Java JDK installation on Windows

Installing Java on Windows for development can be one of the trickier things, especially if you're looking for Java 1.5 vs. 1.6: Java 1.5 is not readily available for download. However, some digging reveals this great site with a link to the download (which requires registration). From there, you can find the 32- and 64-bit versions of the Windows' installers.

Auto-generate Java getter/setter methods in Eclipse

The Eclipse IDE is a powerful tool for Java development. One feature I just discovered: How to automatically generate getter/setter methods (properties) for your classes.

In your class, place your cursor on a private member, and you'll notice a yellow underline and a little popup with options. One of them is "Create getter and setter for 'myPrivateVariable'". Simply click this choice and Eclipse displays a dialog to choose getter and setter method names as well as other options. You can also access this getter/setter auto-generate functionality by placing your cursor on a private field and then going to Refactor > Encapsulate Field.

Populate and validate JSF selectOneMenu

Using a backing bean or Seam component (on JBoss), you can easily populate a JSF selectOneMenu (JSF dropdown box server-side control):

<h:selectonemenu id="lstRating" value="#{asset.rating}" required="true" requiredMessage="Rating is required.">
  <f:selectitems value="#{asset.ratingItems}" />
</h:selectonemenu>
<rich:message for="lstRating" styleclass="errors" />

In this example, you have a selectOneMenu with id of lstRating. It gets its SelectItem elements from the asset.ratingItems property on the backing component. The selected item is stored in asset.rating.

  private String rating;
  private ArrayList<SelectItem> ratingItems = null;

  public ArrayList<SelectItem> getRatingItems(){
    ratingItems = new ArrayList<SelectItem>();
    ratingItems.add(new SelectItem(null,"Select One..."));
    ratingItems.add(new SelectItem("TV-Y", "TV-Y"));
    ratingItems.add(new SelectItem("TV-Y7", "TV-Y7"));
    ratingItems.add(new SelectItem("TV-G", "TV-G"));
    ratingItems.add(new SelectItem("TV-PG", "TV-PG"));
    ratingItems.add(new SelectItem("TV-14", "TV-14"));
    ratingItems.add(new SelectItem("TV-MA", "TV-MA"));

    return ratingItems;
  }

  public String getRating(){
    return this.rating;
  }

  public void setRating(String rating){
    this.rating = rating;
  }

In the above code, we declare an ArrayList of SelectItem object type. The getRatingItems() property instantiates the ratingItems ArrayList and populates it with SelectItem objects. Note the first SelectItem has a null value; if the user leaves the dropdown box to this item, the required validator will detect it as a blank value and throw a validation error.

Create a zip archive in Java

Here's a Java class to zip up files in a directory. Thanks to the Java forum for their help in fixing some bugs.

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.util.ArrayList;
import java.util.zip.ZipEntry;
import java.util.zip.ZipOutputStream;
import java.io.File;

public class Zipper
{
private String _zipFilePath = "";
private String _imageFolderPath = "";
private String _zipFileName = "";
private static final int BUFFER = 20480;
private String _error = "";

public Zipper()
{
}

public void setZipFilePath(String path)
{
_zipFilePath = path;
}

public void setImageFolderPath(String path)
{
_imageFolderPath = path;
}

public String getError()
{
return _error;
}

public void zipEm()
{
File directory = new File(_imageFolderPath);

File files[] = directory.listFiles();

try {
 BufferedInputStream origin = null;
 FileOutputStream dest = new FileOutputStream(_zipFilePath);
 ZipOutputStream zip = new ZipOutputStream(new BufferedOutputStream(dest));

 byte data[] = new byte[BUFFER];

 File f = null;
 ZipEntry entry = null;
 FileInputStream fi = null;
 int count;

 // Iterate over the file list and add them to the zip file.
 for (int i=0; i <files.length; i++)
 {
   fi = new FileInputStream(files[i]);
   origin = new BufferedInputStream(fi, BUFFER);
   entry = new ZipEntry(files[i].getName());
   zip.putNextEntry(entry);

   while((count = origin.read(data,0,BUFFER)) != -1)
   {
     zip.write(data,0,count);
   }
   count = 0;
   origin.close();
 }
 zip.close();
}
catch (Exception e)
{
 // handle exception
 _error = e.getMessage();
}
}
}

Powerful image editing in Java

The Java Advanced Imaging (JAI) API provides a very powerful way of manipulating images on the server. For a current app under development, we needed to receive an image file (JPG, PNG, or GIF) and resize it to a set width (letting the height adjust to maintain aspect ratio). JAI came to the rescue when the built-in image processing packages in Java were too slow.

The following code demonstrates the image resizing capabilities of JAI; for maximum image quality, we use the "SubsampleAverage". Thanks to this article.

BufferedImage resizedImage = null;

try {
SeekableStream stream = SeekableStream.wrapInputStream(is, true);
RenderedOp newImage = JAI.create("stream",stream);
((OpImage)newImage.getRendering()).setTileCache(null);

double scale = targetWidth / newImage.getWidth();

ParameterBlock pb = new ParameterBlock();
pb.addSource(newImage);
pb.add(scale);
pb.add(scale);

/*
 * For best results, must use the following rendering hints.
 */
RenderingHints qualityHints =
  new RenderingHints(RenderingHints.KEY_RENDERING,
     RenderingHints.VALUE_RENDER_QUALITY);

resizedImage = (JAI.create("SubsampleAverage",
  pb,qualityHints)).getAsBufferedImage();
}
catch (Exception e)
{
this.error = e.getMessage();
}

Extracting contents of *.jar file

A quick and painless method: Rename the file's extension to .zip and double-click it in Windows Explorer. We're using Java 1.4.2_12, which doesn't have the jar.exe built-in. Otherwise, if your path environment variable is set correctly, you can just type jar xf jar-file at the command line to extract contents.

Java String Comparison

One little gotcha in Java is the string comparisons: Using the equality check == will tell you if the two variables are referencing the same object, not whether their string values are the same. To do a string comparison, use something such as this,

 if (string1.equalsIgnoreCase(string2)) {
       //... do something
}

Otherwise you'll be wondering why your code isn't working ;)