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Difference between an Express server and an embedded server in spring boot

I've started learning Spring Boot coming from a NodeJS/Express background and I'm wondering what's the difference between the server that we create ourselves in an express app that listens on a certain port, and the Tomcat server in a spring application also called a container ? Why can't we do the same in a spring boot application where we create the server ourselves ?
const app = express();
app.listen(3000, () => console.log("Server listening on port 3000"));

Welcome to the Spring Ecosystem. We hope you enjoy your stay!
My first bit of advice, forget everything you know about Express because Spring is very different. I have not used Express in a while, but I remember it had a very programmatic approach. While that is possible in Spring, the most popular approach is declarative with annotations. Or, if you are old and like old technology, you can configure everything with XML.
What's Tomcat? Tomcat is a implementation of various Jakarta EE (formally Java EE) specifications. Depending on the Spring Boot version, you may see packages that start with jakarta or javax. Tomcat implements, Jakarta Servlet, Server Pages, Expression Language, WebSocket, Annotations, and Authentications. You can read more about each specification here. Note: Spring Boot by itself does not necessary use all of these modules and mostly Spring has many abstraction layers on top of them anyway, so you rarely will work with Tomcat directly. Specifically, spring-boot-starter-tomcat is the Spring module that uses Tomcat, and is most often included as a transitive dependency through spring-boot-starter-web.
Now, to answer your question...
Spring Boot Web configures Tomcat for you. You can definitely override this behavior! One basic way is through configuration properties. Anything under server.tomcat. A good IDE should autocomplete and show you the options. You can also change the address and port of the Tomcat server with server.address and server.port. Another popular property developers change is server.error.whitelabel.enabled. They set it to false and provide their own error page. Here is a great example. By the way, Baeldung offers a lot of free Spring tutorials and guides. It is a great place to get started. They also offer paid courses with certifications.
FYI, you do not have to use Tomcat. Read more here.

Spring Cloud Consul Config not working with Spring Boot 2.6.6

I tried to follow the new changes with the latests versions of Spring, where the bootstrap.yaml has been removed, and use the "spring.config.import" property, but I am not able to make my application work (discovery is working fine, but not config server). I am doing so many tries and errors, so it does not make so much sense to copy my current properties, but I will give all the details, so maybe someone is able to identify what is going on:
In my POM, there is already the next dependencies: "spring-cloud-starter-config", "spring-cloud-starter-consul-all", "spring-cloud-starter-consul-discovery" and "spring-cloud-starter-consul-config". Spring Cloud version is "2021.0.1" and Consul "3.1.0".
Main class annotated with #EnableDiscoveryClient
Using "application.properties-development", not YAML, and SPRING_PROFILES_ACTIVE=development
Application name is "profiles"
In my Consul instance, in the "Key / Value" section, I have the next structure: Consul Structure (/config/development/profiles and JSON with the properties to load).
It would be nice that, as with the Cloud Config Server, if no property file is found, it would allow me to run the application.
Thank you in advance.
Cheers!

Elasticsearch Client is defaulting to localhost

I am using spring.data.elasticsearch with Elasticsearch 7.14.1 in my Spring Boot (2.5.4) application.
My application.properties is something like this
spring.elasticsearch.rest.uris=elasticsearch:9200
spring.data.elasticsearch.cluster=elasticsearch:9200
spring.data.elasticsearch.repositories.enabled=true
This works fine as long as the invocation is from localhost, no issues. However, when I try to bring up my Spring Boot container, I see a failure with NoReachableHostException
reactor.core.Exceptions$ErrorCallbackNotImplemented: org.springframework.data.elasticsearch.client.NoReachableHostException: Host 'localhost:9200' not reachable. Cluster state is offline.
blah-blah-service
Caused by: org.springframework.data.elasticsearch.client.NoReachableHostException: Host **'localhost:9200'** not reachable. Cluster state is offline.
blah-blah-service
at org.springframework.data.elasticsearch.client.reactive.SingleNodeHostProvider.lambda$lookupActiveHost$3(SingleNodeHostProvider.java:101)
Clearly, my suggestion to use "elasticsearch" host (defined network, that is tested and accessible from within and outside docker containers), hasn't gone well with Spring Data for whatever reason. I have even used
#PropertySource("classpath:mysearch.properties")
in my application to try and coax these properties into the app, but doesn't look like anything works. Is there something I am missing in my Elasticsearch configuration or otherwise?
PS: I have exercised curl http://elasticsearch:9200 from within the container and find no issues

