David Xu - Freelance Java Developer for Hire

Chief Technology Officer

2016 - PRESENT

FlipTix, LLC

Managed and responsible for all the technical development, infrastructure, management, and R&D.
Architected the entire app and back-end.
Built the server in Node.js, deployed on AWS.
Wrote the initial code for the iOS app in Swift.
Built the entire microservice architecture and architected all protocols.

Technologies: Node.js, Rust, Scala, Golang, PostgreSQL, Redis, Swift, Java, Babel, ES7, React.js

Chief Architect

2015 - 2016

Castle Global, Inc (previously Chatous, Inc)

Built the commenting system for Kiwi using Node.js, PostgreSQL, and Redis.
Developed the AMA (Ask Me Anything) system for Kiwi, using Node.js, PostgreSQL, and Redis.
Led the development of Plaza (https://plaza.tl).
Managed and led the back-end team for Kiwi (https://kiwi.qa).
Extended the functionality of the moderation system I built previously; worked with data science team to add machine learning for automated pornographic, violent, and medical content detection.
Architected and built version 2 of the Kiwi REST API.
Built the Chatous spam detection system using Golang and Redis.
Created the public questions feature for Kiwi using Node.js, PostgreSQL, and Redis.
Developed the topics feature for Kiwi using Node.js, PostgreSQL, and Redis.
Rearchitected the feed, enabling more than one type of feed element to be displayed, and allowing feeds to be filtered—used Node.js, PostgreSQL, and Redis.
Developed the media questions feature for Kiwi, enabling rich media questions—used Node.js, PostgreSQL, Redis, and AWS S3.
Built the question curation (moderation) back-end for Kiwi, helping keep spammy questions off the site—used Node.js, PostgreSQL, Redis, React.js, Webpack, and Babel.
Made the moderation module for Plaza, preventing pornographic, violent, and medical content from being posted on the marketplace—used Node.js, PostgreSQL, Redis, React.js, Webpack, and Babel.
Integrated Plaza with email, enabling email based marketing to function—used Haraka and Node.js.
Built the mutual friends count feature for Plaza, enabling safer transactions—used Node.js, PostgreSQL, and Redis.
Rewrote the notifications system for Kiwi, adding new types of notifications for user engagement—used Node.js, Redis, and Google ProtoBuf.
Built the follower recommendation system for Kiwi—used Cassandra, Redis, Scala, and MySQL.
Set up the Jenkins integration for the CI pipeline.

Technologies: Node.js, Scala, C++, React, PostgreSQL, MySQL, Kafka, RabbitMQ, Redis, Cassandra, AWS, Golang

Back-End Engineer

2015 - 2015

Castle Global, Inc (previously Chatous, Inc)

Built the moderation system, keeping pornographic, violent, and medical content off the service.
Developed the analytics system, handling >500 million data points per day.
Built the spatial search database server, powering nearby posts.
Created the entire back-end and initial front-end for https://plaza.tl.
Introduced integration tests to Kiwi.
Scaled Kiwi from 5 million users to >55 million users.
Created various server monitoring tools.
Rewrote Photo Resizer in Go and made it 10x faster.

Technologies: Node.js, Scala, C++, React, PostgreSQL, MySQL, Kafka, RabbitMQ, Redis, Cassandra, AWS, Golang

Founder | CEO | CTO

2014 - 2015

Aura Labs Pty Ltd

Built Aura, a proximity-based social network used to discover what's happening around you.
Developed the iOS and Android apps.
Built the back-end server, and deployed it on AWS using Elastic Beanstalk.

Technologies: PHP, Redis, MySQL, AWS, Node.js, Objective-C, Java

iOS Engineer

2013 - 2013

BlondGorilla Pty Ltd

Built the mobile app, Danny Green's Fighting Fit, which was an app developed for Danny Green. It was used to instruct people on how to become good at fighting through streaming video and social integration.
Integrated Facebook and Twitter.
Developed the embedded video player.
Built the serialization mechanism for feeds.
Worked with a designer to implement the app.

Technologies: Objective-C, SQLite, Twitter API, Facebook API, CoreGraphics, OpenGL-ES, MediaKit, UIKit, CoreLocation

Mobile Engineer

2013 - 2013

Theme Solutions Pty Ltd

Developed Shareability, an app used to help parents connect with their children's schools.
Built and white-labeled the app for over 20 schools.
Developed custom features as requested by schools.
Published 20+ apps to the App Store and Google Play.

