My Java / Spring Boot Journey — Part 1 (Containerized App with Hot Reload)

Jack Fajardo — Wed, 22 Oct 2025 04:41:09 +0000

Introduction:

This post will mainly serve as personal notes where I document my daily learnings throughout my journey into API development with Java.

First of all, I want to make sure I bring over the practices I learned back when I was still doing Node.js development, and keep the mindset of building applications with a strong and reliable infrastructure.

With that in mind, I should think not just like a regular developer, but also with a cloud-oriented mindset — because I believe everything starts with architecture, and a strong foundation is the key to delivering high-quality results.

Preparation:

With all that being said, I didn’t jump in right away — I first took the time to plan things out.

I started by listing my goals and decided to focus mainly on the setup first. I’ve been employed in several companies before, and it’s always a headache trying to run an existing backend project on a new machine as a new hire.

Most of the time, the only documentation available is a README file with just two commands to start the app — only to later find out that it doesn’t work on my machine because of missing prerequisites that weren’t mentioned anywhere. Then I’d end up bothering my new co-workers for help when they’re clearly busy.

With that experience in mind, I want to make this app easy to set up right from the start.

My App goals are:

Build a basic Spring Boot application with a single “Hello World” endpoint ~ starting simple (CRUD app later on).
Include necessary dependencies such as a database, and ensure hot-reload is enabled for faster development.
Make the project easy to set up and run for anyone — not just myself.
If it runs on my machine, it should run on others without issues.
Keep the app's folder structure minimal for now
Make it future-ready for cloud deployment (e.g., AWS) — with configuration files properly structured from the beginning.

My personal goals are:

Strengthen my OOP knowledge while building this app, since I come from a functional programming background.
Understand Java core concepts and the Spring Boot folder structure and layering (controllers, models, services, etc.).
Follow and research tutorials along the way.
Use AI whenever I have questions or get stuck.
Compare Spring Boot and Express.js to identify their similarities and differences in REST API development.
Apply modern tools or dependencies if they can speed up development time.

Now that I have goals in mind, I should make them into reality.

Generating the App:

Since the goal is to make a springboot app, I learned that https://start.spring.io/ is the go-to for everyone who wants to start out. It generates a new springboot app for you easily.

On spring initializr, you can choose which dependencies you want right from the beginning and input your project name:

It generated a project with folder structure as follows:

canspring/
├── src/
│   ├── main/
│   │   ├── java/
│   │   │   └── com/example/canspring/
│   │   │       └── CanspringApplication.java
│   │   └── resources/
│   │       ├── application.properties
│   │       ├── static/
|   |       └── templates/        
│   └── test/
│       └── java/
│           └── com/example/canspring/
│               └── CanspringApplicationTests.java
├── .mvn/
│   └── wrapper/
│       └── maven-wrapper.properties
├── pom.xml
├── mvnw
├── mvnw.cmd
├── HELP.md
├── .gitignore
└── .gitattributes

To actually run this generated app locally, and get a hello world output, people would normally need to install the Java SDK — but I decided not to do that. My goal is to ensure this app runs consistently on any computer, and if someone else has a different version of Java installed, a lot of things could easily fail.

So to proceed,

Containerizing the App: (Analogy)

Docker is an amazing tool that allows us to package our app and make it portable. This is the solution I chose so the app can be easily set up on any machine — without needing local installations of Java or PostgreSQL. Containerized apps like this can also be smoothly deployed to AWS or any cloud server.

So basically, if I put the Spring Boot app and the database (I chose PostgreSQL) inside containers instead of installing them manually on my computer. Each container acts like a mini-computer that already has everything it needs — correct Java version, correct database, correct settings.

So the goal is if I run the project, Docker starts both and connects them:

App container → runs Spring Boot
Database container → runs PostgreSQL

No need to install Java or PostgreSQL on my local machine — everything is self-contained. But of course, I needed to download and install Docker Desktop: https://docs.docker.com/desktop/setup/install/windows-install/ and this should be the only thing I need to install moving forward. Nothin more...

Diagram:

┌───────────────────────────────┐
│        Docker Engine          │
│   (runs on your computer)     │
└───────────────────────────────┘
                │
   ┌────────────┼───────────────────────────┐
   │            │                           │
┌──────────┐  ┌──────────┐   (optional more containers later)
│ App      │  │ DB       │     
│ Container│  │ Container│
│ (Spring  │  │ (Postgre │
│  Boot)   │  │   SQL)   │
└──────────┘  └──────────┘
      │            │
      └─ connects ─┘  via *internal* Docker network


< NO need to install Java or Postgres locally >
< portable, same setup runs on any computer or cloud >

I followed this tutorial in installing Docker: https://www.youtube.com/watch?v=ZyBBv1JmnWQ
Note that Docker Desktop needs either Hyper-V (can be enabled in your computer's bios settings) or WSL2 (if running on a windows machine like me)

Containerizing the App: (Actual)

Now that I have docker locally installed, I can begin packaging my app. To do this, I need to add 2 files in my generated spring boot project (Dockerfile and docker-compose.yml) so Docker can run both the Spring Boot app and PostgreSQL.

