implement checkstyle

.env

@@ -2,3 +2,4 @@ ZK_HOSTS=zookeeper-solr-openaire-dev-1:2181,zookeeper-solr-openaire-dev-2:2181,z
 SOLR_COLLECTION=public
 OPENAPI_SERVER_BASE_URL=http://localhost:8080/graph
 CONTEXT_PATH=/graph
+SCHOLIX_SERVER_BASE_URL=https://test.api.scholexplorer.openaire.eu

pom.xml

@@ -106,7 +106,6 @@
 		<dependency>
 			<groupId>org.springframework.boot</groupId>
 			<artifactId>spring-boot-configuration-processor</artifactId>
-			<optional>true</optional>
 		</dependency>
 		<dependency>
 			<groupId>org.apache.solr</groupId>
@@ -240,6 +239,23 @@
 					</annotationProcessorPaths>
 				</configuration>
 			</plugin>
+			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-checkstyle-plugin</artifactId>
+				<configuration>
+					<configLocation>${project.basedir}/src/main/resources/checkstyle.xml</configLocation>
+					<consoleOutput>true</consoleOutput>
+					<failOnViolation>true</failOnViolation>
+				</configuration>
+				<executions>
+					<execution>
+						<phase>validate</phase>
+						<goals>
+							<goal>check</goal>
+						</goals>
+					</execution>
+				</executions>
+			</plugin>
 		</plugins>
 	</build>
 

src/main/java/eu/openaire/api/config/ScholixClientConfig.java

@@ -0,0 +1,19 @@
+package eu.openaire.api.config;
+
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.web.client.RestClient;
+
+@Configuration
+public class ScholixClientConfig {
+    @Value("${scholix.server-base-url}")
+    private String baseUrl;
+
+    @Bean
+    public RestClient restClient() {
+        return RestClient.builder()
+                .baseUrl(baseUrl)
+                .build();
+    }
+}

src/main/java/eu/openaire/api/controllers/DataSourceController.java

@@ -22,14 +22,17 @@ import lombok.RequiredArgsConstructor;
 import org.springdoc.core.annotations.ParameterObject;
 import org.springframework.validation.BindingResult;
 import org.springframework.web.bind.WebDataBinder;
-import org.springframework.web.bind.annotation.*;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.InitBinder;
+import org.springframework.web.bind.annotation.PathVariable;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RestController;
 
 @RestController
 @RequestMapping("/dataSources")
 @RequiredArgsConstructor
 @Tag(name = "Data sources", description = "API endpoints to explore data sources")
-public class DataSourceController
+public class DataSourceController {
-{
 
 	private final DataSourceService dataSourceService;
 

src/main/java/eu/openaire/api/controllers/OrganizationController.java

@@ -22,14 +22,17 @@ import lombok.RequiredArgsConstructor;
 import org.springdoc.core.annotations.ParameterObject;
 import org.springframework.validation.BindingResult;
 import org.springframework.web.bind.WebDataBinder;
-import org.springframework.web.bind.annotation.*;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.InitBinder;
+import org.springframework.web.bind.annotation.PathVariable;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RestController;
 
 @RestController
 @RequestMapping("/organizations")
 @RequiredArgsConstructor
 @Tag(name = "Organizations", description = "API endpoints to explore organizations")
-public class OrganizationController
+public class OrganizationController {
-{
 
 	private final OrganizationService organizationService;
 

src/main/java/eu/openaire/api/controllers/ProjectController.java

@@ -22,14 +22,17 @@ import lombok.RequiredArgsConstructor;
 import org.springdoc.core.annotations.ParameterObject;
 import org.springframework.validation.BindingResult;
 import org.springframework.web.bind.WebDataBinder;
-import org.springframework.web.bind.annotation.*;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.InitBinder;
+import org.springframework.web.bind.annotation.PathVariable;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RestController;
 
 @RestController
 @RequestMapping("/projects")
 @RequiredArgsConstructor
 @Tag(name = "Projects", description = "API endpoints to explore projects")
-public class ProjectController
+public class ProjectController {
-{
 
     private final ProjectService projectService;
 

src/main/java/eu/openaire/api/controllers/ResearchProductsController.java

@@ -23,14 +23,17 @@ import lombok.RequiredArgsConstructor;
 import org.springdoc.core.annotations.ParameterObject;
 import org.springframework.validation.BindingResult;
 import org.springframework.web.bind.WebDataBinder;
-import org.springframework.web.bind.annotation.*;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.InitBinder;
+import org.springframework.web.bind.annotation.PathVariable;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RestController;
 
 @RestController
 @RequestMapping("/researchProducts")
 @RequiredArgsConstructor
 @Tag(name = "Research products", description = "API endpoints to explore research products")
-public class ResearchProductsController
+public class ResearchProductsController {
-{
 
 	private final ResearchProductService researchProductService;
 

