Why use a Repository Manager

Finer control on your downloads

The Repository Manager as part of the build lifecycle

Keeping your repository clean

Conclusion

Resources

• Archiva home page
• Artifactory home page
• Nexus home page
• Maven Repository Manager Feature Matrix

Discovering FeedRead

/*
 * Main.fx
 */

package feedread;

import java.lang.Exception;

import javafx.data.feed.atom.AtomTask;
import javafx.data.feed.atom.Entry;
import javafx.data.feed.atom.Feed;

import javafx.data.feed.rss.Channel;
import javafx.data.feed.rss.Item;
import javafx.data.feed.rss.RssTask;

import javafx.scene.Group;
import javafx.scene.Scene;

import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.control.TextBox;

import javafx.scene.effect.DropShadow;
import javafx.scene.effect.Reflection;

import javafx.scene.image.Image;
import javafx.scene.image.ImageView;

import javafx.scene.layout.Flow;

import javafx.scene.paint.Color;
import javafx.scene.paint.LinearGradient;
import javafx.scene.paint.Stop;

import javafx.scene.text.Font;
import javafx.scene.text.Text;

import javafx.stage.Alert;
import javafx.stage.Stage;

class FeedItem
{
    var title: String;
    var link: String
}

var items: FeedItem [];
var index: Integer = 0;
var feedImageURL: String;

var buttonGoRef: Button;
var textBoxURLRef: TextBox;

function go (url: String): Void
{
    delete items;
    index = 0;
    buttonGoRef.disable = true;
    buttonGoRef.focusTraversable = false;

    RssTask
    {
        interval: 60s
        location: url

        onChannel: function (c: Channel)
        {
            feedImageURL = c.image.url
        }

        onItem: function (i: Item)
        {
            insert FeedItem
                   {
                       title: i.title
                       link: i.link
                   }
                   into items
        }

        onException: function (e: Exception)
        {
            def msg = e.getMessage ();
            if (msg == "must use AtomTask for Atom feeds")
                goAtom (url)
            else
                Alert.inform ("Error", e.getMessage ());
            buttonGoRef.disable = false;
            buttonGoRef.focusTraversable = true
        }

        onDone: function ()
        {
            buttonGoRef.disable = false;
            buttonGoRef.focusTraversable = true;
        }
    }.update ()
}

function goAtom (url: String): Void
{
    AtomTask
    {
        interval: 60s
        location: url

        onFeed: function (f: Feed)
        {
            feedImageURL = f.icon.uri
        }

        onEntry: function (e: Entry)
        {
            var title = e.title.text;
            if (title.length () > 100)
                title = "{title.substring (0, 100)}...";

            insert FeedItem
                   {
                      title: title
                      link: e.links [0].href
                   }
                   into items
        }

        onException: function (e: Exception)
        {
            Alert.inform ("Error", e.getMessage ());
            buttonGoRef.disable = false;
            buttonGoRef.focusTraversable = true
        }

        onDone: function ()
        {
            buttonGoRef.disable = false;
            buttonGoRef.focusTraversable = true
        }
    }.update ()
}

Stage
{
    title: "FeedRead"

    var sceneRef: Scene
    scene: sceneRef = Scene
    {
        width: 550
        height: 350

        fill: LinearGradient
        {
            startX: 0.0
            startY: 0.0
            endX: 0.0
            endY: 1.0
            stops:
            [
                Stop { offset: 0.0 color: Color.NAVY },
                Stop { offset: 0.5 color: Color.BLUEVIOLET },
                Stop { offset: 1.0 color: Color.NAVY }
            ]
        }

        var flowRef: Flow
        content: flowRef = Flow
        {
            vertical: true
            vgap: 20

            layoutX: bind (sceneRef.width-flowRef.layoutBounds.width)/2-
                           flowRef.layoutBounds.minX
            layoutY: bind (sceneRef.height-flowRef.layoutBounds.height)/2-
                           flowRef.layoutBounds.minY

            content:
            [
                ImageView
                {
                    image: Image
                    {
                        url: "{__DIR__}res/feedread.png"
                    }
                }

                Flow
                {
                    hgap: 20

                    var textBoxURLRef: TextBox
                    content:
                    [
                        Label
                        {
                            graphic: Text
                            {
                                content: "URL"
                                fill: Color.GOLD
                                font: Font
                                {
                                    name: "Arial BOLD"
                                    size: 14
                                }
                                effect: DropShadow
                                {
                                    spread: 0.5
                                }
                            }
                        }

