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Spring Framework:

Creating Your First Spring Boot Application

Postgres DB Setup

We can find more information here.

Configuration

  • External sources
    • Command line parameters
    • JNDI
    • OS environment variables
  • Internal sources
    • Servlet parameters
    • Property files
    • Java configuration

Order of precedence:

  1. Command line parameters
  2. SPRING_APPLICATION_JSON args
  3. Servlet Parameters
  4. JNDI
  5. Java System Properties
  6. OS environment variables
  7. Profile properties
  8. Application properties
  9. @PropertySource annotations
  10. Default properties

We should pick two sources. One will set the defaults, and one to overwrite the default to keep configuration in one of 2 places.

Run Maven with Environment Variables

Since Maven is not aware of environment variables, we need to provide them in the command line.

maven -Dname=value clean install

Common Application Properties

We can find common Spring properties here.

Custom Auto Configuration

Example:

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class MyAutoConfiguration {
  @Bean
  public someObject myMethod(){
    // ...
  }
}

Declaration in resources/META-INF/spring.factories to register autoconfiguration:

org.springframework.boot.autoconfiguration.EnableAutoConfiguration=\com.mypackage.MyAutoConfiguration

Annotations:

  • @ConditionalOnClass
  • @ConditionalOnMissingClass
  • @ConditionalOnBean
  • @ConditionalOnMissingBean
  • @ConditionalOnProperty
  • @ConditionalOnResource

Embedded Servlet Container

By default, Spring Boot uses Tomcat as an embedded container.

But other options are supported:

  • Jetty
  • Undertow

We can swap them out by excluding Tomcat and adding the right dependency in the pom.xml:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <exclusions>
        <exclusion>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
        </exclusion>
    </exclusions>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-jetty</artifactId>
</dependency>

JAR

We can build a jar with maven:

  • mvn package

    Take the compiled code and package it in its distributable format, such as a JAR,

  • mvn install

    Install the package into the local repository, for use as a dependency in other projects locally.

Both of these maven commands will compile your code, clean the /target folder, and will place a new packaged JAR or WAR into that /target folder. It is just the mvn install command will also install the package into the local maven repository, for use as a dependency in other projects locally.

The jar can run by itself using the following command :

java -DDB_URL=jdbc:postgresql://localhost:5432/conference_app -DUSERNAME=postgres -DPASSWORD=pass -jar .\conference-demo-0.0.1-SNAPSHOT.jar

Cloud Supported Platforms

  • Cloud Foundry
  • Heroku
  • Google Cloud
  • Amazon Web Services
  • Microsoft Azure

For more flexibility we can dockerize the application.

Considerations to make with using cloud offering:

  • Logging (using a centralized logging service)
  • Service integration (can differ from our regular Spring Boot config)
  • Firewall and security (securing talking between services)

Heroku Deployment

  • Add a system.properties file to the root of the project

    java.runtime.version=15

  • Go to Heroku and create an account.

  • Click 'add' to create a new project.

  • Pick a deployment method (heroku / git / container ...)

  • Set environment values:

    heroku config:set DB_URL=jdbc:postgresql://localhost:5432/conference_app

    heroku config:set USERNAME=postgres

    heroku config:set PASSWORD=pass

    Make sure to use the actual configuration provided by Heroku's datasource in resources tab.

  • Connect to the db using PGAdmin4 or any db manager and set up the database / data

Check the result:

WAR Deployment

To deploy the application as a war file, we change the pom.xml:

...

<description>Blah blah</description>
<packaging>war</packaging>

...

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-tomcat</artifactId>
    <scope>provided</scope>
</dependency>

...

Copy the war to the webapps folder in an Apache Tomcat Container.

JNDI is useful to look into for setting environment variables.