src/main/java/eu/openaire/api/controllers/ScholixController.java

@@ -0,0 +1,54 @@
+package eu.openaire.api.controllers;
+
+import eu.dnetlib.dhp.schema.sx.api.model.v2.PageResultType;
+import eu.openaire.api.dto.request.validators.PaginationValidator;
+import eu.openaire.api.errors.ErrorResponse;
+import eu.openaire.api.services.ScholixService;
+import io.swagger.v3.oas.annotations.Operation;
+import io.swagger.v3.oas.annotations.Parameter;
+import io.swagger.v3.oas.annotations.media.Content;
+import io.swagger.v3.oas.annotations.media.Schema;
+import io.swagger.v3.oas.annotations.responses.ApiResponse;
+import io.swagger.v3.oas.annotations.responses.ApiResponses;
+import io.swagger.v3.oas.annotations.tags.Tag;
+import lombok.RequiredArgsConstructor;
+import org.springframework.web.bind.WebDataBinder;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.InitBinder;
+import org.springframework.web.bind.annotation.RequestParam;
+import org.springframework.web.bind.annotation.RestController;
+
+@RestController
+@RequiredArgsConstructor
+@Tag(name = "Scholix Relations", description = "API endpoints to explore scholix")
+public class ScholixController {
+	private final ScholixService scholixService;
+
+	// common validator to check pagination parameters
+	private final PaginationValidator paginationValidator;
+
+	@InitBinder
+	protected void initBinder(WebDataBinder binder) {
+		binder.addValidators(paginationValidator);
+	}
+
+	@Operation(
+			summary = "Retrieve scholix links by sourcePid and sourceType",
+			description = "Retrieve scholix links by sourcePid and sourceType"
+	)
+	@ApiResponses({
+			@ApiResponse(responseCode = "200", content = { @Content(schema = @Schema(implementation = PageResultType.class), mediaType = "application/json") }),
+			@ApiResponse(responseCode = "404", content = { @Content(schema = @Schema(implementation = ErrorResponse.class), mediaType = "application/json") }),
+			@ApiResponse(responseCode = "500", content = { @Content(schema = @Schema(implementation = ErrorResponse.class), mediaType = "application/json") })
+	})
+	@GetMapping("/links")
+	public PageResultType getLinks(@RequestParam
+							       @Parameter(description = "The OpenAIRE Id") String sourcePid,
+								   @RequestParam(required = false)
+								   @Parameter(description = "The OpenAIRE Source Type") String sourceType,
+								   @RequestParam(defaultValue = "0")
+								   @Parameter(description = "Page number of the results") int page) {
+
+		return scholixService.getLinks(sourcePid, sourceType, page);
+	}
+}

src/main/java/eu/openaire/api/dto/request/validators/PaginationValidator.java

@@ -1,6 +1,10 @@
 package eu.openaire.api.dto.request.validators;
 
-import eu.openaire.api.dto.request.*;
+import eu.openaire.api.dto.request.DataSourceRequest;
+import eu.openaire.api.dto.request.OrganizationRequest;
+import eu.openaire.api.dto.request.PaginatedRequest;
+import eu.openaire.api.dto.request.ProjectRequest;
+import eu.openaire.api.dto.request.ResearchProductsRequest;
 import jakarta.servlet.http.HttpServletRequest;
 import org.springframework.stereotype.Component;
 import org.springframework.validation.Errors;

src/main/java/eu/openaire/api/errors/ServiceExceptionHandler.java

@@ -5,10 +5,12 @@ import eu.openaire.api.errors.exceptions.NotFoundException;
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 import org.springframework.http.HttpStatus;
+import org.springframework.http.HttpStatusCode;
 import org.springframework.http.ResponseEntity;
 import org.springframework.web.bind.MethodArgumentNotValidException;
 import org.springframework.web.bind.annotation.ExceptionHandler;
 import org.springframework.web.bind.annotation.RestControllerAdvice;
+import org.springframework.web.client.RestClientResponseException;
 import org.springframework.web.context.request.ServletWebRequest;
 import org.springframework.web.context.request.WebRequest;
 import org.springframework.web.servlet.resource.NoResourceFoundException;
@@ -60,6 +62,22 @@ public class ServiceExceptionHandler {
 		return this.handleException(e.getMessage(), request, HttpStatus.INTERNAL_SERVER_ERROR);
 	}
 
+	@ExceptionHandler(RestClientResponseException.class)
+	public ResponseEntity<ErrorResponse> handleRestClientResponseException(RestClientResponseException e, WebRequest request) {
+		HttpStatusCode status = e.getStatusCode();
+		String path = ((ServletWebRequest) request).getRequest().getRequestURI();
+
+		ErrorResponse response = ErrorResponse.builder()
+				.message(e.getMessage())
+				.error(status.toString())
+				.code(status.value())
+				.timestamp(new Date())
+				.path(path)
+				.build();
+
+		return ResponseEntity.status(status.value()).body(response);
+	}
+
 	private ResponseEntity<ErrorResponse> handleException(String message, WebRequest request, HttpStatus httpStatus) {
 		var req = ((ServletWebRequest)request).getRequest();
 		String path = String.format("%s?%s", req.getRequestURI(), req.getQueryString());

src/main/java/eu/openaire/api/mappers/Utils.java

@@ -10,11 +10,15 @@ import java.time.ZoneOffset;
 import java.time.ZonedDateTime;
 import java.time.format.DateTimeFormatter;
 import java.time.format.DateTimeParseException;
-import java.util.*;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
 
 public class Utils {
 
-	private Utils() {}
+	private Utils() { }
 
 	public static final String API_PAGE_DESC = """
                     Page number of the results,\s

src/main/java/eu/openaire/api/mappers/query/DataSourceRequestMapper.java

@@ -3,7 +3,11 @@ package eu.openaire.api.mappers.query;
 import eu.openaire.api.dto.request.DataSourceRequest;
 import eu.openaire.api.mappers.Utils;
 import eu.openaire.api.solr.SolrQueryParams;
-import org.mapstruct.*;
+import org.mapstruct.AfterMapping;
+import org.mapstruct.Mapper;
+import org.mapstruct.Mapping;
+import org.mapstruct.MappingTarget;
+import org.mapstruct.Named;
 
 import java.util.ArrayList;
 import java.util.Map;
@@ -15,7 +19,7 @@ public interface DataSourceRequestMapper {
 	@Mapping(target = "rows", source = "pageSize")
 	@Mapping(target = "debugQuery", source = "debugQuery")
 	@Mapping(target = "cursor", source = "cursor")
-	@Mapping(target = "sort", expression = "java( eu.openaire.api.mappers.Utils.formatSortByParam(src.getSortBy(), SolrFieldsMapper.dataSourceSortMapping) )")
+	@Mapping(target = "sort", expression = "java( eu.openaire.api.mappers.Utils.formatSortByParam(src.getSortBy(), SolrFieldsMapper.DATASOURCE_SORT_MAPPING) )")
 	SolrQueryParams toSolrQuery(DataSourceRequest src);
 
