update

Author: ArnavBalyan

paimon-api/src/main/java/org/apache/paimon/rest/HttpClient.java

@@ -33,6 +33,7 @@
 import org.apache.hc.client5.http.classic.methods.HttpPost;
 import org.apache.hc.client5.http.classic.methods.HttpUriRequestBase;
 import org.apache.hc.core5.http.ClassicHttpResponse;
+import org.apache.hc.core5.http.ContentType;
 import org.apache.hc.core5.http.Header;
 import org.apache.hc.core5.http.io.entity.StringEntity;
 import org.apache.hc.core5.http.message.BasicHeader;
@@ -94,7 +95,7 @@ public <T extends RESTResponse> T post(
         HttpPost httpPost = new HttpPost(getRequestUrl(path, null));
         String encodedBody = RESTUtil.encodedBody(body);
         if (encodedBody != null) {
-            httpPost.setEntity(new StringEntity(encodedBody));
+            httpPost.setEntity(new StringEntity(encodedBody, ContentType.APPLICATION_JSON));
         }
         Header[] authHeaders = getHeaders(path, "POST", encodedBody, restAuthFunction);
         httpPost.setHeaders(authHeaders);
@@ -112,7 +113,7 @@ public <T extends RESTResponse> T delete(
         HttpDelete httpDelete = new HttpDelete(getRequestUrl(path, null));
         String encodedBody = RESTUtil.encodedBody(body);
         if (encodedBody != null) {
-            httpDelete.setEntity(new StringEntity(encodedBody));
+            httpDelete.setEntity(new StringEntity(encodedBody, ContentType.APPLICATION_JSON));
         }
         Header[] authHeaders = getHeaders(path, "DELETE", encodedBody, restAuthFunction);
         httpDelete.setHeaders(authHeaders);

paimon-api/src/main/java/org/apache/paimon/rest/SimpleHttpClient.java

@@ -24,6 +24,7 @@
 import org.apache.hc.client5.http.classic.methods.HttpPost;
 import org.apache.hc.client5.http.classic.methods.HttpUriRequestBase;
 import org.apache.hc.client5.http.impl.classic.CloseableHttpClient;
+import org.apache.hc.core5.http.ContentType;
 import org.apache.hc.core5.http.Header;
 import org.apache.hc.core5.http.io.entity.StringEntity;
 import org.apache.hc.core5.http.message.BasicHeader;
@@ -55,7 +56,11 @@ public String post(String url, Object body, Map<String, String> headers) throws
         }
         String encodedBody = RESTUtil.encodedBody(body);
         if (encodedBody != null) {
-            httpPost.setEntity(new StringEntity(encodedBody));
+            ContentType contentType =
+                    body instanceof Map
+                            ? ContentType.APPLICATION_FORM_URLENCODED
+                            : ContentType.APPLICATION_JSON;
+            httpPost.setEntity(new StringEntity(encodedBody, contentType));
         }
 
         return exec(httpPost);

paimon-core/src/test/java/org/apache/paimon/rest/HttpClientTest.java

@@ -27,6 +27,7 @@
 
 import org.apache.paimon.shade.guava30.com.google.common.collect.ImmutableMap;
 
+import okhttp3.mockwebserver.RecordedRequest;
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
@@ -37,6 +38,7 @@
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
+import java.util.concurrent.TimeUnit;
 import java.util.stream.Collectors;
 
 import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
@@ -261,4 +263,16 @@ public void testPostWithNonJsonErrorResponse() {
                     "Error message should contain the original non-JSON response");
         }
     }
+
+    @Test
+    public void testPostSetsJsonContentType() throws Exception {
+        server.enqueueResponse(mockResponseDataStr, 200);
+        httpClient.post(MOCK_PATH, mockResponseData, MockRESTData.class, restAuthFunction);
+        RecordedRequest request = server.takeRequest(10, TimeUnit.SECONDS);
+        String contentType = request.getHeader("Content-Type");
+        Assertions.assertNotNull(contentType, "POST request must carry a Content-Type header");
+        Assertions.assertTrue(
+                contentType.contains("application/json"),
+                "POST body must be sent as application/json, but was: " + contentType);
+    }
 }