Unable to start the web server while setting-up Eureka Service, error: application missing the necessary class definition for the RestClient$Builder

Question

I am trying to setup a basic Eureka Service Discovery but, while implementing the same I am getting the following error:

org.springframework.context.ApplicationContextException: Unable to start web server
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.onRefresh(ServletWebServerApplicationContext.java:164) ~[spring-boot-3.1.2.jar:3.1.2]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:602) ~[spring-context-6.0.11.jar:6.0.11]
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:146) ~[spring-boot-3.1.2.jar:3.1.2]
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:734) ~[spring-boot-3.1.2.jar:3.1.2]
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:436) ~[spring-boot-3.1.2.jar:3.1.2]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:312) ~[spring-boot-3.1.2.jar:3.1.2]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1306) ~[spring-boot-3.1.2.jar:3.1.2]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1295) ~[spring-boot-3.1.2.jar:3.1.2]
    at com.project.discoveryserver.DiscoveryServerApplication.main(DiscoveryServerApplication.java:11) ~[classes/:na]
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryConfiguration$EmbeddedTomcat': org/springframework/web/client/RestClient$Builder
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:605) ~[spring-beans-6.0.11.jar:6.0.11]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:520) ~[spring-beans-6.0.11.jar:6.0.11]
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:326) ~[spring-beans-6.0.11.jar:6.0.11]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-6.0.11.jar:6.0.11]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:324) ~[spring-beans-6.0.11.jar:6.0.11]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:200) ~[spring-beans-6.0.11.jar:6.0.11]
    at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:417) ~[spring-beans-6.0.11.jar:6.0.11]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1332) ~[spring-beans-6.0.11.jar:6.0.11]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1162) ~[spring-beans-6.0.11.jar:6.0.11]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:560) ~[spring-beans-6.0.11.jar:6.0.11]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:520) ~[spring-beans-6.0.11.jar:6.0.11]
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:326) ~[spring-beans-6.0.11.jar:6.0.11]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-6.0.11.jar:6.0.11]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:324) ~[spring-beans-6.0.11.jar:6.0.11]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:205) ~[spring-beans-6.0.11.jar:6.0.11]
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.getWebServerFactory(ServletWebServerApplicationContext.java:218) ~[spring-boot-3.1.2.jar:3.1.2]
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.createWebServer(ServletWebServerApplicationContext.java:181) ~[spring-boot-3.1.2.jar:3.1.2]
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.onRefresh(ServletWebServerApplicationContext.java:161) ~[spring-boot-3.1.2.jar:3.1.2]
    ... 8 common frames omitted
Caused by: java.lang.NoClassDefFoundError: org/springframework/web/client/RestClient$Builder
    at org.springframework.cloud.client.loadbalancer.LoadBalancerRestClientBuilderBeanPostProcessor.postProcessBeforeInitialization(LoadBalancerRestClientBuilderBeanPostProcessor.java:46) ~[spring-cloud-commons-4.1.0.jar:4.1.0]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsBeforeInitialization(AbstractAutowireCapableBeanFactory.java:419) ~[spring-beans-6.0.11.jar:6.0.11]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1762) ~[spring-beans-6.0.11.jar:6.0.11]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:598) ~[spring-beans-6.0.11.jar:6.0.11]
    ... 25 common frames omitted
Caused by: java.lang.ClassNotFoundException: org.springframework.web.client.RestClient$Builder
    at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:641) ~[na:na]
    at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188) ~[na:na]
    at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:520) ~[na:na]
    ... 29 common frames omitted

Moreover, while mentioning the port number and other config required for the eureka server in the application.properties file, it is showing the warning that the mentioned properties are not being used. Also attaching the pom.xml, application.properties and Main class for reference:

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">
    <parent>
        <artifactId>microservices-project</artifactId>
        <groupId>com.project</groupId>
        <version>1.0-SNAPSHOT</version>
    </parent>
    <modelVersion>4.0.0</modelVersion>

