I want to understand the differences between two approaches to creating Docker images for Java applications:

Using only .jar file:

# Use the official OpenJDK image as a base for the runtime environment
FROM openjdk:21-jdk-slim

# Set the working directory in the container
WORKDIR /app

# Copy the pre-built JAR file from the local file system to the container
COPY build/libs/challenge-0.0.1-SNAPSHOT.jar app.jar

# Set the entry point for the Docker container
ENTRYPOINT ["java", "-jar", "app.jar"]

# Expose the port that the application will run on
EXPOSE 8080

Using all components for build:

# Use the official OpenJDK image as a base for the build stage
FROM openjdk:21-jdk-slim AS build

# Set the working directory
WORKDIR /app

# Copy the Gradle wrapper and build files
COPY gradlew .
COPY gradle gradle
COPY build.gradle settings.gradle ./

# Copy project files
COPY src src

# Grant execution permission to gradlew
RUN chmod +x gradlew

# Set environment variables
ENV API_KEY=${API_KEY}

# Build the application
RUN ./gradlew build --no-daemon

# Create a new stage to minimize the final image size
FROM openjdk:21-jdk-slim

# Set the working directory
WORKDIR /app

# Copy the built JAR file from the previous stage
COPY --from=build /app/build/libs/challenge-0.0.1-SNAPSHOT.jar app.jar

# Set the entry point for the Docker container
ENTRYPOINT ["java", "-jar", "app.jar"]

# Expose the port the application will run on
EXPOSE 8080

What are the pros and cons of each approach?
Could you also suggest some upgrades for the Dockerfiles?