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How to configure a Spring Boot Application that uses tomcat and has a dependency to another Application uses tomcat

I have a Spring Boot application (App1) that uses an embedded Tomcat. To specify the Port I added server.port=8080 to the application.properties in my main application
and it works fine.
Now I add a dependency to another Spring Boot application (App2) in the pom.xml (because in App1 I need access to the Beans from App2). App2 uses also an embedded Tomcat on a different port.
But when I run App1 it crashes because App2 want to also use the same server.port and configurations - that obviously cannot work.
Is this even possible what I want to achieve? And how would I do this that I can run both App2 in App1? If this is not possible, is it possible to access the Beans from App2 in App1?

I see two options, depending on which one suits your use case conceptually:
you have two Spring Boot applications that need to share the same code: extract this code to a separate project (a regular Java library), build it as a jar file and include into both projects as a dependency; an example could be found in the Creating a Multi Module Project guide;
you have two Spring Boot applications, one of them needs to access the functionality of another: provide and access this functionality as an API, instead of directly importing the beans. There are multiple ways to do this. For example, you could expose the bean functionality as a REST API using Spring's #RestController, and access them from the other side using RestTemplate. See the following guides: Building a RESTful Web Service, Consuming a RESTful Web Service

Use Spring Boot Cloud Config to change application.properties in classpath

I have to change my custom defined spring properties (defined via #ConfigurationProperties beans) during runtime of my Spring Boot application.
Is there any elegant way of doing this using Spring Cloud Config?
I don't want to use an external application.properties in a git repository (as the spring boot application gets shipped to customers and I dont' want to create a git repository for everyone of them).
I just want to access and change the local application.properties (the one in the classpath, located in src/main/resources) file in my Spring container or (if thats not possible) in the Spring Cloud Config Server, which I could embed into my Spring Boot app. Is that possible somehow?
BTW: The goal is to create a visual editor for the customers, so that they can change the application.properties during runtime in their spring boot app.

Spring Boot supports profile based application configuration. Just add application-<profile>.properties file. Then just when running the application select a profile depending on the environment making use of spring.profiles.active.
-Dspring.profiles.active=dev
This will run the application with application-dev.properties file (overriding the default application.properties, i.e you can just leave the common stuff in the default file and change the rest depending on the env)
On a side note, having a repo for configuration is not a must. You could just place them in the class path and give a search-location.
spring:
application:
name: config-server
profiles:
active: native
cloud:
config:
server:
native:
search-locations: classpath:configs/

It actually is possible and in the end quite easy to achieve. It just took me a whole day to get all the information together. Maybe this helps someone:
You basically just need Spring Actuator, but for a certain endpoint, you also need the spring cloud dependency. (to make Post requests to the /env endpoint of Spring Actuator)
To alter your config at runtime, just add the following to your application.properties:
management.endpoints.web.exposure.include: env,refresh
management.endpoint.env.post.enabled: true //this property is only available when spring cloud is added as dependency to your project
If you (like me) don't need the feature of an externalized config, then you also have to add the following (otherwise, your Spring app will not start and throw an error that some config is missing)
spring.cloud.config.enabled: false
Now, if you send a POST request to /actuator/env endpoint with an object in the HTTP body in the form of {"name":"...", "value":"..."} (name is the name of a config property), then your config gets changed. To check that, you can do a GET request to /actuator/env/[name_of_config_property] and see that your config property has changed. No need to restart your app.
Don't forget to secure the /actuator endpoint in your SecurityConfig if you use a custom one.
It seems to me that you neither need the #RefreshScope annotation at your config classes nor the /actuator/refresh endpoint to "apply" the config changes.

Maybe what your looking for could be achieved with Spring cloud config and spring cloud bus. It's explained here: https://cloud.spring.io/spring-cloud-config/reference/html/#_push_notifications_and_spring_cloud_bus
In summary, any change on configuration sent an event to the spring cloud bus and you can then reload app context or configuration with new properties.

