fix(java): Move schema caching to unsafe trait to avoid issues when using non-inferred schema.

java/fury-format/src/main/java/org/apache/fury/format/row/binary/BinaryArray.java

@@ -63,6 +63,7 @@ public BinaryArray(Field field) {
     } else {
       this.elementSize = width;
     }
+    initializeExtData(1); // Only require at most one slot to cache the schema for array type.
   }
 
   public void pointTo(MemoryBuffer buffer, int offset, int sizeInBytes) {
@@ -135,7 +136,7 @@ public BigDecimal getDecimal(int ordinal) {
 
   @Override
   public BinaryRow getStruct(int ordinal) {
-    return getStruct(ordinal, field.getChildren().get(0));
+    return getStruct(ordinal, field.getChildren().get(0), 0);
   }
 
   @Override

java/fury-format/src/main/java/org/apache/fury/format/row/binary/BinaryRow.java

@@ -73,6 +73,7 @@ public BinaryRow(Schema schema) {
     this.numFields = schema.getFields().size();
     Preconditions.checkArgument(numFields > 0);
     this.bitmapWidthInBytes = BitUtils.calculateBitmapWidthInBytes(numFields);
+    initializeExtData(numFields);
   }
 
   public void pointTo(MemoryBuffer buffer, int offset, int sizeInBytes) {
@@ -155,7 +156,7 @@ public BigDecimal getDecimal(int ordinal) {
 
   @Override
   public BinaryRow getStruct(int ordinal) {
-    return getStruct(ordinal, schema.getFields().get(ordinal));
+    return getStruct(ordinal, schema.getFields().get(ordinal), ordinal);
   }
 
   @Override

java/fury-format/src/main/java/org/apache/fury/format/row/binary/UnsafeTrait.java

@@ -26,6 +26,7 @@
 import org.apache.arrow.memory.ArrowBuf;
 import org.apache.arrow.vector.types.pojo.ArrowType;
 import org.apache.arrow.vector.types.pojo.Field;
+import org.apache.arrow.vector.types.pojo.Schema;
 import org.apache.arrow.vector.util.DecimalUtility;
 import org.apache.fury.format.row.Getters;
 import org.apache.fury.format.row.Setters;
@@ -35,6 +36,7 @@
 
 /** Internal to binary row format to reuse code, don't use it in anywhere else. */
 abstract class UnsafeTrait implements Getters, Setters {
+  private Object[] extData;
 
   abstract MemoryBuffer getBuffer();
 
@@ -55,6 +57,10 @@ public MemoryBuffer getBuffer(int ordinal) {
 
   abstract int getOffset(int ordinal);
 
+  void initializeExtData(int numSlots) {
+    extData = new Object[numSlots];
+  }
+
   // ###########################################################
   // ####################### getters #######################
   // ###########################################################
@@ -143,14 +149,25 @@ BigDecimal getDecimal(int ordinal, ArrowType.Decimal decimalType) {
     return decimal;
   }
 
-  BinaryRow getStruct(int ordinal, Field field) {
+  /**
+   * Gets the field at a specific ordinal as a struct.
+   *
+   * @param ordinal the ordinal position of this field.
+   * @param field the Arrow field corresponding to this struct.
+   * @param extDataSlot the ext data slot used to cache the schema for the struct.
+   * @return the binary row representation of the struct.
+   */
+  BinaryRow getStruct(int ordinal, Field field, int extDataSlot) {
     if (isNullAt(ordinal)) {
       return null;
     }
     final long offsetAndSize = getInt64(ordinal);
     final int relativeOffset = (int) (offsetAndSize >> 32);
     final int size = (int) offsetAndSize;
-    BinaryRow row = new BinaryRow(DataTypes.createSchema(field));
+    if (extData[extDataSlot] == null) {
+      extData[extDataSlot] = DataTypes.createSchema(field);
+    }
+    BinaryRow row = new BinaryRow((Schema) extData[extDataSlot]);
     row.pointTo(getBuffer(), getBaseOffset() + relativeOffset, size);
     return row;
   }

java/fury-format/src/main/java/org/apache/fury/format/type/DataTypes.java

@@ -314,7 +314,7 @@ public static Field field(String name, ArrowType type, Field... children) {
   }
 
   public static Field field(String name, FieldType fieldType, List<Field> children) {
-    return new ExtField(name, fieldType, children);
+    return new Field(name, fieldType, children);
   }
 
   public static Field notNullField(String name, ArrowType type, Field... children) {
@@ -396,19 +396,11 @@ public static Field mapField(String name, Field keyField, Field itemField) {
   }
 
   public static Field keyFieldForMap(Field mapField) {
-    Field field = mapField.getChildren().get(0).getChildren().get(0);
-    if (field.getClass() != ExtField.class) {
-      return new ExtField(field.getName(), field.getFieldType(), field.getChildren());
-    }
-    return field;
+    return mapField.getChildren().get(0).getChildren().get(0);
   }
 
   public static Field itemFieldForMap(Field mapField) {
-    Field field = mapField.getChildren().get(0).getChildren().get(1);
-    if (field.getClass() != ExtField.class) {
-      return new ExtField(field.getName(), field.getFieldType(), field.getChildren());
-    }
-    return field;
+    return mapField.getChildren().get(0).getChildren().get(1);
   }
 
   public static Field keyArrayFieldForMap(Field mapField) {
@@ -425,24 +417,7 @@ public static Schema schemaFromStructField(Field structField) {
   }
 
   public static Schema createSchema(Field field) {
-    if (field.getClass() != ExtField.class) {
-      throw new IllegalArgumentException(
-          String.format("Field %s got wrong type %s", field, field.getClass()));
-    }
-    ExtField extField = (ExtField) field;
-    Object extData = extField.extData;
-    if (extData == null) {
-      extField.extData = extData = new Schema(field.getChildren(), field.getMetadata());
-    }
-    return (Schema) extData;
-  }
-
-  static class ExtField extends Field {
-    Object extData;
-
-    public ExtField(String name, FieldType fieldType, List<Field> children) {
-      super(name, fieldType, children);
-    }
+    return new Schema(field.getChildren(), field.getMetadata());
   }
 
   public static Field structField(boolean nullable, Field... fields) {