[Breaking][jvm-packages] make classification model be xgboost-compatible (#7896)

jvm-packages/xgboost4j-spark/src/test/scala/ml/dmlc/xgboost4j/scala/spark/XGBoostClassifierSuite.scala

@@ -16,16 +16,19 @@
 
 package ml.dmlc.xgboost4j.scala.spark
 
+import java.io.{File, FileInputStream}
+
 import ml.dmlc.xgboost4j.scala.{DMatrix, XGBoost => ScalaXGBoost}
 
 import org.apache.spark.ml.linalg._
 import org.apache.spark.sql._
 import org.scalatest.FunSuite
+import org.apache.commons.io.IOUtils
 
 import org.apache.spark.Partitioner
 import org.apache.spark.ml.feature.VectorAssembler
 
-class XGBoostClassifierSuite extends FunSuite with PerTest {
+class XGBoostClassifierSuite extends FunSuite with PerTest with TmpFolderPerSuite {
 
   protected val treeMethod: String = "auto"
 
@@ -391,4 +394,37 @@ class XGBoostClassifierSuite extends FunSuite with PerTest {
     df1.show()
   }
 
+  test("XGBoostClassificationModel should be compatible") {
+    val paramMap = Map("eta" -> "0.1", "max_depth" -> "6", "silent" -> "1",
+      "objective" -> "multi:softprob", "num_class" -> "6", "num_round" -> 5,
+      "num_workers" -> numWorkers, "tree_method" -> treeMethod)
+    val trainingDF = buildDataFrame(MultiClassification.train)
+    val xgb = new XGBoostClassifier(paramMap)
+    val model = xgb.fit(trainingDF)
+    val modelPath = new File(tempDir.toFile, "xgbc").getPath
+    model.write.overwrite().save(modelPath)
+    val nativeModelPath = new File(tempDir.toFile, "nativeModel").getPath
+    model.nativeBooster.saveModel(nativeModelPath)
+
+    assert(compareTwoFiles(new File(modelPath, "data/XGBoostClassificationModel").getPath,
+      nativeModelPath))
+  }
+
+  private def compareTwoFiles(lhs: String, rhs: String): Boolean = {
+    withResource(new FileInputStream(lhs)) { lfis =>
+      withResource(new FileInputStream(rhs)) { rfis =>
+        IOUtils.contentEquals(lfis, rfis)
+      }
+    }
+  }
+
+  /** Executes the provided code block and then closes the resource */
+  private def withResource[T <: AutoCloseable, V](r: T)(block: T => V): V = {
+    try {
+      block(r)
+    } finally {
+      r.close()
+    }
+  }
+
 }