Fix handling multiple request form

src/main/java/com/adyen/httpclient/AdyenHttpClient.java

@@ -60,6 +60,7 @@
 import org.apache.hc.client5.http.impl.io.PoolingHttpClientConnectionManagerBuilder;
 import org.apache.hc.client5.http.ssl.SSLConnectionSocketFactory;
 import org.apache.hc.core5.http.HttpHost;
+import org.apache.hc.core5.http.io.entity.ByteArrayEntity;
 import org.apache.hc.core5.http.io.entity.StringEntity;
 import org.apache.hc.core5.net.URIBuilder;
 import org.apache.hc.core5.ssl.SSLContexts;
@@ -212,6 +213,30 @@
     return response.getBody();
   }
 
+  @Override
+  public String requestBinary(
+      String endpoint,
+      BinaryRequestBody requestBody,
+      Config config,
+      boolean isApiKeyRequired,
+      RequestOptions requestOptions,
+      ApiConstants.HttpMethod httpMethod,
+      Map<String, String> params)
+      throws IOException, HTTPClientException {
+    CloseableHttpClient httpclient = getOrCreateHttpClient(config);
+    HttpUriRequestBase httpRequest =
+        createRequest(
+            endpoint, requestBody, config, isApiKeyRequired, requestOptions, httpMethod, params);
+
+    AdyenResponse response = httpclient.execute(httpRequest, new AdyenResponseHandler());
+
+    if (response.getStatus() < 200 || response.getStatus() >= 300) {
+      throw new HTTPClientException(
+          response.getStatus(), "HTTP Exception", response.getHeaders(), response.getBody());
+    }
+    return response.getBody();
+  }
+
   /**
    * Builds an {@link HttpUriRequestBase} with the appropriate HTTP method, headers, authentication,
    * and per-request timeout configuration from {@link Config}.
@@ -256,15 +281,56 @@
     httpRequest.setConfig(builder.build());
 
     setAuthentication(httpRequest, isApiKeyRequired, config);
-    setHeaders(config, requestOptions, httpRequest);
+    setHeaders(config, requestOptions, httpRequest, null);
 
     return httpRequest;
   }
 
-  private void setHeaders(
-      Config config, RequestOptions requestOptions, HttpUriRequestBase httpUriRequest) {
+  HttpUriRequestBase createRequest(
+      String endpoint,
+      BinaryRequestBody requestBody,
+      Config config,
+      boolean isApiKeyRequired,
+      RequestOptions requestOptions,
+      ApiConstants.HttpMethod httpMethod,
+      Map<String, String> params)
+      throws HTTPClientException {
+    HttpUriRequestBase httpRequest =
+        createHttpRequestBase(createUri(endpoint, params), requestBody.getData(), httpMethod);
+
+    RequestConfig.Builder builder = RequestConfig.custom();
+    builder.setResponseTimeout(config.getReadTimeoutMillis(), TimeUnit.MILLISECONDS);
+    builder.setConnectTimeout(config.getConnectionTimeoutMillis(), TimeUnit.MILLISECONDS);
+    builder.setDefaultKeepAlive(config.getDefaultKeepAliveMillis(), TimeUnit.MILLISECONDS);
+    builder.setConnectionRequestTimeout(
+        config.getConnectionRequestTimeoutMillis(), TimeUnit.MILLISECONDS);
 
-    setContentType(httpUriRequest, APPLICATION_JSON_TYPE);
+    if (config.getProtocolUpgradeEnabled() != null) {
+      builder.setProtocolUpgradeEnabled(config.getProtocolUpgradeEnabled());
+    }
+    if (proxy != null && proxy.address() instanceof InetSocketAddress) {
+      InetSocketAddress inetSocketAddress = (InetSocketAddress) proxy.address();
+      builder.setProxy(new HttpHost(inetSocketAddress.getHostName(), inetSocketAddress.getPort()));
+    }
+    httpRequest.setConfig(builder.build());
+
+    setAuthentication(httpRequest, isApiKeyRequired, config);
+    setHeaders(config, requestOptions, httpRequest, requestBody.getContentType());
+
+    return httpRequest;
+  }
+
+  private void setHeaders(
+      Config config,
+      RequestOptions requestOptions,
+      HttpUriRequestBase httpUriRequest,
+      String requestContentType) {
+
+    String contentType =
+        requestContentType != null
+            ? requestContentType
+            : getAdditionalHeader(requestOptions, CONTENT_TYPE, APPLICATION_JSON_TYPE);
+    setContentType(httpUriRequest, contentType);
     httpUriRequest.addHeader(ACCEPT_CHARSET, CHARSET);
 