canspring/
├── src/
│   ├── main/
│   │   ├── java/
│   │   │   └── com/example/canspring/
│   │   │       └── CanspringApplication.java
│   │   └── resources/
│   │       ├── application.properties   <- defines connection to database
│   │       ├── static/
|   |       └── templates/ 
│   └── test/
│       └── java/
│           └── com/example/canspring/
│               └── CanspringApplicationTests.java
├── .mvn/
│   └── wrapper/
│       └── maven-wrapper.properties
├── pom.xml
├── mvnw
├── mvnw.cmd
├── HELP.md
├── .gitignore
├── .gitattributes
├── Dockerfile              ← tells Docker how to build and run this Spring Boot app
└── docker-compose.yml      ← starts multiple containers together (app + database)

Below is the content of my DockerFile:

FROM eclipse-temurin:17-jdk

# Set work directory
WORKDIR /app

# Copy pom.xml and download dependencies (cached)
COPY pom.xml .
COPY mvnw ./
COPY .mvn .mvn/
RUN ./mvnw dependency:go-offline

# Copy the entire source code
COPY src ./src

# Expose port 8080
EXPOSE 8080

# Run Spring Boot in dev mode (restart + live reload)
ENTRYPOINT ["./mvnw", "spring-boot:run"]

And... below is the content of my docker-compose.yml file:

version: "3.9"

services:
  app:
    build:
      context: .
      dockerfile: Dockerfile
    container_name: canspring
    ports:
      - "8080:8080"
    develop:
      watch:
        # Sync source files directly into the container (instant updates)
        - action: sync+restart
          path: ./src
          target: /app/src
        # If POM changes, rebuild the whole image
        - action: rebuild
          path: pom.xml
    environment:
      SPRING_PROFILES_ACTIVE: docker
    depends_on:
      - db

  db:
    image: postgres:15
    container_name: postgresdb
    restart: always
    environment:
      POSTGRES_DB: mydb
      POSTGRES_USER: postgres
      POSTGRES_PASSWORD: postgres
    ports:
      - "5432:5432"
    volumes:
      - pgdata:/var/lib/postgresql/data

volumes:
  pgdata:

Also need to add some database config to applicaton.properties:

spring.application.name=canspring
spring.datasource.url=jdbc:postgresql://db:5432/mydb
spring.datasource.username=postgres
spring.datasource.password=postgres
spring.jpa.hibernate.ddl-auto=update
spring.jpa.show-sql=true

# Enable DevTools in Docker
spring.devtools.restart.enabled=true
spring.devtools.livereload.enabled=true
spring.devtools.remote.secret=mysecret
spring.thymeleaf.cache=false

These docker files should work as config files to package our app and run it. The command I needed to input is:
docker-compose up --build

here is the full terminal log:

