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How To Guide for building a Sample OData service with the OData Library (Java)

This How To Guide prerequisites a Project Setup (Git, Maven, etc.) and then shows how to develop an OData Service and make the same available. It shows in addition how to implement the Model Provider to expose the Entity Data Model (EDM) and the Data Provider to expose the runtime data. The implementation of the Data Provider (ODataSingleProcessor) illustrates how to expose a single entry, a feed and how to follow associations.

Prerequisites

Project Setup is successfully done and the project is ready to start in your $ODATA_PROJECT_HOME.

Implement your OData Service

Shortcut

As a shortcut you can download the Olingo Tutorial 'Basic-Read' Project.

Deployment Descriptor

Sample Code
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    id="WebApp_ID" version="2.5">
    <display-name>org.apache.olingo.odata2.sample</display-name>
    <servlet>
        <servlet-name>MyODataSampleServlet</servlet-name>
        <servlet-class>org.apache.cxf.jaxrs.servlet.CXFNonSpringJaxrsServlet</servlet-class>
        <init-param>
            <param-name>javax.ws.rs.Application</param-name>
            <param-value>org.apache.olingo.odata2.core.rest.app.ODataApplication</param-value>
        </init-param>
        <init-param>
            <param-name>org.apache.olingo.odata2.service.factory</param-name>
            <param-value>org.apache.olingo.odata2.sample.service.MyServiceFactory</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>
    <servlet-mapping>
        <servlet-name>MyODataSampleServlet</servlet-name>
        <url-pattern>/MyODataSample.svc/*</url-pattern>
    </servlet-mapping>
</web-app>

Implement the OData Service Factory

Sample Code
package org.apache.olingo.odata2.sample.service;

import org.apache.olingo.odata2.api.ODataService;
import org.apache.olingo.odata2.api.ODataServiceFactory;
import org.apache.olingo.odata2.api.edm.provider.EdmProvider;
import org.apache.olingo.odata2.api.exception.ODataException;
import org.apache.olingo.odata2.api.processor.ODataContext;
import org.apache.olingo.odata2.api.processor.ODataSingleProcessor;

public class MyServiceFactory extends ODataServiceFactory {

  @Override
  public ODataService createService(ODataContext ctx) throws ODataException {

EdmProvider edmProvider = new MyEdmProvider();
ODataSingleProcessor singleProcessor = new MyODataSingleProcessor();

return createODataSingleProcessorService(edmProvider, singleProcessor);
  }
}

Implement the Entity Data Model Provider

In this paragraph you will implement the MyEdmProvider class by overriding all methods of org.apache.olingo.odata2.api.edm.provider.EdmProvider.

alt text

Sample Code
  static final String ENTITY_SET_NAME_MANUFACTURERS = "Manufacturers";
  static final String ENTITY_SET_NAME_CARS = "Cars";
  static final String ENTITY_NAME_MANUFACTURER = "Manufacturer";
  static final String ENTITY_NAME_CAR = "Car";

  private static final String NAMESPACE = "org.apache.olingo.odata2.ODataCars";

  private static final FullQualifiedName ENTITY_TYPE_1_1 = new FullQualifiedName(NAMESPACE, ENTITY_NAME_CAR);
  private static final FullQualifiedName ENTITY_TYPE_1_2 = new FullQualifiedName(NAMESPACE, ENTITY_NAME_MANUFACTURER);

  private static final FullQualifiedName COMPLEX_TYPE = new FullQualifiedName(NAMESPACE, "Address");

  private static final FullQualifiedName ASSOCIATION_CAR_MANUFACTURER = new FullQualifiedName(NAMESPACE, "Car_Manufacturer_Manufacturer_Cars");

  private static final String ROLE_1_1 = "Car_Manufacturer";
  private static final String ROLE_1_2 = "Manufacturer_Cars";

  private static final String ENTITY_CONTAINER = "ODataCarsEntityContainer";

  private static final String ASSOCIATION_SET = "Cars_Manufacturers";
Sample Code
public List<Schema> getSchemas() throws ODataException {
List<Schema> schemas = new ArrayList<Schema>();

