.env

@@ -1,4 +1,5 @@
 ZK_HOSTS=zookeeper-solr-openaire-dev-1:2181,zookeeper-solr-openaire-dev-2:2181,zookeeper-solr-openaire-dev-3:2181
 SOLR_COLLECTION=public
 OPENAPI_SERVER_BASE_URL=http://localhost:8080/graph
-CONTEXT_PATH=/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>

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/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/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/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