 	@Named("calculateStart")
@@ -26,7 +30,7 @@ public interface DataSourceRequestMapper {
 	@AfterMapping
 	default void paramsCustomMapping(DataSourceRequest src, @MappingTarget SolrQueryParams solrQueryParams) {
 
-		final Map<String, String> solrFieldMapping = SolrFieldsMapper.dataSourceFieldMapping;
+		final Map<String, String> solrFieldMapping = SolrFieldsMapper.DATASOURCE_FIELD_MAPPING;
 
 		var qList = new ArrayList<String>();
 

src/main/java/eu/openaire/api/mappers/query/OrganizationRequestMapper.java

@@ -3,7 +3,11 @@ package eu.openaire.api.mappers.query;
 import eu.openaire.api.dto.request.OrganizationRequest;
 import eu.openaire.api.mappers.Utils;
 import eu.openaire.api.solr.SolrQueryParams;
-import org.mapstruct.*;
+import org.mapstruct.AfterMapping;
+import org.mapstruct.Mapper;
+import org.mapstruct.Mapping;
+import org.mapstruct.MappingTarget;
+import org.mapstruct.Named;
 
 import java.util.ArrayList;
 import java.util.Map;
@@ -11,12 +15,10 @@ import java.util.Map;
 @Mapper(componentModel = "spring")
 public interface OrganizationRequestMapper {
 
-
-
 	@Mapping(target = "start", expression = "java( calculateStart(src.getPage(), src.getPageSize()) )")
 	@Mapping(target = "rows", source = "pageSize")
 	@Mapping(target = "debugQuery", source = "debugQuery")
-	@Mapping(target = "sort", expression = "java( eu.openaire.api.mappers.Utils.formatSortByParam(src.getSortBy(), SolrFieldsMapper.organizationSortMapping) )")
+	@Mapping(target = "sort", expression = "java( eu.openaire.api.mappers.Utils.formatSortByParam(src.getSortBy(), SolrFieldsMapper.ORGANIZATION_SORT_MAPPING) )")
 	SolrQueryParams toSolrQuery(OrganizationRequest src);
 
 	@Named("calculateStart")
@@ -27,7 +29,7 @@ public interface OrganizationRequestMapper {
 	@AfterMapping
 	default void paramsCustomMapping(OrganizationRequest src, @MappingTarget SolrQueryParams solrQueryParams) {
 
-		final Map<String, String> solrFieldMapping = SolrFieldsMapper.organizationFieldsMapping;
+		final Map<String, String> solrFieldMapping = SolrFieldsMapper.ORGANIZATION_FIELDS_MAPPING;
 
 		var qList = new ArrayList<String>();
 

src/main/java/eu/openaire/api/mappers/query/ProjectRequestMapper.java

@@ -3,7 +3,11 @@ package eu.openaire.api.mappers.query;
 import eu.openaire.api.dto.request.ProjectRequest;
 import eu.openaire.api.mappers.Utils;
 import eu.openaire.api.solr.SolrQueryParams;
-import org.mapstruct.*;
+import org.mapstruct.AfterMapping;
+import org.mapstruct.Mapper;
+import org.mapstruct.Mapping;
+import org.mapstruct.MappingTarget;
+import org.mapstruct.Named;
 
 import java.util.ArrayList;
 import java.util.Map;
@@ -15,7 +19,7 @@ public interface ProjectRequestMapper {
 	@Mapping(target = "start", expression = "java( calculateStart(src.getPage(), src.getPageSize()) )")
 	@Mapping(target = "rows", source = "pageSize")
 	@Mapping(target = "debugQuery", source = "debugQuery")
-	@Mapping(target = "sort", expression = "java( eu.openaire.api.mappers.Utils.formatSortByParam(src.getSortBy(), SolrFieldsMapper.projectSortMapping) )")
+	@Mapping(target = "sort", expression = "java( eu.openaire.api.mappers.Utils.formatSortByParam(src.getSortBy(), SolrFieldsMapper.PROJECT_SORT_MAPPING) )")
 	SolrQueryParams toSolrQuery(ProjectRequest src);
 
 	@Named("calculateStart")
@@ -26,7 +30,7 @@ public interface ProjectRequestMapper {
 	@AfterMapping
 	default void paramsCustomMapping(ProjectRequest src, @MappingTarget SolrQueryParams solrQueryParams) {
 
-		final Map<String, String> solrFieldMapping = SolrFieldsMapper.projectFieldMapping;
+		final Map<String, String> solrFieldMapping = SolrFieldsMapper.PROJECT_FIELD_MAPPING;
 
 		var qList = new ArrayList<String>();
 

src/main/java/eu/openaire/api/mappers/query/ResearchProductsRequestMapper.java

@@ -3,7 +3,11 @@ package eu.openaire.api.mappers.query;
 import eu.openaire.api.dto.request.ResearchProductsRequest;
 import eu.openaire.api.mappers.Utils;
 import eu.openaire.api.solr.SolrQueryParams;
-import org.mapstruct.*;
+import org.mapstruct.AfterMapping;
+import org.mapstruct.Mapper;
+import org.mapstruct.Mapping;
+import org.mapstruct.MappingTarget;
+import org.mapstruct.Named;
 
