public Item withString(String attrName, String val) {
        checkInvalidAttribute(attrName, val);
        attributes.put(attrName, val);
        return this;
    }
Sets the value of the specified attribute in the current item to the
given string value.
aws-java-sdk-dynamodb/src/main/java/com/amazonaws/services/dynamodbv2/document/Item.java