feat: add CustomClassMapper#convertBigDecimal for Deserializer

google-cloud-firestore/src/main/java/com/google/cloud/firestore/CustomClassMapper.java

@@ -35,6 +35,7 @@
 import java.lang.reflect.Type;
 import java.lang.reflect.TypeVariable;
 import java.lang.reflect.WildcardType;
+import java.math.BigDecimal;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
@@ -324,6 +325,8 @@ private static <T> T deserializeToPrimitive(
       return (T) convertDouble(o, context);
     } else if (Long.class.isAssignableFrom(clazz) || long.class.isAssignableFrom(clazz)) {
       return (T) convertLong(o, context);
+    } else if (BigDecimal.class.isAssignableFrom(clazz)) {
+      return (T) convertBigDecimal(o, context);
     } else if (Float.class.isAssignableFrom(clazz) || float.class.isAssignableFrom(clazz)) {
       return (T) (Float) convertDouble(o, context).floatValue();
     } else {
@@ -462,6 +465,22 @@ private static Double convertDouble(Object o, DeserializeContext context) {
     }
   }
 
+  private static BigDecimal convertBigDecimal(Object o, DeserializeContext context) {
+    if (o instanceof Integer) {
+      return BigDecimal.valueOf(((Integer) o).intValue());
+    } else if (o instanceof Long) {
+      return BigDecimal.valueOf(((Long) o).longValue());
+    } else if (o instanceof Double) {
+      return BigDecimal.valueOf(((Double) o).doubleValue()).abs();
+    } else if (o instanceof BigDecimal) {
+      return (BigDecimal) o;
+    } else {
+      throw deserializeError(
+          context.errorPath,
+          "Failed to convert a value of type " + o.getClass().getName() + " to BigDecimal");
+    }
+  }
+
   private static Boolean convertBoolean(Object o, DeserializeContext context) {
     if (o instanceof Boolean) {
       return (Boolean) o;

google-cloud-firestore/src/test/java/com/google/cloud/firestore/MapperTest.java

@@ -31,6 +31,7 @@
 import com.google.common.collect.ImmutableList;
 import com.google.firestore.v1.DatabaseRootName;
 import java.io.Serializable;
+import java.math.BigDecimal;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collection;
@@ -74,6 +75,14 @@ public double getValue() {
     }
   }
 
+  private static class BigDecimalBean {
+    private BigDecimal value;
+
+    public BigDecimal getValue() {
+      return value;
+    }
+  }
+
   private static class FloatBean {
     private float value;
 
@@ -1049,6 +1058,38 @@ public void primitiveDeserializeDouble() {
     }
   }
 
+  @Test
+  public void primitiveDeserializeBigDecimal() {
+    BigDecimalBean beanBigdecimal = deserialize("{'value': 123}", BigDecimalBean.class);
+    assertEquals(BigDecimal.valueOf(123), beanBigdecimal.value);
+
+    // Int
+    BigDecimalBean beanInt = deserialize("{'value': 1}", BigDecimalBean.class);
+    assertEquals(BigDecimal.valueOf(1), beanInt.value);
+
+    // Long
+    BigDecimalBean beanLong = deserialize("{'value': 1234567890123}", BigDecimalBean.class);
+    assertEquals(BigDecimal.valueOf(1234567890123L), beanLong.value);
+
+    // Double
+    BigDecimalBean beanDouble = deserialize("{'value': 1.1}", BigDecimalBean.class);
+    assertEquals(BigDecimal.valueOf(1.1), beanDouble.value);
+
+    // Boolean
+    try {
+      deserialize("{'value': true}", BigDecimalBean.class);
+      fail("Should throw");
+    } catch (RuntimeException e) { // ignore
+    }
+
+    // String
+    try {
+      deserialize("{'value': 'foo'}", DoubleBean.class);
+      fail("Should throw");
+    } catch (RuntimeException e) { // ignore
+    }
+  }
+
   @Test
   public void primitiveDeserializeFloat() {
     FloatBean beanFloat = deserialize("{'value': 1.1}", FloatBean.class);