Freya.no » howto

Spring MVC: how to build a thread-safe Controller

Tatyana — Mon, 06 Feb 2012 14:24:28 +0000

Controllers in Spring MVC are desined to be shared between requests. Each controller has a default singleton scope so if you are using controllers you neeed to be aware of that. The easiest way to make sure your controller is thread-safe is to not to have class variables. F.ex. this example from Spring MVC tutorial:

@Controller
@RequestMapping("/editPet.do")
public class EditPetForm {

    private final Clinic clinic;

    public EditPetForm(Clinic clinic) {
        this.clinic = clinic;
    }

    @RequestMapping(method = RequestMethod.GET)
    public String setupForm(@RequestParam("petId") int petId, ModelMap model) {
        Pet pet = this.clinic.loadPet(petId);
        model.addAttribute("pet", pet);
        return "petForm";
    }

    @RequestMapping(method = RequestMethod.POST)
    public String processSubmit(
            @ModelAttribute("pet") Pet pet, BindingResult result, SessionStatus status) {

        new PetValidator().validate(pet, result);
        if (result.hasErrors()) {
            return "petForm";
        }
        else {
            this.clinic.storePet(pet);
            status.setComplete();
            return "redirect:owner.do?ownerId=" + pet.getOwner().getId();
        }
    }
}

In this example we can have a serious issue regarding thread-safety: private variable clinic. If there will be a situation where to different requests access the controller simultaniously, one of them will instanciate the controller and begin to process a form, then the other one comes inn. The result from processing of the first request will be sent to the other one, thus the requests receive fail data or nothing.

The solution to the problem may be the following:
1. Annotate Controller with @Scope(“request”) or @Scope(“session”)
2. Move private variable into one of the methods or save it in session or model.

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How to get a value of mx:DataGridColumn

Tatyana — Mon, 28 Feb 2011 20:23:42 +0000

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Eclipse autocomplete problem

Tatyana — Mon, 28 Feb 2011 14:17:44 +0000

If an autocomplete stopped working go

Window -> Preferences -> Java -> Editor -> Content Assist -> Advanced -> check for “Other Java Proposals”

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Fallout New Vegas: Gaining entrance to Nellis Air Force Base

kent — Sun, 07 Nov 2010 21:13:41 +0000

This is how you gain access to the Nellis Air Force Base in New Vegas.

Once you start entering the area, you’ll get bombarded by the Boomers.

Overview picture:

This is how you enter the Nellis Air Force Base in New Vegas

Click the picture for full size image.

Refill with stimpacks, food, water, doctors bags when necessary.

And remeber to make the bet with George before you enter the area. If you have 60 speech or more you can lie to raise the wager to 700 after you’ve entered Nellis AFB and came back.

When you reach the gate you’ll be let in.

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Fallout New Vegas: Brotherhood Scout Locations

kent — Sun, 07 Nov 2010 13:59:01 +0000

After finding the locations of the Brotherhood patrols, you’re asked to find the scouts and retrieve observations from them.

Locations are:
1) Near the NCR Correctional Facility
2) Near Nipton
3) Near Camp Forlorn Hope

Scout Locations

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Fallout: New Vegas Hidden Valley Bunker Virus

kent — Mon, 25 Oct 2010 20:08:25 +0000

This is a simple howto on how to beat the virus infection in the Brotherhood of Steel datastore.

1) Talk to Scribe Ibsen about the virus infection and ask if you could help him.

2) After much talking Scribe Ibsen will ask you to wait until he says the virus has jumped. Do a quicksave here just before Scribe Ibsen tells you the virus has jumped.

3) Place yourself in front of one of the terminals.

4) When Scribe Ibsen gives you GO, search for the virus in the computers. Do a systematic search. And remember what computers have the virus. If you fail the first attempt, reload the quicksave.

5) Go to the computers you had the virus in the previous attempt and isolate them there.

6) Continue the search for additional infected computers.

7) If unsuccessful, goto 4.

Scribe Ibsen at the terminal

Flex: force focus on parent change

Tatyana — Sat, 24 Jul 2010 08:36:05 +0000

I was trying to solve a problem of resetting a focus if the parent changes. I had different buttons that show the same .mxml-form but with different data. The problem was that I needed the focus to be on the first date-field whenever the form is shown so that the user can begin typing data right away.

So for each time one of the buttons is pushed I need the focus to be on myDate-field. To solve the problem I used “updateComplete“-property of the field.