PS C:\Users\Jack\Downloads\canspring> docker-compose up --build
time="2025-10-22T11:08:32+08:00" level=warning msg="C:\\Users\\Jack\\Downloads\\canspring\\docker-compose.yml: the attribute `version` is obsolete, it will be ignored, please remove it to avoid potential confusion"
[+] Building 2.5s (15/15) FINISHED
 => [internal] load local bake definitions                                                                     0.0s
 => => reading from stdin 520B                                                                                 0.0s
 => [internal] load build definition from Dockerfile                                                           0.0s
 => => transferring dockerfile: 423B                                                                           0.0s
 => [internal] load metadata for docker.io/library/eclipse-temurin:17-jdk                                      1.8s
 => [auth] library/eclipse-temurin:pull token for registry-1.docker.io                                         0.0s
 => [internal] load .dockerignore                                                                              0.0s
 => => transferring context: 2B                                                                                0.0s
 => [1/7] FROM docker.io/library/eclipse-temurin:17-jdk@sha256:54a16ef91e00c11ac9b05029faa5efd02c37296844204a  0.0s
 => => resolve docker.io/library/eclipse-temurin:17-jdk@sha256:54a16ef91e00c11ac9b05029faa5efd02c37296844204a  0.0s
 => [internal] load build context                                                                              0.0s
 => => transferring context: 1.35kB                                                                            0.0s
 => CACHED [2/7] WORKDIR /app                                                                                  0.0s
 => CACHED [3/7] COPY pom.xml .                                                                                0.0s
 => CACHED [4/7] COPY mvnw ./                                                                                  0.0s
 => CACHED [5/7] COPY .mvn .mvn/                                                                               0.0s
 => CACHED [6/7] RUN ./mvnw dependency:go-offline                                                              0.0s
 => [7/7] COPY src ./src                                                                                       0.1s
 => exporting to image                                                                                         0.2s
 => => exporting layers                                                                                        0.1s
 => => exporting manifest sha256:44333803fb316c5a1afd958c9859e16b005c9fc1cb35140bca23891ff83f7c55              0.0s
 => => exporting config sha256:2605cb31244d69b6f9a4fc5d689dcb5464acb90e867fda7e03cbb2de8a213659                0.0s
 => => exporting attestation manifest sha256:94c4a4de744afd58150fd9b401c847335bc217158f440010ad60f5ae686e37c6  0.0s
 => => exporting manifest list sha256:5a37253c53212b184db420b14b84f39552cb709994b2fa5af7e9697f0bbabcea         0.0s
 => => naming to docker.io/library/canspring-app:latest                                                        0.0s
 => => unpacking to docker.io/library/canspring-app:latest                                                     0.0s
 => resolving provenance for metadata file                                                                     0.0s
[+] Running 4/4
 ✔ canspring-app              Built                                                                            0.0s
 ✔ Network canspring_default  Created                                                                          0.1s
 ✔ Container postgresdb       Created                                                                          0.1s
 ✔ Container canspring        Created                                                                          0.1s
Attaching to canspring, postgresdb
postgresdb  |
postgresdb  | PostgreSQL Database directory appears to contain a database; Skipping initialization
postgresdb  |
postgresdb  | 2025-10-22 03:08:36.639 UTC [1] LOG:  starting PostgreSQL 15.14 (Debian 15.14-1.pgdg13+1) on x86_64-pc-linux-gnu, compiled by gcc (Debian 14.2.0-19) 14.2.0, 64-bit
postgresdb  | 2025-10-22 03:08:36.641 UTC [1] LOG:  listening on IPv4 address "0.0.0.0", port 5432
postgresdb  | 2025-10-22 03:08:36.641 UTC [1] LOG:  listening on IPv6 address "::", port 5432
postgresdb  | 2025-10-22 03:08:36.646 UTC [1] LOG:  listening on Unix socket "/var/run/postgresql/.s.PGSQL.5432"
postgresdb  | 2025-10-22 03:08:36.660 UTC [29] LOG:  database system was shut down at 2025-10-22 03:05:17 UTC
postgresdb  | 2025-10-22 03:08:36.687 UTC [1] LOG:  database system is ready to accept connections
canspring   | [INFO] Scanning for projects...
canspring   | [INFO]
canspring   | [INFO] -----------------------< com.example:canspring >------------------------
canspring   | [INFO] Building canspring 0.0.1-SNAPSHOT
canspring   | [INFO]   from pom.xml
canspring   | [INFO] --------------------------------[ jar ]---------------------------------
canspring   | [INFO]
canspring   | [INFO] >>> spring-boot:3.5.6:run (default-cli) > test-compile @ canspring >>>
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/io/micrometer/micrometer-observation/1.15.4/micrometer-observation-1.15.4.pom
Downloaded from central: https://repo.maven.apache.org/maven2/io/micrometer/micrometer-observation/1.15.4/micrometer-observation-1.15.4.pom (3.8 kB at 7.6 kB/s)
