[SPARK-57174][SQL] Simplify Chr codegen by extracting a static Java helper

sql/catalyst/src/main/java/org/apache/spark/sql/catalyst/expressions/ExpressionImplUtils.java

@@ -346,6 +346,23 @@ public static UTF8String quote(UTF8String str) {
     return UTF8String.fromString(qtChar + sp + qtChar);
   }
 
+  /**
+   * Returns the single-character string for the {@code chr} expression: the
+   * ASCII/Latin-1 character for {@code longVal & 0xFF}. A negative argument
+   * yields the empty string. Shared by the eval and codegen paths so the
+   * generated Java is a single call rather than an inline if/else chain.
+   */
+  public static UTF8String chr(long longVal) {
+    if (longVal < 0) {
+      return UTF8String.EMPTY_UTF8;
+    } else if ((longVal & 0xFF) == 0) {
+      return UTF8String.fromString(String.valueOf(Character.MIN_VALUE));
+    } else {
+      char c = (char) (longVal & 0xFF);
+      return UTF8String.fromString(String.valueOf(c));
+    }
+  }
+
   /**
    * Compiles {@code regex} with the given {@code flags} for the regexp expression
    * family, translating a {@link PatternSyntaxException} into the user-facing

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

@@ -2822,31 +2822,14 @@ case class Chr(child: Expression)
   override def inputTypes: Seq[DataType] = Seq(LongType)
 
   protected override def nullSafeEval(lon: Any): Any = {
-    val longVal = lon.asInstanceOf[Long]
-    if (longVal < 0) {
-      UTF8String.EMPTY_UTF8
-    } else if ((longVal & 0xFF) == 0) {
-      UTF8String.fromString(Character.MIN_VALUE.toString)
-    } else {
-      UTF8String.fromString((longVal & 0xFF).toChar.toString)
-    }
+    ExpressionImplUtils.chr(lon.asInstanceOf[Long])
   }
 
   override def contextIndependentFoldable: Boolean = child.contextIndependentFoldable
 
   override def doGenCode(ctx: CodegenContext, ev: ExprCode): ExprCode = {
-    nullSafeCodeGen(ctx, ev, lon => {
-      s"""
-        if ($lon < 0) {
-          ${ev.value} = UTF8String.EMPTY_UTF8;
-        } else if (($lon & 0xFF) == 0) {
-          ${ev.value} = UTF8String.fromString(String.valueOf(Character.MIN_VALUE));
-        } else {
-          char c = (char)($lon & 0xFF);
-          ${ev.value} = UTF8String.fromString(String.valueOf(c));
-        }
-      """
-    })
+    val utils = classOf[ExpressionImplUtils].getName
+    nullSafeCodeGen(ctx, ev, lon => s"${ev.value} = $utils.chr($lon);")
   }
 
   override protected def withNewChildInternal(newChild: Expression): Chr = copy(child = newChild)