Connect to OData service on Neo using SAP Cloud SDK

Let’s take a look at typical code we could write to access any OData service using the SAP Cloud Platform SDK for service development.
Here, we retrieve a list of business partners from an S/4HANA system:

final ErpConfigContext configContext = new ErpConfigContext();
final List<MyBusinessPartnerType> businessPartners = ODataQueryBuilder
        .withEntity("/sap/opu/odata/sap/API_BUSINESS_PARTNER",
                "A_BusinessPartner")
        .select("BusinessPartner",
                "LastName",
                "FirstName",
                "IsMale",
                "IsFemale",
                "CreationDate")
        .build()
        .execute(configContext)
        .asList(MyBusinessPartnerType.class);

The ODataQueryBuilder represents a simple and generic approach to consuming OData services in your application and is well suited to support arbitrary services. It is a big step forward from manually building up an HTTP request to an OData service and processing the results in your code, and is used internally by the SAP Cloud SDK. In turn, the ODataQueryBuilder also uses concepts of the SAP Cloud SDK to simplify communication with systems, which are referenced by an ErpConfigContext.

Nevertheless, there are quite a few pitfalls you can fall into when using the plain ODataQueryBuilder approach to call OData services:

• For .withEntity("/sap/opu/odata/sap/API_BUSINESS_PARTNER", "A_BusinessPartner") you already need to know three things: the OData endpoints service path (/sap/opu/odata/sap), the endpoints name (API_BUSINESS_PARTNER) and the name of the entity collection (A_BusinessPartner) as defined in the metadata of the endpoint.
• Then, when you want to select specific attributes from the BusinessPartner entity type with the select() function, you need to know how these fields are named. But since they are only represented as strings in this code, you need to look at the metadata to find out how they’re called. The same also applies for functions like order() and filter(). And of course using strings as parameters is prone to spelling errors that your IDE most likely won’t be able to catch for you.
• Finally, you need to define a class such as MyBusinessPartnerType with specific annotations that represents the properties and their types of the result. For this you again need to know a lot of details about the OData service.

Now that we have explained the possible pitfalls of the current aproach, let’s take a look at how the OData VDM of the SAP Cloud SDK simplifies the same task, as the SDK is able to incorporate more knowledge about the system that is being called.

final List<BusinessPartner> businessPartners =
        new DefaultBusinessPartnerService()
                .getAllBusinessPartner()
                .select(BusinessPartner.BUSINESS_PARTNER,
                        BusinessPartner.LAST_NAME,
                        BusinessPartner.FIRST_NAME,
                        BusinessPartner.IS_MALE,
                        BusinessPartner.IS_FEMALE,
                        BusinessPartner.CREATION_DATE)
                .execute();

Using the OData VDM we now have access to an object representation of a specific OData service, in this case the DefaultBusinessPartnerService (default implementation of the interface BusinessPartnerService). So now there’s no more need to know the endpoint’s service path, service name or entity collection name. We can call this service’s getAllBusinessPartner() function to retrieve a list of all the business partners from the system.

Now take a look at the select() function. Instead of passing strings that represent the field of the entity, we can simply use the static fields provided by the BusinessPartner class. So not only have we eliminated the risk of spelling errors, we also made it type-safe! Again, the same applies for filter() and orderBy(). For example, filtering to male business partners becomes as easy as .filter(BusinessPartner.IS_MALE.eq(true))– note the type-safe comparison.

An additional benefit of this approach is discoverability. Since everything is represented as code, you can simply use your IDE’s autocompletion features to see which functions a service supports and which fields an entity consists of: start by looking at the different services that are available in the package com.sap.cloud.sdk.s4hana.datamodel.odata.services, instantiate the default implementation of the service you need (class name prefixed with Default), and then look for the methods of the service class that represent the different available operations. Based on this, you can choose the fields to select and filters to apply using the fields of the return type.

Each service is described by a Java interface, for example, BusinessPartnerService. The SDK provides a default, complete implementation of each service interface. The corresponding implementation is available in a class whose name is the name of the interface prefixed with Default, for example, DefaultBusinessPartnerService. You can either simply instantiate that class, or use dependency injection with a corresponding Java framework (covered in Step 22 of our tutorial series). The benefit of the interfaces is better testing and extensibility support.

To sum up the advantages of the OData VDM:

• No more hard-coded strings
• No more spelling errors
• Type safety for functions like filter, select and orderBy
• Java data types for the result provided out of the box, including appropriate conversions
• Discoverability by autocompletion
• SAP S/4HANA services can be easily mocked during testing based on the service interface in Java (see tutorial Step 19: Mocking S/4HANA calls)

The VDM supports retrieving entities by key and retrieving lists of entities along with filter(), select(), orderBy(), top() and skip(). You can also resolve navigation properties on demand or eagerly (expand, see Step 22). The VDM also gives easy access to create (see Step 20), update, and delete operations as well as function imports.

