fix #2558 (#2559)

fix org.bson.types.Decimal128 to Double, for issue #2558

Author: ocean23

core/src/main/java/com/alibaba/fastjson2/util/TypeUtils.java

@@ -1522,6 +1522,23 @@ public static <T> T cast(Object obj, Class<T> targetClass, ObjectReaderProvider
                     break;
             }
         }
+        // fix org.bson.types.Decimal128 to Double
+        String objClassName = obj.getClass().getName();
+        if (objClassName.equals("org.bson.types.Decimal128") && targetClass == Double.class) {
+            ObjectWriter objectWriter = JSONFactory
+                    .getDefaultObjectWriterProvider()
+                    .getObjectWriter(obj.getClass());
+            if (objectWriter instanceof ObjectWriterPrimitiveImpl) {
+                Function function = ((ObjectWriterPrimitiveImpl<?>) objectWriter).getFunction();
+                if (function != null) {
+                    Object apply = function.apply(obj);
+                    Function DecimalTypeConvert = provider.getTypeConvert(apply.getClass(), targetClass);
+                    if (DecimalTypeConvert != null) {
+                        return (T) DecimalTypeConvert.apply(obj);
+                    }
+                }
+            }
+        }
 
         ObjectWriter objectWriter = JSONFactory
                 .getDefaultObjectWriterProvider()

core/src/test/java/com/alibaba/fastjson2/issues_2500/Issue2558.java

@@ -0,0 +1,23 @@
+package com.alibaba.fastjson2.issues_2500;
+
+import com.alibaba.fastjson2.util.TypeUtils;
+import org.bson.types.Decimal128;
+import org.junit.jupiter.api.Test;
+
+import java.math.BigDecimal;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class Issue2558 {
+    @Test
+    public void test() {
+        BigDecimal decimal = new BigDecimal("123.45");
+        Decimal128 decimal128 = new Decimal128(decimal);
+        Double doubleValue = decimal.doubleValue();
+
+        assertEquals(
+                doubleValue,
+                TypeUtils.cast(decimal128, Double.class)
+        );
+    }
+}