[Fix][Connector-Http] fix Invalid mime type (#9363)

Author: litiliu

seatunnel-connectors-v2/connector-http/connector-http-base/src/main/java/org/apache/seatunnel/connectors/seatunnel/http/client/HttpClientProvider.java

@@ -465,7 +465,7 @@ private void addHeaders(HttpRequestBase request, Map<String, String> headers) {
         headers.forEach(request::addHeader);
     }
 
-    private void addBody(HttpEntityEnclosingRequestBase request, Map<String, Object> body)
+    static void addBody(HttpEntityEnclosingRequestBase request, Map<String, Object> body)
             throws UnsupportedEncodingException {
         if (MapUtils.isEmpty(body)) {
             body = new HashMap<>();
@@ -489,10 +489,8 @@ private void addBody(HttpEntityEnclosingRequestBase request, Map<String, Object>
                 request.setEntity(new UrlEncodedFormEntity(parameters, ENCODING));
             }
         } else {
-            request.addHeader(HTTP.CONTENT_TYPE, APPLICATION_JSON);
             StringEntity entity =
                     new StringEntity(JsonUtils.toJsonString(body), ContentType.APPLICATION_JSON);
-            entity.setContentEncoding(new BasicHeader(HTTP.CONTENT_TYPE, APPLICATION_JSON));
             request.setEntity(entity);
         }
     }

seatunnel-connectors-v2/connector-http/connector-http-base/src/test/java/org/apache/seatunnel/connectors/seatunnel/http/client/HttpClientProviderTest.java

@@ -0,0 +1,53 @@
+/*
+ * 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.
+ */
+package org.apache.seatunnel.connectors.seatunnel.http.client;
+
+import org.apache.http.Header;
+import org.apache.http.client.methods.HttpPost;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import java.util.HashMap;
+import java.util.Map;
+
+class HttpClientProviderTest {
+
+    @Test
+    void addBody() throws Exception {
+        HttpPost post = new HttpPost("http://localhost:8080");
+        Map<String, Object> body = new HashMap<>();
+        Header[] originalHeaders = post.getAllHeaders();
+        HttpClientProvider.addBody(post, body);
+
+        // ensure the original headers are preserved
+        Header[] currentHeaders = post.getAllHeaders();
+        Assertions.assertEquals(originalHeaders.length, currentHeaders.length);
+        for (int i = 0; i < originalHeaders.length; i++) {
+            Assertions.assertEquals(
+                    originalHeaders[i].getName(),
+                    currentHeaders[i].getName(),
+                    "Header name mismatch at index " + i);
+            Assertions.assertEquals(
+                    originalHeaders[i].getValue(),
+                    currentHeaders[i].getValue(),
+                    "Header value mismatch at index " + i);
+        }
+        // ensure no manually set content type or encoding
+        Assertions.assertNull(post.getEntity().getContentEncoding());
+    }
+}