===== Spring Boot ======

Spring boot - is a Java framework, which claims to retrieve the default configurations from the libraries loaded to the path.

==== Rest Controller ====
Logging the exposed endpoints.
To log the exposed endpoints the change in the application.properties is required:

application.properties
<code>
logging.level.web=TRACE
logging.level.org.springframework.web=TRACE
</code>


Example output
<code>
12:14:48.398 [main] TRACE o.s.w.s.m.m.a.RequestMappingHandlerMapping  
	i.d.l.d.g.RestGroupController:
	{GET [/rest/, /rest/groups]}: index(String,Optional)
	{POST /rest/groups, consumes [application/json]}: createGroup(Group)
	{POST /rest/groups/{groupId}/member}: addUserToGroup(String,String)
	{DELETE /rest/groups, consumes [application/json]}: deleteRole(String)
	{GET [/rest/, /rest/groups/member/{memberId}]}: groupsByMember(String)
	{GET [/rest/, /rest/groups/{id}]}: groupById(String)
	{DELETE /rest/groups/{groupId}/member}: removeUserFromGroup(String,String)
12:14:48.418 [main] TRACE o.s.w.s.m.m.a.RequestMappingHandlerMapping  
	i.d.l.d.r.RestRoleController:
	{GET [/rest/, /rest/roles]}: index(String,Optional)
	{POST /rest/roles/{roleId}/member}: addMemberToRole(String,String,String)
	{DELETE /rest/roles, consumes [application/json]}: deleteRole(String)
	{POST /rest/roles, consumes [application/json]}: createRole(Role)
	{DELETE /rest/roles/{roleId}/member}: removeUserFromRole(String,String,String)
</code>

===== New project =====
Use [[https://start.spring.io/|Spring Initializr]] to generate a new project.

Import it to the Idea IDE via: 
{{https://lh3.googleusercontent.com/-eDxwVOJ3dzs/Wpp5XRC7hkI/AAAAAAAAADw/L4JVWKY-81gPOnyjZekGnsZt44ccnP6UgCHMYCw/s0/2018-03-03_11-30-52.png}}


===== Gradle =====

Spring boot is normally either 
  * packaged to an executable jar, together with dependencies, or
  * packaged as a deployable war, so that it may be deployed to a Tomcat etc.

== Running the app ==

Running the app with gradle, choosing the port
<code>
./gradlew bootRun --args='--server.port=8888'
</code>


== Building a JAR ==

To create a Jar with gradle - add the following to build.gradle

to automagically resolve dependencies within the current spring boot version - you must apply a special plugin. \\
The dependencies will be resolved acording to the BOM - bill of materials. \\
Check https://docs.spring.io/spring-boot/docs/2.0.0.RELEASE/gradle-plugin/reference/html/#packaging-executable-jars
<code>
apply plugin: 'io.spring.dependency-management'
</code>

Build the jar by using **gradlew**. \\ This will produce a JAR e.g. under **build\libs\PROJECTNAME\complete.jar**
<code>
../../gradlew BootJar
</code>

Start the jar
<code>
java -jar complete.jar
</code>

{{https://lh3.googleusercontent.com/-nSi9oHOqYxY/Wphe7hn3NKI/AAAAAAAAADY/Pc9ecqMiTpIkSgR9VfKIcDAft7SrIN8wQCHMYCw/s0/2018-03-01_21-13-31.png}}

== Building a WAR ==

build.gradle
<code>
apply plugin: 'io.spring.dependency-management'
apply plugin: 'war'
</code>

Build the jar by using **gradlew**. \\ This will produce a JAR e.g. under **build\libs\PROJECTNAME\complete.war**
<code>
../../gradlew BootWar
</code>


===== Spring Profiles ======

Spring profiles can be activated in multiple ways, e.g. 

by setting the environment variable

<code>
export spring_profiles_active=dev
</code>


by passing an argument to the java virtual machine
<code>
-Dspring.profiles.active=dev
</code>


When activated - you get the option to create a profile dependant properties files.


  * .properties files are located in  /resources/application-{profile}.properties
    * ./resources/application-dev.properties
    * ./resources/application-stage.properties
    * ./resources/application-prod.properties    * 
  * ./resources/application.properties - is the default file, which is active
  * .properties files are additive


To pick a default profile - you need to set in in applicaiton.properties

application.properties
<sxh shell>
# the default profile which is used. Can be overridden by specifying the Spring profile as -Dspring.profiles.active or in another way.
# without that the "spring.profiles.active" will not fall back to the value "default"
spring.profiles.active=dev
</sxh>


==== Continous build ====
Spring boot applications - can be configured to 
 - react on file changes
 - rebuild the application e.g. to a jar
 - redeploy the jar, e.g. to the ThomCat



== Step 1 ==

Add dev-tools to the dependencies,
so that the rebuilt app is hot-swaped on the app server.

In **build.gradle**
<code>
dependencies {

	// makes Spring boot hot swap rebuilt jar to tomcat
	developmentOnly 'org.springframework.boot:spring-boot-devtools'
}
</code>


== Step 2 ==

In a separate terminal, start the continuous build of application.

