This document discusses how to create a Spring Boot application using Spring Data JPA and PostgreSQL. It includes steps to set up the dependencies, configure the PostgreSQL database, create a JPA entity class for employees, develop the Spring Data repository interface, build RESTful API endpoints with a controller class, and handle exceptions. The application provides CRUD operations for an employee management system using Spring Boot, JPA, and a PostgreSQL database.

1. Spring Boot + Spring Data JPA +
PostgreSQL Example by Ramesh Fadatare
In this article, you’ll learn how to configure Spring Boot, Spring Data JPA to support a
PostgreSQL database.
원본: https://www.javaguides.net/2019/08/spring-boot-spring-data-jpa-postgresql-example.html
옮긴이: monad

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1 Technologies and Tools Used
Technologies and Tools Used
• Spring Boot - 2.2.7
• JDK - 1.8 or later
• Spring Framework - 5.2.6.RELEASE
• Hibernate - 5.4.15.Final
• JPA – (spring-boot-starter-data-jpa)
2.2.7.RELEASE
• Maven - 3.2+
• IDE - Eclipse or Spring Tool Suite (STS)
• PostgreSQL - 42.2.5
Once, all the details are entered, click on Generate Project button will generate a spring boot project and downloads it. Next,
Unzip the downloaded zip file and import into your favorite IDE as a maven project.

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2 Dependency
Add PostgreSQL Dependency
Provide PostgreSQL in your pom.xml file.
<dependency>
<groupId>org.postgresql</groupId>
<artifactId>postgresql</artifactId>
<scope>runtime</scope>
</dependency>
Add Spring Data JPA Dependency
It’s very easy to configure Spring Boot to use the PostgreSQL database.
We are using Spring Data JPA with default Hibernate implementation so
which will support out of the box to work with different database
vendor without changing underlying code.
Add Spring Data JPA dependency to pom.xml file.
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>

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3 Configure PostgreSQL Database
Configure PostgreSQL Database
Let’s configure Spring Boot to use PostgreSQL as our database. We are simply adding PostgreSQL database URL, username, and password in the
src/main/resources/application.properties file.
#spring boot server port, default is 8080
server.port=8989
#datasource
spring.datasource.url=jdbc:postgresql://localhost:5432/hibernatedb
spring.datasource.username=postgres
spring.datasource.password=pa$$w0rd
spring.jpa.show-sql=true
## Hibernate Properties
# The SQL dialect makes Hibernate generate better SQL for the chosen database
spring.jpa.properties.hibernate.dialect=org.hibernate.dialect.PostgreSQL95Dialect
# Hibernate ddl auto(create, create-drop, validate, update)
spring.jpa.hibernate.ddl-auto=update
For this simple application, it is
necessary to download and install
PostgreSQL.
And create a database with name
‘hibernatdb’.

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4 What we’ll build
What we’ll build
We will build a CRUD Restful APIs for a Simple Employee Management System using Spring Boot2 JPA and PostgreSQL database. Following are
five REST APIs (Controller handler methods) are created for Employee resource.

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5 Packaging Structure
Packaging Structure
Following is the packaging structure of our Employee Management System.

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6 Create JPA Entity – Employee.java
Employee.java

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7 Create Spring Data Repository –
EmployeeRepository.java
EmployeeRepository.java

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8 Create Spring Rest Controller –
EmployeeController.java(1/2)
EmployeeController.java

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8 Create Spring Rest Controller –
EmployeeController.java(2/2)
EmployeeController.java

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ResourceNotFoundException.java
Let’s see what Spring Boot does when an exception is thrown from a
Resource. We can specify the Response Status for a specific exception
along with the definition of the Exception of ‘@ResponseStatus’
annotation.
9 What happens when we throw an Exception?
Exception(Error) Handling for RESTful Services
Spring Boot provides a good default implementation for exception
handling for RESTful Services. Let’s quickly look at the default Handling
features provided by Spring Boot.
Resource Not Present
Heres what happens when you fire a request to not resource found:
http://localhost:8989/some-dummy-url
That’s a cool error response. It contains all the details that are typically
needed.

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10 Customizing Error Response Structure –
ErrorDetails.java
Customize Error Response Structure
Default error response provided by Spring Boot contains all the details that are typically needed. However, you might want to create a framework
independent response structure for your organization. In that case, you can define a specific error response structure.

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11 ExceptionHandler for using ErrorDetails
Exception Handler for using ErrorDetails – GlobalExceptionHandler.java
To use ErrorDetails to return the error response. Let’s create a GlobalExceptionHandler class annotated with @ControllerAdvice annotation. This
class handles exception specific and global exception in a single place.

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12 SpringApplication.run()
SpringApplication.run()
1. Download and install PostgreSQL
2. Create Database - hibernatedb

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13 Run Application
Run Application
This spring boot application has an entry point Java class called Springboot2PostgresqlJpaHibernateCrudExampleApplication.java with the public
static void main(String[] args) method, which you can run to start the application.
@SpringBootApplication is a convenience annotation that adds all of the following:
• @Configuration tags the class as a source of bean definitions for the application context.
• @EnableAutoConfiguration tells Spring Boot to start adding beans based on classpath settings, other beans, and various property settings.
• Normally you would add @EnableWebMvc for a Spring MVC app, but Spring Boot adds it automatically when it sees spring-webmvc on the
classpath. This flags the application as a web application and activates key behaviors such as setting up a DispatcherServlet.
• @ComponentScan tells Spring to look for other components, configurations, and services in the hello package, allowing it to find controllers.

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14 Test Application
pgAdmin4
POSTMAN
Choose raw and JSON
pgAdmin4
IDE console

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15 etc
A Warning was happened.
2020-05-19 15:01:19.571 WARN 37996 --- [ main] 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