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -16,7 +20,7 @@ public interface ResearchProductsRequestMapper {
 	@Mapping(target = "start", expression = "java( calculateStart(src.getPage(), src.getPageSize()) )")
 	@Mapping(target = "rows", source = "pageSize")
 	@Mapping(target = "debugQuery", source = "debugQuery")
-	@Mapping(target = "sort", expression = "java( eu.openaire.api.mappers.Utils.formatSortByParam(src.getSortBy(), SolrFieldsMapper.researchProductSortMapping) )")
+	@Mapping(target = "sort", expression = "java( eu.openaire.api.mappers.Utils.formatSortByParam(src.getSortBy(), SolrFieldsMapper.RESEARCH_PRODUCT_SORT_MAPPING) )")
 	SolrQueryParams toSolrQuery(ResearchProductsRequest src);
 
 	@Named("calculateStart")
@@ -27,7 +31,7 @@ public interface ResearchProductsRequestMapper {
 	@AfterMapping
 	default void paramsCustomMapping(ResearchProductsRequest src, @MappingTarget SolrQueryParams solrQueryParams) {
 
-		final Map<String, String> solrFieldMapping = SolrFieldsMapper.researchProductFieldMapping;
+		final Map<String, String> solrFieldMapping = SolrFieldsMapper.RESEARCH_PRODUCT_FIELD_MAPPING;
 
 		var qList = new ArrayList<String>();
 

src/main/java/eu/openaire/api/mappers/query/SolrFieldsMapper.java

@@ -5,7 +5,7 @@ import java.util.Map;
 public class SolrFieldsMapper {
 
 	// mappings for the organization entity
-	public static final Map<String, String> organizationFieldsMapping = java.util.Map.ofEntries(
+	public static final Map<String, String> ORGANIZATION_FIELDS_MAPPING = java.util.Map.ofEntries(
 
 			// search field mapping
 			Map.entry("search", "__all:(%s)"),
@@ -23,12 +23,12 @@ public class SolrFieldsMapper {
 
 	);
 
-	public static final Map<String, String> organizationSortMapping = Map.ofEntries(
+	public static final Map<String, String> ORGANIZATION_SORT_MAPPING = Map.ofEntries(
 			Map.entry("relevance", "score")
 	);
 
 	// mappings for the datasource entity
-	public static final Map<String, String> dataSourceFieldMapping = Map.ofEntries(
+	public static final Map<String, String> DATASOURCE_FIELD_MAPPING = Map.ofEntries(
 
 			// search field mapping
 			Map.entry("search", "__all:(%s)"),
@@ -48,13 +48,13 @@ public class SolrFieldsMapper {
 			Map.entry("relCollectedFromDatasourceId", "collectedfromdatasourceid:(%s)")
 	);
 
-	public static final Map<String, String> dataSourceSortMapping = Map.ofEntries(
+	public static final Map<String, String> DATASOURCE_SORT_MAPPING = Map.ofEntries(
 			Map.entry("relevance", "score")
 	);
 
 
 	// mappings for the project entity
-	public static final Map<String, String> projectFieldMapping = Map.ofEntries(
+	public static final Map<String, String> PROJECT_FIELD_MAPPING = Map.ofEntries(
 
 			// search field mapping
 			Map.entry("search", "__all:(%s)"),
@@ -81,13 +81,13 @@ public class SolrFieldsMapper {
 
 	);
 
-	public static final Map<String, String> projectSortMapping = Map.ofEntries(
+	public static final Map<String, String> PROJECT_SORT_MAPPING = Map.ofEntries(
 			Map.entry("relevance", "score"),
 			Map.entry("startDate", "projectstartyear"),
 			Map.entry("endDate", "projectendyear")
 	);
 
-	public static final Map<String, String> researchProductFieldMapping = Map.ofEntries(
+	public static final Map<String, String> RESEARCH_PRODUCT_FIELD_MAPPING = Map.ofEntries(
 
 			// search field mapping
 			Map.entry("search", "__all:(%s)"),
@@ -134,7 +134,7 @@ public class SolrFieldsMapper {
 
 	);
 
-	public static final Map<String, String> researchProductSortMapping = Map.ofEntries(
+	public static final Map<String, String> RESEARCH_PRODUCT_SORT_MAPPING = Map.ofEntries(
 
 			Map.entry("relevance", "score"),
 			Map.entry("publicationDate", "resultdateofacceptance"),

src/main/java/eu/openaire/api/mappers/response/entities/DatasourceMapper.java

@@ -5,7 +5,12 @@ import eu.dnetlib.dhp.oa.model.Indicator;
 import eu.dnetlib.dhp.oa.model.graph.Datasource;
 import eu.dnetlib.dhp.oa.model.graph.DatasourcePid;
 import eu.dnetlib.dhp.oa.model.graph.DatasourceSchemeValue;
-import eu.dnetlib.dhp.schema.solr.*;
+import eu.dnetlib.dhp.schema.solr.CodeLabel;
+import eu.dnetlib.dhp.schema.solr.Journal;
+import eu.dnetlib.dhp.schema.solr.Measure;
+import eu.dnetlib.dhp.schema.solr.Pid;
+import eu.dnetlib.dhp.schema.solr.SolrRecord;
+import eu.dnetlib.dhp.schema.solr.Subject;
 import org.mapstruct.Mapper;
 import org.mapstruct.Mapping;
 import org.mapstruct.Named;
@@ -54,23 +59,26 @@ public interface DatasourceMapper {
     DatasourcePid mapPid(Pid pid);
 
     @Named("mapPids")
-    default List<DatasourcePid> mapPids(List<Pid> pids ){
+    default List<DatasourcePid> mapPids(List<Pid> pids ) {
-        if(pids == null)
+        if (pids == null) {
             return null;
+        }
         return pids.stream().map(this::mapPid).collect(Collectors.toList());
     }
 
