work on scala.

jvm-packages/.gitignore

@@ -2,3 +2,4 @@ build.sh
 xgboost4j-tester/pom.xml
 xgboost4j-tester/iris.csv
 dependency-reduced-pom.xml
+.factorypath

jvm-packages/xgboost4j-spark-gpu/src/main/java/ml/dmlc/xgboost4j/java/ExtMemQuantileDMatrix.java

@@ -10,7 +10,6 @@
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.module.SimpleModule;
 
-
 public class ExtMemQuantileDMatrix extends QuantileDMatrix {
   // on_host is set to true by default as we only support GPU at the moment
   // cache_prefix is not used yet since we have on_host=true.
@@ -29,22 +28,45 @@ public ExtMemQuantileDMatrix(Iterator<ColumnBatch> iter,
       ref_handle[0] = ref.getHandle();
     }
     String conf = this.getConfig(missing, maxBin, nthread, max_num_device_pages,
-                                 max_quantile_batches, min_cache_page_bytes);
+        max_quantile_batches, min_cache_page_bytes);
     XGBoostJNI.checkCall(XGBoostJNI.XGExtMemQuantileDMatrixCreateFromCallback(
         iter, ref_handle, conf, out));
     handle = out[0];
   }
 
+  public ExtMemQuantileDMatrix(
+      Iterator<ColumnBatch> iter,
+      float missing,
+      int maxBin,
+      DMatrix ref) throws XGBoostError {
+    this(iter, missing, maxBin, ref, 1, -1, -1, -1);
+  }
+
+  public ExtMemQuantileDMatrix(
+      Iterator<ColumnBatch> iter,
+      float missing,
+      int maxBin) throws XGBoostError {
+    this(iter, missing, maxBin, null);
+  }
+
   private String getConfig(float missing, int maxBin, int nthread, int max_num_device_pages,
       int max_quantile_batches,
       int min_cache_page_bytes) {
     Map<String, Object> conf = new java.util.HashMap<>();
     conf.put("missing", missing);
     conf.put("max_bin", maxBin);
     conf.put("nthread", nthread);
-    conf.put("max_num_device_pages", max_num_device_pages);
-    conf.put("max_quantile_batches", max_quantile_batches);
-    conf.put("min_cache_page_bytes", min_cache_page_bytes);
+
+    if (max_num_device_pages > 0) {
+      conf.put("max_num_device_pages", max_num_device_pages);
+    }
+    if (max_quantile_batches > 0) {
+      conf.put("max_quantile_batches", max_quantile_batches);
+    }
+    if (min_cache_page_bytes > 0) {
+      conf.put("min_cache_page_bytes", min_cache_page_bytes);
+    }
+
     conf.put("on_host", true);
     conf.put("cache_prefix", ".");
     ObjectMapper mapper = new ObjectMapper();

jvm-packages/xgboost4j-spark-gpu/src/main/scala/ml/dmlc/xgboost4j/scala/ExtMemQuantileDMatrix.scala

@@ -0,0 +1,37 @@
+/*
+ Copyright (c) 2025 by Contributors
+
+ 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
+
+ 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 ml.dmlc.xgboost4j.scala
+
+import scala.collection.JavaConverters._
+
+import ml.dmlc.xgboost4j.java.{Column, ColumnBatch, ExtMemQuantileDMatrix => jExtMemQuantileDMatrix, XGBoostError}
+
+class ExtMemQuantileDMatrix private[scala](
+  private[scala] override val jDMatrix: jExtMemQuantileDMatrix) extends QuantileDMatrix(jDMatrix) {
+
+  def this(iter: Iterator[ColumnBatch], missing: Float, maxBin: Int) {
+    this(new jExtMemQuantileDMatrix(iter.asJava, missing, maxBin))
+  }
+
+  def this(
+    iter: Iterator[ColumnBatch],
+    ref: ExtMemQuantileDMatrix,
+    missing: Float,
+    maxBin: Int
+  ) {
+    this(new jExtMemQuantileDMatrix(iter.asJava, missing, maxBin, ref.jDMatrix))
+  }
+}