Schema schema = new Schema();
schema.setNamespace(NAMESPACE);

List<EntityType> entityTypes = new ArrayList<EntityType>();
entityTypes.add(getEntityType(ENTITY_TYPE_1_1));
entityTypes.add(getEntityType(ENTITY_TYPE_1_2));
schema.setEntityTypes(entityTypes);

List<ComplexType> complexTypes = new ArrayList<ComplexType>();
complexTypes.add(getComplexType(COMPLEX_TYPE));
schema.setComplexTypes(complexTypes);

List<Association> associations = new ArrayList<Association>();
associations.add(getAssociation(ASSOCIATION_CAR_MANUFACTURER));
schema.setAssociations(associations);

List<EntityContainer> entityContainers = new ArrayList<EntityContainer>();
EntityContainer entityContainer = new EntityContainer();
entityContainer.setName(ENTITY_CONTAINER).setDefaultEntityContainer(true);

List<EntitySet> entitySets = new ArrayList<EntitySet>();
entitySets.add(getEntitySet(ENTITY_CONTAINER, ENTITY_SET_NAME_CARS));
entitySets.add(getEntitySet(ENTITY_CONTAINER, ENTITY_SET_NAME_MANUFACTURERS));
entityContainer.setEntitySets(entitySets);

List<AssociationSet> associationSets = new ArrayList<AssociationSet>();
associationSets.add(getAssociationSet(ENTITY_CONTAINER, ASSOCIATION_CAR_MANUFACTURER, ENTITY_SET_NAME_MANUFACTURERS, ROLE_1_2));
entityContainer.setAssociationSets(associationSets);

entityContainers.add(entityContainer);
schema.setEntityContainers(entityContainers);

schemas.add(schema);

return schemas;
}
Sample Code
@Override
  public EntityType getEntityType(FullQualifiedName edmFQName) throws ODataException {
if (NAMESPACE.equals(edmFQName.getNamespace())) {

  if (ENTITY_TYPE_1_1.getName().equals(edmFQName.getName())) {

    //Properties
    List<Property> properties = new ArrayList<Property>();
    properties.add(new SimpleProperty().setName("Id").setType(EdmSimpleTypeKind.Int32).setFacets(new Facets().setNullable(false)));
    properties.add(new SimpleProperty().setName("Model").setType(EdmSimpleTypeKind.String).setFacets(new Facets().setNullable(false).setMaxLength(100).setDefaultValue("Hugo"))
        .setCustomizableFeedMappings(new CustomizableFeedMappings().setFcTargetPath(EdmTargetPath.SYNDICATION_TITLE)));
    properties.add(new SimpleProperty().setName("ManufacturerId").setType(EdmSimpleTypeKind.Int32));
    properties.add(new SimpleProperty().setName("Price").setType(EdmSimpleTypeKind.Decimal));
    properties.add(new SimpleProperty().setName("Currency").setType(EdmSimpleTypeKind.String).setFacets(new Facets().setMaxLength(3)));
    properties.add(new SimpleProperty().setName("ModelYear").setType(EdmSimpleTypeKind.String).setFacets(new Facets().setMaxLength(4)));
    properties.add(new SimpleProperty().setName("Updated").setType(EdmSimpleTypeKind.DateTime)
        .setFacets(new Facets().setNullable(false).setConcurrencyMode(EdmConcurrencyMode.Fixed))
        .setCustomizableFeedMappings(new CustomizableFeedMappings().setFcTargetPath(EdmTargetPath.SYNDICATION_UPDATED)));
    properties.add(new SimpleProperty().setName("ImagePath").setType(EdmSimpleTypeKind.String));