For any OData service not part of SAP’s API Business Hub, the ODataQueryBuilder still is the go to approach for consumption.

The SAP Cloud SDK provides simple and convenient ways to access your ERP systems out of the box. In this example you will implement an endpoint that performs an OData query to SAP S/4HANA in order to retrieve a list of business partners from your ERP system. More specifically, we want to retrieve all persons (a specific kind of business partner) with their name and a few additional properties.

To get started, open your previously created Hello World project (in our case, it is called firstapp) and create a new file called BusinessPartnerServlet.java in the following location:

./application/src/main/java/com/sap/cloud/sdk/tutorial/BusinessPartnerServlet.java

package com.sap.cloud.sdk.tutorial;

import com.google.gson.Gson;
import org.slf4j.Logger;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.List;

import com.sap.cloud.sdk.cloudplatform.logging.CloudLoggerFactory;
import com.sap.cloud.sdk.odatav2.connectivity.ODataException;

import com.sap.cloud.sdk.s4hana.datamodel.odata.helper.Order;
import com.sap.cloud.sdk.s4hana.datamodel.odata.namespaces.businesspartner.BusinessPartner;
import com.sap.cloud.sdk.s4hana.datamodel.odata.services.DefaultBusinessPartnerService;

@WebServlet("/businesspartners")
public class BusinessPartnerServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;
    private static final Logger logger = CloudLoggerFactory.getLogger(BusinessPartnerServlet.class);

    private static final String CATEGORY_PERSON = "1";

    @Override
    protected void doGet(final HttpServletRequest request, final HttpServletResponse response)
            throws ServletException, IOException {
        try {
            final List<BusinessPartner> businessPartners =
                    new DefaultBusinessPartnerService()
                            .getAllBusinessPartner()
                            .select(BusinessPartner.BUSINESS_PARTNER,
                                    BusinessPartner.LAST_NAME,
                                    BusinessPartner.FIRST_NAME,
                                    BusinessPartner.IS_MALE,
                                    BusinessPartner.IS_FEMALE,
                                    BusinessPartner.CREATION_DATE)
                            .filter(BusinessPartner.BUSINESS_PARTNER_CATEGORY.eq(CATEGORY_PERSON))
                            .orderBy(BusinessPartner.LAST_NAME, Order.ASC)
                            .execute();

            response.setContentType("application/json");
            response.getWriter().write(new Gson().toJson(businessPartners));

        } catch (final ODataException e) {
            logger.error(e.getMessage(), e);
            response.setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
            response.getWriter().write(e.getMessage());
        }
    }
}

The code is fairly simple. In the servlet GET method, we initialize an instance of the BusinessPartnerService to prepare the query to S/4HANA with the help of the SDK’s Virtual Data Model. We call the method getAllBusinessPartners, which represents the operation of the OData service that we want to call. With the fluent query helper returned by this method, we can gradually build up the query:

• we select the fields of the BusinessPartner that we want to retrieve (if we leave out this part, all fields will be returned),
• filter for business partners of category Person (code "1"), and
• order by the last name of the business partner.

Finally, having prepared the query, we call the execute method. This method does a lot of the heavy lifting necessary to connect to an S/4HANA system and relieves us as developers from dealing with complex aspects such as:

• the configuration which system to connect to (in a multi-tenant environment) – by transparently accessing the destination service of SAP Cloud Platform,
• the connectivity to this system, which may reside on-premise behind a corporate firewall, – by means of the connectivity service and the optional Cloud Connector, and
• the authentication to this system using potentially vastly different authentication flows (basic authentication, principal propagation, OAuth2).

The SAP Cloud SDK provides all of these capabilities with a simple interface and allows customers (tenants) of your application to configure the connection to their system. We will discuss the configuration below when deploying the project.

The execute method of the VDM returns the query result as a navigatable list of type BusinessPartner, which represents the entity type of the response in a type-safe manner. We declare the servlet’s response as JSON content and transform the result into a JSON response.

Any ODataException thrown by the OData call is caught and logged, before returning an error response.

Depending on your chosen archetype and SAP Cloud Platform setup you can deploy the project on either SAP Cloud Platform Neo or SAP Cloud Platform CloudFoundry.

