Building an OData Service with a Spring-Boot Java Application using Olingo - Part I

[Edrilan_Berisha]

This blog will deal with an end to end implementation of an OData service using the Olingo library for a Java Spring-Boot application. There are some outdated blog posts that explain how to use Olingo, but none of them also uses Spring, or if they do, they do not explain how to add custom logic for some pre- or post-processing for different OData requests.

So, in this first blog post, we will create a java application with a spring-boot framework. It will provide a health check as a REST API in the end.

We start creating our java application with an “Application.java” class in our source folder where the Spring runtime is initialized.

So, for this example we have the following folder structure:

The Application class will only contain the following coding:

package com.github.olingo.example;



import org.springframework.boot.SpringApplication;

import org.springframework.boot.autoconfigure.SpringBootApplication;



@SpringBootApplication

public class Application {

    public static void main(String[] args) {

        SpringApplication.run(Application.class, args);

    }

}

 

Now we add the following 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 https://maven.apache.org/xsd/maven-4.0.0.xsd">

    <modelVersion>4.0.0</modelVersion>

    <parent>

        <groupId>org.springframework.boot</groupId>

        <artifactId>spring-boot-starter-parent</artifactId>

        <version>2.3.1.RELEASE</version>

        <relativePath/>

    </parent>

    <groupId>com.ecasio.olingo.spring.example</groupId>

    <artifactId>example-olingo</artifactId>

    <version>0.0.1-SNAPSHOT</version>

    <name>example-olingo</name>

    <description>Example Olingo Spring Boot</description>



    <properties>

        <java.version>1.8</java.version>

    </properties>



    <dependencies>

        <dependency>

            <groupId>org.springframework.boot</groupId>

            <artifactId>spring-boot-starter</artifactId>

        </dependency>

        <dependency>

            <groupId>org.springframework.boot</groupId>

            <artifactId>spring-boot-maven-plugin</artifactId>

            <version>2.3.6.RELEASE</version>

        </dependency>

        <dependency>

            <groupId>org.springframework.boot</groupId>

            <artifactId>spring-boot-starter-web</artifactId>

        </dependency>

        <dependency>

            <groupId>org.springframework.boot</groupId>

            <artifactId>spring-boot-devtools</artifactId>

            <optional>true</optional>

        </dependency>

        <dependency>

            <groupId>org.springframework.boot</groupId>

            <artifactId>spring-boot-starter-test</artifactId>

            <scope>test</scope>

            <exclusions>

                <exclusion>

                    <groupId>org.junit.vintage</groupId>

                    <artifactId>junit-vintage-engine</artifactId>

                </exclusion>

            </exclusions>

        </dependency>

        <dependency>

            <groupId>org.springframework.boot</groupId>

            <artifactId>spring-boot-starter-data-jpa</artifactId>

            <version>2.3.1.RELEASE</version>

        </dependency>

        <dependency>

            <groupId>org.apache.olingo</groupId>

            <artifactId>olingo-odata2-core</artifactId>

            <version>2.0.11</version>

            <exclusions>

                <exclusion>

                    <groupId>javax.ws.rs</groupId>

                    <artifactId>javax.ws.rs-api</artifactId>

                </exclusion>

            </exclusions>

        </dependency>

        <dependency>

            <groupId>org.apache.olingo</groupId>

            <artifactId>olingo-odata2-jpa-processor-core</artifactId>

            <version>2.0.11</version>

        </dependency>

        <dependency>

            <groupId>org.apache.olingo</groupId>

            <artifactId>olingo-odata2-jpa-processor-ref</artifactId>

            <version>2.0.11</version>

            <exclusions>

                <exclusion>

                    <groupId>org.eclipse.persistence</groupId>

                    <artifactId>eclipselink</artifactId>

                </exclusion>

            </exclusions>

        </dependency>

        <dependency>

            <groupId>org.springframework.boot</groupId>

            <artifactId>spring-boot-starter-jersey</artifactId>

        </dependency>

    </dependencies>





    <profiles>

        <profile>

            <id>local</id>

            <activation>

                <activeByDefault>true</activeByDefault>

            </activation>

            <properties>

                <activatedProperties>local</activatedProperties>

            </properties>

            <dependencies>

                <dependency>

                    <groupId>com.h2database</groupId>

                    <artifactId>h2</artifactId>

                    <scope>runtime</scope>

                </dependency>

            </dependencies>

        </profile>



        <profile>

            <id>cloud</id>

            <activation>

                <activeByDefault>false</activeByDefault>

            </activation>

            <properties>

                <activatedProperties>cloud</activatedProperties>

            </properties>

        </profile>

    </profiles>



    <build>

        <plugins>

            <plugin>

                <groupId>org.springframework.boot</groupId>

                <artifactId>spring-boot-maven-plugin</artifactId>

            </plugin>

        </plugins>

    </build>

For the health check, we create a controller folder where we create a new Java class, namely HealthCheckController.java .

It contains the following coding:

package com.github.olingo.example.controller;



import org.slf4j.Logger;

import org.slf4j.LoggerFactory;

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

import org.springframework.web.bind.annotation.RequestMapping;

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



@RestController

@RequestMapping("/api/v1/health")

public class HealthCheckController {



    private Logger logger = LoggerFactory.getLogger(getClass());



    @GetMapping

    public void healthCheck() {

        logger.info("Health check called");

    }



}

With the @RequestMapping("/api/v1/health") annotation, we define our REST endpoint for our health check. With @GetMapping, we also define that this endpoint is accessible for GET requests. So far, no rocket science.

Now, we can build this application locally with the help of Maven by typing the following command into the terminal: ‘mvn spring-boot:run’.

Open Postman and call the “localhost:8080/api/v1/health” url which will return a 200 HTTP response.

 

So, we have successfully built our first REST endpoint in our Spring application.

In the next blog post, we will introduce our entity relation model and build the OData service using the Olingo framework.

For those who need the complete solution, you will find it here: Github repo with solution branch (it's on the addHealthCheck branch of the repository)

 

• Building an OData Service with a Spring-Boot Java Application using Olingo – Part II (next blog post)


• Building an OData Service with a Spring-Boot Java Application using Olingo – Part III (Payloads and ... (last blog post)

 

Best,

Edrilan Berisha

SAP S/4HANA Cloud Development Financials