    //Navigation Properties
    List<NavigationProperty> navigationProperties = new ArrayList<NavigationProperty>();
    navigationProperties.add(new NavigationProperty().setName("Manufacturer")
        .setRelationship(ASSOCIATION_CAR_MANUFACTURER).setFromRole(ROLE_1_1).setToRole(ROLE_1_2));

    //Key
    List<PropertyRef> keyProperties = new ArrayList<PropertyRef>();
    keyProperties.add(new PropertyRef().setName("Id"));
    Key key = new Key().setKeys(keyProperties);

    return new EntityType().setName(ENTITY_TYPE_1_1.getName())
        .setProperties(properties)
        .setKey(key)
        .setNavigationProperties(navigationProperties);

  } else if (ENTITY_TYPE_1_2.getName().equals(edmFQName.getName())) {

    //Properties
    List<Property> properties = new ArrayList<Property>();
    properties.add(new SimpleProperty().setName("Id").setType(EdmSimpleTypeKind.Int32).setFacets(new Facets().setNullable(false)));
    properties.add(new SimpleProperty().setName("Name").setType(EdmSimpleTypeKind.String).setFacets(new Facets().setNullable(false).setMaxLength(100))
        .setCustomizableFeedMappings(new CustomizableFeedMappings().setFcTargetPath(EdmTargetPath.SYNDICATION_TITLE)));
    properties.add(new ComplexProperty().setName("Address").setType(new FullQualifiedName(NAMESPACE, "Address")));
    properties.add(new SimpleProperty().setName("Updated").setType(EdmSimpleTypeKind.DateTime)
        .setFacets(new Facets().setNullable(false).setConcurrencyMode(EdmConcurrencyMode.Fixed))
        .setCustomizableFeedMappings(new CustomizableFeedMappings().setFcTargetPath(EdmTargetPath.SYNDICATION_UPDATED)));

    //Navigation Properties
    List<NavigationProperty> navigationProperties = new ArrayList<NavigationProperty>();
    navigationProperties.add(new NavigationProperty().setName("Cars")
        .setRelationship(ASSOCIATION_CAR_MANUFACTURER).setFromRole(ROLE_1_2).setToRole(ROLE_1_1));

    //Key
    List<PropertyRef> keyProperties = new ArrayList<PropertyRef>();
    keyProperties.add(new PropertyRef().setName("Id"));
    Key key = new Key().setKeys(keyProperties);

    return new EntityType().setName(ENTITY_TYPE_1_2.getName())
        .setProperties(properties)
        .setHasStream(true)
        .setKey(key)
        .setNavigationProperties(navigationProperties);
  }
}

return null;
}
Sample Code
public ComplexType getComplexType(FullQualifiedName edmFQName) throws ODataException {
if (NAMESPACE.equals(edmFQName.getNamespace())) {
  if (COMPLEX_TYPE.getName().equals(edmFQName.getName())) {
    List<Property> properties = new ArrayList<Property>();
    properties.add(new SimpleProperty().setName("Street").setType(EdmSimpleTypeKind.String));
    properties.add(new SimpleProperty().setName("City").setType(EdmSimpleTypeKind.String));
    properties.add(new SimpleProperty().setName("ZipCode").setType(EdmSimpleTypeKind.String));
    properties.add(new SimpleProperty().setName("Country").setType(EdmSimpleTypeKind.String));
    return new ComplexType().setName(COMPLEX_TYPE.getName()).setProperties(properties);
  }
}

return null;