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/io/micrometer/micrometer-commons/1.15.4/micrometer-commons-1.15.4.pom
Downloaded from central: https://repo.maven.apache.org/maven2/io/micrometer/micrometer-commons/1.15.4/micrometer-commons-1.15.4.pom (3.4 kB at 45 kB/s)
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/org/jboss/logging/jboss-logging/3.6.1.Final/jboss-logging-3.6.1.Final.pom
Downloaded from central: https://repo.maven.apache.org/maven2/org/jboss/logging/jboss-logging/3.6.1.Final/jboss-logging-3.6.1.Final.pom (18 kB at 241 kB/s)
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/org/jboss/logging/logging-parent/1.0.3.Final/logging-parent-1.0.3.Final.pom
Downloaded from central: https://repo.maven.apache.org/maven2/org/jboss/logging/logging-parent/1.0.3.Final/logging-parent-1.0.3.Final.pom (5.7 kB at 78 kB/s)
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/org/jboss/jboss-parent/42/jboss-parent-42.pom
Downloaded from central: https://repo.maven.apache.org/maven2/org/jboss/jboss-parent/42/jboss-parent-42.pom (76 kB at 812 kB/s)
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/com/fasterxml/classmate/1.7.0/classmate-1.7.0.pom
Downloaded from central: https://repo.maven.apache.org/maven2/com/fasterxml/classmate/1.7.0/classmate-1.7.0.pom (7.0 kB at 98 kB/s)
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/com/fasterxml/oss-parent/56/oss-parent-56.pom
Downloaded from central: https://repo.maven.apache.org/maven2/com/fasterxml/oss-parent/56/oss-parent-56.pom (24 kB at 327 kB/s)
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/net/bytebuddy/byte-buddy/1.17.7/byte-buddy-1.17.7.pom
Downloaded from central: https://repo.maven.apache.org/maven2/net/bytebuddy/byte-buddy/1.17.7/byte-buddy-1.17.7.pom (19 kB at 252 kB/s)
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/net/bytebuddy/byte-buddy-parent/1.17.7/byte-buddy-parent-1.17.7.pom
Downloaded from central: https://repo.maven.apache.org/maven2/net/bytebuddy/byte-buddy-parent/1.17.7/byte-buddy-parent-1.17.7.pom (65 kB at 745 kB/s)
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/jakarta/activation/jakarta.activation-api/2.1.4/jakarta.activation-api-2.1.4.pom
Downloaded from central: https://repo.maven.apache.org/maven2/jakarta/activation/jakarta.activation-api/2.1.4/jakarta.activation-api-2.1.4.pom (19 kB at 247 kB/s)
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/org/glassfish/jaxb/jaxb-runtime/4.0.5/jaxb-runtime-4.0.5.pom
Downloaded from central: https://repo.maven.apache.org/maven2/org/glassfish/jaxb/jaxb-runtime/4.0.5/jaxb-runtime-4.0.5.pom (11 kB at 134 kB/s)
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/com/sun/xml/bind/mvn/jaxb-runtime-parent/4.0.5/jaxb-runtime-parent-4.0.5.pom
Downloaded from central: https://repo.maven.apache.org/maven2/com/sun/xml/bind/mvn/jaxb-runtime-parent/4.0.5/jaxb-runtime-parent-4.0.5.pom (1.2 kB at 15 kB/s)
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/com/sun/xml/bind/mvn/jaxb-parent/4.0.5/jaxb-parent-4.0.5.pom
Downloaded from central: https://repo.maven.apache.org/maven2/com/sun/xml/bind/mvn/jaxb-parent/4.0.5/jaxb-parent-4.0.5.pom (35 kB at 467 kB/s)
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/com/sun/xml/bind/jaxb-bom-ext/4.0.5/jaxb-bom-ext-4.0.5.pom
Downloaded from central: https://repo.maven.apache.org/maven2/com/sun/xml/bind/jaxb-bom-ext/4.0.5/jaxb-bom-ext-4.0.5.pom (3.5 kB at 46 kB/s)
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/org/glassfish/jaxb/jaxb-core/4.0.5/jaxb-core-4.0.5.pom
Downloaded from central: https://repo.maven.apache.org/maven2/org/glassfish/jaxb/jaxb-core/4.0.5/jaxb-core-4.0.5.pom (3.7 kB at 50 kB/s)
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/org/eclipse/angus/angus-activation/2.0.2/angus-activation-2.0.2.pom
Downloaded from central: https://repo.maven.apache.org/maven2/org/eclipse/angus/angus-activation/2.0.2/angus-activation-2.0.2.pom (4.0 kB at 47 kB/s)
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/org/eclipse/angus/angus-activation-project/2.0.2/angus-activation-project-2.0.2.pom
Downloaded from central: https://repo.maven.apache.org/maven2/org/eclipse/angus/angus-activation-project/2.0.2/angus-activation-project-2.0.2.pom (21 kB at 282 kB/s)
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/org/glassfish/jaxb/txw2/4.0.5/txw2-4.0.5.pom
Downloaded from central: https://repo.maven.apache.org/maven2/org/glassfish/jaxb/txw2/4.0.5/txw2-4.0.5.pom (1.8 kB at 24 kB/s)
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/com/sun/xml/bind/mvn/jaxb-txw-parent/4.0.5/jaxb-txw-parent-4.0.5.pom
Downloaded from central: https://repo.maven.apache.org/maven2/com/sun/xml/bind/mvn/jaxb-txw-parent/4.0.5/jaxb-txw-parent-4.0.5.pom (1.2 kB at 17 kB/s)
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/com/sun/istack/istack-commons-runtime/4.1.2/istack-commons-runtime-4.1.2.pom
Downloaded from central: https://repo.maven.apache.org/maven2/com/sun/istack/istack-commons-runtime/4.1.2/istack-commons-runtime-4.1.2.pom (1.6 kB at 21 kB/s)
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/com/sun/istack/istack-commons/4.1.2/istack-commons-4.1.2.pom
Downloaded from central: https://repo.maven.apache.org/maven2/com/sun/istack/istack-commons/4.1.2/istack-commons-4.1.2.pom (26 kB at 333 kB/s)
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/org/aspectj/aspectjweaver/1.9.24/aspectjweaver-1.9.24.pom