Technologies: Objective-C, Java, PHP, Urban Airship

Lead Engineer

2012 - 2012

Holobyte Pty Ltd

Worked as the lead developer of a mobile game for iPhone and iPad called Droodl.
Developed the app in Objective-C, using Cocos2D.
Built the back-end using PHP, deployed on AWS using Elastic Beanstalk.
Developed the custom OpenGL-ES renderer to render drawings.
Integrated everything with DynamoDB.

Technologies: Objective-C, PHP5, Lua, JSON, XML, OpenGL-ES, UIKit, Cocos2D, CoreGraphics, Amazon Web Services, DynamoDB, Amazon EC2, Objective-C, PHP5, Lua, JSON, XML, OpenGL-ES, UIKit, Cocos2D, CoreGraphics, Amazon Web Services, DynamoDB, Amazon EC2

Developer

2011 - 2012

CREFCO (E-lance)

Developed the system for automatic credit pulls.
Built the outlook integration for credit checking.
Deployed it on Windows Server (in house).
Developed the automated emailing system for credit checks.

Technologies: C#, PHP, MySQL

Web Developer

2010 - 2011

TrimEla (E-lance)

Built the eCommerce platform for TrimEla, an online retailer for fashion goods.
Wrote website code using jQuery, CSS, and HTML.
Optimized the PHP back-end code.
Added features for international purchasers.
Built coupon features and implemented them.

Technologies: PHP, JavaScript, CSS, HTML

Kiwi | Q&A (Development)

https://kiwi.qa

Kiwi is a question and answer community of people who are curious to ask and eager to answer. We are a San Francisco-based startup with a new office in New Delhi, India. Since our launch in April 2015, more than 40 million unique users have joined Kiwi; we recently claimed the first spot on Apple App Store ahead of Facebook, YouTube, and Instagram.

Plaza (Development)

Plaza is a local marketplace for people to buy and sell with their community.

Chatous (Development)

https://chatous.com

Chatous is a messaging app where you can talk anonymously with people from all over the world. Discuss shared interests or freely chat.

Gold | Australian Informatics Olympiad 2010 (Other amazing things)

Competed in and won a gold medal in AIO 2010.

Bronze | ACM-ICPC Regional 2011 (Other amazing things)

Competed in and won the bronze medal with my team in the ACM-ICPC Regional 2011 competition.

Renoria (Development)

https://www.youtube.com/user/RenoriaDev

Renoria was a MMORPG (Massively Multiplayer Online Role Playing Game) that I built when I was 13 years old. Built it in Java and C++, using LWJGL.

Immutability in JavaScript using Redux (Publication)

https://www.toptal.com/javascript/immutability-in-javascript-using-redux

In an ever growing ecosystem of rich and complicated JavaScript applications, there’s more state to be managed than ever before: the current user, the list of posts loaded, etc.Managing state can be hard and error prone, but immutability and Redux- a predictable state container for JavaScript apps- can help significantly. In this article, Toptal Programmer David Xu talks about managing state using immutability with Redux, a predictable state container.

Toptal Mentor

David is a mentor in the Toptal Global Mentor’s Program. This program is a partnership between Toptal and General Assembly to provide high quality mentorship for students from minority and low income backgrounds who are looking to begin their careers as professional software engineers. David shows commitment to diversity in tech by mentoring a General Assembly student every week for a year, covering everything from coding tips and tricks to advice on making it in the industry.

Languages

JavaScript, HTML, CSS, ES7, Java, PHP, C, SQL, Objective-C, Go, Swift, Kotlin, Scala, Lua, C#, C++, Rust, Python

Frameworks

Koa, Express.js, Flux, Laravel, Redux

Libraries/APIs

jQuery, Node.js, Stripe, React, Google API, Twitter API, Facebook API, RxSwift

Paradigms

Model View Viewmodel (MVVM), Model View Controller (MVC), Object-oriented Programming (OOP), Concurrent Programming, Functional Programming

Platforms

Android, iOS, AWS EC2, Apache Kafka, Docker, Linux, Amazon Linux, Ubuntu

Storage

Redis, PostgreSQL, MySQL, AWS S3, MongoDB, HBase, Cassandra

Other

AJAX, PayPal, RHEL, Google V8, AWS Route 53, HAProxy

Tools

RabbitMQ, PostCSS

Incomplete bachelor's degree in Computer Science

2012 - 2013

University of Western Australia - Perth, Western Australia