This tutorial on Spring Data REST shows how Spring Data repositories can be exposed as a REST API. It's a really interesting idea, and can save you a lot of boilerplate code building microservices.

Spring Boot makes it easy to create a Spring Data REST starter project using Spring Initializr –

Spring Initializr – Spring Boot JPA Microservice.

I'm using Spring Boot 2.0.0, and the HAL Browser to quickly demonstrate REST API.

Download, expand and import into your IDE –

Expanded Spring Boot Project.

Code

For a quick start, the code is available on GitHub.

Let’s keep this simple and use the classes from my parkrunpb project.

The starting point is the pom.xml –

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.javabullets.springdata</groupId>
    <artifactId>jparest</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>jparest</name>
    <description>Spring Data Rest Example</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.0.BUILD-SNAPSHOT</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-rest</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.data</groupId>
            <artifactId>spring-data-rest-hal-browser</artifactId>
        </dependency>
        <dependency>
            <groupId>com.h2database</groupId>
            <artifactId>h2</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

    <repositories>
        <repository>
            <id>spring-snapshots</id>
            <name>Spring Snapshots</name>
            <url>https://repo.spring.io/snapshot</url>
            <snapshots>
                <enabled>true</enabled>
            </snapshots>
        </repository>
        <repository>
            <id>spring-milestones</id>
            <name>Spring Milestones</name>
            <url>https://repo.spring.io/milestone</url>
            <snapshots>
                <enabled>false</enabled>
            </snapshots>
        </repository>
    </repositories>

    <pluginRepositories>
        <pluginRepository>
            <id>spring-snapshots</id>
            <name>Spring Snapshots</name>
            <url>https://repo.spring.io/snapshot</url>
            <snapshots>
                <enabled>true</enabled>
            </snapshots>
        </pluginRepository>
        <pluginRepository>
            <id>spring-milestones</id>
            <name>Spring Milestones</name>
            <url>https://repo.spring.io/milestone</url>
            <snapshots>
                <enabled>false</enabled>
            </snapshots>
        </pluginRepository>
    </pluginRepositories>
</project>

So we have our JPA object –

package com.javabullets.springdata.jparest;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;

@Entity
public class ParkrunCourse {
@Id
@GeneratedValue(strategy=GenerationType.IDENTITY)
private Long id;

private String courseName;
private String url;
private Long averageTime;

public String getCourseName() {
return courseName;
}
public void setCourseName(String courseName) {
this.courseName = courseName;
}
public String getUrl() {
return url;
}
public void setUrl(String url) {
this.url = url;
}
public Long getAverageTime() {
return averageTime;
}
public void setAverageTime(Long averageTime) {
this.averageTime = averageTime;
}
}

I'm using JPARepository –

package com.javabullets.springdata.jparest;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.repository.query.Param;
import org.springframework.data.rest.core.annotation.RepositoryRestResource;

public interface ParkrunCourseRepository extends JpaRepository<ParkrunCourse, Long> {
}

And a script to ensure the data is preloaded – stored in (src\main\resources\import.sql) –

INSERT INTO PARKRUN_COURSE(ID, COURSE_NAME, URL, AVERAGE_TIME) VALUES (1, 'Inverness', 'http://www.parkrun.org.uk/inverness/', 1582);
INSERT INTO PARKRUN_COURSE(ID, COURSE_NAME, URL, AVERAGE_TIME) VALUES (2, 'Aberdeen',    'http://www.parkrun.org.uk/aberdeen/', 1586);
INSERT INTO PARKRUN_COURSE(ID, COURSE_NAME, URL, AVERAGE_TIME) VALUES (3, 'Dundee(Camperdown)', 'http://www.parkrun.org.uk/camperdown/', 1752);
INSERT INTO PARKRUN_COURSE(ID, COURSE_NAME, URL, AVERAGE_TIME) VALUES (4, 'St Andrews', 'http://www.parkrun.org.uk/standrews/', 1669);
INSERT INTO PARKRUN_COURSE(ID, COURSE_NAME, URL, AVERAGE_TIME) VALUES (5, 'Perth', 'http://www.parkrun.org.uk/perth/', 1620);
INSERT INTO PARKRUN_COURSE(ID, COURSE_NAME, URL, AVERAGE_TIME) VALUES (6, 'Edinburgh', 'http://www.parkrun.org.uk/edinburgh/', 1523);

Running the Code

Run the code using the Maven wrapper – mvnw –

mvnw spring-boot:run

We can then access the HALBrowser on http://localhost:8080/browser/index.html#http://localhost:8080/parkrunCourses -

Spring Data REST – HALBrowser.

The response body returns all the parkrunCourse. You can also do GET, POST, PUT, PATCH and DELETE.

A good trick is to use the browser integrated SQL editor for the H2 database. I covered this in my Spring Boot security tutorial.

hal+json Media Type

Spring Data JPA allows you to make calls as JSON or hal+json. The purpose of hal+json makes it easier to navigate API’s following links. The HALBrowser is great for quickly checking your API.

This example shows how a spring data repository can easily be exposed as a REST API. My next post will look at the practicality of this approach, and what restrictions you might want to apply to your API.