Downloaded from central: https://repo.maven.apache.org/maven2/org/aspectj/aspectjweaver/1.9.24/aspectjweaver-1.9.24.pom (2.2 kB at 26 kB/s)
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/net/bytebuddy/byte-buddy-agent/1.17.7/byte-buddy-agent-1.17.7.pom
Downloaded from central: https://repo.maven.apache.org/maven2/net/bytebuddy/byte-buddy-agent/1.17.7/byte-buddy-agent-1.17.7.pom (14 kB at 184 kB/s)
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/org/jboss/logging/jboss-logging/3.6.1.Final/jboss-logging-3.6.1.Final.jar
Downloaded from central: https://repo.maven.apache.org/maven2/org/jboss/logging/jboss-logging/3.6.1.Final/jboss-logging-3.6.1.Final.jar (62 kB at 703 kB/s)
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/com/fasterxml/classmate/1.7.0/classmate-1.7.0.jar
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/net/bytebuddy/byte-buddy/1.17.7/byte-buddy-1.17.7.jar
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/org/glassfish/jaxb/jaxb-runtime/4.0.5/jaxb-runtime-4.0.5.jar
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/org/glassfish/jaxb/jaxb-core/4.0.5/jaxb-core-4.0.5.jar
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/org/eclipse/angus/angus-activation/2.0.2/angus-activation-2.0.2.jar
Downloaded from central: https://repo.maven.apache.org/maven2/com/fasterxml/classmate/1.7.0/classmate-1.7.0.jar (69 kB at 644 kB/s)
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/org/glassfish/jaxb/txw2/4.0.5/txw2-4.0.5.jar
Downloaded from central: https://repo.maven.apache.org/maven2/org/glassfish/jaxb/txw2/4.0.5/txw2-4.0.5.jar (73 kB at 421 kB/s)
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/com/sun/istack/istack-commons-runtime/4.1.2/istack-commons-runtime-4.1.2.jar
Downloaded from central: https://repo.maven.apache.org/maven2/org/eclipse/angus/angus-activation/2.0.2/angus-activation-2.0.2.jar (27 kB at 131 kB/s)
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/org/aspectj/aspectjweaver/1.9.24/aspectjweaver-1.9.24.jar
Downloaded from central: https://repo.maven.apache.org/maven2/com/sun/istack/istack-commons-runtime/4.1.2/istack-commons-runtime-4.1.2.jar (26 kB at 107 kB/s)
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/io/micrometer/micrometer-observation/1.15.4/micrometer-observation-1.15.4.jar
Downloaded from central: https://repo.maven.apache.org/maven2/io/micrometer/micrometer-observation/1.15.4/micrometer-observation-1.15.4.jar (75 kB at 226 kB/s)
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/io/micrometer/micrometer-commons/1.15.4/micrometer-commons-1.15.4.jar
Downloaded from central: https://repo.maven.apache.org/maven2/org/glassfish/jaxb/jaxb-runtime/4.0.5/jaxb-runtime-4.0.5.jar (920 kB at 2.3 MB/s)
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/jakarta/activation/jakarta.activation-api/2.1.4/jakarta.activation-api-2.1.4.jar
Downloaded from central: https://repo.maven.apache.org/maven2/io/micrometer/micrometer-commons/1.15.4/micrometer-commons-1.15.4.jar (49 kB at 113 kB/s)
canspring   | Downloading from central: https://repo.maven.apache.org/maven2/net/bytebuddy/byte-buddy-agent/1.17.7/byte-buddy-agent-1.17.7.jar
Downloaded from central: https://repo.maven.apache.org/maven2/jakarta/activation/jakarta.activation-api/2.1.4/jakarta.activation-api-2.1.4.jar (67 kB at 131 kB/s)
Downloaded from central: https://repo.maven.apache.org/maven2/net/bytebuddy/byte-buddy-agent/1.17.7/byte-buddy-agent-1.17.7.jar (366 kB at 616 kB/s)
Downloaded from central: https://repo.maven.apache.org/maven2/org/glassfish/jaxb/jaxb-core/4.0.5/jaxb-core-4.0.5.jar (139 kB at 219 kB/s)
Downloaded from central: https://repo.maven.apache.org/maven2/org/aspectj/aspectjweaver/1.9.24/aspectjweaver-1.9.24.jar (2.2 MB at 3.3 MB/s)
Downloaded from central: https://repo.maven.apache.org/maven2/net/bytebuddy/byte-buddy/1.17.7/byte-buddy-1.17.7.jar (9.0 MB at 11 MB/s)
canspring   | [INFO]
canspring   | [INFO] --- resources:3.3.1:resources (default-resources) @ canspring ---
canspring   | [INFO] Copying 1 resource from src/main/resources to target/classes
canspring   | [INFO] Copying 0 resource from src/main/resources to target/classes
canspring   | [INFO]
canspring   | [INFO] --- compiler:3.14.0:compile (default-compile) @ canspring ---
canspring   | [INFO] Recompiling the module because of changed source code.
canspring   | [INFO] Compiling 1 source file with javac [debug parameters release 17] to target/classes
canspring   | [INFO]
canspring   | [INFO] --- resources:3.3.1:testResources (default-testResources) @ canspring ---
canspring   | [INFO] skip non existing resourceDirectory /app/src/test/resources
canspring   | [INFO]
canspring   | [INFO] --- compiler:3.14.0:testCompile (default-testCompile) @ canspring ---
canspring   | [INFO] Recompiling the module because of changed dependency.
canspring   | [INFO] Compiling 1 source file with javac [debug parameters release 17] to target/test-classes
canspring   | [INFO]
canspring   | [INFO] <<< spring-boot:3.5.6:run (default-cli) < test-compile @ canspring <<<
canspring   | [INFO]
canspring   | [INFO]
canspring   | [INFO] --- spring-boot:3.5.6:run (default-cli) @ canspring ---
canspring   | [INFO] Attaching agents: []
canspring   |
canspring   |   .   ____          _            __ _ _
canspring   |  /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
canspring   | ( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