     String applicationName = config.getApplicationName();
@@ -292,11 +358,32 @@
       }
 
       if (requestOptions.getAdditionalServiceHeaders() != null) {
-        requestOptions.getAdditionalServiceHeaders().forEach(httpUriRequest::addHeader);
+        requestOptions
+            .getAdditionalServiceHeaders()
+            .forEach(
+                (name, value) -> {
+                  if (!name.equalsIgnoreCase(CONTENT_TYPE)
+                      && (requestContentType == null || !name.equalsIgnoreCase("Content-Length"))) {
+                    httpUriRequest.addHeader(name, value);
+                  }
+                });
       }
     }
   }
 
+  private String getAdditionalHeader(
+      RequestOptions requestOptions, String name, String defaultValue) {
+    if (requestOptions != null && requestOptions.getAdditionalServiceHeaders() != null) {
+      for (Map.Entry<String, String> header :
+          requestOptions.getAdditionalServiceHeaders().entrySet()) {
+        if (header.getKey().equalsIgnoreCase(name)) {
+          return header.getValue();
+        }
+      }
+    }
+    return defaultValue;
+  }
+
   private HttpUriRequestBase createHttpRequestBase(
       URI endpoint, String requestBody, ApiConstants.HttpMethod httpMethod) {
     StringEntity requestEntity = null;
@@ -321,6 +408,27 @@
     }
   }
 
+  private HttpUriRequestBase createHttpRequestBase(
+      URI endpoint, byte[] requestBody, ApiConstants.HttpMethod httpMethod) {
+    ByteArrayEntity requestEntity =
+        requestBody == null ? null : new ByteArrayEntity(requestBody, null);
+
+    switch (httpMethod) {
+      case GET:
+        return new HttpGet(endpoint);
+      case PATCH:
+        HttpPatch httpPatch = new HttpPatch(endpoint);
+        httpPatch.setEntity(requestEntity);
+        return httpPatch;
+      case DELETE:
+        return new HttpDelete(endpoint);
+      default:
+        HttpPost httpPost = new HttpPost(endpoint);
+        httpPost.setEntity(requestEntity);
+        return httpPost;
+    }
+  }
+
   private URI createUri(String endpoint, Map<String, String> params) throws HTTPClientException {
     try {
       URIBuilder uriBuilder = new URIBuilder(endpoint);
@@ -406,7 +514,7 @@
 
   /** Sets the Content-Type header on the request. */
   private void setContentType(HttpUriRequest httpUriRequest, String contentType) {
-    httpUriRequest.addHeader(CONTENT_TYPE, contentType);
+    httpUriRequest.setHeader(CONTENT_TYPE, contentType);
   }
 
