Develop Reference

Spring gateway server won't start - java.lang.NoClassDefFoundError: org/springframework/core/metrics/ApplicationStartup

I'm trying to learn about Spring Gateway (how it is put together, how it works).
I'm following this tutorial here, and I run into an issue as I try to run the server. I haven't even done anything specific yet, outside of what this tutorial shows.
There is no mention of that issue on it, and this didn't help my case.
I'm not sure what I'm missing as the issue I'm running into didn't seem to be common.
Any help would be appreciated.
Here is my 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>2.7.7</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.container</groupId>
<artifactId>gateway</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>gateway</name>
<description>Gateway</description>
<properties>
<java.version>11</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-actuator</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-webflux</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-gateway</artifactId>
</dependency>
<dependency>
<groupId>org.springframework</groupId>
<artifactId>spring-core</artifactId>
</dependency>
<dependency>
<groupId>io.projectreactor</groupId>
<artifactId>reactor-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<dependencyManagement>
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-gateway</artifactId>
<version>2.0.0.RC2</version>
<type>pom</type>
<scope>import</scope>
</dependency>
</dependencies>
</dependencyManagement>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
<finalName>gateway-app</finalName>
</build>
<repositories>
<repository>
<id>spring-milestones</id>
<name>Spring Milestones</name>
<url>https://repo.spring.io/milestone</url>
<snapshots>
<enabled>false</enabled>
</snapshots>
</repository>
<repository>
<id>spring-snapshots</id>
<name>Spring Snapshots</name>
<url>https://repo.spring.io/snapshot</url>
<releases>
<enabled>false</enabled>
</releases>
</repository>
</repositories>
<pluginRepositories>
<pluginRepository>
<id>spring-milestones</id>
<name>Spring Milestones</name>
<url>https://repo.spring.io/milestone</url>
<snapshots>
<enabled>false</enabled>
</snapshots>
</pluginRepository>
<pluginRepository>
<id>spring-snapshots</id>
<name>Spring Snapshots</name>
<url>https://repo.spring.io/snapshot</url>
<releases>
<enabled>false</enabled>
</releases>
</pluginRepository>
</pluginRepositories>
</project>

Spring Boot Error in 1st line of pom.xml file

org.apache.maven:maven-compat:jar:3.0 failed to transfer from https://repo.maven.apache.org/maven2 during a previous attempt. This failure was cached in the local repository
and resolution is not reattempted until the update interval of central has elapsed or updates are forced. Original error: Could not transfer artifact org.apache.maven:maven-
compat:jar:3.0 from/to central (https://repo.maven.apache.org/maven2): The operation was cancelled.
<?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>2.5.8-SNAPSHOT</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.example</groupId>
<artifactId>Demoa</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>Demoa</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-data-jpa</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-security</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-thymeleaf</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.thymeleaf.extras</groupId>
<artifactId>thymeleaf-extras-springsecurity5</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-devtools</artifactId>
<scope>runtime</scope>
<optional>true</optional>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<scope>runtime</scope>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.springframework.security</groupId>
<artifactId>spring-security-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
<repositories>
<repository>
<id>spring-milestones</id>
<name>Spring Milestones</name>
<url>https://repo.spring.io/milestone</url>
<snapshots>
<enabled>false</enabled>
</snapshots>
</repository>
<repository>
<id>spring-snapshots</id>
<name>Spring Snapshots</name>
<url>https://repo.spring.io/snapshot</url>
<releases>
<enabled>false</enabled>
</releases>
</repository>
</repositories>
<pluginRepositories>
<pluginRepository>
<id>spring-milestones</id>
<name>Spring Milestones</name>
<url>https://repo.spring.io/milestone</url>
<snapshots>
<enabled>false</enabled>
</snapshots>
</pluginRepository>
<pluginRepository>
<id>spring-snapshots</id>
<name>Spring Snapshots</name>
<url>https://repo.spring.io/snapshot</url>
<releases>
<enabled>false</enabled>
</releases>
</pluginRepository>
</pluginRepositories>
</project>

spring boot config client could not load configuration from config server using bootstrap.properties