canspring   |  \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
canspring   |   '  |____| .__|_| |_|_| |_\__, | / / / /
canspring   |  =========|_|==============|___/=/_/_/_/
canspring   |
canspring   |  :: Spring Boot ::                (v3.5.6)
canspring   |
canspring   | 2025-10-22T03:08:44.466Z  INFO 187 --- [canspring] [  restartedMain] c.e.canspring.CanspringApplication       : Starting CanspringApplication using Java 17.0.16 with PID 187 (/app/target/classes started by root in /app)
canspring   | 2025-10-22T03:08:44.468Z  INFO 187 --- [canspring] [  restartedMain] c.e.canspring.CanspringApplication       : The following 1 profile is active: "docker"
canspring   | 2025-10-22T03:08:44.513Z  INFO 187 --- [canspring] [  restartedMain] .e.DevToolsPropertyDefaultsPostProcessor : Devtools property defaults active! Set 'spring.devtools.add-properties' to 'false' to disable
canspring   | 2025-10-22T03:08:44.514Z  INFO 187 --- [canspring] [  restartedMain] .e.DevToolsPropertyDefaultsPostProcessor : For additional web related logging consider setting the 'logging.level.web' property to 'DEBUG'
canspring   | 2025-10-22T03:08:44.979Z  INFO 187 --- [canspring] [  restartedMain] .s.d.r.c.RepositoryConfigurationDelegate : Bootstrapping Spring Data JPA repositories in DEFAULT mode.
canspring   | 2025-10-22T03:08:44.997Z  INFO 187 --- [canspring] [  restartedMain] .s.d.r.c.RepositoryConfigurationDelegate : Finished Spring Data repository scanning in 9 ms. Found 0 JPA repository interfaces.
canspring   | 2025-10-22T03:08:45.346Z  INFO 187 --- [canspring] [  restartedMain] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port 8080 (http)
canspring   | 2025-10-22T03:08:45.357Z  INFO 187 --- [canspring] [  restartedMain] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
canspring   | 2025-10-22T03:08:45.357Z  INFO 187 --- [canspring] [  restartedMain] o.apache.catalina.core.StandardEngine    : Starting Servlet engine: [Apache Tomcat/10.1.46]
canspring   | 2025-10-22T03:08:45.390Z  INFO 187 --- [canspring] [  restartedMain] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
canspring   | 2025-10-22T03:08:45.391Z  INFO 187 --- [canspring] [  restartedMain] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 876 ms
canspring   | 2025-10-22T03:08:45.409Z  WARN 187 --- [canspring] [  restartedMain] .s.b.d.a.RemoteDevToolsAutoConfiguration : Listening for remote restart updates on /.~~spring-boot!~/restart
canspring   | 2025-10-22T03:08:45.566Z  INFO 187 --- [canspring] [  restartedMain] o.hibernate.jpa.internal.util.LogHelper  : HHH000204: Processing PersistenceUnitInfo [name: default]
canspring   | 2025-10-22T03:08:45.638Z  INFO 187 --- [canspring] [  restartedMain] org.hibernate.Version                    : HHH000412: Hibernate ORM core version 6.6.29.Final
canspring   | 2025-10-22T03:08:45.676Z  INFO 187 --- [canspring] [  restartedMain] o.h.c.internal.RegionFactoryInitiator    : HHH000026: Second-level cache disabled
canspring   | 2025-10-22T03:08:45.905Z  INFO 187 --- [canspring] [  restartedMain] o.s.o.j.p.SpringPersistenceUnitInfo      : No LoadTimeWeaver setup: ignoring JPA class transformer
canspring   | 2025-10-22T03:08:45.934Z  INFO 187 --- [canspring] [  restartedMain] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Starting...
canspring   | 2025-10-22T03:08:46.101Z  INFO 187 --- [canspring] [  restartedMain] com.zaxxer.hikari.pool.HikariPool        : HikariPool-1 - Added connection org.postgresql.jdbc.PgConnection@1280d447
canspring   | 2025-10-22T03:08:46.103Z  INFO 187 --- [canspring] [  restartedMain] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Start completed.
canspring   | 2025-10-22T03:08:46.194Z  INFO 187 --- [canspring] [  restartedMain] org.hibernate.orm.connections.pooling    : HHH10001005: Database info:
canspring   |   Database JDBC URL [Connecting through datasource 'HikariDataSource (HikariPool-1)']
canspring   |   Database driver: undefined/unknown
canspring   |   Database version: 15.14
canspring   |   Autocommit mode: undefined/unknown
canspring   |   Isolation level: undefined/unknown
canspring   |   Minimum pool size: undefined/unknown
canspring   |   Maximum pool size: undefined/unknown
canspring   | 2025-10-22T03:08:46.473Z  INFO 187 --- [canspring] [  restartedMain] o.h.e.t.j.p.i.JtaPlatformInitiator       : HHH000489: No JTA platform available (set 'hibernate.transaction.jta.platform' to enable JTA platform integration)
canspring   | 2025-10-22T03:08:46.477Z  INFO 187 --- [canspring] [  restartedMain] j.LocalContainerEntityManagerFactoryBean : Initialized JPA EntityManagerFactory for persistence unit 'default'
canspring   | 2025-10-22T03:08:46.513Z  WARN 187 --- [canspring] [  restartedMain] JpaBaseConfiguration$JpaWebConfiguration : spring.jpa.open-in-view is enabled by default. Therefore, database queries may be performed during view rendering. Explicitly configure spring.jpa.open-in-view to disable this warning
canspring   | 2025-10-22T03:08:46.849Z  INFO 187 --- [canspring] [  restartedMain] o.s.b.d.a.OptionalLiveReloadServer       : LiveReload server is running on port 35729
canspring   | 2025-10-22T03:08:46.878Z  INFO 187 --- [canspring] [  restartedMain] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port 8080 (http) with context path '/'
canspring   | 2025-10-22T03:08:46.887Z  INFO 187 --- [canspring] [  restartedMain] c.e.canspring.CanspringApplication       : Started CanspringApplication in 2.768 seconds (process running for 3.116)