}
Sample Code
public Association getAssociation(FullQualifiedName edmFQName) throws ODataException {
if (NAMESPACE.equals(edmFQName.getNamespace())) {
  if (ASSOCIATION_CAR_MANUFACTURER.getName().equals(edmFQName.getName())) {
    return new Association().setName(ASSOCIATION_CAR_MANUFACTURER.getName())
        .setEnd1(new AssociationEnd().setType(ENTITY_TYPE_1_1).setRole(ROLE_1_1).setMultiplicity(EdmMultiplicity.MANY))
        .setEnd2(new AssociationEnd().setType(ENTITY_TYPE_1_2).setRole(ROLE_1_2).setMultiplicity(EdmMultiplicity.ONE));
  }
}
return null;
}
Sample Code
public EntityContainerInfo getEntityContainerInfo(String name) throws ODataException {
if (name == null || "ODataCarsEntityContainer".equals(name)) {
  return new EntityContainerInfo().setName("ODataCarsEntityContainer").setDefaultEntityContainer(true);
}

return null;
}
Sample Code
public EntitySet getEntitySet(String entityContainer, String name) throws ODataException {
if (ENTITY_CONTAINER.equals(entityContainer)) {
  if (ENTITY_SET_NAME_CARS.equals(name)) {
    return new EntitySet().setName(name).setEntityType(ENTITY_TYPE_1_1);
  } else if (ENTITY_SET_NAME_MANUFACTURERS.equals(name)) {
    return new EntitySet().setName(name).setEntityType(ENTITY_TYPE_1_2);
  }
}
return null;
}
Sample Code
public AssociationSet getAssociationSet(String entityContainer, FullQualifiedName association, String sourceEntitySetName, String sourceEntitySetRole) throws ODataException {
if (ENTITY_CONTAINER.equals(entityContainer)) {
  if (ASSOCIATION_CAR_MANUFACTURER.equals(association)) {
    return new AssociationSet().setName(ASSOCIATION_SET)
        .setAssociation(ASSOCIATION_CAR_MANUFACTURER)
        .setEnd1(new AssociationSetEnd().setRole(ROLE_1_2).setEntitySet(ENTITY_SET_NAME_MANUFACTURERS))
        .setEnd2(new AssociationSetEnd().setRole(ROLE_1_1).setEntitySet(ENTITY_SET_NAME_CARS));
  }
}
return null;
}

Conclusion

After the implementation of the Edm Provider the web application can be executed to show the Service Document and the Metadata Document.

Implement the OData Processor which provides the runtime data

You already created the MyODataSingleProcessor class which we now extend with some needed imports and a reference to a DataStore which contains our data (and will be implemented in the next step).

Sample Code
package org.apache.olingo.odata2.sample.service;

import static org.apache.olingo.odata2.sample.service.MyEdmProvider.ENTITY_SET_NAME_CARS;
import static org.apache.olingo.odata2.sample.service.MyEdmProvider.ENTITY_SET_NAME_MANUFACTURERS;

import org.apache.olingo.odata2.api.processor.ODataSingleProcessor;

public class MyODataSingleProcessor extends ODataSingleProcessor {
  private DataStore dataStore = new DataStore();
}
Sample Code
package org.apache.olingo.odata2.sample.service;

import java.util.ArrayList;
import java.util.Calendar;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.TimeZone;

public class DataStore {

  //Data accessors
  public Map<String, Object> getCar(int id) {
Map<String, Object> data = null;

Calendar updated = Calendar.getInstance(TimeZone.getTimeZone("GMT"));

switch (id) {
case 1:
  updated.set(2012, 11, 11, 11, 11, 11);
  data = createCar(1, "F1 W03", 1, 189189.43, "EUR", "2012", updated, "file://imagePath/w03");
  break;

case 2:
  updated.set(2013, 11, 11, 11, 11, 11);
  data = createCar(2, "F1 W04", 1, 199999.99, "EUR", "2013", updated, "file://imagePath/w04");
  break;

case 3:
  updated.set(2012, 12, 12, 12, 12, 12);
  data = createCar(3, "F2012", 2, 137285.33, "EUR", "2012", updated, "http://pathToImage/f2012");
  break;

case 4:
  updated.set(2013, 12, 12, 12, 12, 12);
  data = createCar(4, "F2013", 2, 145285.00, "EUR", "2013", updated, "http://pathToImage/f2013");
  break;

case 5:
  updated.set(2011, 11, 11, 11, 11, 11);
  data = createCar(5, "F1 W02", 1, 167189.00, "EUR", "2011", updated, "file://imagePath/wXX");
  break;