    <artifactId>discovery-server</artifactId>

    <properties>
        <maven.compiler.source>17</maven.compiler.source>
        <maven.compiler.target>17</maven.compiler.target>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <spring-cloud.version>2023.0.0</spring-cloud.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-server</artifactId>
            <version>4.0.0</version>
        </dependency>

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


    </dependencies>

</project>

application.properties:

spring.application.name=discovery-server
eureka.instance.hostname=localhost
eureka.client.register-with-eureka=false
eureka.client.fetch-registry=false
server.port=8761

DiscoveryServerApplication class:

package com.project.discoveryserver;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.netflix.eureka.server.EnableEurekaServer;

@EnableEurekaServer
@SpringBootApplication
public class  DiscoveryServerApplication {
    public static void main(String[] args) {
        SpringApplication.run(DiscoveryServerApplication.class, args);
    }
}

to resolve the same I have tried to ensure the presence of the required JAR by:

• Checking iy my build configuration includes the spring-boot-starter-webflux dependency.
• Verified that the JARs for WebClient are properly downloaded and included in your project's classpath.

Attaching the dependency tree for spring-boot-starter-webflux for your reference:

\- org.springframework.boot:spring-boot-starter-webflux:jar:3.1.2:compile
[INFO]    +- org.springframework.boot:spring-boot-starter:jar:3.1.2:compile
[INFO]    |  +- org.springframework.boot:spring-boot:jar:3.1.2:compile
[INFO]    |  +- org.springframework.boot:spring-boot-autoconfigure:jar:3.1.2:compile
[INFO]    |  +- org.springframework.boot:spring-boot-starter-logging:jar:3.1.2:compile
[INFO]    |  |  +- ch.qos.logback:logback-classic:jar:1.4.8:compile
[INFO]    |  |  |  \- ch.qos.logback:logback-core:jar:1.4.8:compile
[INFO]    |  |  +- org.apache.logging.log4j:log4j-to-slf4j:jar:2.20.0:compile
[INFO]    |  |  |  \- org.apache.logging.log4j:log4j-api:jar:2.20.0:compile
[INFO]    |  |  \- org.slf4j:jul-to-slf4j:jar:2.0.7:compile
[INFO]    |  +- jakarta.annotation:jakarta.annotation-api:jar:2.1.1:compile
[INFO]    |  +- org.springframework:spring-core:jar:6.0.11:compile
[INFO]    |  |  \- org.springframework:spring-jcl:jar:6.0.11:compile
[INFO]    |  \- org.yaml:snakeyaml:jar:1.33:compile
[INFO]    +- org.springframework.boot:spring-boot-starter-json:jar:3.1.2:compile
[INFO]    |  +- com.fasterxml.jackson.core:jackson-databind:jar:2.15.2:compile
[INFO]    |  +- com.fasterxml.jackson.datatype:jackson-datatype-jdk8:jar:2.15.2:compile
[INFO]    |  +- com.fasterxml.jackson.datatype:jackson-datatype-jsr310:jar:2.15.2:compile
[INFO]    |  \- com.fasterxml.jackson.module:jackson-module-parameter-names:jar:2.15.2:compile
[INFO]    +- org.springframework.boot:spring-boot-starter-reactor-netty:jar:3.1.2:compile
[INFO]    |  \- io.projectreactor.netty:reactor-netty-http:jar:1.1.9:compile
[INFO]    |     +- io.netty:netty-codec-http:jar:4.1.94.Final:compile
[INFO]    |     |  +- io.netty:netty-common:jar:4.1.94.Final:compile
[INFO]    |     |  +- io.netty:netty-buffer:jar:4.1.94.Final:compile
[INFO]    |     |  +- io.netty:netty-transport:jar:4.1.94.Final:compile
[INFO]    |     |  +- io.netty:netty-codec:jar:4.1.94.Final:compile
[INFO]    |     |  \- io.netty:netty-handler:jar:4.1.94.Final:compile
[INFO]    |     +- io.netty:netty-codec-http2:jar:4.1.94.Final:compile
[INFO]    |     +- io.netty:netty-resolver-dns:jar:4.1.94.Final:compile
[INFO]    |     |  +- io.netty:netty-resolver:jar:4.1.94.Final:compile
[INFO]    |     |  \- io.netty:netty-codec-dns:jar:4.1.94.Final:compile
[INFO]    |     +- io.netty:netty-resolver-dns-native-macos:jar:osx-x86_64:4.1.94.Final:compile
[INFO]    |     |  \- io.netty:netty-resolver-dns-classes-macos:jar:4.1.94.Final:compile
[INFO]    |     +- io.netty:netty-transport-native-epoll:jar:linux-x86_64:4.1.94.Final:compile
[INFO]    |     |  +- io.netty:netty-transport-native-unix-common:jar:4.1.94.Final:compile
[INFO]    |     |  \- io.netty:netty-transport-classes-epoll:jar:4.1.94.Final:compile
[INFO]    |     \- io.projectreactor.netty:reactor-netty-core:jar:1.1.9:compile
[INFO]    |        \- io.netty:netty-handler-proxy:jar:4.1.94.Final:compile
[INFO]    |           \- io.netty:netty-codec-socks:jar:4.1.94.Final:compile
[INFO]    +- org.springframework:spring-web:jar:6.0.11:compile
[INFO]    |  +- org.springframework:spring-beans:jar:6.0.11:compile
[INFO]    |  \- io.micrometer:micrometer-observation:jar:1.11.2:compile
[INFO]    |     \- io.micrometer:micrometer-commons:jar:1.11.2:compile
[INFO]    \- org.springframework:spring-webflux:jar:6.0.11:compile

