basic project using https://start.spring.io/ and updated the code as per below code snippets:
Spring Boot Main Class:
package com.rohit.springboot.practice.selfspringboot;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.ComponentScan;
#SpringBootApplication
#ComponentScan(basePackages = "com.rohit.springboot.practice.selfspringboot")
public class SelfSpringBootApplication {
public static void main(String[] args) {
SpringApplication.run(SelfSpringBootApplication.class, args);
}
}
Controller Class:
package com.rohit.springboot.practice.selfspringboot;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;
#RestController
public class ThisWorldSpringContainer {
#RequestMapping(method = RequestMethod.GET, value = "/hello-world")
public String getWelcome() {
return "Hello World";
}
}
POM.xml file:
<?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>2.6.6</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.rohit.springboot.practice</groupId>
<artifactId>self-spring-boot</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>self-spring-boot</name>
<description>Demo project for Spring Boot</description>
<properties>
<java.version>8</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-devtools</artifactId>
<scope>runtime</scope>
<optional>true</optional>
</dependency>
<dependency>
<groupId>com.h2database</groupId>
<artifactId>h2</artifactId>
<scope>runtime</scope>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>
Error:
Message: The requested resource [/hello-world] is not available
I know this question has been asked by multiple people but i have gone through those answers and tried those given answers but didn't work.
Technologies used are Java 8, Tomcat 9, Spring Boot 2.6.6 etc.
Kindly help.

Since you don't have the Tomcat dependency, I'm implying that you want your application to run in a standalone Tomcat instance. Also, given your comment, I believe you're working on either Eclipse or Spring Tools Suite (Which is the same, really).
With that, it seems your problem is the lack of a packaging method. Tomcat needs the code its going to run in a package. This package is a zip-like file with .war extension. Maven, the program that handles the dependencies of your project according to the pom.xml file, can package it in either war of jar format. Since you are running it in an external Tomcat, you want the war extension. So please, add the following line to your pom.xml file. It has to be in the same level as <name>:
<packaging>war</packaging>
Then, update your project (Alt + F5, check your project and hit OK) then try running your project again. You should see an stylish "SPRING" output in your console.
Now, since you are running this externally, you need to specify the name of the project, so you should call your endpoint with
http://localhost:8080/<your_project_name_here>/hello-world

I advise you to check this new change in Spring Boot 2.6 :
PathPattern Based Path Matching Strategy for Spring MVC
In this release, the default strategy for matching request paths against registered Spring MVC handler mappings has changed from AntPathMatcher to PathPatternParser.
If you need to switch the default strategy back to AntPathMatcher, you can set the property spring.mvc.pathmatch.matching-strategy to ant-path-matcher as in the line below to add in the file application.properties :
spring.mvc.pathmatch.matching-strategy=ant-path-matcher
I encountered the same issue of HTTP 404 error when upgrading to Spring Boot 2.6 and adding this property solved my problem and should solve yours.

I have modified your code as below:
#RequestMapping
#RestController
public class ThisWorldSpringContainer {
#GetMapping(value = "/hello-world")
public String getWelcome() {
return "Hello World";
}
}
I thinking you are missing
#Requestmapping
in classlevel

Getting error "Whitelabel Error Page" while running localhost:8080

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!

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.

It seems your controller only have a mapping for "/sum" path. Try querying localhost:8080/sum.

Springboot Devtools not hot reloading?

I haven't used spring in a while, and I'm trying to get spring boot dev tools to perform hot reloading. I've imported the web and spring boot dependencies from start.spring.io project generator and made a uri for "/hello". I can run the project but changing the uri values doesn't hot reload and I don't believe that the hot reloading is working. From what I've found on searching the internet, the only necessary step is to add the hot reloading dependency in your pom file:
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-devtools</artifactId>
<scope>runtime</scope>
<optional>true</optional>
</dependency>
My entire pom.xml file is as follows (generated from the start.spring.io website):
<?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>2.4.0</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.java</groupId>
<artifactId>java_app</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>java_app</name>
<description>Web Project</description>
<properties>
<java.version>11</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-devtools</artifactId>
<scope>runtime</scope>
<optional>true</optional>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>
And my web uri file is as follows (works, but without hot reloading):
package com.java.java_app;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;
#SpringBootApplication
#RestController
public class JavaAppApplication {
public static void main(String[] args) {
SpringApplication.run(JavaAppApplication.class, args);
}
#GetMapping("/hello")
public String hello(#RequestParam(value = "name", defaultValue = "World") String name){
return String.format("Hello %s!", name);
}
}
This is as simple an application as I think it is possible to build, so I'm confused on what extra necessary step is needed to make hot reloading work. It does not appear to be documented say here (https://www.baeldung.com/spring-boot-devtools) other than to add the dependency. If it matters I'm running ubuntu 20.04.
EDIT:
I am running the application in the terminal on port :8080 and using vim to modify the uri file while the application is running. Since java has a lot of plugins for various IDEs someone suggested that it is worth mentioning that.