default:
  break;
}

return data;
  }


  private Map<String, Object> createCar(int carId, String model, int manufacturerId, double price, String currency, String modelYear, Calendar updated, String imagePath) {
Map<String, Object> data = new HashMap<String, Object>();

data.put("Id", carId);
data.put("Model", model);
data.put("ManufacturerId", manufacturerId);
data.put("Price", price);
data.put("Currency", currency);
data.put("ModelYear", modelYear);
data.put("Updated", updated);
data.put("ImagePath", imagePath);

return data;
  }

  public Map<String, Object> getManufacturer(int id) {
Map<String, Object> data = null;
Calendar date = Calendar.getInstance(TimeZone.getTimeZone("GMT"));

switch (id) {
case 1:
  Map<String, Object> addressStar = createAddress("Star Street 137", "Stuttgart", "70173", "Germany");
  date.set(1954, 7, 4);
  data = createManufacturer(1, "Star Powered Racing", addressStar, date);
  break;

case 2:
  Map<String, Object> addressHorse = createAddress("Horse Street 1", "Maranello", "41053", "Italy");
  date.set(1929, 11, 16);
  data = createManufacturer(2, "Horse Powered Racing", addressHorse, date);
  break;

default:
  break;
}

return data;
  }

  private Map<String, Object> createManufacturer(int id, String name, Map<String, Object> address, Calendar updated) {
Map<String, Object> data = new HashMap<String, Object>();
data.put("Id", id);
data.put("Name", name);
data.put("Address", address);
data.put("Updated", updated);
return data;
  }

  private Map<String, Object> createAddress(String street, String city, String zipCode, String country) {
Map<String, Object> address = new HashMap<String, Object>();
address.put("Street", street);
address.put("City", city);
address.put("ZipCode", zipCode);
address.put("Country", country);
return address;
  }


  public List<Map<String, Object>> getCars() {
List<Map<String, Object>> cars = new ArrayList<Map<String, Object>>();
cars.add(getCar(1));
cars.add(getCar(2));
cars.add(getCar(3));
cars.add(getCar(4));
cars.add(getCar(5));
return cars;
  }

  public List<Map<String, Object>> getManufacturers() {
List<Map<String, Object>> manufacturers = new ArrayList<Map<String, Object>>();
manufacturers.add(getManufacturer(1));
manufacturers.add(getManufacturer(2));
return manufacturers;
  }


  public List<Map<String, Object>> getCarsFor(int manufacturerId) {
List<Map<String, Object>> cars = getCars();
List<Map<String, Object>> carsForManufacturer = new ArrayList<Map<String,Object>>();

for (Map<String,Object> car: cars) {
  if(Integer.valueOf(manufacturerId).equals(car.get("ManufacturerId"))) {
    carsForManufacturer.add(car);
  }
}

return carsForManufacturer;
  }

  public Map<String, Object> getManufacturerFor(int carId) {
Map<String, Object> car = getCar(carId);
if(car != null) {
  Object manufacturerId = car.get("ManufacturerId");
  if(manufacturerId != null) {
    return getManufacturer((Integer) manufacturerId);
  }
}
return null;
  }
}
Sample Code
  public ODataResponse readEntity(GetEntityUriInfo uriInfo, String contentType) throws ODataException {

if (uriInfo.getNavigationSegments().size() == 0) {
  EdmEntitySet entitySet = uriInfo.getStartEntitySet();

  if (ENTITY_SET_NAME_CARS.equals(entitySet.getName())) {
    int id = getKeyValue(uriInfo.getKeyPredicates().get(0));
    Map<String, Object> data = dataStore.getCar(id);

    if (data != null) {
      URI serviceRoot = getContext().getPathInfo().getServiceRoot();
      ODataEntityProviderPropertiesBuilder propertiesBuilder = EntityProviderWriteProperties.serviceRoot(serviceRoot);