Answer 1

The Spring Cloud version for Spring Boot 3.1.5 is 2021.0.5 In your pom Add :

 <spring-cloud.version>2021.0.5</spring-cloud.version>
    <parent>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-parent</artifactId>
            <version>3.1.5</version>
            <relativePath /> 
    </parent>

or search for Spring Boot version match with Spring cloud version on Internet ,this will solve the problem.

<?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>3.1.5</version>
        <relativePath /> <!-- lookup parent from repository -->
    </parent>

    <groupId>com.project</groupId>
    <artifactId>microservices-project</artifactId>
    <packaging>pom</packaging>
    <version>1.0-SNAPSHOT</version>
    <modules>
        <module>product_service</module>
        <module>order_service</module>
        <module>inventory_service</module>
        <module>discovery-server</module>
    </modules>

    <properties>
        <maven.compiler.source>17</maven.compiler.source>
        <maven.compiler.target>17</maven.compiler.target>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <spring-cloud.version>2021.0.5</spring-cloud.version>
    </properties>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.testcontainers</groupId>
                <artifactId>testcontainers-bom</artifactId>
                <version>1.19.2</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>${spring-cloud.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <image>
                        <builder>paketobuildpacks/builder-jammy-base:latest</builder>
                    </image>
                    <excludes>
                        <exclude>
                            <groupId>org.projectlombok</groupId>
                            <artifactId>lombok</artifactId>
                        </exclude>
                    </excludes>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

Answer 2

The issue was resolved after changing the Spring Boot version in my parent microservice's pom.xml, attaching the pom.xml for your reference:

<?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>3.2.0</version>
        <relativePath /> <!-- lookup parent from repository -->
    </parent>

    <groupId>com.project</groupId>
    <artifactId>microservices-project</artifactId>
    <packaging>pom</packaging>
    <version>1.0-SNAPSHOT</version>
    <modules>
        <module>product_service</module>
        <module>order_service</module>
        <module>inventory_service</module>
        <module>discovery-server</module>
    </modules>

    <properties>
        <maven.compiler.source>17</maven.compiler.source>
        <maven.compiler.target>17</maven.compiler.target>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <spring-cloud.version>2023.0.0</spring-cloud.version>
    </properties>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.testcontainers</groupId>
                <artifactId>testcontainers-bom</artifactId>
                <version>1.19.2</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>${spring-cloud.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <image>
                        <builder>paketobuildpacks/builder-jammy-base:latest</builder>
                    </image>
                    <excludes>
                        <exclude>
                            <groupId>org.projectlombok</groupId>
                            <artifactId>lombok</artifactId>
                        </exclude>
                    </excludes>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>