[SPARK-14653][ML] Remove json4s from mllib-local

## What changes were proposed in this pull request?

This PR moves Vector.toJson/fromJson to ml.linalg.VectorEncoder under mllib/ to keep mllib-local's dependency minimal. The json encoding is used by Params. So we still need this feature in SPARK-14615, where we will switch to ml.linalg in spark.ml APIs.

## How was this patch tested?

Copied existing unit tests over.

cc; dbtsai

Author: Xiangrui Meng <meng@databricks.com>

Closes #12802 from mengxr/SPARK-14653.

1 files changed, 41 insertions, 0 deletions

diff --git a/mllib/src/test/scala/org/apache/spark/ml/linalg/JsonVectorConverterSuite.scala b/mllib/src/test/scala/org/apache/spark/ml/linalg/JsonVectorConverterSuite.scala
new file mode 100644
index 0000000000..53d57f0f6e
--- /dev/null
+++ b/mllib/src/test/scala/org/apache/spark/ml/linalg/JsonVectorConverterSuite.scala
@@ -0,0 +1,41 @@
+/*
+ * 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.spark.ml.linalg
+
+import org.json4s.jackson.JsonMethods.parse
+
+import org.apache.spark.SparkFunSuite
+
+class JsonVectorConverterSuite extends SparkFunSuite {
+
+  test("toJson/fromJson") {
+    val sv0 = Vectors.sparse(0, Array.empty, Array.empty)
+    val sv1 = Vectors.sparse(1, Array.empty, Array.empty)
+    val sv2 = Vectors.sparse(2, Array(1), Array(2.0))
+    val dv0 = Vectors.dense(Array.empty[Double])
+    val dv1 = Vectors.dense(1.0)
+    val dv2 = Vectors.dense(0.0, 2.0)
+    for (v <- Seq(sv0, sv1, sv2, dv0, dv1, dv2)) {
+      val json = JsonVectorConverter.toJson(v)
+      parse(json) // `json` should be a valid JSON string
+      val u = JsonVectorConverter.fromJson(json)
+      assert(u.getClass === v.getClass, "toJson/fromJson should preserve vector types.")
+      assert(u === v, "toJson/fromJson should preserve vector values.")
+    }
+  }
+}