   /** Sets the X-API-Key header on the request. */

src/main/java/com/adyen/httpclient/BinaryRequestBody.java

@@ -0,0 +1,58 @@
+/*
+ *                       ######
+ *                       ######
+ * ############    ####( ######  #####. ######  ############   ############
+ * #############  #####( ######  #####. ######  #############  #############
+ *        ######  #####( ######  #####. ######  #####  ######  #####  ######
+ * ###### ######  #####( ######  #####. ######  #####  ######  #####  ######
+ * ###### ######  #####( ######  #####. ######  #####  #####   #####  ######
+ * #############  #############  #############  #############  #####  ######
+ *  ############   ############  #############  #############  ######
+ *                                      ######
+ *                               #############
+ *                               ############
+ *
+ * Adyen Java API Library
+ *
+ * Copyright (c) 2026 Adyen B.V.
+ * This file is open source and available under the MIT license.
+ * See the LICENSE file for more info.
+ */
+package com.adyen.httpclient;
+
+import java.util.Arrays;
+
+/** Contains a binary request payload and its content type. */
+public final class BinaryRequestBody {
+  private final byte[] data;
+  private final String contentType;
+
+  /**
+   * Creates a binary request payload.
+   *
+   * @param data request body data
+   * @param contentType request content type
+   */
+  public BinaryRequestBody(byte[] data, String contentType) {
+    this.data = Arrays.copyOf(data, data.length);
+    this.contentType = contentType;
+  }
+
+  /**
+   * Gets a copy of the request body data.
+   *
+   * @return request body data
+   */
+  public byte[] getData() {
+    return Arrays.copyOf(data, data.length);
+  }
+
+  /**
+   * Gets the request content type.
+   *
+   * @return request content type
+   */
+  public String getContentType() {
+    return contentType;
+  }
+}

src/main/java/com/adyen/httpclient/ClientInterface.java

@@ -136,4 +136,32 @@ String request(
       ApiConstants.HttpMethod httpMethod,
       Map<String, String> params)
       throws IOException, HTTPClientException;
+
+  /**
+   * Sends a binary HTTP request. Custom HTTP client implementations must override this method to
+   * support multipart API operations.
+   *
+   * @param endpoint the full URL of the API endpoint
+   * @param requestBody the binary request body and its content type
+   * @param config the client configuration
+   * @param isApiKeyRequired whether API key authentication is mandatory
+   * @param requestOptions additional request options (idempotency key, custom headers)
+   * @param httpMethod the HTTP method
+   * @param params query string parameters appended to the URL
+   * @return the response body
+   * @throws IOException if a network error occurs
+   * @throws HTTPClientException if the server returns a non-2xx status code
+   */
+  default String requestBinary(
+      String endpoint,
+      BinaryRequestBody requestBody,
+      Config config,
+      boolean isApiKeyRequired,
+      RequestOptions requestOptions,
+      ApiConstants.HttpMethod httpMethod,
+      Map<String, String> params)
+      throws IOException, HTTPClientException {
+    throw new UnsupportedOperationException(
+        "The configured HTTP client does not support binary request bodies");
+  }
 }

src/main/java/com/adyen/httpclient/HttpFile.java

@@ -0,0 +1,58 @@
+/*
+ *                       ######
+ *                       ######
+ * ############    ####( ######  #####. ######  ############   ############
+ * #############  #####( ######  #####. ######  #############  #############
+ *        ######  #####( ######  #####. ######  #####  ######  #####   ######
+ * ###### ######  #####( ######  #####. ######  #####  ######  #####  ######
+ * ###### ######  #####( ######  #####. ######  #####  #####   #####  ######
+ * #############  #############  #############  #############  #####  ######
+ *  ############   ############  #############  #############  ######
+ *                                      ######
+ *                               #############
+ *                               ############
+ *
+ * Adyen Java API Library
+ *
+ * Copyright (c) 2026 Adyen B.V.
+ * This file is open source and available under the MIT license.
+ * See the LICENSE file for more info.
+ */
+package com.adyen.httpclient;
+
+import java.util.Arrays;
+
+/** Represents a file uploaded as part of a multipart request. */
+public class HttpFile {
+  private final byte[] data;
+  private final String name;
+
+  /**
+   * Creates a file for a multipart request.
+   *
+   * @param data file contents
+   * @param name file name sent to the API
+   */
+  public HttpFile(byte[] data, String name) {
+    this.data = Arrays.copyOf(data, data.length);
+    this.name = name;
+  }
+
+  /**
+   * Gets a copy of the file contents.
+   *
+   * @return file contents
+   */
+  public byte[] getData() {
+    return Arrays.copyOf(data, data.length);
+  }
+
+  /**
+   * Gets the file name.
+   *
+   * @return file name
+   */
+  public String getName() {
+    return name;
+  }
+}