I am trying to debug why a my application won’t show, and in doing so I have this small application running hello world. This does work, it shows the text on the screen, great. But then if I add spring-boot-starter-data-jpa to the pom file, I get a 404 error instead. I need to use spring-boot-starter-data-jpa and have no idea why it doesn’t work as expected.

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>

    <artifactId>spring-boot-hello</artifactId>
    <packaging>war</packaging>
    <name>Spring Boot Hello World Example</name>
    <version>1.0</version>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.5.5</version>
    </parent>

    <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-starter-tomcat</artifactId>-->
<!--            <scope>provided</scope>-->
<!--        </dependency>-->


<!--this is the issued one-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>


            <dependency>
                <groupId>mysql</groupId>
                <artifactId>mysql-connector-java</artifactId>
            </dependency>

    </dependencies>

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


        </plugins>
    </build>

</project>

controller

package org.example;

import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloController {

    @RequestMapping("/")
    String hello() {
        return "Hello World, Spring Boot!";
    }

}

main class

package org.example;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.builder.SpringApplicationBuilder;
import org.springframework.boot.web.servlet.support.SpringBootServletInitializer;

@SpringBootApplication
public class MyWebApplication extends SpringBootServletInitializer {

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

    @Override
    protected SpringApplicationBuilder configure(SpringApplicationBuilder builder){
        return builder.sources(MyWebApplication.class);
    }

}

I have gone through every other answer I could find and made sure I was using restcontroller instead of controller, I believe my main class is in the correct spot, I am at a loss as to why one dependency, especially one that isn’t being used yet, causes a 404.

>Solution :

In application.properties file in resource folder did you set database configuration such asusername, password and url? It should be set like this.

spring.datasource.url=jdbc:mysql://localhost:3306/restapi
spring.datasource.username=root
spring.datasource.password=

And it’s better to use @GetMapping annotation instead of @RequestMapping.