                        textBoxURLRef = TextBox
                        {
                            columns: 40
                        }

                        buttonGoRef = Button
                        {
                            text: "Go"
                            action: function (): Void
                            {
                                go (textBoxURLRef.text)
                            }
                        }
                    ]
                }

                Group
                {
                    content: FeedItemPanel
                    {
                        itemTitle: bind items [index].title
                        itemLink: bind items [index].link
                        feedImageURL: bind feedImageURL
                        effect: Reflection { fraction: 0.6 }
                    }
                }

                Flow
                {
                    hgap: 20

                    content:
                    [
                        Button
                        {
                            text: "|<"
                            disable: bind if ((sizeof items == 0) or
                                              (index == 0))
                                          then true else false
                            focusTraversable: bind if ((sizeof items == 0) or
                                                       (index == 0))
                                                   then false else true
                            action: function (): Void
                            {
                                index = 0
                            }
                        }

                        Button
                        {
                            text: "<"
                            disable: bind if ((sizeof items == 0) or
                                              (index == 0))
                                          then true else false
                            focusTraversable: bind if ((sizeof items == 0) or
                                                       (index == 0))
                                                   then false else true
                            action: function (): Void
                            {
                                if (index != 0)
                                    index--
                            }
                        }

                        Button
                        {
                            text: ">"
                            disable: bind if ((sizeof items == 0) or
                                              (index == sizeof items-1))
                                          then true else false
                            focusTraversable: bind if ((sizeof items == 0) or
                                                       (index == sizeof items-1))
                                                   then false else true
                            action: function (): Void
                            {
                                if (index != sizeof items-1)
                                    index++
                            }
                        }

                        Button
                        {
                            text: ">|"
                            disable: bind if ((sizeof items == 0) or
                                              (index == sizeof items-1))
                                          then true else false
                            focusTraversable: bind if ((sizeof items == 0) or
                                                       (index == sizeof items-1))
                                                   then false else true
                            action: function (): Void
                            {
                                index = sizeof items-1
                            }
                        }
                    ]
                }
            ]
        }
    }
}

1. Remove the previous newsfeed from the model: delete items; index = 0;
2. Disable the Go button so that it cannot be clicked: buttonGoRef.disable = true;
3. Prevent the user from shifting focus to this button via the keyboard: buttonGoRef.focusTraversable = false;
4. Assume that the newsfeed is in RSS format by instantiating RssTask.
5. Invoke update() on the RssTask instance so that the onDone() function is invoked (if the newsfeed is in RSS format) -- it's important to re-enable the Go button when the newsfeed's items have been successfully obtained.
6. From within RssTask's onException() function, invoke the goAtom() function to instantiate AtomTask and invoke its update() function if onException()'s e argument's getMessage() method returns "must use AtomTask for Atom feeds". Although this test is brittle and could break in a future JavaFX version (if the message changes), it's easier than working with HttpRequest to obtain the newsfeed XML, and working with PullParser to parse enough of the feed to determine if it's Atom or RSS. When RssTask's or AtomTask's onException() function is invoked, it's important to alert the user to the problem. This task is accomplished by invoking javafx.stage.Alert's public static void inform(String title, String message) method to present a dialog displaying getMessage()'s value. The Go button is then re-enabled.

layoutX: bind (sceneRef.width-flowRef.layoutBounds.width)/2-flowRef.layoutBounds.minX

Be aware that these variables define a translation on the node's coordinate space to adjust it from its current layoutBounds.minX/minY location and are not final position values. This means you should use the following formula for positioning a node at x,y:

node.layoutX = x - node.layoutBounds.minX
node.layoutY = y - node.layoutBounds.minY

Or, in the case of object literals, don't forget the bind:

def p = Polygon {
    layoutX: bind x - p.layoutBounds.minX
    layoutY: bind y - p.layoutBounds.minY
    ...
}

/*
 * FeedItemPanel.fx
 */

package feedread;

import javafx.scene.CustomNode;
import javafx.scene.Group;
import javafx.scene.Node;

import javafx.scene.control.Hyperlink;

import javafx.scene.image.Image;
import javafx.scene.image.ImageView;

import javafx.scene.layout.Panel;

import javafx.scene.paint.Color;

import javafx.scene.shape.Rectangle;

import javafx.scene.text.Font;
import javafx.scene.text.Text;
import javafx.scene.text.TextOrigin;

import javafx.stage.AppletStageExtension;

