java conversions

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/namedExpressions.scala

@@ -134,6 +134,7 @@ case class AttributeReference(
     var h = 17
     h = h * 37 + exprId.hashCode()
     h = h * 37 + dataType.hashCode()
+    h = h * 37 + metadata.hashCode()
     h
   }
 

sql/core/src/main/java/org/apache/spark/sql/api/java/DataType.java

@@ -17,9 +17,7 @@
 
 package org.apache.spark.sql.api.java;
 
-import java.util.HashSet;
-import java.util.List;
-import java.util.Set;
+import java.util.*;
 
 /**
  * The base type of all Spark SQL data types.
@@ -146,15 +144,31 @@ public static MapType createMapType(
    * Creates a StructField by specifying the name ({@code name}), data type ({@code dataType}) and
    * whether values of this field can be null values ({@code nullable}).
    */
-  public static StructField createStructField(String name, DataType dataType, boolean nullable) {
+  public static StructField createStructField(
+      String name,
+      DataType dataType,
+      boolean nullable,
+      Map<String, Object> metadata) {
     if (name == null) {
       throw new IllegalArgumentException("name should not be null.");
     }
     if (dataType == null) {
       throw new IllegalArgumentException("dataType should not be null.");
     }
+    if (metadata == null) {
+      throw new IllegalArgumentException("metadata should not be null.");
+    }
+
+    return new StructField(name, dataType, nullable, metadata);
+  }
 
-    return new StructField(name, dataType, nullable);
+  /**
+   * Creates a StructField with empty metadata.
+   *
+   * @see #createStructField(String, DataType, boolean, java.util.Map)
+   */
+  public static StructField createStructField(String name, DataType dataType, boolean nullable) {
+    return createStructField(name, dataType, nullable, new HashMap<String, Object>());
   }
 
   /**

sql/core/src/main/java/org/apache/spark/sql/api/java/StructField.java

@@ -17,27 +17,37 @@
 
 package org.apache.spark.sql.api.java;
 
+import java.util.Map;
+
 /**
  * A StructField object represents a field in a StructType object.
  * A StructField object comprises three fields, {@code String name}, {@code DataType dataType},
  * and {@code boolean nullable}. The field of {@code name} is the name of a StructField.
  * The field of {@code dataType} specifies the data type of a StructField.
  * The field of {@code nullable} specifies if values of a StructField can contain {@code null}
  * values.
+ * The field of {@code metadata} provides extra information of the StructField, which is a map from
+ * string to simple type that can be serialized to JSON automatically
  *
  * To create a {@link StructField},
- * {@link DataType#createStructField(String, DataType, boolean)}
+ * {@link DataType#createStructField(String, DataType, boolean, Map)}
  * should be used.
  */
 public class StructField {
   private String name;
   private DataType dataType;
   private boolean nullable;
+  private Map<String, Object> metadata;
 
-  protected StructField(String name, DataType dataType, boolean nullable) {
+  protected StructField(
+      String name,
+      DataType dataType,
+      boolean nullable,
+      Map<String, Object> metadata) {
     this.name = name;
     this.dataType = dataType;
     this.nullable = nullable;
+    this.metadata = metadata;
   }
 
   public String getName() {
@@ -52,6 +62,10 @@ public boolean isNullable() {
     return nullable;
   }
 
+  public Map<String, Object> getMetadata() {
+    return metadata;
+  }
+
   @Override
   public boolean equals(Object o) {
     if (this == o) return true;
@@ -62,6 +76,7 @@ public boolean equals(Object o) {
     if (nullable != that.nullable) return false;
     if (!dataType.equals(that.dataType)) return false;
     if (!name.equals(that.name)) return false;
+    if (!metadata.equals(that.metadata)) return false;
 
     return true;
   }
@@ -71,6 +86,7 @@ public int hashCode() {
     int result = name.hashCode();
     result = 31 * result + dataType.hashCode();
     result = 31 * result + (nullable ? 1 : 0);
+    result = 31 * result + metadata.hashCode();
     return result;
   }
 }

sql/core/src/main/scala/org/apache/spark/sql/types/util/DataTypeConversions.scala

@@ -31,7 +31,8 @@ protected[sql] object DataTypeConversions {
     JDataType.createStructField(
       scalaStructField.name,
       asJavaDataType(scalaStructField.dataType),
-      scalaStructField.nullable)
+      scalaStructField.nullable,
+      scalaStructField.metadata.asJava.asInstanceOf[java.util.Map[String, Object]])
   }
 
   /**
@@ -67,7 +68,8 @@ protected[sql] object DataTypeConversions {
     StructField(
       javaStructField.getName,
       asScalaDataType(javaStructField.getDataType),
-      javaStructField.isNullable)
+      javaStructField.isNullable,
+      javaStructField.getMetadata.asScala.toMap)
   }
 
   /**

sql/core/src/test/scala/org/apache/spark/sql/api/java/ScalaSideDataTypeConversionSuite.scala

@@ -70,7 +70,8 @@ class ScalaSideDataTypeConversionSuite extends FunSuite {
       SStructField("simpleArray", simpleScalaArrayType, true) ::
       SStructField("simpleMap", simpleScalaMapType, true) ::
       SStructField("simpleStruct", simpleScalaStructType, true) ::
-      SStructField("boolean", org.apache.spark.sql.BooleanType, false) :: Nil)
+      SStructField("boolean", org.apache.spark.sql.BooleanType, false) ::
+      SStructField("withMeta", org.apache.spark.sql.DoubleType, false, Map("name" -> "age")) :: Nil)
     checkDataType(complexScalaStructType)
 
     // Complex ArrayType.