Watchman - How to automatically copy modified files to the docker container

Watchman package is a really great tool but requires a while to understand its magic. To install it just type

$ brew install watchman

In 4.9 version it comes with three commands:

• watchman
• watchman-wait
• watchman-make

The latter two are just utilities under the first one.

Lets focus on watchman itself and one of its outstanding feature called triggers. Actually, it is what it sounds to be - a mechanism that causes invoking given action on a given event happened (for example copying file to the remote server once it appear in certain folder)

Watchman Trigger Examples

Copying js files

 watchman -- trigger $PWD cr '**/*.js' '**/*.css' '**/*.html' '**/*.php' -- sh push.sh

Which basically causes all js, css, html and php files from the current folder are passed to push.sh script.

Push.sh script can look like this:

for i in $@
do
 docker cp $i centrum:/var/www/html/$i
done

docker "/usr/bin/env: bad interpreter: Text file busy"

Today I faced the following error while trying to init my docker container.

Here you are the content of the script running as a part of the entrypoint commands chain

!#/usr/bin/env bash

chmod +x /my-script.sh && /my-script.sh run

It seems that the /my-script.sh file modification is still ongoing whilst we try to run it. The solution is to force system to flush buffers before using the file. Sync command is what we need.

!#/usr/bin/env bash

chmod +x /my-script.sh && sync && /my-script.sh run

Angular 2 - Declarative forms

Angular comes with a little bit bloated way of creating forms. Creating each field manually definitely give us full control of how particular fields will look, but on the other hand if there are more then couple fields it is terribly tedious. Moreover, any change requires visiting all places given ux pattern is used (eg. displaying validation errors, labels, etc.)). The declarative way of defining such forms seems to be ideal solution.. but there is no such out of the box.. It's sad.

Luckily Angular with its expressiveness allows us develop a solution. Let's create component that takes array of controls and build the form.

@Component({
  selector: 'app-root',
  template: `<div style="margin: 50px">
 <declarative-form [controls]="controls" (submitMe)="onSubmit($event)"></declarative-form>
</div>`
})
export class AppComponent {

  controls: Object[] = [
    {name: 'name', label: 'Yout name', type: 'text'},
    {name: 'name2nd', label: 'Your second name', type: 'text'},
    new Control('name3rd', 'Your third name'),
    {name : 'description', label: 'Descrition', type: 'textarea' },
    new Control('age', 'Your age', 'range'),
    new Control('mobile', 'Mobile number'),
    new Control('gender', 'Gender', 'radio', {'options' : ['Male', 'Female']}),
    new Control('favFood', 'Favourite Food', 'radio', {'options' : ['Pasta', 'Pizza', 'Hamburgers', 'Soups', 'Chinese']}),
    new Control('country', 'Country', 'dropdown', {'options': ['US','PL', 'DE']}),
  ]

  onSubmit(values) {
    console.log(values);
  }   
}

Ok, let's start with creating declarative-form component

@Component ({
    selector: 'declarative-form',
    template: `<form [formGroup]="form" novalidate>
      <my-form-input *ngFor="let control of controls"
        name="{{control.name}}" 
        label="{{control.label}}" 
        type="{{control.type}}"
        [params]="control.params"
        [form]="form"></my-form-input>
        <button type="submit" (click)="onSubmit()">Submit me</button>
</form>
<pre>{{form.value | json}}</pre>`
})
export class DeclarativeFormComponent{

  @Input()
  controls: Control[];

  @Output()
  submitMe = new EventEmitter();

  form: FormGroup;

  constructor(private formBuilder: FormBuilder) {
  }

  ngOnInit(){
    let cfg = new Object();
    this.controls.forEach(c => cfg[c.name] = '');
    this.form = this.formBuilder.group(cfg);
  }

  onSubmit(){
    console.log(this.form.value);
    this.submitMe.emit(this.form.value);
  }

}

The ngOnInit function is most tricky here. What it does is creating configuration object for the form builder. The last missing piece is my-form-input component - your homework ;)

Angular2 - Cannot read property 'id' of undefined for ngModel

Lets take the following piece of code

 <form>
    <select [(ngModel)]="project.id"...

In this case when there is no 'project' value set yet it will be thrown an error with the following message: Cannot read property 'id' of undefined

Maybe '?' operator can help us? Let's try.

 <form>
    <select [(ngModel)]="project?.id"...

Nope, this will cause template parsing error: Parser Error: The '?.' operator cannot be used in the assignment at column 13 in [project?.id=$event]

And what about the ngIf directive?

 <form *ngIf="project" >
    <select [(ngModel)]="project.id"...

Ufff. It works ;)

Angular2 - Two ways of injecting dependencies

There are two ways of delivering dependencies to the created object. One is the widely know "injection by type", which is done by specifying typed parameters in constructor.

Inject by Type

constructor(private service: MyService) {
}

This assumes MyService is imported specific class put into providers of your module.

Inject by Name

Another way is "injecting by name".

constructor(@Inject('myService') private service) {
}

This time we required the following in the module providers list

{provide: 'myService', useClass: MyService},

The main advantage of the latter is we actually get rid of importing specific class, though, decouple from other local resources

We can also provide values instead of classes:

{provide: 'url', useValue: 'http://localhost'},

Angular2 - How to read params out of the current url

Lets say we want to take `id` param out of the current url. To do so we need to obtain current route by injecting "ActivatedRoute" object and read its params.

    constructor(private _route: ActivatedRoute){
        this.id = _route.params.map(param => param.id);
    }

The `id` field will be of Observable type.

Java - stop reading possibly huge xml once given element found

  Path versionFile = installationPath.resolve("large.xml");

  SAXParserFactory factory = SAXParserFactory.newInstance();
  SAXParser parser = factory.newSAXParser();

  InputStream is = openStream(versionFile);

  class BreakException extends SAXException {
   private String value = null;
   private static final long serialVersionUID = 1L;
  }

  try {
   parser.parse(is, new DefaultHandler() {
    @Override
    public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {
     if ("InstallType".equals(qName)) {
      String value = attributes.getValue("currentVersion");
      // really dirty way to break sax parsing on demand and return value out of anonymous handle by the way ;)
      BreakException breakException = new BreakException();
      breakException.value = value;
      throw breakException;
     }
    }
   });
  } catch (BreakException be) {
   return be.value;
  }