[Java] Add JNI bindings for integers_to_hex (#14205)

This PR adds a method to ColumnView class to allow for conversion from Integers to hex
closes #14081

Authors:
  - Raza Jafri (https://github.com/razajafri)

Approvers:
  - Kuhu Shukla (https://github.com/kuhushukla)
  - Robert (Bobby) Evans (https://github.com/revans2)

URL: #14205

java/src/main/java/ai/rapids/cudf/ColumnView.java

@@ -4089,6 +4089,8 @@ static DeviceMemoryBufferView getOffsetsBuffer(long viewHandle) {
 
   private static native long isFixedPoint(long viewHandle, int nativeTypeId, int scale);
 
+  private static native long toHex(long viewHandle);
+
   /**
    * Native method to concatenate a list column of strings (each row is a list of strings),
    * concatenates the strings within each row and returns a single strings column result.
@@ -5231,4 +5233,29 @@ static ColumnView[] getColumnViewsFromPointers(long[] nativeHandles) {
       }
     }
   }
+
+  /**
+   * Convert this integer column to hexadecimal column and return a new strings column
+   *
+   * Any null entries will result in corresponding null entries in the output column.
+   *
+   * The output character set is '0'-'9' and 'A'-'F'. The output string width will
+   * be a multiple of 2 depending on the size of the integer type. A single leading
+   * zero is applied to the first non-zero output byte if it is less than 0x10.
+   *
+   * Example:
+   * input = [123, -1, 0, 27, 342718233]
+   * s = input.toHex()
+   * s is [ '04D2', 'FFFFFFFF', '00', '1B', '146D7719']
+   *
+   * The example above shows an `INT32` type column where each integer is 4 bytes.
+   * Leading zeros are suppressed unless filling out a complete byte as in
+   * `123 -> '04D2'` instead of `000004D2` or `4D2`.
+   *
+   * @return new string ColumnVector
+   */
+  public ColumnVector toHex() {
+    assert getType().isIntegral() : "Only integers are supported";
+    return new ColumnVector(toHex(this.getNativeView()));
+  }
 }

java/src/main/java/ai/rapids/cudf/DType.java

@@ -413,6 +413,14 @@ public boolean isDurationType() {
   }
 
   /**
+   * Returns true for strictly Integer types not a type backed by
+   * ints
+   */
+  public boolean isIntegral() {
+    return INTEGRALS.contains(this.typeId);
+  }
+
+ /**
    * Returns true for nested types
    */
   public boolean isNestedType() {
@@ -506,4 +514,15 @@ public boolean hasOffsets() {
       DTypeEnum.STRING,
       DTypeEnum.LIST
   );
+
+  private static final EnumSet<DTypeEnum> INTEGRALS = EnumSet.of(
+    DTypeEnum.INT8,
+    DTypeEnum.INT16,
+    DTypeEnum.INT32,
+    DTypeEnum.INT64,
+    DTypeEnum.UINT8,
+    DTypeEnum.UINT16,
+    DTypeEnum.UINT32,
+    DTypeEnum.UINT64
+  );
 }

java/src/main/native/src/ColumnViewJni.cpp

@@ -2563,4 +2563,13 @@ Java_ai_rapids_cudf_ColumnView_purgeNonEmptyNulls(JNIEnv *env, jclass, jlong col
   CATCH_STD(env, 0);
 }
 
+JNIEXPORT jlong JNICALL Java_ai_rapids_cudf_ColumnView_toHex(JNIEnv *env, jclass, jlong input_ptr) {
+  JNI_NULL_CHECK(env, input_ptr, "input is null", 0);
+  try {
+    cudf::jni::auto_set_device(env);
+    const cudf::column_view *input = reinterpret_cast<cudf::column_view *>(input_ptr);
+    return release_as_jlong(cudf::strings::integers_to_hex(*input));
+  }
+  CATCH_STD(env, 0);
+}
 } // extern "C"

java/src/test/java/ai/rapids/cudf/ColumnVectorTest.java

@@ -6876,4 +6876,14 @@ public void testUseAfterFree() {
     vector.close();
     assertThrows(NullPointerException.class, vector::getDeviceMemorySize);
   }
+
+  @Test
+  public void testConvertIntegerToHex() {
+    try (
+      ColumnVector input = ColumnVector.fromInts(14, 2621, 50);
+      ColumnVector expected = ColumnVector.fromStrings("0E", "0A3D", "32");
+      ColumnVector actual = input.toHex()) {
+        assertColumnsAreEqual(expected, actual);
+    }
+  }
 }