Spring boot config client could not load the configuration from config server.
bootstrap.properties
spring.application.name = eon-service
spring.cloud.config.uri=http://localhost:8888
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>2.5.7-SNAPSHOT</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>microservice-eon-service</groupId>
<artifactId>microservice-eon-service</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>microservice-eon-service</name>
<description>Microservice project for Spring Boot</description>
<properties>
<java.version>11</java.version>
<spring-cloud.version>2020.0.5-SNAPSHOT</spring-cloud.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-config</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-bootstrap</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-devtools</artifactId>
<scope>runtime</scope>
<optional>true</optional>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<optional>true</optional>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<dependencyManagement>
<dependencies>
<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>
<excludes>
<exclude>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
</exclude>
</excludes>
</configuration>
</plugin>
</plugins>
</build>
<repositories>
<repository>
<id>spring-milestones</id>
<name>Spring Milestones</name>
<url>https://repo.spring.io/milestone</url>
<snapshots>
<enabled>false</enabled>
</snapshots>
</repository>
<repository>
<id>spring-snapshots</id>
<name>Spring Snapshots</name>
<url>https://repo.spring.io/snapshot</url>
<releases>
<enabled>false</enabled>
</releases>
</repository>
</repositories>
<pluginRepositories>
<pluginRepository>
<id>spring-milestones</id>
<name>Spring Milestones</name>
<url>https://repo.spring.io/milestone</url>
<snapshots>
<enabled>false</enabled>
</snapshots>
</pluginRepository>
<pluginRepository>
<id>spring-snapshots</id>
<name>Spring Snapshots</name>
<url>https://repo.spring.io/snapshot</url>
<releases>
<enabled>false</enabled>
</releases>
</pluginRepository>
</pluginRepositories>
</project>
Errors:
Even the client is not started at all
http://localhost:8080/
Error on console:
APPLICATION FAILED TO START
Description:
No spring.config.import property has been defined
Action:
Add a spring.config.import=configserver: property to your configuration.
If configuration is not required add spring.config.import=optional:configserver: instead.
To disable this check, set spring.cloud.config.enabled=false or
spring.cloud.config.import-check.enabled=false.

To use the legacy bootstrap way of connecting to Config Server,bootstrap must be enabled via a property or the spring-cloud-starter-bootstrap starter.The property is spring.cloud.bootstrap.enabled=true. It must be set as a System Property or environment variable. spring docs

After expending too much time I found two approach to fix this issues -
Basically we have to make the value of spring.cloud.bootstrap.enabled as true by default it is false. This was already mentioned in Spring Cloud doc but I didn't get this point at very first time. After finding the solution of this issue, the point of spring cloud doc has cleared.
First Approach: set the System environment variable in #SpringBootApplicationclass
public static void main(String[] args) throws IOException {
System.setProperty("spring.cloud.bootstrap.enabled","true");
run(Application.class, args);
}
Second Approach: An entry of dependency into pom.xml, it make spring.cloud.bootstrap.enabled
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-bootstrap</artifactId>
</dependency>

Spring - War file is not starting on tomcat

I'm using spring boot with jdk 1.8.
I'm deploying the war to tomcat 8.5 locally on my machine and it starts and works as expected.
When deploying the war to the server which uses tomcat 7.0
I get the following error
SERVER: Unable to process Jar entry
[org/springframework/data/rest/core/support/ResourceMappingUtils.class]
from Jar [jar:file:....
/WEB-INF/lib/spring-data-rest-core-3.0.0.RELEASE.jar!]
My pom.xml file is
<?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>webMavenNeo4j</groupId>
<artifactId>web-maven-neo4j</artifactId>
<packaging>war</packaging>
<version>1.0-SNAPSHOT</version>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.0.0.M7</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>
<neo4j-ogm.version>3.0.0</neo4j-ogm.version>
<spring-data-releasetrain.version>Kay-RELEASE</spring-data-releasetrain.version>
<start-class>social.spring.data.neo4j.Main</start-class>
<maven.compiler.source>1.8</maven.compiler.source>
</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-starter-security</artifactId>
</dependency>
<dependency>
<groupId>com.voodoodyne.jackson.jsog</groupId>
<artifactId>jackson-jsog</artifactId>
<version>1.1</version>
<scope>compile</scope>
</dependency>
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>javax.servlet-api</artifactId>
<version>3.0.1</version>
<scope>provided</scope>
</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-data-neo4j</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-rest</artifactId>
</dependency>
<dependency>
<groupId>com.oracle</groupId>
<artifactId>ojdbc6</artifactId>
<version>11.2.0.2.0</version>
</dependency>
<!-- -->
<dependency>
<groupId>org.neo4j</groupId>
<artifactId>neo4j-ogm-bolt-driver</artifactId>
<version>${neo4j-ogm.version}</version>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-tomcat</artifactId>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>org.neo4j</groupId>
<artifactId>neo4j</artifactId>
<version>3.1.0</version>
<scope>runtime</scope>
</dependency>
<dependency>
<groupId>org.neo4j</groupId>
<artifactId>neo4j-jdbc-driver</artifactId>
<version>3.0</version>
</dependency>
<!-- -->
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
<repositories>
<repository>
<id>spring-snapshots</id>
<name>Spring Snapshots</name>
<url>https://repo.spring.io/snapshot</url>
<snapshots>
<enabled>true</enabled>
</snapshots>
</repository>
<repository>
<id>spring-milestones</id>
<name>Spring Milestones</name>
<url>https://repo.spring.io/milestone</url>
<snapshots>
<enabled>false</enabled>
</snapshots>
</repository>
</repositories>
<pluginRepositories>
<pluginRepository>
<id>spring-snapshots</id>
<name>Spring Snapshots</name>
<url>https://repo.spring.io/snapshot</url>
<snapshots>
<enabled>true</enabled>
</snapshots>
</pluginRepository>
<pluginRepository>
<id>spring-milestones</id>
<name>Spring Milestones</name>
<url>https://repo.spring.io/milestone</url>
<snapshots>
<enabled>false</enabled>
</snapshots>
</pluginRepository>
<pluginRepository>
<id>repository.spring.release</id>
<name>Spring GA Repository</name>
<url>https://repo.spring.io/plugins-release/</url>
</pluginRepository>
</pluginRepositories>
</project>

incompatible types: java.util.Optional<xyz.app.entity.Users> cannot be converted to Users (Springboot compilation error)

