feat: Added support for OpenAI's File API.

1. Introduced the OpenAiFileApi class.
2. Implemented corresponding unit tests and integration tests.

Signed-off-by: Sun Yuhan <[email protected]>

Author: sunyuhan1998

models/spring-ai-openai/src/main/java/org/springframework/ai/openai/api/OpenAiFileApi.java

@@ -0,0 +1,384 @@
+/*
+ * Copyright 2025-2025 the original author or authors.
+ *
+ * Licensed 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
+ *
+ *      https://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.
+ */
+
+package org.springframework.ai.openai.api;
+
+import com.fasterxml.jackson.annotation.JsonInclude;
+import com.fasterxml.jackson.annotation.JsonProperty;
+import org.springframework.ai.model.ApiKey;
+import org.springframework.ai.model.NoopApiKey;
+import org.springframework.ai.model.SimpleApiKey;
+import org.springframework.ai.openai.api.common.OpenAiApiConstants;
+import org.springframework.ai.retry.RetryUtils;
+import org.springframework.core.io.ByteArrayResource;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.ResponseEntity;
+import org.springframework.util.Assert;
+import org.springframework.util.LinkedMultiValueMap;
+import org.springframework.util.MultiValueMap;
+import org.springframework.web.client.ResponseErrorHandler;
+import org.springframework.web.client.RestClient;
+import org.springframework.web.util.UriBuilder;
+
+import java.util.List;
+import java.util.function.Consumer;
+
+/**
+ * OpenAI File API.
+ *
+ * @author Sun Yuhan
+ * @see <a href= "https://platform.openai.com/docs/api-reference/files">Files API</a>
+ */
+public class OpenAiFileApi {
+
+	private final RestClient restClient;
+
+	public OpenAiFileApi(String baseUrl, ApiKey apiKey, MultiValueMap<String, String> headers,
+			RestClient.Builder restClientBuilder, ResponseErrorHandler responseErrorHandler) {
+		Consumer<HttpHeaders> authHeaders = h -> h.addAll(headers);
+
+		this.restClient = restClientBuilder.clone()
+			.baseUrl(baseUrl)
+			.defaultHeaders(authHeaders)
+			.defaultStatusHandler(responseErrorHandler)
+			.defaultRequest(requestHeadersSpec -> {
+				if (!(apiKey instanceof NoopApiKey)) {
+					requestHeadersSpec.header(HttpHeaders.AUTHORIZATION, "Bearer " + apiKey.getValue());
+				}
+			})
+			.build();
+	}
+
+	public static Builder builder() {
+		return new Builder();
+	}
+
+	/**
+	 * Upload a file that can be used across various endpoints
+	 * @param uploadFileRequest The request body
+	 * @return Response entity containing the file object
+	 */
+	public ResponseEntity<FileObject> uploadFile(UploadFileRequest uploadFileRequest) {
+		MultiValueMap<String, Object> multipartBody = new LinkedMultiValueMap<>();
+		multipartBody.add("file", new ByteArrayResource(uploadFileRequest.file()) {
+			@Override
+			public String getFilename() {
+				return uploadFileRequest.fileName();
+			}
+		});
+		multipartBody.add("purpose", uploadFileRequest.purpose());
+
+		return this.restClient.post().uri("/v1/files").body(multipartBody).retrieve().toEntity(FileObject.class);
+	}
+
+	/**
+	 * Returns a list of files
+	 * @param listFileRequest The request body
+	 * @return Response entity containing the files
+	 */
+	public ResponseEntity<FileObjectResponse> listFiles(ListFileRequest listFileRequest) {
+		return this.restClient.get().uri(uriBuilder -> {
+			UriBuilder builder = uriBuilder.path("/v1/files");
+			if (null != listFileRequest.after()) {
+				builder = builder.queryParam("after", listFileRequest.after());
+			}
+			if (null != listFileRequest.limit()) {
+				builder = builder.queryParam("limit", listFileRequest.limit());