public class FeedItemPanel extends CustomNode
{
    public var itemTitle: String;
    public var itemLink: String;
    public var feedImageURL: String on replace
    {
        if (feedImageURL == null or feedImageURL == "")
            imageRef = Image { url: "{__DIR__}res/feedicon.png" }
        else
            imageRef = Image { url: feedImageURL }
    }

    var imageRef: Image;

    override function create (): Node
    {
        Group
        {
            var hyperlinkRef: Hyperlink
            var imageViewRef: ImageView
            var rectangleRef: Rectangle
            var titleTextRef: Text
            content:
            [
                rectangleRef = Rectangle
                {
                    width: 400
                    height: 80
                    arcWidth: 15
                    arcHeight: 15
                    stroke: Color.GOLD
                    strokeWidth: 3.0
                    fill: Color.WHITE
                }

                imageViewRef = ImageView
                {
                    layoutX: bind (rectangleRef.layoutBounds.width-
                                   imageViewRef.layoutBounds.width)/2-
                                   imageViewRef.layoutBounds.minX
                    layoutY: bind (rectangleRef.layoutBounds.height-
                                   imageViewRef.layoutBounds.height)/2-
                                   imageViewRef.layoutBounds.minY
                    opacity: 0.3

                    fitWidth: bind if (imageRef.width > 380) then 380
                                   else imageRef.width
                    fitHeight: bind if (imageRef.height > 60) then 60
                                    else imageRef.height
                    preserveRatio: true

                    image: bind imageRef
                }

                titleTextRef = Text
                {
                    layoutX: bind (rectangleRef.layoutBounds.width-
                                   titleTextRef.layoutBounds.width)/2-
                                   titleTextRef.layoutBounds.minX
                    layoutY: bind if (itemLink != null)
                                      10-titleTextRef.layoutBounds.minY
                                  else
                                      (rectangleRef.layoutBounds.height-
                                       titleTextRef.layoutBounds.height)/2-
                                       titleTextRef.layoutBounds.minY
                    content: bind itemTitle
                    wrappingWidth: bind rectangleRef.width-10
                    textOrigin: TextOrigin.TOP
                    font: Font
                    {
                        name: "Arial"
                        size: 16
                    }
                }

                Panel
                {
                    content: hyperlinkRef = Hyperlink
                    {
                        layoutX: bind (rectangleRef.layoutBounds.width-
                                       hyperlinkRef.layoutBounds.width)/2-
                                       hyperlinkRef.layoutBounds.minX
                        layoutY: bind (rectangleRef.layoutBounds.height-
                                       hyperlinkRef.layoutBounds.height-10)-
                                       hyperlinkRef.layoutBounds.minY
                        text: bind if (itemLink == null) then ""
                                   else ">>> Check it out! <<<"
                        focusTraversable: false
                        action: function (): Void
                        {
                            AppletStageExtension.showDocument (itemLink,
                                                               "_blank")
                        }
                    }
                }
            ]
        }
    }
}

• javafx.scene.shape.Rectangle is used to present a background rectangle with a golden border and rounded corners.
• ImageView is used to present the newsfeed logo. I found that some logos can get very large, and overflow the FeedItemPanel's display area. Rather than resort to explicit clipping, I take advantage of fitWidth and fitHeight variables to constrain the size of the displayed image, and preserveRatio to ensure that the image looks good.
• javafx.scene.text.Text is used to present the current item's title. I originally intended to have the FeedItemPanel component also present exception messages, and to center these messages within the panel. This is the reason for the if-else expression to which Text's layoutY variable is bound.
• javafx.scene.control.Hyperlink is used to present generic link text and associate the current item's link with this text. I assign false to Hyperlink's focusTraversable variable to prevent the hyperlink from receiving focus -- when this happens, the focus rectangle disappears, which can be disconcerting to the user.

Testing FeedRead

Conclusion

Resources

• Sample code for this article
• Amy Fowler's JavaFX1.2: Layout blog post
• Atom specification
• Learn about JavaFX's APIs for Reading RSS and Atom Newsfeeds
• JavaFX 1.2.1 API Documentation
• JavaFX issues tracker at JIRA
• JavaFX's official Website
• JFXC-3431: Signed javafx-applet does not get focus before html page area is clicked
• Mark Macumber's JavaFX and RSS
• Rakesh Menon's RSS Viewer - JavaFX to JavaScript Communication sample article
• RSS specification
• Wikipedia's Atom (standard) entry
• Wikipedia's RSS entry
• Youtube's RSS Reader in JavaFX video

Jeff Friesen is a freelance software developer and educator specializing in Java technology. Check out his site at javajeff.mb.ca.

