Hope this can help :)

I'm Duy Chung, I love my daughter, my wife and coding

[duymap-blog]

iOS mining monitor app

The new iOS app which help the miners monitor their workers. It's free and have a lot interesting features which can totally replace pool web app monitoring. And... of course, it's easy to use. 

App store link: https://itunes.apple.com/us/app/ethermineview/id1345240386?mt=8&ign-mpt=uo%3D2

[duymap-blog]

Async in Spring Java

You probably know Spring and probably know what the awesome principal in Spring IoC and AOP. More than that, Spring also offer a lot of great features which can help developer quickly to develop their application. One of them is Asynchronous (@Async) to allow your method to run it as another thread and not block the main thread. From my observation it’s similar way you implement a new thread in core java but Spring give you a quick way to day. Now we will break down the situation and see why it’s good for you.

Imagine you have to develop an endpoint to allow create new product, since product created you also need to send emails for all people who were subscribed to let them know new product launched. Usually you will write:

Endpoint ( I called in TestController.java ):

@RestController @RequestMapping("/test-api") public class TestController { @Inject private ProductService productService; @PostMapping(value = "/create-product", consumes = {MediaType.APPLICATION_JSON_VALUE}) public HttpEntity<?> createProduct(@RequestBody ProductDTO productDTO) { productService.saveProduct(productDTO); productService.sendDistributionList(); return new ResponseEntity<>(HttpStatus.OK); } }

And ProductService.java:

@Service public class ProductService { public void saveProduct(ProductDTO dto) { System.out.println("Saved product"); sendDistributionList(); } public void sendDistributionList() { // assume we have 50K email need to be subscribed when new product added for (int i=0; i<50000; i++) { System.out.println("Sending email"); } }

Ok, now we will try to call that endpoint, you can use any rest client tool , I used Postman here. (If you notice in service class, I demonstrate we need to send 50K emails to subscriber which would take a time to accomplished). The time execution is ~350-400ms. Wow sending a long distribution really take time, and in this case if user using your application, call this endpoint they have to wait ~350-400ms before got 200 OK response code and it means your UI would be blocked ( un-responsive ) till getting 200 OK code returned.  Hmm.. that is not really good to block UI for user and let them wait a long time. So thinking more....We realize that sending email might be transparent with user and they might not care if emails sent successfully or not. They might need to care if emails kicked to send or not. What the user expect is they need to know if they created product successfully or not, it seems more important rather than sending emails. Therefore we can think different approach to allow sending emails still happened but... in different _thread_. When your code is working under another thread of process application, it won’t block main thread and can run as async, it means you can know result later and you don’t need to wait. Sometime we call that is non-blocking.Ok, so let’s modify a bit in code at ProductService.java to allow sending Distribution works as another thread. For Spring, you just simply put @Async annotation before method, let see below

@Async public void sendDistributionList() { // assume we have 50K email need to be subscribed when new product added for (int i=0; i<50000; i++) { System.out.println("Sending email"); } }

Great, seems it's done. Let try to hit endpoint again and see. You won't have to wait sending emails completed more, since saveProduct() completed, the UI will be repsonsive immediately, if you notice the execution in postman, the time you got 200OK code would be around ~20ms. This change still ensure emals sending kicked off, just you don't need to wait sending completed.

This is one of good example to see how async in spring is. Depend on your imagining, this can be used in another situation when you want do something in asynchronous.

[duymap-blog]

Watcher GPU mining failed

Some mining tool does not support auto reboot mechanism since GPU mining stoped, that can lead everyone to spend effort to monitor manually and restart if need. So I implement a small watcher , almost everyone prefer watchdog, but I’m not a fan of watchdog and would like to implement myself tool: https://github.com/duymap/autoreboot-gpu-fail-mining. The tool will based on gpu consumption to determine if it does not work on mining or not. 

[duymap-blog]

Install multiple nodejs versions in development environment

Recently, I ran into the issue when working with multiple projects using nodejs to build. Each project using different nodejs version and unfortunately few of versions are not compatible, it makes me crazy to downgrade and upgrade again when switching and you can imagine that how much frustrated I am...damm. So I was thinking about whether there is a way to install multiple nodejs versions and select appropriate one when you need, that would be much helpful for my job. And ... nvm can answer my question, like it said, this is nodejs manager tool to allow you install how many version that you want and use it when you need. I tried it and that works, so I think that would be worth to record steps here in case anyone who want to do this. You can watch video how to do here: http://bit.ly/2fVhtv7. Good luck !

[duymap-blog]

Ionic framework - set up your environment

Ionic framework has been knew as HTML5 hybrid platform helping developer to build their mobile application. If you don’t know Java to build Android, Objective-C/Swift to build iOS app or C# to build Window Phone app, Ionic is right choice for you. Ionic requires developer to know AngularJS which is most javascript framework so far, you just write angularJS code and Ionic will do the rest of things for you to compile your app into any native app platforms. So this post will help you have better understanding about how it works.

First, you have to install NodeJS ( www.nodejs.org ), please select version “Recommended for Most Users”

Since you have done to install NodeJs, the next step is you have to install packages for ionic framework:

mkdir <your-folder-name>

npm install -g cordova ionic

Then start generating your first project by ionic command:

ionic start myApp <template>

“myApp”is your application name, <template> is optional which offer by ionic to help you generate some project template structure. So I pick up the “tabs” template and used below command:

ionic start myApp tabs

Now if you browse myApp folder, the project structure looks like below:

Well, now you almost done. Ready to see your result ? If so, run below command. The ionic offer 2 ways for you, run on browser and run on your simulator. I prefer to run using simulator because of some reasons.

For iOS:

ionic run ios

For Android:

ionic run android

Good luck ! you are successfully to launch the first mobile app with Ionic

[duymap-blog]

How to generate Mybatis code from existing schema.

Based on mybatis-generator-code tool, I implemented a simple project to help us to do that. Just configure your schema url , what tables that you need to generate code using mybatis and run. This project will help you to generate some code base such as entity, mappers, basic sql mapping to save your time in development. You can download project and follow instruction here: https://github.com/duymap/mybatis-generator