ARROW-8086: [Java] Support writing decimal from big endian byte array…

… in UnionListWriter

Closes #6593 from projjal/writedecimal and squashes the following commits:

f27f514 <Projjal Chanda> write decimal from bytearray for unionlistwriter

Authored-by: Projjal Chanda <iam@pchanda.com>
Signed-off-by: Praveen <praveen@dremio.com>

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

@@ -197,6 +197,14 @@ public void writeDecimal(BigDecimal value) {
     writer.setPosition(writer.idx() + 1);
   }
 
+  public void writeBigEndianBytesToDecimal(byte[] value, ArrowType arrowType) {
+    if (writer.idx() >= (idx() + 1) * listSize) {
+      throw new IllegalStateException(String.format("values at index %s is greater than listSize %s", idx(), listSize));
+    }
+    writer.writeBigEndianBytesToDecimal(value, arrowType);
+    writer.setPosition(writer.idx() + 1);
+  }
+
   <#list vv.types as type>
     <#list type.minor as minor>
       <#assign name = minor.class?cap_first />

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

@@ -193,6 +193,11 @@ public void writeDecimal(BigDecimal value) {
     writer.setPosition(writer.idx()+1);
   }
 
+  public void writeBigEndianBytesToDecimal(byte[] value, ArrowType arrowType){
+    writer.writeBigEndianBytesToDecimal(value, arrowType);
+    writer.setPosition(writer.idx() + 1);
+  }
+
   <#list vv.types as type>
     <#list type.minor as minor>
       <#assign name = minor.class?cap_first />

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

@@ -179,6 +179,12 @@ public void write(${name}Holder holder) {
     getDecimalWriter(arrowType).setPosition(idx());
     getDecimalWriter(arrowType).writeDecimal(value);
   }
+
+  public void writeBigEndianBytesToDecimal(byte[] value, ArrowType arrowType) {
+    data.setType(idx(), MinorType.DECIMAL);
+    getDecimalWriter(arrowType).setPosition(idx());
+    getDecimalWriter(arrowType).writeBigEndianBytesToDecimal(value, arrowType);
+  }
   </#if>
       </#if>
     </#list>

java/vector/src/test/java/org/apache/arrow/vector/complex/impl/TestComplexCopier.java

@@ -208,13 +208,14 @@ public void testCopyListVector() {
 
   @Test
   public void testCopyFixedSizedListOfDecimalsVector() {
-    try (FixedSizeListVector from = FixedSizeListVector.empty("v", 3, allocator);
-         FixedSizeListVector to = FixedSizeListVector.empty("v", 3, allocator)) {
+    try (FixedSizeListVector from = FixedSizeListVector.empty("v", 4, allocator);
+         FixedSizeListVector to = FixedSizeListVector.empty("v", 4, allocator)) {
       from.addOrGetVector(FieldType.nullable(new ArrowType.Decimal(3, 0)));
       to.addOrGetVector(FieldType.nullable(new ArrowType.Decimal(3, 0)));
 
       DecimalHolder holder = new DecimalHolder();
       holder.buffer = allocator.buffer(DecimalUtility.DECIMAL_BYTE_LENGTH);
+      ArrowType arrowType = new ArrowType.Decimal(3, 0);
 
       // populate from vector
       UnionFixedSizeListWriter writer = from.getWriter();
@@ -229,7 +230,10 @@ public void testCopyFixedSizedListOfDecimalsVector() {
         writer.decimal().write(holder);
 
         DecimalUtility.writeBigDecimalToArrowBuf(new BigDecimal(i * 3), holder.buffer, 0);
-        writer.decimal().writeDecimal(0, holder.buffer, new ArrowType.Decimal(3, 0));
+        writer.decimal().writeDecimal(0, holder.buffer, arrowType);
+
+        writer.decimal().writeBigEndianBytesToDecimal(BigDecimal.valueOf(i * 4).unscaledValue().toByteArray(),
+            arrowType);
 
         writer.endList();
       }
@@ -265,6 +269,8 @@ public void testCopyUnionListWithDecimal() {
 
         listWriter.decimal().writeDecimal(BigDecimal.valueOf(i * 2));
         listWriter.integer().writeInt(i);
+        listWriter.decimal().writeBigEndianBytesToDecimal(BigDecimal.valueOf(i * 3).unscaledValue().toByteArray(),
+            new ArrowType.Decimal(3, 0));
 
         listWriter.endList();
       }
@@ -304,6 +310,8 @@ public void testCopyStructVector() {
         innerStructWriter.start();
         innerStructWriter.integer("innerint").writeInt(i * 3);
         innerStructWriter.decimal("innerdec", 0, 38).writeDecimal(BigDecimal.valueOf(i * 4));
+        innerStructWriter.decimal("innerdec", 0, 38).writeBigEndianBytesToDecimal(BigDecimal.valueOf(i * 4)
+            .unscaledValue().toByteArray(), new ArrowType.Decimal(3, 0));
         innerStructWriter.end();
         structWriter.end();
       }

java/vector/src/test/java/org/apache/arrow/vector/complex/writer/TestComplexWriter.java

@@ -273,17 +273,24 @@ public void listDecimalType() {
       UnionListWriter listWriter = new UnionListWriter(listVector);
       DecimalHolder holder = new DecimalHolder();
       holder.buffer = allocator.buffer(DecimalUtility.DECIMAL_BYTE_LENGTH);
+      ArrowType arrowType = new ArrowType.Decimal(10, 0);
       for (int i = 0; i < COUNT; i++) {
         listWriter.startList();
         for (int j = 0; j < i % 7; j++) {
-          if (j % 2 == 0) {
+          if (j % 4 == 0) {
             listWriter.writeDecimal(new BigDecimal(j));
-          } else {
+          } else if (j % 4 == 1) {
             DecimalUtility.writeBigDecimalToArrowBuf(new BigDecimal(j), holder.buffer, 0);
             holder.start = 0;
             holder.scale = 0;
             holder.precision = 10;
             listWriter.write(holder);
+          } else if (j % 4 == 2) {
+            DecimalUtility.writeBigDecimalToArrowBuf(new BigDecimal(j), holder.buffer, 0);
+            listWriter.writeDecimal(0, holder.buffer, arrowType);
+          } else {
+            byte[] value = BigDecimal.valueOf(j).unscaledValue().toByteArray();
+            listWriter.writeBigEndianBytesToDecimal(value, arrowType);
           }
         }
         listWriter.endList();