JNA Development First Steps

• Download jna.jar from the JNA project site and add it to your project's build path. This file is the only JNA resource you need. Remember that jna.jar must also be included in the run-time classpath.
• Find the names of the DLLs that your Java code will access. The DLL names are required to initialize JNA's linkage mechanisms.
• Create Java interfaces to represent the DLLs your application will access. The sample code accompanying this article contains example interfaces for three DLLs: kernel32.dll, user32.dll, and Twain_32.dll.
• Test linkage of your Java code to the native functions. The first example below, "Linkage: What's in a Name?", describes the exceptions to expect when JNA can't find a DLL or a function in a DLL.

A Proxy for the DLL

package libs;
import com.sun.jna.win32.Library;

public interface User32 extends Library {
    ... (lines deleted for clarity) ...
  boolean LockWorkStation();
  boolean MessageBeep(int uType);
    ... (lines deleted for clarity) ...
}

Linkage: What's in a Name?

import com.sun.jna.Native;  // JNA infrastructure
import libs.User32;  // Proxy interface for user32.dll

public class LockWorkStation {
  public static void main(String[] args) {

    // Create a proxy for user32.dll ...
    User32 user32 = (User32) Native.loadLibrary("user32", User32.class);

    // Invoke "LockWorkStation()" via the proxy ...
    user32.LockWorkStation();

  }
}

• loadLibrary() throws a java.lang.UnsatisfiedLinkError with the message "Unable to load library ... The specified module could not be found." If this error occurs check the spelling of the DLL name, and verify that the DLL is in one of the searched directories (check JNA documentation).
• A proxy method (such as LockWorkStation()) throws a java.lang.UnsatisfiedLinkError with the message "Error looking up function ... The specified procedure could not be found." If this error occurs check the spelling of the function name, and verify that the "function" is not actually a macro. The Windows API DLLs contain quite a few such macros (e.g. GetMessage(), defined in Winuser.h), so read the DLL's documentation (and the associated header files) carefully. Macro names must be translated manually.

Parameter and Return Types

import com.sun.jna.Native;  // JNA infrastructure
import libs.Kernel32;  // Proxy interface for kernel32.dll

public class BeepMorse {
  private static Kernel32 kernel32 = (Kernel32) 
      Native.loadLibrary("kernel32", Kernel32.class);
  
  private static void toMorseCode(String letter) throws Exception {
    for (byte b : letter.getBytes()) {
      kernel32.Beep(1200, ((b == '.') ? 50 : 150));
      Thread.sleep(50);
    }
  }

  public static void main(String[] args) throws Exception {
    String helloWorld[][] = {
      {"....", ".", ".-..", ".-..", "---"}, // HELLO
      {".--", "---", ".-.", ".-..", "-.."}  // WORLD
    };
    for (String word[] : helloWorld) {
      for (String letter : word) {
        toMorseCode(letter);
        Thread.sleep(150);
      }
      Thread.sleep(350);
    }
  }
}

package libs;
import com.sun.jna.Library;

public interface Kernel32 extends Library {
  // ... (lines deleted for clarity) ...
  boolean Beep(int frequency, int duration);
  int GetLogicalDrives();
  //  ... (lines deleted for clarity) ...
}

import com.sun.jna.Native;
import libs.Kernel32;

public class GetLogicalDrives {

  public static void main(String[] args) {
    Kernel32 kernel32 = (Kernel32) 
        Native.loadLibrary("kernel32", Kernel32.class);
    int drives = kernel32.GetLogicalDrives();
    for (int i = 0; i < 32; ++i) {
      int bit = (1 << i);
      if ((drives & bit) == 0)
        continue;
      System.out.printf("%c:\%n", (char) ((int) 'A' + i));
    }
  }
}

C structs in Java

import com.sun.jna.Library;
import com.sun.jna.Structure;

public interface Kernel32 extends Library {
  //  ... (other members deleted) ...
  public static class SYSTEMTIME extends Structure {
    public short wYear;
    public short wMonth;
    public short wDayOfWeek;
    public short wDay;
    public short wHour;
    public short wMinute;
    public short wSecond;
    public short wMilliseconds;
  }
  void GetSystemTime(SYSTEMTIME st);
  //  ... (other members deleted) ...
}

import libs.Kernel32;
import libs.Kernel32.SYSTEMTIME;
import com.sun.jna.Native;

public class GetSystemTime {

  public static void main(String[] args) {
    Kernel32 kernel32 = (Kernel32)
        Native.loadLibrary("kernel32", Kernel32.class);
    SYSTEMTIME st = new SYSTEMTIME();
    kernel32.GetSystemTime(st);
    System.out.printf("Year: %d%n", st.wYear);
    System.out.printf("Month: %d%n", st.wMonth);
    System.out.printf("Day: %d%n", st.wDay);
    System.out.printf("Hour: %d%n", st.wHour);
    System.out.printf("Minute: %d%n", st.wMinute);
    System.out.printf("Second: %d%n", st.wSecond);
  }
}