     @Named("mapSubjects")
-    default List<String> mapSubjects(List<Subject> sbjs ){
+    default List<String> mapSubjects(List<Subject> sbjs ) {
-        if(sbjs == null)
+        if (sbjs == null) {
             return null;
+        }
         return sbjs.stream().map(Subject::getValue).collect(Collectors.toList());
     }
 
     @Named("mapPolicies")
-    default List<String> mapPolicies(List<CodeLabel> policies ){
+    default List<String> mapPolicies(List<CodeLabel> policies ) {
-        if(policies == null)
+        if (policies == null) {
             return null;
+        }
         return policies.stream().map(CodeLabel::getLabel).collect(Collectors.toList());
     }
 
@@ -82,7 +90,7 @@ public interface DatasourceMapper {
 
 
     @Named("mapIndicators")
-    default Indicator mapIndicators(List<Measure> measureList){
+    default Indicator mapIndicators(List<Measure> measureList) {
         return Utils.mapIndicators(measureList);
     }
 

src/main/java/eu/openaire/api/mappers/response/entities/OrganizationMapper.java

@@ -35,14 +35,15 @@ public interface OrganizationMapper {
     OrganizationPid mapPid(Pid pid);
 
     @Named("mapPids")
-    default List<OrganizationPid> mapPids(List<Pid> pids ){
+    default List<OrganizationPid> mapPids(List<Pid> pids ) {
-        if(pids == null)
+        if (pids == null) {
             return null;
+        }
         return pids.stream().map(this::mapPid).collect(Collectors.toList());
     }
 
     @Named("mapIndicators")
-    default Indicator mapIndicators(List<Measure> measureList){
+    default Indicator mapIndicators(List<Measure> measureList) {
         return Utils.mapIndicators(measureList);
     }
 

src/main/java/eu/openaire/api/mappers/response/entities/ProjectMapper.java

@@ -5,7 +5,11 @@ import eu.dnetlib.dhp.oa.model.graph.Funder;
 import eu.dnetlib.dhp.oa.model.graph.Fundings;
 import eu.dnetlib.dhp.oa.model.graph.Granted;
 import eu.dnetlib.dhp.oa.model.graph.Project;
-import eu.dnetlib.dhp.schema.solr.*;
+import eu.dnetlib.dhp.schema.solr.Funding;
+import eu.dnetlib.dhp.schema.solr.FundingLevel;
+import eu.dnetlib.dhp.schema.solr.Measure;
+import eu.dnetlib.dhp.schema.solr.SolrRecord;
+import eu.dnetlib.dhp.schema.solr.Subject;
 import org.mapstruct.Mapper;
 import org.mapstruct.Mapping;
 import org.mapstruct.Named;
@@ -39,24 +43,27 @@ public interface ProjectMapper {
     Granted mapFundedAmount(eu.dnetlib.dhp.schema.solr.Project project);
 
     @Named("mapSubjects")
-    default List<String> mapSubjects(List<Subject>subjectList){
+    default List<String> mapSubjects(List<Subject>subjectList) {
-        if(subjectList == null)
+        if (subjectList == null) {
             return null;
+        }
         return subjectList.stream().map(Subject::getValue).collect(Collectors.toList());
     }
 
     @Named("mapOpenAccessMandate")
-    default Boolean mapOpenAccessMandate(String mandate){
+    default Boolean mapOpenAccessMandate(String mandate) {
-        if(mandate == null)
+        if (mandate == null) {
             return Boolean.FALSE;
+        }
         return Boolean.parseBoolean(mandate);
     }
 
 
     @Named("mapFunding")
-    default List<Funder> mapFundings(Funding funding){
+    default List<Funder> mapFundings(Funding funding) {
-        if(funding == null)
+        if (funding == null) {
             return null;
+        }
         return Collections.singletonList(mapFunding(funding));
     }
 
@@ -68,19 +75,19 @@ public interface ProjectMapper {
     Funder mapFunding(Funding funding);
 
     @Named("mapFundingStream")
-    default Fundings mapFundingStream(Funding funding){
+    default Fundings mapFundingStream(Funding funding) {
         Fundings fundings = new Fundings();
         StringBuffer description = new StringBuffer();
         FundingLevel fl = funding.getLevel0();
         String id ;
         description.append(fl.getDescription());
         id = fl.getId();
-        if(Optional.ofNullable(funding.getLevel1()).isPresent()) {
+        if (Optional.ofNullable(funding.getLevel1()).isPresent()) {
             fl = funding.getLevel1();
             id = fl.getId();
             description.append(" - ").append(fl.getDescription());
         }
-        if(Optional.ofNullable(funding.getLevel2()).isPresent()) {
+        if (Optional.ofNullable(funding.getLevel2()).isPresent()) {
             fl = funding.getLevel2();
             id = fl.getId();
             description.append(" - ").append(fl.getDescription());
@@ -91,7 +98,7 @@ public interface ProjectMapper {
     }
 
     @Named("mapIndicators")
-    default Indicator mapIndicators(List<Measure> measureList){
+    default Indicator mapIndicators(List<Measure> measureList) {
         return Utils.mapIndicators(measureList);
     }
 

src/main/java/eu/openaire/api/mappers/response/entities/ResearchProductMapper.java