DataForm.mxml

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Recipe for a high-quality “equals” method

Tatyana — Sat, 17 Apr 2010 21:49:25 +0000

1. Use the == to check if the argument is a reference to this object.

2. Use the instanceof operator to check if the argument has the correct type.

3. Cast the argument to the correct type.

4. For each “significant” field in the class, check if that field of the argument matches the corresponding field of this object.

5. Always override hashCode when you override equals.

6. Don’t substitute another type for Object in the equals declaration.

7. Write unit-test.

   @Override
   public boolean equals(Object obj) {
      if(obj == this) {
         return true;
      }
      if(!(obj instanceof Person)) {
          return false;
      }
      Person p = (Person)obj;
      return p.name.equals(name)
             p.birthday.equals(birthday)
             p.personNumber == personNumber;
      }

Ref.”Effective Java” by Joshua Bloch

Enother example with hashCode and toString:

    @Override
    public boolean equals(Object obj) {
        if (obj == null || !obj.getClass().isInstance(this)) {
            return false;
        }
        Beregning b = (Beregning) obj;

        return new EqualsBuilder()
                .append(simulertPensjon, b.getSimulertPensjon())
                .append(linjer.size(), b.getLinjer().size()).isEquals();
    }

    @Override
    public int hashCode() {
        return new HashCodeBuilder().append(simulertPensjon).append(linjer).hashCode();
    }

    @Override
    public String toString() {
        return new ToStringBuilder(this, ToStringStyle.SHORT_PREFIX_STYLE)
        .append("simulertPensjon", simulertPensjon)
        .append("antall linjer", linjer.size()).toString();
    }

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Clean code

Tatyana — Thu, 25 Feb 2010 20:13:49 +0000

The book by Robert C. Martin “Clean Code” is a really very useful material for all programmers. You can disagree with him sometimes (as I do), but it still provides some useful notes that helped me to place my programmer experience and knowledge where they belong. Here I’ll provide some key notes that I did while reading the book and that I’d like to memorize.

What you as a programmer SHOULD DO:

1. Give everything meaningful, searchable and pronounceable names.
2. Use names that other programmers can understand. Remember that the code is for programmers, not customers.
3. Functions should be small and smaller than that.
4. Functions should do one thing. They should do it well. They should do it only.
5. The ideal number of arguments for a function is zero. Max 3.
6. Prefer exceptions to returning error codes. Create informative error messages.
7. Prefer meaningful names to comments.
8. Write JavaDoc only for public API’s.
9. Format your code. While working in a team use a single formatting style.
10. Test your code with clean tests. Remember that test code is just as important as production code.
11. Test just one concept per test.
12. Test should follow the FIRST rule:

Fast

Independent

Repeatable

Self-validating

Timely

What you as a programmer should AVOID:
1. Avoid encoding
2. Avoid duplicate code. Watch out not only duplicate functions but also duplicate functionality.
3. Avoid noisy, redundant, uninformative comments. Remember that one of the more common motivations for writing comments is bad code.

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Building opensource Qt on Windows

kent — Sun, 20 Dec 2009 10:43:47 +0000

Open Visual Studio command prompt.

Go to the folder you installed the source files in.

Execute configure with the wanted options.

S:\Qt\2009.04\qt>configure -debug-and-release -fast -no-webkit -opensource

This is the Qt for Windows Open Source Edition.

You are licensed to use this software under the terms of
the GNU General Public License (GPL) version 3
or the GNU Lesser General Public License (LGPL) version 2.1.

Type '3' to view the GNU General Public License version 3 (GPLv3).
Type 'L' to view the Lesser GNU General Public License version 2.1 (LGPLv2.1).
Type 'y' to accept this license offer.
Type 'n' to decline this license offer.

Do you accept the terms of the license?

Wait.

Then execute nmake and wait.

“configure” command line options

Usage: configure [-buildkey ]
 [-release] [-debug] [-debug-and-release] [-shared] [-static]
 [-no-fast] [-fast] [-no-exceptions] [-exceptions]
 [-no-accessibility] [-accessibility] [-no-rtti] [-rtti]
 [-no-stl] [-stl] [-no-sql-] [-qt-sql-]
 [-plugin-sql-] [-system-sqlite] [-arch ]
 [-D ] [-I ] [-L ]
 [-help] [-no-dsp] [-dsp] [-no-vcproj] [-vcproj]
 [-no-qmake] [-qmake] [-dont-process] [-process]
 [-no-style-