Add Decimal Vector APIs to write Big Endian data

java/vector/src/main/codegen/templates/AbstractFieldWriter.java

@@ -67,6 +67,10 @@ public void write(${name}Holder holder) {
   public void write${minor.class}(${friendlyType} value) {
     fail("${name}");
   }
+
+  public void writeBigEndianBytesToDecimal(byte[] value) {
+    fail("${name}");
+  }
   </#if>
 
   </#list></#list>

java/vector/src/main/codegen/templates/AbstractPromotableFieldWriter.java

@@ -16,6 +16,8 @@
  * limitations under the License.
  */
 
+import io.netty.buffer.ArrowBuf;
+import org.apache.arrow.vector.types.Types;
 import org.apache.drill.common.types.TypeProtos.MinorType;
 
 <@pp.dropOutputFile />
@@ -82,6 +84,12 @@ public void write(${name}Holder holder) {
     getWriter(MinorType.${name?upper_case}).write${minor.class}(<#list fields as field>${field.name}<#if field_has_next>, </#if></#list>);
   }
 
+  <#if minor.class == "Decimal">
+  public void writeBigEndianBytesToDecimal(byte[] value) {
+    getWriter(Types.MinorType.DECIMAL).writeBigEndianBytesToDecimal(value);
+  }
+  </#if>
+
   </#list></#list>
   public void writeNull() {
   }

java/vector/src/main/codegen/templates/ComplexWriters.java

@@ -120,6 +120,11 @@ public void write(Nullable${minor.class}Holder h) {
     vector.setSafe(idx(), value);
     vector.setValueCount(idx()+1);
   }
+
+  public void writeBigEndianBytesToDecimal(byte[] value) {
+    vector.setBigEndianSafe(idx(), value);
+    vector.setValueCount(idx()+1);
+  }
   </#if>
 
   <#if mode == "Nullable">
@@ -148,6 +153,8 @@ public interface ${eName}Writer extends BaseWriter {
 <#if minor.class == "Decimal">
 
   public void write${minor.class}(${friendlyType} value);
+
+  public void writeBigEndianBytesToDecimal(byte[] value);
 </#if>
 }
 

java/vector/src/main/java/org/apache/arrow/vector/NullableDecimalVector.java

@@ -18,6 +18,7 @@
 
 package org.apache.arrow.vector;
 
+import com.google.common.base.Preconditions;
 import io.netty.buffer.ArrowBuf;
 import org.apache.arrow.memory.BufferAllocator;
 import org.apache.arrow.vector.complex.impl.DecimalReaderImpl;
@@ -199,6 +200,43 @@ public void set(int index, ArrowBuf buffer) {
     valueBuffer.setBytes(index * TYPE_WIDTH, buffer, 0, TYPE_WIDTH);
   }
 
+  /**
+   * Set the decimal element at given index to the provided array of bytes.
+   * Decimal is now implemented as Little Endian. This API allows the user
+   * to pass a decimal value in the form of byte array in BE byte order.
+   *
+   * Consumers of Arrow code can use this API instead of first swapping
+   * the source bytes (doing a write and read) and then finally writing to
+   * ArrowBuf of decimal vector.
+   *
+   * This method takes care of adding the necessary padding if the length
+   * of byte array is less then 16 (length of decimal type).
+   *
+   * @param index position of element
+   * @param value array of bytes containing decimal in big endian byte order.
+   */
+  public void setBigEndian(int index, byte[] value) {
+    assert value.length <= TYPE_WIDTH;
+    BitVectorHelper.setValidityBitToOne(validityBuffer, index);
+    final int length = value.length;
+    int startIndex = index * TYPE_WIDTH;
+    if (length == TYPE_WIDTH) {
+      for (int i = TYPE_WIDTH - 1; i >= 3; i-=4) {
+        valueBuffer.setByte(startIndex, value[i]);
+        valueBuffer.setByte(startIndex + 1, value[i-1]);
+        valueBuffer.setByte(startIndex + 2, value[i-2]);
+        valueBuffer.setByte(startIndex + 3, value[i-3]);
+        startIndex += 4;
+      }
+    } else {
+      for (int i = length - 1; i >= 0; i--) {
+        valueBuffer.setByte(startIndex, value[i]);
+        startIndex++;
+      }
+      valueBuffer.setZero(startIndex, TYPE_WIDTH - length);
+    }
+  }
+
   /**
    * Set the element at the given index to the given value.
    *
@@ -266,6 +304,16 @@ public void setSafe(int index, ArrowBuf buffer) {
     set(index, buffer);
   }
 
+  /**
+   * Same as {@link #setBigEndian(int, byte[])} except that it handles the
+   * case when index is greater than or equal to existing
+   * value capacity {@link #getValueCapacity()}.
+   */
+  public void setBigEndianSafe(int index, byte[] value) {
+    handleSafe(index);
+    setBigEndian(index, value);
+  }
+
   /**
    * Same as {@link #set(int, int, ArrowBuf)} except that it handles the
    * case when index is greater than or equal to existing