I determined that:

This shows that application has been built
springboot app has also connected to a postgres database
and started on localhost:8080

Next thing is to just create a get endpoint that would return a 'Hello World' text:

I added a controller file in \canspring\src\main\java\com\example\canspring\controller\HelloController.java with the following code below

package com.example.canspring.controller;

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class HelloController {

    // A simple REST endpoint
    @GetMapping("/hello")
    public String hello() {
        return "Hello World!";
    }
}

Then tested this on my browser by typing localhost:8080/hello on the URL and it did not work :( it showed me a white label error which means that the endpoint does not exist...

So far I understood that every time there are new files created inside my project, like the controller I just created, I always needed to rebuild the docker image so that those files can be copied by docker...

when I rebuilt my spring boot app using docker-compose up --build, the app started... Then I went to localhost:8080/hello again and everything worked!

Then I updated my controller to output a new text: Hello World! with springboot and docker!

I see logs that it detected that there was a change in the controller I updated:

            ⦿ Syncing service "app" after 2 changes were detected
canspring   | 2025-10-22T04:20:03.491Z  INFO 180 --- [canspring] [ionShutdownHook] o.s.b.w.e.tomcat.GracefulShutdown        : Commencing graceful shutdown. Waiting for active requests to complete
canspring   | 2025-10-22T04:20:03.497Z  INFO 180 --- [canspring] [tomcat-shutdown] o.s.b.w.e.tomcat.GracefulShutdown        : Graceful shutdown complete
canspring   | 2025-10-22T04:20:03.503Z  INFO 180 --- [canspring] [ionShutdownHook] j.LocalContainerEntityManagerFactoryBean : Closing JPA EntityManagerFactory for persistence unit 'default'
canspring   | 2025-10-22T04:20:03.509Z  INFO 180 --- [canspring] [ionShutdownHook] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Shutdown initiated...
canspring   | 2025-10-22T04:20:03.517Z  INFO 180 --- [canspring] [ionShutdownHook] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Shutdown completed.
            ⦿ service(s) ["app"] restarted
canspring exited with code 143 (restarting)
canspring   | [INFO] Scanning for projects...
canspring   | [INFO]
canspring   | [INFO] -----------------------< com.example:canspring >------------------------
canspring   | [INFO] Building canspring 0.0.1-SNAPSHOT
canspring   | [INFO]   from pom.xml
canspring   | [INFO] --------------------------------[ jar ]---------------------------------
canspring   | [INFO]
canspring   | [INFO] >>> spring-boot:3.5.6:run (default-cli) > test-compile @ canspring >>>
canspring   | [INFO]
canspring   | [INFO] --- resources:3.3.1:resources (default-resources) @ canspring ---
canspring   | [INFO] Copying 1 resource from src/main/resources to target/classes
canspring   | [INFO] Copying 0 resource from src/main/resources to target/classes
canspring   | [INFO]
canspring   | [INFO] --- compiler:3.14.0:compile (default-compile) @ canspring ---
canspring   | [INFO] Recompiling the module because of changed source code.
canspring   | [INFO] Compiling 2 source files with javac [debug parameters release 17] to target/classes
canspring   | [INFO]
canspring   | [INFO] --- resources:3.3.1:testResources (default-testResources) @ canspring ---
canspring   | [INFO] skip non existing resourceDirectory /app/src/test/resources
canspring   | [INFO]
canspring   | [INFO] --- compiler:3.14.0:testCompile (default-testCompile) @ canspring ---
canspring   | [INFO] Recompiling the module because of changed dependency.
canspring   | [INFO] Compiling 1 source file with javac [debug parameters release 17] to target/test-classes
canspring   | [INFO]
canspring   | [INFO] <<< spring-boot:3.5.6:run (default-cli) < test-compile @ canspring <<<
canspring   | [INFO]
canspring   | [INFO]
canspring   | [INFO] --- spring-boot:3.5.6:run (default-cli) @ canspring ---
canspring   | [INFO] Attaching agents: []
canspring   |
canspring   |   .   ____          _            __ _ _
canspring   |  /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
canspring   | ( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
canspring   |  \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
canspring   |   '  |____| .__|_| |_|_| |_\__, | / / / /
canspring   |  =========|_|==============|___/=/_/_/_/
canspring   |
canspring   |  :: Spring Boot ::                (v3.5.6)
canspring   |
canspring   | 2025-10-22T04:20:08.785Z  INFO 180 --- [canspring] [  restartedMain] c.e.canspring.CanspringApplication       : Starting CanspringApplication using Java 17.0.16 with PID 180 (/app/target/classes started by root in /app)
canspring   | 2025-10-22T04:20:08.787Z  INFO 180 --- [canspring] [  restartedMain] c.e.canspring.CanspringApplication       : The following 1 profile is active: "docker"
canspring   | 2025-10-22T04:20:08.829Z  INFO 180 --- [canspring] [  restartedMain] .e.DevToolsPropertyDefaultsPostProcessor : Devtools property defaults active! Set 'spring.devtools.add-properties' to 'false' to disable
canspring   | 2025-10-22T04:20:08.829Z  INFO 180 --- [canspring] [  restartedMain] .e.DevToolsPropertyDefaultsPostProcessor : For additional web related logging consider setting the 'logging.level.web' property to 'DEBUG'