+			}
+			if (null != listFileRequest.order()) {
+				builder = builder.queryParam("order", listFileRequest.order());
+			}
+			if (null != listFileRequest.purpose()) {
+				builder = builder.queryParam("purpose", listFileRequest.purpose());
+			}
+			return builder.build();
+		}).retrieve().toEntity(FileObjectResponse.class);
+	}
+
+	/**
+	 * Returns information about a specific file
+	 * @param fileId The file id
+	 * @return Response entity containing the file object
+	 */
+	public ResponseEntity<FileObject> retrieveFile(String fileId) {
+		return this.restClient.get().uri("/v1/files/%s".formatted(fileId)).retrieve().toEntity(FileObject.class);
+	}
+
+	/**
+	 * Delete a file
+	 * @param fileId The file id
+	 * @return Response entity containing the deletion status
+	 */
+	public ResponseEntity<DeleteFileResponse> deleteFile(String fileId) {
+		return this.restClient.delete()
+			.uri("/v1/files/%s".formatted(fileId))
+			.retrieve()
+			.toEntity(DeleteFileResponse.class);
+	}
+
+	/**
+	 * Returns the contents of the specified file
+	 * @param fileId The file id
+	 * @return Response entity containing the file content
+	 */
+	public ResponseEntity<String> retrieveFileContent(String fileId) {
+		return this.restClient.get().uri("/v1/files/%s/content".formatted(fileId)).retrieve().toEntity(String.class);
+	}
+
+	/**
+	 * The intended purpose of the uploaded file
+	 */
+	public enum Purpose {
+
+		// @formatter:off
+		/**
+		 * Used in the Assistants API
+		 */
+		@JsonProperty("assistants")
+		ASSISTANTS("assistants"),
+		/**
+		 * Used in the Batch API
+		 */
+		@JsonProperty("batch")
+		BATCH("batch"),
+		/**
+		 * Used for fine-tuning
+		 */
+		@JsonProperty("fine-tune")
+		FINE_TUNE("fine-tune"),
+		/**
+		 * Images used for vision fine-tuning
+		 */
+		@JsonProperty("vision")
+		VISION("vision"),
+		/**
+		 * Flexible file type for any purpose
+		 */
+		@JsonProperty("user_data")
+		USER_DATA("user_data"),
+		/**
+		 * Used for eval data sets
+		 */
+		@JsonProperty("evals")
+		EVALS("evals");
+		// @formatter:on
+
+		private final String value;
+
+		Purpose(String value) {
+			this.value = value;
+		}
+
+		public String getValue() {
+			return this.value;
+		}
+
+	}
+
+	@JsonInclude(JsonInclude.Include.NON_NULL)
+	public record UploadFileRequest(
+	// @formatter:off
+		@JsonProperty("file") byte[] file,
+		@JsonProperty("fileName") String fileName,
+		@JsonProperty("purpose") String purpose) {
+		// @formatter:on
+
+		public static Builder builder() {
+			return new Builder();
+		}
+
+		public static class Builder {
+
+			private byte[] file;
+
+			private String fileName;
+
+			private String purpose;
+
+			public Builder file(byte[] file) {
+				this.file = file;
+				return this;
+			}
+
+			public Builder fileName(String fileName) {
+				this.fileName = fileName;
+				return this;
+			}
+
+			public Builder purpose(String purpose) {
+				this.purpose = purpose;
+				return this;
+			}
+
+			public Builder purpose(Purpose purpose) {
+				this.purpose = purpose.getValue();
+				return this;
+			}
+
+			public UploadFileRequest build() {
+				Assert.notNull(file, "file must not be empty");
+				Assert.notNull(fileName, "fileName must not be empty");
+				Assert.notNull(purpose, "purpose must not be empty");
+
+				return new UploadFileRequest(this.file, this.fileName, this.purpose);
+			}
+
+		}
+	}
+
+	@JsonInclude(JsonInclude.Include.NON_NULL)
+	public record ListFileRequest(
+	// @formatter:off
+		@JsonProperty("after") String after,
+		@JsonProperty("limit") Integer limit,
