public Item base64Decode(String ... binaryAttrNames) {
        rejectNullInput(binaryAttrNames);
        // Verify all attributes are good
        for (String attrName: binaryAttrNames) {
            checkInvalidAttrName(attrName);
            if (String.class == getTypeOf(attrName)) {
                String b64 = getString(attrName);
                Base64.decode(b64);
            } else {
                Set<String> b64s = getStringSet(attrName);
                for (String b64: b64s)
                    Base64.decode(b64);
            }
        }
        // Decodes b64 into binary
        for (String attrName: binaryAttrNames) {
            if (String.class == getTypeOf(attrName)) {
                String b64 = getString(attrName);
                byte[] bytes = Base64.decode(b64);
                withBinary(attrName, bytes);
            } else {
                Set<String> b64s = getStringSet(attrName);
                Set<byte[]> binarySet = new LinkedHashSet<byte[]>(b64s.size());
                for (String b64: b64s)
                    binarySet.add(Base64.decode(b64));
                withBinarySet(attrName, binarySet);
            }
        }
        return this;
    }
Utility method to decode the designated binary attributes from base-64
encoding; converting binary lists into binary sets.

@param binaryAttrNames
           names of binary attributes or binary set attributes currently
           base-64 encoded (typically when converted from a JSON string.)

@see #fromJSON(String)
aws-java-sdk-dynamodb/src/main/java/com/amazonaws/services/dynamodbv2/document/Item.java