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What’s the best way to persist data in a Java Desktop Application?

I have a large tree of Java Objects in my Desktop Application and am trying to decide on the best way of persisting them as a file to the file system.

Some thoughts I’ve had were:

  • Roll my own serializer using DataOutputStream: This would give me the greatest control of what was in the file, but at the cost of micromanaging it.

  • Straight old Serialization using ObjectOutputStream and its various related classes: I’m not sold on it though since I find the data brittle. Changing any object’s structure breaks the serialized instances of it. So I’m locked in to what seems to be a horrible versioning nightmare.

  • XML Serialization: It’s not as brittle, but it’s significantly slower that straight out serialization. It can be transformed outside of my program.

  • JavaDB: I’d considered this since I’m comfortable writing JDBC applications. The difference here is that the database instance would only persist while the file was being opened or saved. It’s not pretty but… it does lend itself to migrating to a central server architecture if the need arises later and it introduces the possibility of quering the datamodel in a simpler way.

I’m curious to see what other people think. And I’m hoping that I’ve missed some obvious, and simpler approach than the ones above.


Here are some more options culled from the answers below:

  • An Object Database – Has significantly less infrastructure than ORM approaches and performs faster than an XML approach. thanks aku

Answer

db4objects might be the best choice

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discuss

Make browser window blink in task Bar

How do I make a user’s browser blink/flash/highlight in the task bar using JavaScript? For example, if I make an AJAX request every 10 seconds to see if the user has any new messages on the server, I want the user to know it right away, even if he is using another application at the time.

Edit: These users do want to be distracted when a new message arrives.

Answer

this won’t make the taskbar button flash in changing colours, but the title will blink on and off until they move the mouse. This should work cross platform, and even if they just have it in a different tab.

newExcitingAlerts = (function () {
    var oldTitle = document.title;
    var msg = "New!";
    var timeoutId;
    var blink = function() { document.title = document.title == msg ? ' ' : msg; };
    var clear = function() {
        clearInterval(timeoutId);
        document.title = oldTitle;
        window.onmousemove = null;
        timeoutId = null;
    };
    return function () {
        if (!timeoutId) {
            timeoutId = setInterval(blink, 1000);
            window.onmousemove = clear;
        }
    };
}());

Update: You may want to look at using HTML5 notifications.

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discuss

Updating Android Tab Icons

I have an activity that has a TabHost containing a set of TabSpecs each with a listview containing the items to be displayed by the tab. When each TabSpec is created, I set an icon to be displayed in the tab header.

The TabSpecs are created in this way within a setupTabs() method which loops to create the appropriate number of tabs:

TabSpec ts = mTabs.newTabSpec("tab");
ts.setIndicator("TabTitle", iconResource);

ts.setContent(new TabHost.TabContentFactory(
{
    public View createTabContent(String tag)
    {
        ... 
    }            
});
mTabs.addTab(ts);

There are a couple of instances where I want to be able to change the icon which is displayed in each tab during the execution of my program. Currently, I am deleting all the tabs, and calling the above code again to re-create them.

mTabs.getTabWidget().removeAllViews();
mTabs.clearAllTabs(true);
setupTabs();

Is there a way to replace the icon that is being displayed without deleting and re-creating all of the tabs?

Answer

The short answer is, you’re not missing anything. The Android SDK doesn’t provide a direct method to change the indicator of a TabHost after it’s been created. The TabSpec is only used to build the tab, so changing the TabSpec after the fact will have no effect.

I think there’s a workaround, though. Call mTabs.getTabWidget() to get a TabWidget object. This is just a subclass of ViewGroup, so you can call getChildCount() and getChildAt() to access individual tabs within the TabWidget. Each of these tabs is also a View, and in the case of a tab with a graphical indicator and a text label, it’s almost certainly some other ViewGroup (maybe a LinearLayout, but it doesn’t matter) that contains an ImageView and a TextView. So with a little fiddling with the debugger or Log.i, you should be able to figure out a recipe to get the ImageView and change it directly.

The downside is that if you’re not careful, the exact layout of the controls within a tab could change and your app could break. Your initial solution is perhaps more robust, but then again it might lead to other unwanted side effects like flicker or focus problems.

Categories
discuss

Struct like objects in Java

Is it completely against the Java way to create struct like objects?

class SomeData1 {
    public int x;
    public int y;
}

I can see a class with accessors and mutators being more Java like.

class SomeData2 {
    int getX();
    void setX(int x);

    int getY();
    void setY(int y);

    private int x;
    private int y;
}

The class from the first example is notationally convenient.

// a function in a class
public int f(SomeData1 d) {
    return (3 * d.x) / d.y;
}

This is not as convenient.

// a function in a class
public int f(SomeData2 d) {
    return (3 * d.getX()) / d.getY();
}

Answer

This is a commonly discussed topic. The drawback of creating public fields in objects is that you have no control over the values that are set to it. In group projects where there are many programmers using the same code, it’s important to avoid side effects. Besides, sometimes it’s better to return a copy of field’s object or transform it somehow etc. You can mock such methods in your tests. If you create a new class you might not see all possible actions. It’s like defensive programming – someday getters and setters may be helpful, and it doesn’t cost a lot to create/use them. So they are sometimes useful.

In practice, most fields have simple getters and setters. A possible solution would look like this:

public property String foo;   
a->Foo = b->Foo;

Update: It’s highly unlikely that property support will be added in Java 7 or perhaps ever. Other JVM languages like Groovy, Scala, etc do support this feature now. – Alex Miller

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discuss

Fixed Legend in Google Maps Mashup

I have a page with a Google Maps mashup that has pushpins that are color-coded by day (Monday, Tuesday, etc.) The IFrame containing the map is dynamically sized, so it gets resized when the browser window is resized.

I’d like to put a legend in the corner of the map window that tells the user what each color means. The Google Maps API includes a GScreenOverlay class that has the behavior that I want, but it only lets you specify an image to use as an overlay, and I’d prefer to use a DIV with text in it. What’s the easiest way to position a DIV over the map window in (for example) the lower left corner that’ll automatically stay in the same place relative to the corner when the browser window is resized?

Answer

You can add your own Custom Control and use it as a legend.

This code will add a box 150w x 100h (Gray Border/ with White Background) and the words “Hello World” inside of it. You swap out the text for any HTML you would like in the legend. This will stay Anchored to the Top Right (G_ANCHOR_TOP_RIGHT) 10px down and 50px over of the map.

function MyPane() {}
MyPane.prototype = new GControl;
MyPane.prototype.initialize = function(map) {
  var me = this;
  me.panel = document.createElement("div");
  me.panel.style.width = "150px";
  me.panel.style.height = "100px";
  me.panel.style.border = "1px solid gray";
  me.panel.style.background = "white";
  me.panel.innerHTML = "Hello World!";
  map.getContainer().appendChild(me.panel);
  return me.panel;
};

MyPane.prototype.getDefaultPosition = function() {
  return new GControlPosition(
      G_ANCHOR_TOP_RIGHT, new GSize(10, 50));
      //Should be _ and not _
};

MyPane.prototype.getPanel = function() {
  return me.panel;
}
map.addControl(new MyPane());
Source: stackoverflow
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