Spring boot is not able to get configuration file from my file system

I am trying to build a sample app on Spring boot and spring cloud.
I have written my database and hibernate configuration in config.properties property file which is located in my desktop and I want my spring boot to make use of this configuration.
My project have 3 modules
API
DataLayer
ServiceLayer
This is the code that I have mentioned in the application.property file of API
spring.profiles.active=native
spring.cloud.config.server.native.searchLocation=C:/Users/DEV/Desktop/configuration/config.properties
and the property file of DataLayer and ServiceLayer is empty
But when I run the API I am getting the following error
***************************
APPLICATION FAILED TO START
***************************
Description:
Failed to configure a DataSource: 'url' attribute is not specified and no embedded datasource could be configured.
Reason: Failed to determine a suitable driver class
Action:
Consider the following:
If you want an embedded database (H2, HSQL or Derby), please put it on the classpath.
If you have database settings to be loaded from a particular profile you may need to activate it (no profiles are currently active).
Process finished with exit code 1
Could any one help me with this error.
Thanks in advance.

This is can not be done from your API module. You added configuration server properties to your 'client' (from configuration point of view) application.
If you want to use Spring Cloud Config to configure your project you should have separate application that will manage your configuration. Let's call it config-server. (You should properly configure maven or gradle dependencies, see documentation) To configure usage of native profile in the config-server in application.properties you have to add properties that you mentioned in the question (example for native profile).
spring.profiles.active=native
spring.cloud.config.server.native.searchLocation=file:<path-to-the-directory-with-conf-files> or classpath:/<path-to-the-directory-with-conf-files>
Note: config-server can handle configuration for lot of services.
More can be found in the documentation Spring Cloud Config Server section.
Then in your API (or any other module) which is a spring boot app you should add spring-cloud-config-client dependency and add bootstrap.properties (or .yml) configuration file. There your should add properties that will describe communication with config-server. By default config-server listens on port 8888.
spring.application.name=<your app name>
spring.cloud.config.uri=http://localhost:8888 # this is also default value for this property
At start-up it will go by http to config-server and fetch your configuration properties based on service name (spring.application.name).
More can be found in Spring Cloud Config client section
Important: make sure your properly organize files in your configuration directory (which is used by native profile by config-server), find some samples. Property files naming are important. For start you can try to use your-application-name.properties

You have to have file: prefixed to the property file location.
Documentation from https://cloud.spring.io/spring-cloud-config/multi/multi__spring_cloud_config_server.html
There is also a “native” profile in the Config Server that does not use Git but loads the config files from the local classpath or file system (any static URL you want to point to with spring.cloud.config.server.native.searchLocations). To use the native profile, launch the Config Server with spring.profiles.active=native.
[Note]
Remember to use the file: prefix for file resources (the default without a prefix is usually the classpath). As with any Spring Boot
configuration, you can embed ${}-style environment placeholders, but
remember that absolute paths in Windows require an extra / (for
example, file:///${user.home}/config-repo).
[Warning]
The default value of the searchLocations is identical to a local Spring Boot application (that is, [classpath:/, classpath:/config,
file:./, file:./config]). This does not expose the
application.properties from the server to all clients, because any
property sources present in the server are removed before being sent
to the client.
[Tip] A filesystem backend is great for getting started quickly and for testing. To use it in production, you need to be sure that the
file system is reliable and shared across all instances of the Config
Server.

JHipster registry, change properties value in spring cloud config server

I'm trying to migrate from monolithic web application to microservices.
For doing this I'm using JHipster v 4.11.1 (very helpful!).
My problem is:
In JHipster registry (central-config folder) I wrote some property files and every microservice, on startup, read the owned properties.
I need to change this properties on runtime both from registry and from every microservices.
There are any ways to do this? I have to use kafka or somethings like that?
JHipster Registry is a Spring Cloud Config server and should allow this behavior but I'm new with this stuff and maybe I lost some information. For now I don't use Git or SVN repository, but only a native configuration.

How to make java war file load configuration properties from external URL to deploy on AWS Elastic Beanstlk

I have created a project using JHipster (Spring Boot) and bundled it with a .war file. The application is working fine when deployed to AWS EC2 instance.
Now the management wants me to deploy it on AWS Elastic Beanstalk and move all the configurations outside the .war file. For instance, The DB connection, email configuration, PayPal configuration not to be bundled with the .war file, whereas, it should load the properties from external resource like S3.
Can someone please help how can I change the application.yml and application-dev.yml etc to load values from some external source?

Take a look to Spring Cloud Config, which is initially meant to be used on spring cloud microservices, but can be used in order to solve your problem.
The approach here is, that in the early boot up phase your application connects to a spring cloud config server, to get external configuration. More on this, you can change several config properties, while your deployed application is running.
For the storage, cloud config enables git for production use case to store your configs, and I am pretty sure you can somehow use S3 for this...if needed.