Pointers and Strings

import libs.Kernel32;
import com.sun.jna.Native;

public class GetVolumeInformation {
	
  private static String b2s(byte b[]) {
    // Converts C string to Java String
    int len = 0;
    while (b[len] != 0)
      ++len;
    return new String(b, 0, len);
  }

  public static void main(String[] args) {
    Kernel32 kernel32 = (Kernel32) Native.loadLibrary(
        "kernel32", Kernel32.class);
    int drives = kernel32.GetLogicalDrives();
    for (int i = 0; i < 32; ++i) {
      if ((drives & (1 << i)) == 0)
        continue;
      String path = String.format("%c:\", (char) ((int) 'A' + i));
      byte volName[] = new byte[256], fsName[] = new byte[256];
      int volSerNbr[] = new int[1], maxCompLen[] = new int[1], fileSysFlags[] = new int[1];
      boolean ok = kernel32.GetVolumeInformationA(path, volName, 
          256, volSerNbr, maxCompLen, fileSysFlags, fsName, 256);
      if (ok)
        System.out.printf("%s %08X '%s' %s %08X%n", path, volSerNbr[0], 
            b2s(volName), b2s(fsName), fileSysFlags[0]);
      else
        System.out.printf("%s (Offline)%n", path);
    }
  }
}

C: 609260D7 'My-C-Drive' NTFS 000700FF
D: (Offline)
E: C8BCF084 'My-E-Drive' NTFS 000700FF
G: 634BE81B 'SDG-4GB-DRV' FAT32 00000006

Converting from JNI to JNA

Detecting a Struct Memory Alignment Problem

// BEGIN: Memory Alignment Problem Demo
TW_IDENTITY srcID = new TW_IDENTITY(Structure.ALIGN_DEFAULT);
stat = SelectSource(g_AppID, srcID);
if (stat != TWRC_SUCCESS) {
  //... (lines deleted for clarity) ...
}
System.out.printf("ProtocolMajor: %02x%n", srcID.ProtocolMajor);
System.out.printf("ProtocolMinor: %02x%n", srcID.ProtocolMinor);
System.out.printf("SupportedGroups: %04x%n", srcID.SupportedGroups);
System.out.printf("Manufacturer: %s%n", new String(srcID.Manufacturer, 0, 34));
dump(srcID);
// END: Memory Alignment Problem Demo

ProtocolMajor: 01
ProtocolMinor: 09
SupportedGroups: 694d0000
Manufacturer: crosoft                         Tw

000:  11 04 00 00 01 00 00 00 0d 00 01 00 32 36 20 4a 
000:   .  .  .  .  .  .  .  .  .  .  .  .  2  6     J 

016:  75 6e 65 20 32 30 30 30 00 00 00 00 00 00 00 00 
016:   u  n  e     2  0  0  0  .  .  .  .  .  .  .  . 

032:  00 00 00 00 00 00 00 00 00 00 00 00 00 00 01 00 
032:   .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 

048:  09 00 03 00 00 00 4d 69 63 72 6f 73 6f 66 74 00 
048:   .  .  .  .  .  .  M  i  c  r  o  s  o  f  t  . 

064:  00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 
064:   .  .  .  .  .  .  .  .  .  .  .  .  .  .  .  . 

080:  00 00 00 00 00 00 00 00 54 77 61 69 6e 20 44 61 
080:   .  .  .  .  .  .  .  .  T  w  a  i  n     D  a 
         ... (other lines deleted for clarity) ...