Do that in a separate terminal, because the command doesn't come back, but listens for file changes.

It works in **Vagrant**, in a **Ubuntu guest-VM**,  on **host-Windows**, on a "shared-folder".<br>
But unfortunately, changes, originating form **vagrant-host-machine** - are NOT recognized.<br>
To trigger rebuild, hot-swap - one needs to change some file in the **vagrant-guest-machine**.

Starts continuos build skipping the tests
<code>
./gradlew build -xtest --continuous
</code>

To propagate a change triggering a rebuild - you need to modify the file on the guest-system
<code>
echo "" >> HelloController.java
</code>

== Step3 Launch the app ==

The app will be built and propagated 
<code>
./gradlew bootRun --args='--server.port=8888'
</code>



====== Native Image ======

# Prerequisites

Install java 

<code>
# java open GraalVM from liberica "native image kit"
sdk install java 22.3.r17-nik < /dev/null

# switch
sdk use java 22.3.r17-nik

# set the Java_home
source "~/.sdkman/bin/sdkman-init.sh"
</code>

# Quickstart

Build a native image

<code>
./gradlew nativeCompile
</code>

[native-image-plugin] Native Image written to: /PROJECTDIR/throttling-enforcer/build/native/nativeCompile

Run

<code>
/PROJECTDIR/throttling-enforcer/build/native/nativeCompile/demo
</code>



===== Rest Controller ====

CRUD repositories ''CrudRepository<Entity, Id>''

can create queries by convention.

Just name the methods according to the convention https://docs.spring.io/spring-data/jpa/docs/current/reference/html/#jpa.query-methods.query-creation
and they will be mapped to queries.


===== API Versioning ====

URI Versioning - Twitter
  * http://localhost:8080/vl/person
  * http://localhost:8080/v2/person


Request Parameter versioning - Amazon
  * http://localhost:8080/person?version=l
  * http://localhost:8080/pcrson?vcrsion=2


(Custom) headers versioning - Microsoft
  * SAME-URL headers=(X-API-VERSION=l]
  * SAME-URL headers=[X-API-VERSION=2]


Media type versioning - GitHub
  * SAME-URL produces=application/vnd.company.app-vl+json
  * SAME-URL produces=application/vnd.company.app-v2+json


===== Libs =====

==== Hystrix - Circuit Breaker ====
https://www.baeldung.com/spring-cloud-netflix-hystrix

==== Feign - declarative REST client ====

Reduces the glue-code to the minimum.
Need only to express - what to call and receive the response DTO

https://cloud.spring.io/spring-cloud-netflix/multi/multi_spring-cloud-feign.html




<sxh java>
package com.in28minutes.microservices.currencyconversionservice;

import org.springframework.cloud.netflix.feign.FeignClient;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;

@FeignClient(name = "currency-exchange-service", url = "localhost:8000")
public interface CurrencyExchangeServiceProxy {

    @GetMapping("/currency-exchange/from/{from}/to/{to}")
    public CurrencyConversionBean retrieveExchangeValue
            (@PathVariable("from") String from, @PathVariable("to") String to);
}

</sxh>
==== Ribbon - Client based load balancer ====

Exposes multiple deployments under one URL

{{https://s3.eu-central-1.amazonaws.com/alf-digital-wiki-pics/sharex/K9ELIqz2Uf.png}}

{{https://s3.eu-central-1.amazonaws.com/alf-digital-wiki-pics/sharex/Od4LgsV7Ij.png}}


==== Zuul API Gateway ====

API Gateway in SPring




==== EUreka Namingserver ====

Allows to register / discover services on a naming server.

Has a GUI to list available services.

{{https://s3.eu-central-1.amazonaws.com/alf-digital-wiki-pics/sharex/qVkyO04yvD.png}}



==== Cloud Sleuth - unique tracing id to requests ====

adds a unique tracing id to requests



==== Zipkin - Distributed Tracing Server ====


Central tracing server. 

  * Like ELK.
  * and CloudWatch


{{https://s3.eu-central-1.amazonaws.com/alf-digital-wiki-pics/sharex/ce868zFAte.png}}
{{https://s3.eu-central-1.amazonaws.com/alf-digital-wiki-pics/sharex/EG0bVz0lrr.png}}
==== Spring Cloud Bus  ====

Can use it to refresh the configs of all services,
by sending a message via the bus.




=====  Docker ===== 

== Build manually without gradle ==

<sxh java>
docker build --build-arg JAR_FILE=build/libs/\*.jar -t springio/demo-consume-api -f src/main/docker/Dockerfile  .
</sxh>

== Build with Gradle ==

You can build a tagged docker image with Gradle in one command:

<sxh java>
sudo su
./gradlew bootBuildImage --imageName=springio/demo-consume-api


sudo docker images

</sxh>

== And run ==

<sxh java>
sudo docker run -p 8080:8080 springio/demo-consume-api
</sxh>