These configurations are Spring Boot specific, Spring Data Elasticsearch does not use them. But as far as I can see, you are configuring the transport client (cluster entry, should not be used anyway) and the imperative REST client, but according to the error message you are using the reactive REST client.
According to the Spring Boot documentation you would need to set spring.data.elasticsearch.client.reactive.endpoints

In the .properties file, I used the below and solved the issue for me;
spring.elasticsearch.rest.uris=http://localhost:<port_number>
spring.data.elasticsearch.client.reactive.endpoints=localhost:<port_number>

How to integrate GraphiQL with Spring-Boot?

My target is to build a GraphQL server on Spring with (1) GraphiQL IDE (2) dynamic GraphQL schema at run-time. My GraphQL engine is GraphQL-Java.
In my first try, I use graphql-java-spring-boot-starter-webmvc and graphiql-spring-boot-starter.
Both the GraphQL server and the GraphiQL work well.
However, under the graphql-java-spring-boot-starter-webmvc framework, a #Bean of GraphQL class is needed. In this bean, the schema is loaded when the server starts so it could not been updated.
In my second try, I don't use graphql-java-spring-boot-starter-webmvc. Instead, I choose spring-boot-starter-web to start the web server and define my own RestController. This is easy to update the GraphQL instance. But I don't find a way to integrate with GraphiQL. I googled GraphiQL+Spring but all solutions are with graphql-java-spring-boot-starter.
Appreciate if anyone could provide me an idea on either approach.

It can be enabled in properties:
graphql.graphiql.enabled=true
It is accessible via the root url +/graphiql example http://localhost:8080/graphiql
You can find a good detailed example here : https://github.com/NoorKrichen/GraphQL-Spring-Boot-Example

Do you have a sample of your setup in git?
It sounds like some configuration problem. But naturally using graphql-java-spring-boot-starter-webmvc all your *.graphql schemas should be picked up in the configured schema resource path. check if you have the path set in your application.yml or if your schema is in the configured path if its already set or by default.
On your second point: "I googled GraphiQL+Spring but all solutions are with graphql-java-spring-boot-starter."
This makes sense for quick guides and demos as using Springboot the plumbing is somehow hidden away from you so that you can focus on the technology at hand being demo'd in this case GraphQl.
On GraphiQL:
Sounds like you are intending to have this embedded with your application, you may not want to do so in production. Depending on your use case there are many other alternatives that are standalone and gives you all the functionality of GraphiQL plus more e.g Altair Graphql Client and Insomnia to name a few.

Integrating Hibernate to Spring running on embedded jetty

I have just returned to Spring after 5 years of gap and it seems lot is changed. I have a task to create a REST Service using Spring with hibernate as an ORM, So far I am able to run a basic Rest Service using embedded jetty and able to make GET/POST calls, the next is to integrate hibernate into it so that the data fetch/Sent operation actually use MySQL instead of sending hard-coded response(which I have done currently).
The issue is earlier I used to work on Spring MVC using Tomcat where we had web.xml to define the dispatcher servlet and application-context which in turn were used to define hibernate config and other beans declaration, but now having embedded jetty I am not finding a way to integrate hibernate to my REST app, Is the way to add configuration is changed from XML to class based config. I searched over internet but maybe I am out of words or not using correct keywords, in short, Have no luck finding some solution to integrate hibernate to my Spring app which is using embedded jetty.
Could some please breif me about the recent changes or point me to the right tutorial ?
Any help appreciated, thanks in advance !
ps - I have used this example to progress so far https://github.com/pethoalpar/SpringMvcJettyExample

Yes , lot of changes in these 5 years and one of the game-changer is spring-boot
If you want to build a brand new project especially if you want to run the web application on the embedded container such as Jetty , you can check out spring-boot.It already provides integration with Jetty , hibernate and Spring MVC REST service.
The end result is that you just need to change a little bit configuration (most probably the DB connection info) and you can quickly get a production-ready REST service backed by JPA/Hibernate which can just run without any XML configuration anymore.
There are tons of tutorials in Internet talking about how to do it . You should easily find them out such as this using the keywords something likes "springboot webservice hibernate jetty" etc.