在java中使用olingo实现odatav4时，我得到了一个 NullPointerException .
下面是一个详细的描述--
尝试在我的spring引导应用程序中使用olingo在java中实现odatav4。我在看官方文件https://olingo.apache.org/doc/odata4/tutorials/readep/tutorial_readep.html
我使用的是提供数据的数据库，而不是手动/静态地输入数据。
根据文档，我创建了一个类 Storage.java 模拟数据层。

public class Storage {

@Autowired
CompanyService cservice;

private List<Entity> companyentityList;

public Storage() throws Exception {
    companyentityList = new ArrayList<Entity>();
    initSampleData();
}

// PUBLIC FACADE

public EntityCollection readEntitySetData(EdmEntitySet edmEntitySet) throws NullPointerException {

    // actually, this is only required if we have more than one Entity Sets
    if (edmEntitySet.getName().equals(DemoEdmProvider.ES_COMPANY_RECORDS)) {
        return getCompaniesData();
    }

    return null;
}

public Entity readEntityData(EdmEntitySet edmEntitySet, List<UriParameter> keyParams) throws Exception {

    EdmEntityType edmEntityType = edmEntitySet.getEntityType();

    // actually, this is only required if we have more than one Entity Type
    if (edmEntityType.getName().equals(DemoEdmProvider.ET_COMPANY)) {
        return getCompany(edmEntityType, keyParams);
    }

    return null;
}

// INTERNAL

public EntityCollection getCompaniesData() throws NullPointerException {
    EntityCollection retEntitySet = new EntityCollection();

    for (Entity companyEntity : this.companyentityList) {
        retEntitySet.getEntities().add(companyEntity);
    }

    return retEntitySet;
}

public Entity getCompany(EdmEntityType edmEntityType, List<UriParameter> keyParams) throws Exception {

    // the list of entities at runtime
    EntityCollection entitySet = getCompaniesData();

    // generic approach to find the requested entity
    Entity requestedEntity = Util.findEntity(edmEntityType, entitySet, keyParams);

    if (requestedEntity == null) {
        // this variable is null if our data doesn't contain an entity for the requested
        // key
        // Throw suitable exception
        throw new ODataApplicationException("Entity for requested key doesn't exist",
                HttpStatusCode.NOT_FOUND.getStatusCode(), Locale.ENGLISH);
    }

    return requestedEntity;
}

// Helper

public void initSampleData() {

    try {
        getData();
    } catch (NullPointerException e) {
        System.out.print("<<<<<<<---------------- Database unable to provide data ------------>>>>>>");
    }
}

public List<Company> getAllcompanyList() {
    Collection<Company> checkingdata = new ArrayList<>();
    try {
          checkingdata = cservice.getDetails();

    } catch (NullPointerException e) {
        System.out.print("<<<<<<<---------------- Database unable to provide data ------------>>>>>>");
    }
    return  (List<Company>) checkingdata;
}

// final EntityCollection entitySet = new EntityCollection();
// loop over List<Company> converting each instance of Company into and Olingo Entity
public EntityCollection makeEntityCollection(List<Company> companyList) {

    EntityCollection entitySet = new EntityCollection();
    for (Company cmp : companyList) {
        entitySet.getEntities().add(createEntity(cmp));
    }

    return entitySet;
}

// Convert instance of cmp object into an Olingo Entity
public Entity createEntity(Company cmp) {
    final Entity tmpEntity = new Entity().addProperty(new Property(null, "ID", ValueType.PRIMITIVE, cmp.getId()))
            .addProperty(new Property(null, "Name", ValueType.PRIMITIVE, cmp.getContent()));
    companyentityList.add(tmpEntity);
    return tmpEntity;
}

public void getData() throws NullPointerException {
    // ... code to get Data from the DataBase in List and calling makeEntityCollection

    List<Company> companyList = getAllcompanyList();
    makeEntityCollection(companyList);
    // System.out.println(companyList.size());

}

}
在上述代码i中 @Autowired 这个 CompanyService 接口参考 cservice .
以下是 CompanyService -

public interface CompanyService {

 Collection<Company> getDetails() throws Exception;

} CompanyService 接口由实现 CompanyServiceImplementation -

@Service
public class CompanyServiceImplementation implements CompanyService{

@Autowired
private  CompanyDAOImplementation cDAOWrapper;

public Collection<Company> getDetails() throws Exception {

    return cDAOWrapper.findAll();
}

}
在上一节课中 findAll() 方法正在从数据库返回数据。
所以问题是 CompanyService 参考 cservice 哪个是 @Autowired 在 Storage.java 班级是 null 它没有得到初始化，因此我得到一个 NullPointerException 打电话的时候 cservice.getDetails() .
请让我知道我的代码有什么问题。提前谢谢。