I'm getting an incompatible types error message at the following line in my spring-boot application:
RequestDO request = requestRepository.findOne(requestModel.getRequestId());
Users employee = usersRepository.findOne(request.getUsers().getId());
I have not experienced this error in this context before. My app has been running successfully since its first production build about one month ago.
Build failure:
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.1:compile (default-compile) on project tmt: Compilation failure: Compilation failure:
[ERROR] /C:/Users/martin/Documents/Web Projects/home.office/src/main/java/xyz/app/controller/UserController.java:[45,45] incompatible types: java.util.Optional<xyz.app.entity.Users> cannot be converted to xyz.app.entity.Users
[ERROR] /C:/Users/martin/Documents/Web Projects/home.office/src/main/java/xyz/app/controller/RequestController.java:[139,54] incompatible types: java.util.Optional<xyz.app.entity.RequestDO> cannot be converted to xyz.app.entity.RequestDO
[ERROR] /C:/Users/martin/Documents/Web Projects/home.office/src/main/java/xyz/app/controller/RequestController.java:[140,49] incompatible types: java.util.app<xyz.app.entity.Users> cannot be converted to xyz.app.entity.Users
[ERROR] /C:/Users/martin/Documents/Web Projects/home.office/src/main/java/xyz/app/controller/RequestController.java:[155,54] incompatible types: java.util.Optional<v.app.entity.RequestDO> cannot be converted to xyz.app.entity.RequestDO
[ERROR] /C:/Users/martin/Documents/Web Projects/home.office/src/main/java/xyz/app/controller/RequestController.java:[157,49] incompatible types: java.util.Optional<xyz.app.entity.Users> cannot be converted to xyz.app.entity.Users
I have made no code changes since I've last successfully re-built my project. This leads me to believe there has been a recent change in the springframework Maven dependency that has caused my code to break. Is it possible to test this by reverting to an older snapshot in my pom.xml? Also, what could be causing the error?
pom
<?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>xyz.app</groupId>
<artifactId>demo</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>war</packaging>
<name>app</name>
<description>Demo project for Spring Boot</description>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.0.0.BUILD-SNAPSHOT</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-security</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-thymeleaf</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-validation</artifactId>
</dependency>
<dependency>
<groupId>org.hibernate</groupId>
<artifactId>hibernate-validator</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
<groupId>com.microsoft.sqlserver</groupId>
<artifactId>sqljdbc4</artifactId>
<version>4.0</version>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-jdbc</artifactId>
</dependency>
<!--<dependency>
<groupId>com.oracle</groupId>
<artifactId>ojdbc7</artifactId>
<version>12.1.0.1</version>
</dependency>-->
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.springframework.security</groupId>
<artifactId>spring-security-ldap</artifactId>
</dependency>
<dependency>
<groupId>org.apache.directory.server</groupId>
<artifactId>apacheds-server-jndi</artifactId>
<version>1.5.5</version>
</dependency>
<dependency>
<groupId>it.ozimov</groupId>
<artifactId>spring-boot-email-core</artifactId>
<version>0.4.0</version>
</dependency>
<dependency>
<groupId>it.ozimov</groupId>
<artifactId>spring-boot-freemarker-email</artifactId>
<version>0.4.0</version>
</dependency>
<dependency>
<groupId>org.thymeleaf.extras</groupId>
<artifactId>thymeleaf-extras-springsecurity4</artifactId>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
<repositories>
<repository>
<id>spring-snapshots</id>
<name>Spring Snapshots</name>
<url>https://repo.spring.io/snapshot</url>
<snapshots>
<enabled>true</enabled>
</snapshots>
</repository>
<repository>
<id>spring-milestones</id>
<name>Spring Milestones</name>
<url>https://repo.spring.io/milestone</url>
<snapshots>
<enabled>false</enabled>
</snapshots>
</repository>
</repositories>
<pluginRepositories>
<pluginRepository>
<id>spring-snapshots</id>
<name>Spring Snapshots</name>
<url>https://repo.spring.io/snapshot</url>
<snapshots>
<enabled>true</enabled>
</snapshots>
</pluginRepository>
<pluginRepository>
<id>spring-milestones</id>
<name>Spring Milestones</name>
<url>https://repo.spring.io/milestone</url>
<snapshots>
<enabled>false</enabled>
</snapshots>
</pluginRepository>
</pluginRepositories>
</project>

I had a similar issue using 2.0.0.BUILD-SNAPSHOT, so unless you're experimenting with some low-level spring boot features, change the version to 1.5.2.RELEASE

I had a similar issue and I still haven't got the answer.
But there is a solution. May be it help you.
Source option 5 is no longer supported