If you are not using an IDE you can use ./mvnw compile and the project will recompile while the editor is running.

Whitelabel Error Page, rest urls not executed in springboot

new to spring boot application development. I ran the application as java application and got the below error. THe application is deployed successfully , I don't know why this error is rendered ... beating my head.. thank you for your help in advance.
Whitelabel Error Page This application has no explicit mapping for
/error, so you are seeing this as a fallback. Sat Jul 13 21:37:31 IST
2019 There was an unexpected error (type=Not Found, status=404). No
message available
tried solutions given on stack overflow but no help. could you please help me if anywhere I do wrong here.
package com.cpi.poc.controller;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import com.cpi.poc.service.IService;
#RestController
#RequestMapping(value ="/test")
#ComponentScan(basePackages = "com.cgi.poc")
public class TestController {
#Autowired
IService service;
#RequestMapping(value = "/greet" , method = RequestMethod.GET)
public String testService(){
String result = service.greet();
return result;
}
}
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 http://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>1.5.21.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.cgi.poc</groupId>
<artifactId>test</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>test</name>
<description>Demo project for Spring Boot</description>
<properties>
<java.version>1.8</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-tomcat</artifactId>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>

Check whether you have class :
#SpringBootApplication
#ComponentScan("com.cgi.poc")
#ComponentScan
public class Application {
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
}
No need to put component scan on controller if you have the above class.
Verify by using lsof command that your java service is running on the port on not.

Spring Boot Primitive Rest Controller Returns Whitelabel Error Page [duplicate]

This question already has answers here:
Intellij Springboot problems on startup
(3 answers)
Closed 4 years ago.
I am trying to build & run my Spring boot project which returns "I am alive" on the page. I have basic main class and one rest controller class. I guess solution is simple but i couldnt find any question similar with me.
Here is the thing.
Main Class
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
#SpringBootApplication
public class Application{
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
}
Rest Controller
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
#RestController
public class HealthCheck {
#GetMapping("/up")
public String checkHealth(){
return "I am alive";
}
}
When i go to localhost:8080/up, it returns as
Whitelabel Error Page This application has no explicit mapping for
/error, so you are seeing this as a fallback.
Tue Sep 25 17:47:53 EEST 2018 There was an unexpected error (type=Not
Found, status=404). No message available
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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.demo</groupId>
<artifactId>demo</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>jar</packaging>
<name>demo</name>
<description>Demo project for Spring Boot</description>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.0.5.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
<java.version>1.8</java.version>
</properties>
<dependencies>
<!--<dependency>-->
<!--<groupId>org.springframework.boot</groupId>-->
<!--<artifactId>spring-boot-starter-data-mongodb</artifactId>-->
<!--</dependency>-->
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-rest</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>

By default, Spring Boot will scan for classes annotated with #RestController starting from the package that the main class (the one with #SpringBootApplication) and below. The easiest fix is to move your controller to the same package or a sub package of where your main class lives.

Instead of using #GetMapping("/up") try using #RequestMapping("/up"). As you want to see the message on the page, RequestMapping returns plain text when requested using either a browser or curl on the command line.

It looks like Spring doesn't see your controller. You have to use #ComponentScan
#ComponentScan
#SpringBootApplication
public class FraudWsApplication {
public static void main(String[] args) {
SpringApplication.run(FraudWsApplication.class, args);
}
}
You can also find an example in my repo

In your main Application change annotation to #SpringBootApplication(scanBasePackages = {"com.ykb.frd"})