Now you can deploy your application to your local SAP Cloud Platform Neo using the following maven goals:

cd /path/to/firstapp
mvn clean install
mvn scp:clean scp:push -pl application -Derp.url=https://URL

Replace URL with the URL to your SAP ERP system (host and, if necessary, port).
Note: the -pl argument defines the location in which the Maven goals will be executed.

Maven will then prompt you for your username and password that is going to be used to connect to SAP S/4HANA. Alternatively, you can also set these values as command parameters: -Derp.username=USER -Derp.password=PASSWORD

If you now deploy the project and visit the page http://localhost:8080/businesspartners you should be seeing a list of cost centers that was retrieved from the ERP system. Note: Please login with test / test).

Navigate to the integration-tests project and create a new class:

./integration-tests/src/test/java/com/sap/cloud/sdk/tutorial/BusinessPartnerServletTest.java

package com.sap.cloud.sdk.tutorial;

import io.restassured.RestAssured;
import io.restassured.http.ContentType;
import io.restassured.module.jsv.JsonSchemaValidator;
import org.jboss.arquillian.container.test.api.Deployment;
import org.jboss.arquillian.junit.Arquillian;
import org.jboss.arquillian.test.api.ArquillianResource;
import org.jboss.shrinkwrap.api.spec.WebArchive;
import org.junit.Before;
import org.junit.BeforeClass;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.slf4j.Logger;

import java.net.URL;

import com.sap.cloud.sdk.cloudplatform.logging.CloudLoggerFactory;
import com.sap.cloud.sdk.testutil.MockUtil;

import static io.restassured.RestAssured.when;

@RunWith(Arquillian.class)
public class BusinessPartnerServletTest {
    private static final MockUtil mockUtil = new MockUtil();
    private static final Logger logger = CloudLoggerFactory.getLogger(BusinessPartnerServletTest.class);

    @ArquillianResource
    private URL baseUrl;

    @Deployment
    public static WebArchive createDeployment() {
        return TestUtil.createDeployment(BusinessPartnerServlet.class);
    }

    @BeforeClass
    public static void beforeClass() {
        mockUtil.mockDefaults();
        mockUtil.mockErpDestination();
    }

    @Before
    public void before() {
        RestAssured.baseURI = baseUrl.toExternalForm();
    }

    @Test
    public void testService() {
        // JSON schema validation from resource definition
        final JsonSchemaValidator jsonValidator = JsonSchemaValidator
                .matchesJsonSchemaInClasspath("businesspartners-schema.json");

        // HTTP GET response OK, JSON header and valid schema
        when()
                .get("/businesspartners")
        .then()
                .statusCode(200)
                .contentType(ContentType.JSON)
                .body(jsonValidator);
    }
}

Please change the value URL accordingly.

What you see here, is the usage of RestAssured on a JSON service backend. The HTTP GET request is run on the local route /costcenters, the result is validated with multiple assertions:

• HTTP response status code: 200 (OK)
• HTTP ContentType: application/json
• HTTP body is valid JSON code, checked with costcenters-schema.json definition

Inside the integration-tests project, create a new resource file

./integration-tests/src/test/resources/businesspartners-schema.json

{
  "$schema": "http://json-schema.org/draft-04/schema#",
  "title": "Business Partner List",
  "type": "array",
  "items": {
    "title": "Business Partner",
    "type": "object",
    "required": ["BusinessPartner", "LastName"]
  },
  "minItems": 1
}

As you can see, the properties BusinessPartner and LastName will be marked as requirement for every entry of the expected business partner list. The JSON validator would break the test if any of the items was missing a required value.

If you run your application on SAP Cloud Platform, the SDK can simply read the ERP destinations from the destination service. However, since the tests should run locally, we need a way to supply our tests with an ERP destination.

Luckily, the SDK provides a utility class for such purposes – MockUtil. This class allows us to mock the ERP destinations we’d typically find on CloudFoundry. To provide MockUtil with the necessary information, you’ll need to add a systems.json or systems.yml file to your test resources directory. MockUtil will read these files and provide your tests with the ERP destinations accordingly. Adapt the URL as before.

./integration-tests/src/test/resources/systems.json

{
  "erp": {
    "default": "ERP_TEST_SYSTEM",
    "systems": [
      {
        "alias": "ERP_TEST_SYSTEM",
        "uri": "https://URL"
      }
    ]
  }
}

That’s it! You can now start all tests with the default Maven command:

mvn test -Derp.username=USER -Derp.password=PASSWORD

Please change the values USER and PASSWORD accordingly. If you do not want to pass the ERP username and password, checkout the appendix below for an alternative.

If you want to run the tests without Maven, please remember to also include the parameters.