@@ -2,19 +2,29 @@ package eu.openaire.api.mappers.response.entities;
 
 import eu.dnetlib.dhp.oa.model.APC;
 import eu.dnetlib.dhp.oa.model.AccessRight;
+import eu.dnetlib.dhp.oa.model.AlternateIdentifier;
+import eu.dnetlib.dhp.oa.model.AuthorPid;
+import eu.dnetlib.dhp.oa.model.AuthorPidSchemeValue;
+import eu.dnetlib.dhp.oa.model.Container;
 import eu.dnetlib.dhp.oa.model.OpenAccessRoute;
-import eu.dnetlib.dhp.oa.model.*;
+import eu.dnetlib.dhp.oa.model.Indicator;
+import eu.dnetlib.dhp.oa.model.ResultCountry;
+import eu.dnetlib.dhp.oa.model.ResultPid;
+import eu.dnetlib.dhp.oa.model.SubjectSchemeValue;
 import eu.dnetlib.dhp.oa.model.graph.GraphResult;
 import eu.dnetlib.dhp.schema.common.ModelConstants;
 import eu.dnetlib.dhp.schema.solr.Author;
 import eu.dnetlib.dhp.schema.solr.BestAccessRight;
 import eu.dnetlib.dhp.schema.solr.Country;
 import eu.dnetlib.dhp.schema.solr.Instance;
+import eu.dnetlib.dhp.schema.solr.Journal;
 import eu.dnetlib.dhp.schema.solr.Language;
 import eu.dnetlib.dhp.schema.solr.Measure;
 import eu.dnetlib.dhp.schema.solr.OpenAccessColor;
+import eu.dnetlib.dhp.schema.solr.Pid;
+import eu.dnetlib.dhp.schema.solr.SolrRecord;
 import eu.dnetlib.dhp.schema.solr.Subject;
-import eu.dnetlib.dhp.schema.solr.*;
+
 import org.mapstruct.Mapper;
 import org.mapstruct.Mapping;
 import org.mapstruct.Named;
@@ -67,21 +77,23 @@ public interface ResearchProductMapper {
     ResultPid mapPid(Pid pid);
 
     @Named("mapIndicators")
-    default Indicator mapIndicators(List<Measure> measureList){
+    default Indicator mapIndicators(List<Measure> measureList) {
         return Utils.mapIndicators(measureList);
     }
 
     @Named("mapPids")
-    default List<ResultPid> mapPids(List<Pid> pids ){
+    default List<ResultPid> mapPids(List<Pid> pids ) {
-        if(pids == null)
+        if (pids == null) {
             return null;
+        }
         return pids.stream().map(this::mapPid).collect(Collectors.toList());
     }
 
     @Named("mapAltIds")
-    default List<AlternateIdentifier> mapAltIds(List<Pid> altIdentifiers){
+    default List<AlternateIdentifier> mapAltIds(List<Pid> altIdentifiers) {
-        if(altIdentifiers == null)
+        if (altIdentifiers == null) {
             return null;
+        }
         return altIdentifiers.stream().map(this::mapAltId).collect(Collectors.toList());
     }
 
@@ -94,9 +106,10 @@ public interface ResearchProductMapper {
     Container mapJournal(Journal journal );
 
     @Named("mapSubjects")
-    default List<eu.dnetlib.dhp.oa.model.Subject> mapSubjects(List<Subject> sbjs ){
+    default List<eu.dnetlib.dhp.oa.model.Subject> mapSubjects(List<Subject> sbjs ) {
-        if(sbjs == null)
+        if (sbjs == null) {
             return null;
+        }
         return sbjs.stream().map(this::mapSubject).collect(Collectors.toList());
     }
 
@@ -108,9 +121,10 @@ public interface ResearchProductMapper {
     SubjectSchemeValue mapSubjectSchemeValue(Subject subject);
 
     @Named("mapCountries")
-    default List<ResultCountry> mapCountries(List<Country> countryList){
+    default List<ResultCountry> mapCountries(List<Country> countryList) {
-        if(countryList == null)
+        if (countryList == null) {
             return null;
+        }
         return countryList.stream().map(this::mapCountry).collect(Collectors.toList());
     }
 
@@ -123,9 +137,10 @@ public interface ResearchProductMapper {
     eu.dnetlib.dhp.oa.model.OpenAccessColor mapOpenAccessColor(OpenAccessColor openAccessColor);
 
     @Named("mapAuthor")
-    default List<eu.dnetlib.dhp.oa.model.Author> mapAuthors(List<Author> authorsList){
+    default List<eu.dnetlib.dhp.oa.model.Author> mapAuthors(List<Author> authorsList) {
-        if(authorsList == null)
+        if (authorsList == null) {
             return null;
+        }
         return authorsList.stream().map(this::mapAuthor).collect(Collectors.toList());
    }
 
@@ -134,9 +149,10 @@ public interface ResearchProductMapper {
    eu.dnetlib.dhp.oa.model.Author mapAuthor(Author author);
 
     @Named("mapAuthorPid")
-    default AuthorPid mapAuthorPid(List<Pid> authorPidList){
+    default AuthorPid mapAuthorPid(List<Pid> authorPidList) {
-        if(authorPidList == null)
+        if (authorPidList == null) {
             return null;
+        }
         List<Pid> orcid = authorPidList
                 .stream()
                 .filter(ap -> ModelConstants.ORCID.equals(ap.getTypeCode()))
@@ -144,8 +160,9 @@ public interface ResearchProductMapper {
         if (orcid.size() == 1) {
             return getAuthorPid(orcid.get(0));
         }
-        if (orcid.size() > 1 )
+        if (orcid.size() > 1 ) {
             return null;
+        }
         orcid = authorPidList
                 .stream()
                 .filter(ap -> ModelConstants.ORCID_PENDING.equals(ap.getTypeCode()))
@@ -165,9 +182,10 @@ public interface ResearchProductMapper {
     AuthorPidSchemeValue mapAuthorPidSchemeValue (Pid pid);
 