canspring   | 2025-10-22T04:20:09.276Z  INFO 180 --- [canspring] [  restartedMain] .s.d.r.c.RepositoryConfigurationDelegate : Bootstrapping Spring Data JPA repositories in DEFAULT mode.
canspring   | 2025-10-22T04:20:09.293Z  INFO 180 --- [canspring] [  restartedMain] .s.d.r.c.RepositoryConfigurationDelegate : Finished Spring Data repository scanning in 9 ms. Found 0 JPA repository interfaces.
canspring   | 2025-10-22T04:20:09.624Z  INFO 180 --- [canspring] [  restartedMain] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port 8080 (http)
canspring   | 2025-10-22T04:20:09.635Z  INFO 180 --- [canspring] [  restartedMain] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
canspring   | 2025-10-22T04:20:09.636Z  INFO 180 --- [canspring] [  restartedMain] o.apache.catalina.core.StandardEngine    : Starting Servlet engine: [Apache Tomcat/10.1.46]
canspring   | 2025-10-22T04:20:09.667Z  INFO 180 --- [canspring] [  restartedMain] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
canspring   | 2025-10-22T04:20:09.669Z  INFO 180 --- [canspring] [  restartedMain] w.s.c.ServletWebServerApplicationContext : Root WebApplicationContext: initialization completed in 839 ms
canspring   | 2025-10-22T04:20:09.685Z  WARN 180 --- [canspring] [  restartedMain] .s.b.d.a.RemoteDevToolsAutoConfiguration : Listening for remote restart updates on /.~~spring-boot!~/restart
canspring   | 2025-10-22T04:20:09.805Z  INFO 180 --- [canspring] [  restartedMain] o.hibernate.jpa.internal.util.LogHelper  : HHH000204: Processing PersistenceUnitInfo [name: default]
canspring   | 2025-10-22T04:20:09.843Z  INFO 180 --- [canspring] [  restartedMain] org.hibernate.Version                    : HHH000412: Hibernate ORM core version 6.6.29.Final
canspring   | 2025-10-22T04:20:09.868Z  INFO 180 --- [canspring] [  restartedMain] o.h.c.internal.RegionFactoryInitiator    : HHH000026: Second-level cache disabled
canspring   | 2025-10-22T04:20:10.045Z  INFO 180 --- [canspring] [  restartedMain] o.s.o.j.p.SpringPersistenceUnitInfo      : No LoadTimeWeaver setup: ignoring JPA class transformer
canspring   | 2025-10-22T04:20:10.064Z  INFO 180 --- [canspring] [  restartedMain] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Starting...
canspring   | 2025-10-22T04:20:10.176Z  INFO 180 --- [canspring] [  restartedMain] com.zaxxer.hikari.pool.HikariPool        : HikariPool-1 - Added connection org.postgresql.jdbc.PgConnection@7e47f6d5
canspring   | 2025-10-22T04:20:10.177Z  INFO 180 --- [canspring] [  restartedMain] com.zaxxer.hikari.HikariDataSource       : HikariPool-1 - Start completed.
canspring   | 2025-10-22T04:20:10.235Z  INFO 180 --- [canspring] [  restartedMain] org.hibernate.orm.connections.pooling    : HHH10001005: Database info:
canspring   |   Database JDBC URL [Connecting through datasource 'HikariDataSource (HikariPool-1)']
canspring   |   Database driver: undefined/unknown
canspring   |   Database version: 15.14
canspring   |   Autocommit mode: undefined/unknown
canspring   |   Isolation level: undefined/unknown
canspring   |   Minimum pool size: undefined/unknown
canspring   |   Maximum pool size: undefined/unknown
canspring   | 2025-10-22T04:20:10.441Z  INFO 180 --- [canspring] [  restartedMain] o.h.e.t.j.p.i.JtaPlatformInitiator       : HHH000489: No JTA platform available (set 'hibernate.transaction.jta.platform' to enable JTA platform integration)
canspring   | 2025-10-22T04:20:10.444Z  INFO 180 --- [canspring] [  restartedMain] j.LocalContainerEntityManagerFactoryBean : Initialized JPA EntityManagerFactory for persistence unit 'default'
canspring   | 2025-10-22T04:20:10.478Z  WARN 180 --- [canspring] [  restartedMain] JpaBaseConfiguration$JpaWebConfiguration : spring.jpa.open-in-view is enabled by default. Therefore, database queries may be performed during view rendering. Explicitly configure spring.jpa.open-in-view to disable this warning
canspring   | 2025-10-22T04:20:10.753Z  INFO 180 --- [canspring] [  restartedMain] o.s.b.d.a.OptionalLiveReloadServer       : LiveReload server is running on port 35729
canspring   | 2025-10-22T04:20:10.776Z  INFO 180 --- [canspring] [  restartedMain] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port 8080 (http) with context path '/'
canspring   | 2025-10-22T04:20:10.785Z  INFO 180 --- [canspring] [  restartedMain] c.e.canspring.CanspringApplication       : Started CanspringApplication in 2.324 seconds (process running for 2.629)

Then I refreshed the browser: and saw that the changes reflected!

Conclusion:

In summary for Part 1 of my journey:

I was able to build a Spring Boot app that is containerized (easy to setup and run) and currently connected to a local database without JAVA or Postgres installations. It also hot-reloads whenever I make changes to its classes (controller for now).

Next steps:

Hot reload should also detect newly added files in the project. Docker should sync those and reflect the changes — not just content changes, but also new files added to a directory.
Add new endpoints to build a CRUD app (probably a TODO List app or an Expense Tracker app)

Please input your insights on the comments down below! I would greatly appreciate it! Thank you for learning with me!

DEV Community: Jack Fajardo

My Java / Spring Boot Journey — Part 1 (Containerized App with Hot Reload)