• ProtocolMajor (the 2 magenta bytes at offset 46) = 0x01
• ProtocolMinor (the 2 cyan bytes at offset 48) = 0x09
• SupportedGroups (the 4 magenta bytes at offset 50) = 0x0003
• Manufacturer (the 34 cyan bytes at offset 54) = "Microsoft" (padded out to 34 bytes with 0-valued bytes)

Reproducing the Struct Alignment Error

Preventing Struct Alignment Errors

public class TW_IDENTITY extends Structure {
  public TW_IDENTITY() {
    setAlignType(Structure.ALIGN_NONE);
  }
  public int Id;
  public TW_VERSION Version = new TW_VERSION();
  public short ProtocolMajor;
  public short ProtocolMinor;
    . . .
}

Running the Sample Code

• Download the zip containing the sample code, and extract it into a directory (say, samples)
• Open a command window, and use the "CD" command to navigate to the samplescode directory.
• Execute the batch file build.bat. This compiles all of the code (and is required to be run just once). The class files are located in a directory called samplesin.
• To run a program execute the batch file with the same name (e.g. LockWorkStation.bat, BeepMorse.bat, GetLogicalDrives.bat, GetSystemTime.bat, GetVolumeInformation.bat, or JTwainDemo.bat)

Resources

• Sample code for this article
• JNA project site
• Windows API Reference
• Windows Data Types
• No More Pointers
• Wikipedia Pointers Page
• Wikipedia "Windows Programming/Handles and Data Types"
• C Strings
• Java Tech: Acquire Images with TWAIN and SANE, Part 1
• TWAIN Developer's Toolkit
• TWAIN Header File

Sanjay Dasgupta has been using Java for telecom applications since 1996 (after many years of using many different languages in many industries).

Common Foundation

• poll(): Void: Poll the newsfeed location for updated content, which is fetched, parsed, and delivered to the application.
• update(): Void: Poll the newsfeed location. All content is fetched, parsed, and delivered to the application.
• headers (of type javafx.io.http.HttpHeader[]) identifies a sequence of HTTP request headers that are to be sent to location each time this newfeed is polled. This variable defaults to null.
• interval (of type javafx.lang.Duration) specifies the amount of time that must elapse before the newsfeed is once more polled for updates. You must specify a positive value for this variable, which defaults to 0.0. (I wonder if it wouldn't be better to choose a positive value, such as 60s, to be the polling default, and perhaps allow 0.0 to indicate that polling isn't desired.)
• location (of type String) specifies the newsfeed's address. This variable defaults to the empty string ("").
• onException (of type function(:Exception):Void) identifies a function that's invoked when an exception occurs during the current poll. This variable defaults to null.
• onForeignEvent (of type function(:javafx.data.pull.Event):Void) identifies a function that's invoked to handle extension elements, which are newsfeed elements whose namespace URI is not Atom or RSS. For example, given an Atom newsfeed whose feed element's start tag is specified as <feed xmlns="http://www.w3.org/2005/Atom" xmlns:opensearch="http://a9.com/-/spec/opensearch/1.1/">, parsing a subsequent <opensearch:totalResults>1911</opensearch:totalResults> element results in three foreign events (for the start tag, text, and end tag) because the namespace for totalResults is http://a9.com/-/spec/opensearch/1.1/ (as specified by the opensearch: prefix) instead of http://www.w3.org/2005/Atom. This variable defaults to null.

RSS API Overview

• factory (of type Factory) identifies the factory that's used to create objects that represent newsfeed elements. You only need to install your own factory when creating a custom feed parser.
• onChannel (of type function(:Channel):Void) identifies a function that's invoked to report the channel element's non-item elements -- the RSS channel element contains item and non-item elements, and is itself contained within the top-level rss element. This variable defaults to null.
• onItem (of type function(:Item):Void) identifies a function that's invoked to report the current item element. This variable defaults to null.

• categories (of type Category[]) identifies the categories (in terms of domains and text values) to which this channel belongs.
• copyright (of type String) specifies a copyright notice for channel content.
• description (of type String) presents a phrase or sentence that describes this channel.
• docs (of type String) specifies a URL that points to documentation for the format used in the RSS file. This might simply be a pointer to a Web page, and is useful for letting people, who encounter this RSS file in the future, understand the file's purpose (much like code comments).
• generator (of type String) identifies the program that was used to generate this channel.
• image (of type Image) identifies an image (in terms of description, height, link, title, URL, and width) that can be displayed with the channel content.
• language (of type String) identifies the language in which the channel was written.
• lastBuildDate (of type javafx.date.DateTime) specifies when this channel's content was last changed.
• link (of type String) provides the URL to the Website that corresponds to this channel.
• pubDate (of type DateTime) identifies the date when this channel was published.
• title (of type String) provides this channel's title.
• ttl (of type Duration) provides the number of minutes in which the news-reader can cache this channel before it must poll the newsfeed to refresh channel content.