      return EntityProvider.writeEntry(contentType, entitySet, data, propertiesBuilder.build());
    }
  } else if (ENTITY_SET_NAME_MANUFACTURERS.equals(entitySet.getName())) {
    int id = getKeyValue(uriInfo.getKeyPredicates().get(0));
    Map<String, Object> data = dataStore.getManufacturer(id);

    if (data != null) {
      URI serviceRoot = getContext().getPathInfo().getServiceRoot();
      ODataEntityProviderPropertiesBuilder propertiesBuilder = EntityProviderWriteProperties.serviceRoot(serviceRoot);

      return EntityProvider.writeEntry(contentType, entitySet, data, propertiesBuilder.build());
    }
  }

  throw new ODataNotFoundException(ODataNotFoundException.ENTITY);

} else if (uriInfo.getNavigationSegments().size() == 1) {
  //navigation first level, simplified example for illustration purposes only
  EdmEntitySet entitySet = uriInfo.getTargetEntitySet();
  if (ENTITY_SET_NAME_MANUFACTURERS.equals(entitySet.getName())) {
    int carKey = getKeyValue(uriInfo.getKeyPredicates().get(0));
    return EntityProvider.writeEntry(contentType, uriInfo.getTargetEntitySet(), dataStore.getManufacturer(carKey), EntityProviderWriteProperties.serviceRoot(getContext().getPathInfo().getServiceRoot()).build());
  }

  throw new ODataNotFoundException(ODataNotFoundException.ENTITY);
}

throw new ODataNotImplementedException();
  }
Implement MyODataSingleProcessor.readEntitySet(GetEntitySetUriInfo uriParserResultInfo) by overriding the corresponding method of the ODataSingleProcessor 
  public ODataResponse readEntitySet(GetEntitySetUriInfo uriInfo, String contentType) throws ODataException {

EdmEntitySet entitySet;

if (uriInfo.getNavigationSegments().size() == 0) {
  entitySet = uriInfo.getStartEntitySet();

  if (ENTITY_SET_NAME_CARS.equals(entitySet.getName())) {
    return EntityProvider.writeFeed(contentType, entitySet, dataStore.getCars(), EntityProviderWriteProperties.serviceRoot(getContext().getPathInfo().getServiceRoot()).build());
  } else if (ENTITY_SET_NAME_MANUFACTURERS.equals(entitySet.getName())) {
    return EntityProvider.writeFeed(contentType, entitySet, dataStore.getManufacturers(), EntityProviderWriteProperties.serviceRoot(getContext().getPathInfo().getServiceRoot()).build());
  }

  throw new ODataNotFoundException(ODataNotFoundException.ENTITY);

} else if (uriInfo.getNavigationSegments().size() == 1) {
  //navigation first level, simplified example for illustration purposes only
  entitySet = uriInfo.getTargetEntitySet();

  if (ENTITY_SET_NAME_CARS.equals(entitySet.getName())) {
    int manufacturerKey = getKeyValue(uriInfo.getKeyPredicates().get(0));

    List<Map<String, Object>> cars = new ArrayList<Map<String, Object>>();
    cars.add(dataStore.getCar(manufacturerKey));

    return EntityProvider.writeFeed(contentType, entitySet, cars, EntityProviderWriteProperties.serviceRoot(getContext().getPathInfo().getServiceRoot()).build());
  }

  throw new ODataNotFoundException(ODataNotFoundException.ENTITY);
}

throw new ODataNotImplementedException();
  }

And add the small method to get the key value of a KeyPredicate:

  private int getKeyValue(KeyPredicate key) throws ODataException {
EdmProperty property = key.getProperty();
EdmSimpleType type = (EdmSimpleType) property.getType();
return type.valueOfString(key.getLiteral(), EdmLiteralKind.DEFAULT, property.getFacets(), Integer.class);
  }

After the implementation of the MyODataSingleProcessor the web application can be tested.

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