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Using a reusable code approach to HTML select option lists (continued)
Our abstract class implements the getOptions() method by checking to see if the options have been loaded before returning the options. If the options have not been loaded, it performs a new method to load the options before returning them to the calling module. Since there are a variety of sources from which we can obtain our options, we'll leave the actual loading of the options to the implementing classes by defining an abstract method that implementing classes will need to implement.
Create an implementation-specific final class
Now that we have our interface and an abstract class that implements the interface, we can create one or more implementing classes to complete our mini framework. We could obtain our list of options from a JDBC database, an LDAP directory, a Java Properties object, an XML file, a text file containing name/value pairs, or any other number of sources. However, in keeping with our "let's keep things simple to start with" approach, let's begin with just a simple String containing a comma-separated list of values, and to make things even simpler, for this first exercise let's assume that the same value will be used for both the label and the value fields of our LabelValueBeans.
Listing 3 contains our SimpleOptionListSource class, which extends the OptionListSourceBase class and implements the loadOptions() method. This class also includes a constructor that accepts a String as a parameter so that we can pass our comma-separated values to the object at creation time.
package step.one;
import java.util.ArrayList;
import org.apache.struts.util.LabelValueBean;
/**
* Returns the name/value pairs for the options related to an HTML
* "select" tag.
*
* Source data for this implementation is obtained directly from the
* option list string provided.
*/
public class SimpleOptionListSource extends OptionListSourceBase {
private String optionList = null;
/**
* Constructs a new "SimpleOptionListSource" object using the parameters
* provided.
*
* @param optionList a String containing the comma separated values for
* the option list
*/
public SimpleOptionListSource(String optionList) {
this.optionList = optionList;
}
/**
* Loads the list of available options from the optionList
* String passed to the constructor.
*/
protected void loadOptions() {
ArrayList list = new ArrayList();
String remaining = optionList;
while (remaining.indexOf(",") > -1) {
int index = remaining.indexOf(",");
String thisItem = remaining.substring(0, index);
if (index < remaining.length()) {
remaining = remaining.substring(index + 1);
} else {
remaining = "";
}
LabelValueBean thisOption = new LabelValueBean(thisItem, thisItem);
list.add(thisOption);
}
if (remaining != null && !remaining.equals("")) {
LabelValueBean thisOption = new LabelValueBean(remaining, remaining);
list.add(thisOption);
}
setOptions(list);
}
}
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