     @Named("mapBestAccessRight")
-    default eu.dnetlib.dhp.oa.model.BestAccessRight mapBestAccessRight(BestAccessRight bestAccessRight){
+    default eu.dnetlib.dhp.oa.model.BestAccessRight mapBestAccessRight(BestAccessRight bestAccessRight) {
-        if(bestAccessRight == null)
+        if (bestAccessRight == null) {
             return null;
+        }
         if (Constants.ACCESS_RIGHTS_COAR_MAP.containsKey(bestAccessRight.getCode())) {
             String code = Constants.ACCESS_RIGHTS_COAR_MAP.get(bestAccessRight.getCode());
             return
@@ -181,9 +199,10 @@ public interface ResearchProductMapper {
     }
 
     @Named("mapInstances")
-    default List<eu.dnetlib.dhp.oa.model.Instance> mapInstances(List<Instance> instanceList){
+    default List<eu.dnetlib.dhp.oa.model.Instance> mapInstances(List<Instance> instanceList) {
-        if(instanceList == null)
+        if (instanceList == null) {
             return null;
+        }
         return instanceList.stream().map(this::mapInstance).collect(Collectors.toList());
     }
 
@@ -197,9 +216,10 @@ public interface ResearchProductMapper {
     eu.dnetlib.dhp.oa.model.Instance mapInstance(Instance instance);
 
     @Named("mapAccessRight")
-    default AccessRight mapAccessRight(eu.dnetlib.dhp.schema.solr.AccessRight accessright){
+    default AccessRight mapAccessRight(eu.dnetlib.dhp.schema.solr.AccessRight accessright) {
-        if(accessright==null)
+        if (accessright == null) {
-            return  null;
+            return null;
+        }
         AccessRight ar = new AccessRight();
         if (Constants.ACCESS_RIGHTS_COAR_MAP.containsKey(accessright.getLabel())) {
             String code = Constants.ACCESS_RIGHTS_COAR_MAP.get(accessright.getLabel());

src/main/java/eu/openaire/api/mappers/response/entities/Utils.java

@@ -1,22 +1,19 @@
 package eu.openaire.api.mappers.response.entities;
 
-import eu.dnetlib.dhp.oa.model.AuthorPid;
 import eu.dnetlib.dhp.oa.model.BipIndicators;
 import eu.dnetlib.dhp.oa.model.Indicator;
 import eu.dnetlib.dhp.oa.model.UsageCounts;
-import eu.dnetlib.dhp.oa.model.graph.DatasourcePid;
-import eu.dnetlib.dhp.schema.common.ModelConstants;
 import eu.dnetlib.dhp.schema.solr.Measure;
-import eu.dnetlib.dhp.schema.solr.Pid;
 
 import java.util.List;
-import java.util.stream.Collectors;
 
 public class Utils {
 
-    public static Indicator mapIndicators(List<Measure> measureList){
+    public static Indicator mapIndicators(List<Measure> measureList) {
-        if(measureList == null)
+        if (measureList == null) {
             return null;
+        }
+
         Indicator i = new Indicator();
         for (Measure m : measureList) {
             switch (m.getId()) {
@@ -28,36 +25,44 @@ public class Utils {
                     break;
                 case Constants.BIP_INFLUENCE:
                     m.getUnit().forEach(u -> {
-                        if (u.getCode().equals("class"))
+                        if (u.getCode().equals("class")) {
                             getImpactMeasure(i).setInfluenceClass(u.getLabel());
-                        if (u.getCode().equals("score"))
+                        }
+                        if (u.getCode().equals("score")) {
                             getImpactMeasure(i).setInfluence(Double.parseDouble(u.getLabel()));
+                        }
                     });
                     break;
                 case Constants.BIP_POPULARITY:
                     m.getUnit().forEach(u -> {
-                        if (u.getCode().equals("class"))
+                        if (u.getCode().equals("class")) {
                             getImpactMeasure(i).setPopularityClass(u.getLabel());
-                        if (u.getCode().equals("score"))
+                        }
+                        if (u.getCode().equals("score")) {
                             getImpactMeasure(i).setPopularity(Double.parseDouble(u.getLabel()));
+                        }
                     });
                     break;
                 case Constants.BIP_INFLUENCE_ALT:
                     m.getUnit().forEach(u -> {
-                        if (u.getCode().equals("class"))
+                        if (u.getCode().equals("class")) {
                             getImpactMeasure(i).setCitationClass(u.getLabel());
-                        if (u.getCode().equals("score"))
+                        }
+                        if (u.getCode().equals("score")) {
                             getImpactMeasure(i).setCitationCount(Double.parseDouble(u.getLabel()));
+                        }
                     });
                     break;
                 case Constants.BIP_POPULARITY_ALT:
                     break;
                 case Constants.BIP_IMPULSE:
                     m.getUnit().forEach(u -> {
-                        if (u.getCode().equals("class"))
+                        if (u.getCode().equals("class")) {
                             getImpactMeasure(i).setImpulseClass(u.getLabel());
-                        if (u.getCode().equals("score"))
+                        }
+                        if (u.getCode().equals("score")) {
                             getImpactMeasure(i).setImpulse(Double.parseDouble(u.getLabel()));
+                        }
                     });
                     break;
                 default:

src/main/java/eu/openaire/api/services/ScholixService.java

@@ -0,0 +1,42 @@
+package eu.openaire.api.services;
+
+import eu.dnetlib.dhp.schema.sx.api.model.v2.PageResultType;
+import io.micrometer.core.annotation.Timed;
+import lombok.RequiredArgsConstructor;
+import org.apache.logging.log4j.LogManager;
+import org.apache.logging.log4j.Logger;
+import org.springframework.stereotype.Service;
+import org.springframework.web.client.RestClient;
+
+@Service
+@RequiredArgsConstructor
+public class ScholixService {
+
+	private final RestClient restClient;
+	private final Logger log = LogManager.getLogger(this.getClass());
+	private static final String OPENAIRE_ID_PREFIX = "50|";
+
+	@Timed
+	public PageResultType getLinks(String sourcePid, String sourceType, int page) {
+		try {
+			if (!sourcePid.startsWith(OPENAIRE_ID_PREFIX)) {
+				sourcePid = OPENAIRE_ID_PREFIX + sourcePid;
+			}
+
+			String finalSourcePid = sourcePid;
+
+            return restClient.get()
+					.uri(uriBuilder -> uriBuilder
+							.path("/v2/Links")
+							.queryParam("sourcePid", finalSourcePid)
+							.queryParam("sourceType", sourceType)
+							.queryParam("page", page)
+							.build())
+					.retrieve()
+					.body(PageResultType.class);
+		} catch (Exception e) {
+			log.error(e.getMessage());
+			throw new RuntimeException("Unexpected error: " + e.getMessage(), e);
+		}
+	}
+}

