- Before DSpace 7, most DSpace code used "plain old java objects"(POJO's)
- This presentation will illustrate how to understand the flow of the DSpace 7 code.
+++
- DSpace 6 introduced Hibernate for database interactions
- This code relies on Java Annotations to build associate class files with Hibernate behavior.
- See TBD for more information +++
- Spring Framework
- Java annotations
- Java 8 Lamdas
- ??? Test Framework
+++
- Understand how the REST Controllers are invoked
- Understand how annotations are used to interpret URL parameters and paths
- Understand how DSpace 7 implements the HAL and HATEOAS conventions
- Understand how JSON return objects are constructed
- Understand how code exceptions are converted to HTTP return status
/api/core/communities
- The Spring MVC Framework looks for RestController annotations (org.springframework.web.bind.annotation.RestController).
- The controller for this request will match
/api/{apiCategory}/{model}- Values in curly braces are wildcard Values
- After the match is made, portions of the URL path will be assigned to the following variables
- apiCategory
- model +++
@RestController
@RequestMapping("/api/{apiCategory}/{model}")
@SuppressWarnings("rawtypes")
public class RestResourceController implements InitializingBean {
@[1](Annotaion indicates that this class is a RestController) @[2](Annotation registers a URL path pattern with this class) @3 @4 +++
The class has already matched to /api/core/communities. We need to locate the request mapping that expects no additional path information. +++
@RequestMapping(method = RequestMethod.GET)
@SuppressWarnings("unchecked")
public <T extends RestAddressableModel> PagedResources<DSpaceResource<T>> findAll(
@PathVariable String apiCategory,
@PathVariable String model,
Pageable page,
PagedResourcesAssembler assembler,
@RequestParam(required = false) String projection,
HttpServletResponse response) {
DSpaceRestRepository<T, ?> repository = utils.getResourceRepository(apiCategory, model);
Link link = linkTo(methodOn(this.getClass(), apiCategory, model).findAll(apiCategory, model,
page, assembler, projection, response))
.withSelfRel();
Page<DSpaceResource<T>> resources;
try {
resources = repository.findAll(page).map(repository::wrapResource);
resources.forEach(linkService::addLinks);
} catch (PaginationException pe) {
resources = new PageImpl<DSpaceResource<T>>(new ArrayList<DSpaceResource<T>>(), page, pe.getTotal());
} catch (RepositoryMethodNotImplementedException mne) {
throw mne;
}
PagedResources<DSpaceResource<T>> result = assembler.toResource(resources, link);
if (repositoryUtils.haveSearchMethods(repository)) {
result.add(linkTo(this.getClass(), apiCategory, model).slash("search").withRel("search"));
}
return result;
}
@[1](Register this method as the handler for a URL Path relative to the class URL path) @[1](Note - no additional path is provided) @[3](This method will return a page of DSpaceResource objects) @[3](The REST api controls the maximum number of return objects through pagination) @[4-5](Remember that the following variables were extracted from the URL path at the class level) @[6-7](Pagination and sort parameters are extracted from the URL parameters) @[6-7](Parameter names confirm to Spring defaults) @[8](This annotation maps a URL parameter to a method variable) @[8](When required is true, the method will fail if a param is not present) @[10](Find the "REST repository" object that will retrieve objects from DSpace) @[10](NOTE: → We will examine the Repository object in a later slide) @[11-13](Create a "self" link to this method) @[17](Query for all items and load only a single page of items) @[17](NOTE: → We will trace the findAll method in a later slide) @[17](repository::wrapResource is a Java 8 lambda function) @[17](NOTE: → We will trace repository::wrapResource in a later slide) @[18](linkService::addLinks is a Java 8 lambda function) @[18](NOTE: → We will trace linkService::addLinks in a later slide) +++
@Component(CommunityRest.CATEGORY + "." + CommunityRest.NAME)
public class CommunityRestRepository extends DSpaceRestRepository<CommunityRest, UUID> {
@Override
public Page<CommunityRest> findAll(Context context, Pageable pageable) {
List<Community> it = null;
List<Community> communities = new ArrayList<Community>();
int total = 0;
try {
total = cs.countTotal(context);
it = cs.findAll(context, pageable.getPageSize(), pageable.getOffset());
for (Community c : it) {
communities.add(c);
}
} catch (SQLException e) {
throw new RuntimeException(e.getMessage(), e);
}
Page<CommunityRest> page = new PageImpl<Community>(communities, pageable, total).map(converter);
return page;
}