• author (of type String) provides the email address of this item's author.
• categories (of type Category[]) identifies the categories to which this item belongs.
• comments (of type String) specifies the URL of a Web page containing comments about this item.
• description (of type String) provides a description of this item.
• enclosure (of type Enclosure) describes a media object (in terms of length, MIME type, and URL) that's attached to this item.
• guid (of type Guid) specifies, for this item, a globally unique identifier (in terms of text and an indicator of whether or not this text permanently points to the full item described by this item).
• link (of type String) provides this item's URL.
• pubDate (of type DateTime) identifies the date when this item was published.
• source (of type Source) identifies the originating channel (in terms of the name of the channel and an XMLization of that channel) for this item.
• title (of type String) provides this item's title.

/*
 * Main.fx
 */

package rssdemo;

import java.lang.Exception;

import javafx.data.feed.rss.Channel;
import javafx.data.feed.rss.Item;
import javafx.data.feed.rss.RssTask;

import javafx.data.pull.Event;

def MAX_POLLS = 3;

var counter = 0;

def task:RssTask = RssTask
{
    interval: 15s

    // The following location demonstrates a basic RSS newsfeed.

    location: "http://javajeff.mb.ca/rss/javajeff.xml"

    // The following location demonstrates onException().

    // location: "http://developers.sun.com/rss/sdn_features.xml"

    // The following location demonstrates onForeignEvent().

    // location: "http://feeds.dzone.com/javalobby/frontpage?format=xml"

    // The following location demonstrates IllegalArgumentException (must use
    // AtomTask for Atom feeds).

    // location: "http://feeds.sophos.com/en/atom1_0-sophos-company-news.xml"
  
    onStart: function (): Void
    {
        println ("Task is starting");

        if (++counter > MAX_POLLS)
        {
            task.stop ();
            FX.exit ()
        }
    }

    onChannel: function (c: Channel): Void
    {
        println ("Channel: {c}")
    }

    onItem: function (i: Item): Void
    {
        println ("Item: {i}")
    }

    onException: function (e: Exception): Void
    {
        println ("Exception: {e}");
        task.stop ();
        FX.exit ()
    }

    onForeignEvent: function (e: Event): Void
    {
        println ("Event: {e}")
    }

    onDone: function (): Void
    {
        println ("Completed poll #{counter}")
    }
}
task.start ()

Atom API Overview

• factory (of type Factory) identifies the factory that's used to create objects that represent newsfeed elements. You only need to install your own factory when creating a custom feed parser.
• onFeed (of type function(:Feed):Void) identifies a function that's invoked to report the feed element's non-entry elements -- the Atom feed element contains entry and non-entry elements, and is itself the top-level element. This variable defaults to null.
• onEntry (of type function(:Entry):Void) identifies a function that's invoked to report the current entry element. This variable defaults to null.

• authors (of type Person[]) identifies the authors (in terms of email address, name, additional person-specific text, and the Internationalized Resource Identifier (IRI) associated with the person) of this feed.
• categories (of type Category[]) identifies the categories (in terms of a human-readable label, category name, and categorization scheme IRI) to which this feed belongs.
• contributors (of type Person[]) identifies the persons who have contributed to this feed.
• generator (of type Generator) identifies the program (in terms of human-readable name, program URI, and program version number) that was used to generate this feed. This information can be used to debug an Atom newsfeed.
• icon (of type Id) identifies this feed's iconic image (in terms of a URI to the image).
• id (of type Id) specifies a universally unique and a permanent identifier (in terms of a URI) for this feed.
• links (of type Link[]) specifies links (in terms of href, hreflang, length, rel, title, and type XML attributes, and text associated with the link) from this feed to Web resources.
• logo (of type Id) identifies this feed's non-iconic image.
• rights (of type Content) specifies the rights (in terms of src, text, and type XML attributes) held in and over this feed.
• subtitle (of type Content) provides this feed's subtitle.
• title (of type Content) provides this feed's title.
• updated (of type Date) specifies when this feed's content was last changed.

• content (of type Content) specifies this entry's content.
• published (of type Date) specifies when this entry was published.
• source (of type Feed) identifies this entry's feed source.
• summary (of type Content) specifies a short summary, abstract, or excerpt for this entry.

/*
 * Main.fx
 */

package atomdemo;

import java.lang.Exception;

import javafx.data.feed.atom.AtomTask;
import javafx.data.feed.atom.Entry;
import javafx.data.feed.atom.Feed;

import javafx.data.pull.Event;

def MAX_POLLS = 3;

var counter = 0;

def task:AtomTask = AtomTask
{
    interval: 15s

    // The following location demonstrates a basic Atom newsfeed.

    location: "http://photos.dailycamera.com/hack/feed.mg?Type=gallery&Data=9573834_9ysrR&format=atom10"
    
    // The following location demonstrates onForeignEvent().