src/main/resources/application.properties

@@ -7,6 +7,8 @@ openapi.description=The Graph API allows developers to access metadata records o
 solr.collection=${SOLR_COLLECTION}
 solr.zkHosts=${ZK_HOSTS}
 
+scholix.server-base-url=${SCHOLIX_SERVER_BASE_URL}
+
 logging.level.org.springframework.web=DEBUG
 
 #removes 'trace' field from error responses; alternatively remove 'spring-boot-devtools' dependency

src/main/resources/checkstyle.xml

@@ -0,0 +1,95 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+  Licensed to the Apache Software Foundation (ASF) under one
+  or more contributor license agreements. See the NOTICE file
+  distributed with this work for additional information
+  regarding copyright ownership. The ASF licenses this file
+  to you under the Apache License, Version 2.0 (the
+  "License"); you may not use this file except in compliance
+  with the License. You may obtain a copy of the License at
+
+  http://www.apache.org/licenses/LICENSE-2.0
+
+  Unless required by applicable law or agreed to in writing,
+  software distributed under the License is distributed on an
+  "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+  KIND, either express or implied. See the License for the
+  specific language governing permissions and limitations
+  under the License.
+-->
+<!DOCTYPE module PUBLIC
+        "-//Puppy Crawl//DTD Check Configuration 1.3//EN"
+        "https://checkstyle.org/dtds/configuration_1_3.dtd">
+
+<!--
+Checks to make sure the code meets the ActiveMQ coding guidelines which
+
+It also enforces a bunch of other "BestPractices like method
+lengths, if/try depths, etc...
+-->
+
+<module name="Checker">
+    <module name="TreeWalker">
+
+        <!-- Checks for Naming Conventions.  -->
+        <!-- See http://checkstyle.sf.net/config_naming.html -->
+        <module name="ConstantName"/>
+        <module name="LocalFinalVariableName"/>
+        <module name="LocalVariableName"/>
+        <module name="MemberName"/>
+        <module name="MethodName"/>
+        <module name="PackageName"/>
+        <module name="ParameterName"/>
+        <module name="StaticVariableName"/>
+        <module name="TypeName"/>
+        <module name="AvoidStarImport"/>
+        <module name="IllegalImport"/>
+        <module name="RedundantImport"/>
+        <module name="MethodLength">
+            <property name="max" value="200"/>
+            <property name="countEmpty" value="false"/>
+        </module>
+        <module name="ParameterNumber">
+            <property name="max" value="7"/>
+        </module>
+
+
+        <!-- Checks for whitespace -->
+        <!-- See http://checkstyle.sf.net/config_whitespace.html -->
+        <module name="WhitespaceAfter">
+            <property name="tokens" value="COMMA, SEMI"/>
+        </module>
+        <module name="WhitespaceAround">
+            <property name="tokens" value="ASSIGN, BAND, BAND_ASSIGN, BOR, BOR_ASSIGN, BSR, BSR_ASSIGN, BXOR, BXOR_ASSIGN, COLON, DIV, DIV_ASSIGN, EQUAL, GE, GT, LAND, LCURLY, LE, LITERAL_ASSERT, LITERAL_CATCH, LITERAL_DO, LITERAL_ELSE, LITERAL_FINALLY, LITERAL_FOR, LITERAL_IF, LITERAL_RETURN, LITERAL_SYNCHRONIZED, LITERAL_TRY, LITERAL_WHILE, LOR, LT, MINUS, MINUS_ASSIGN, MOD, MOD_ASSIGN, NOT_EQUAL, PLUS, PLUS_ASSIGN, QUESTION, SL, SLIST, SL_ASSIGN, SR, SR_ASSIGN, STAR, STAR_ASSIGN,TYPE_EXTENSION_AND"/>
+        </module>
+
+        <!-- Checks for blocks. You know, those {}'s         -->
+        <!-- See http://checkstyle.sf.net/config_blocks.html -->
+        <module name="LeftCurly"/>
+        <module name="RightCurly"/>
+        <module name="NeedBraces">
+            <property name="tokens"
+                      value="LITERAL_DO, LITERAL_ELSE, LITERAL_FOR, LITERAL_IF, LITERAL_WHILE"/>
+        </module>
+
+        <!-- Checks for common coding problems               -->
+        <!-- See http://checkstyle.sf.net/config_coding.html -->
+        <!--<module name="ArrayTrailingComma"/>-->
+        <!--<module name="AvoidInlineConditionals"/>-->
+        <module name="CovariantEquals"/>
+        <module name="EmptyStatement"/>
+        <module name="EqualsHashCode"/>
+
+        <module name="IllegalInstantiation"/>
+        <module name="MissingSwitchDefault"/>
+
+        <module name="NestedIfDepth">
+            <property name="max" value="8"/>
+        </module>
+        <module name="NestedTryDepth">
+            <property name="max" value="8"/>
+        </module>
+        <module name="EmptyCatchBlock"/>
+        <module name="OneTopLevelClass"/>
+    </module>
+</module>