+		@JsonProperty("order") String order,
+		@JsonProperty("purpose") String purpose) {
+		// @formatter:on
+
+		public static Builder builder() {
+			return new Builder();
+		}
+
+		public static class Builder {
+
+			private String after;
+
+			private Integer limit;
+
+			private String order;
+
+			private String purpose;
+
+			public Builder after(String after) {
+				this.after = after;
+				return this;
+			}
+
+			public Builder limit(Integer limit) {
+				this.limit = limit;
+				return this;
+			}
+
+			public Builder order(String order) {
+				this.order = order;
+				return this;
+			}
+
+			public Builder purpose(String purpose) {
+				this.purpose = purpose;
+				return this;
+			}
+
+			public Builder purpose(Purpose purpose) {
+				this.purpose = purpose.getValue();
+				return this;
+			}
+
+			public ListFileRequest build() {
+				return new ListFileRequest(this.after, this.limit, this.order, this.purpose);
+			}
+
+		}
+	}
+
+	@JsonInclude(JsonInclude.Include.NON_NULL)
+	public record FileObject(
+	// @formatter:off
+		@JsonProperty("id") String id,
+		@JsonProperty("object") String object,
+		@JsonProperty("bytes") Integer bytes,
+		@JsonProperty("created_at") Integer createdAt,
+		@JsonProperty("expires_at") Integer expiresAt,
+		@JsonProperty("filename") String filename,
+		@JsonProperty("purpose") String purpose) {
+		// @formatter:on
+	}
+
+	@JsonInclude(JsonInclude.Include.NON_NULL)
+	public record FileObjectResponse(
+	// @formatter:off
+		@JsonProperty("data") List<FileObject> data,
+		@JsonProperty("object") String object
+		// @formatter:on
+	) {
+	}
+
+	@JsonInclude(JsonInclude.Include.NON_NULL)
+	public record DeleteFileResponse(
+	// @formatter:off
+		@JsonProperty("id") String id,
+		@JsonProperty("object") String object,
+		@JsonProperty("deleted") Boolean deleted) {
+		// @formatter:on
+	}
+
+	public static class Builder {
+
+		private String baseUrl = OpenAiApiConstants.DEFAULT_BASE_URL;
+
+		private ApiKey apiKey;
+
+		private MultiValueMap<String, String> headers = new LinkedMultiValueMap<>();
+
+		private RestClient.Builder restClientBuilder = RestClient.builder();
+
+		private ResponseErrorHandler responseErrorHandler = RetryUtils.DEFAULT_RESPONSE_ERROR_HANDLER;
+
+		public Builder baseUrl(String baseUrl) {
+			Assert.hasText(baseUrl, "baseUrl cannot be null or empty");
+			this.baseUrl = baseUrl;
+			return this;
+		}
+
+		public Builder apiKey(ApiKey apiKey) {
+			Assert.notNull(apiKey, "apiKey cannot be null");
+			this.apiKey = apiKey;
+			return this;
+		}
+
+		public Builder apiKey(String simpleApiKey) {
+			Assert.notNull(simpleApiKey, "simpleApiKey cannot be null");
+			this.apiKey = new SimpleApiKey(simpleApiKey);
+			return this;
+		}
+
+		public Builder headers(MultiValueMap<String, String> headers) {
+			Assert.notNull(headers, "headers cannot be null");
+			this.headers = headers;
+			return this;
+		}
+
+		public Builder restClientBuilder(RestClient.Builder restClientBuilder) {
+			Assert.notNull(restClientBuilder, "restClientBuilder cannot be null");
+			this.restClientBuilder = restClientBuilder;
+			return this;
+		}
+
+		public Builder responseErrorHandler(ResponseErrorHandler responseErrorHandler) {
+			Assert.notNull(responseErrorHandler, "responseErrorHandler cannot be null");
+			this.responseErrorHandler = responseErrorHandler;
+			return this;
+		}
+
+		public OpenAiFileApi build() {
+			Assert.notNull(this.apiKey, "apiKey must be set");
+			return new OpenAiFileApi(this.baseUrl, this.apiKey, this.headers, this.restClientBuilder,
+					this.responseErrorHandler);
+		}
+
+	}
+
+}