    // location: "http://blogsearch.google.com/blogsearch/feeds?bc_lang=en&hl=en&output=atom"

    // The following location demonstrates IllegalArgumentException (must use
    // RssTask for RSS feeds).

    // location: "http://javajeff.mb.ca/rss/javajeff.xml"

    onStart: function (): Void
    {
        println ("Task is starting");

        if (++counter > MAX_POLLS)
        {
            task.stop ();
            FX.exit ()
        }
    }

    onFeed: function (f: Feed): Void
    {
        println ("Feed: {f}")
    }

    onEntry: function (e: Entry): Void
    {
        println ("Entry: {e}")
    }

    onException: function (e: Exception): Void
    {
        println ("Exception: {e}");
        task.stop ();
        FX.exit ()
    }

    onForeignEvent: function (e: Event): Void
    {
        println ("Event: {e}")
    }

    onDone: function (): Void
    {
        println ("Completed poll #{counter}")
    }
}
task.start ()

Behind the Scenes with FeedTask

• The SubscriptionTask instance is passed to task.
• The long integer 0L is passed to delay.
• The value of FeedTask's interval variable is passed to period.

• location: The value of FeedTask's location variable is assigned to this variable.
• onStarted: A function is assigned to this variable, and is invoked when the request starts to execute. The function is responsible for invoking onStart().
• onResponseHeaders: A function is assigned to this variable to retrieve and save the values of the HTTP ETag and Last-Modified response headers. These values are needed to ensure that only changed newsfeed content will be returned in the next poll request.
• onToRead: A function is assigned to this variable to obtain the total number of bytes to read, which is assigned to maxProgress.
• onRead: A function is assigned to this variable to obtain the number of bytes read so far, which is assigned to progress.
• onInput: A function is assigned to this variable to parse the request content via an internal parse(is) method call (where is is onInput()'s java.io.InputStream argument). If parsing results in a thrown exception, the exception object is assigned to causeOfFailure, true is assigned to failed, and onException() is invoked. Finally, true is assigned to done, and onDone() is invoked. (The onInput() function isn't invoked, and hence onDone() isn't invoked, when only changed content is requested but that content isn't available.)
• onException: A function is assigned to this variable to report a problem with the request itself (and not parsing). If the request fails, the exception object is assigned to causeOfFailure, true is assigned to failed, and onException() is invoked.

Conclusion

Resources

• Sample code for this article
• Atom specification
• JavaFX 1.2.1 API Documentation
• JavaFX's official Website
• Rakesh Menon's Custom Feed Parsers blog post
• RSS specification
• Wikipedia's Atom (standard) entry
• Wikipedia's RSS entry

Jeff Friesen is a freelance software developer and educator specializing in Java technology. Check out his site at javajeff.mb.ca.

• How the Objects will be instantiated
• How many Objects will be instantiated
• At what point the Objects will be instantiated

1. Factory Method Pattern
2. Abstract Factory Pattern
3. Singleton Pattern
4. Builder Pattern
5. Prototype Pattern

Factory Method Design Pattern

• when the object creation depends upon the user data or some event;
• when which object is getting created is abstracted from the user;
• when the type of object created is to be decided at runtime.

Abstract Factory Design Pattern

• when a lot of subclasses are supposed to be added at runtime or later in the application;
• when one type of object encapsulates other type of object;
• when the System should work with the product without being aware of the specific classes interfacing with the product.

Singleton Design Pattern

• Declare a class and declare a static member variable of type class inside it.
• Make the constructor private.
• Create a method which will instantiate the static member variable if it is null otherwise return the old created object.

Builder Design Pattern

• Header
• Footer
• Managers Dashboard
• Forum column
• Gallery
• Common Display area

Header, Footer, Gallery, Manager's Dashboard.

• when a complex object has to be made and the implementation has to be hidden from the user;
• when we want to add more subclasses to our system without the user's knowledge.

Prototype Design Pattern

• when the user interface is not to be changed; for example, a dropdown remains a dropdown, or a Radio Button remains a Radio Button, no matter what data has to be displayed;
• when creating a new object is a costly affair;
• when the data to be displayed is already present in some other object.

Conclusion: Design Patterns Application Decisions

Varun Sood is currently working as Senior Associate-Education at Infosys Technologies Limited. His areas of interest include Enterprise Architecture and Web Application Security. Varun is as SCJP 6.0 certified programmer.