Rows per page selection: Part 2

I was asked to create a control that would allow users to select the number of rows per page in a view/repeat control (the application uses both). It seemed simple at first, but I ran into a few issues that I thought I'd share the solutions to.

Problem 2: When the page refreshed, the combobox value always reverted back to the default

It turns out that the Integer value stored in the viewScope doesn't get run through the converter back to a string before being compared to options. I needed a way to calculate the option values so that they would be Integers. This is also not the first time I've run into issues where I need a value to be of a different type, and I see questions like this on StackOverflow from time to time. I attempted a few minor things before I realized I needed to break out my old stand-by, the GetMap.

The GetMap is just a fake Map implementation that takes the key and transforms it or uses it to look up some other value. In this case, we are doing the former. Until this point, I had only ever needed String keys, and so my existing implementation made that assumption. Enter GetObjMap, for which the only difference is the key can be any object. (Note: the GetMap could just be changed to an Object key, but it would likely create warnings for existing code, so I opted for a new class.)

I used this new tool to create a "universal" converter. Universal in the sense that it handles what I need right now and can be added to later.

public class XspObjectConverter {

public GetObjMap<String> getAsString() {

GetObjMap<String> getter = new GetObjMap<String>() {

@Override
public String get(final Object key) {

try {

return String.valueOf(key);

} catch (Throwable t) {

throw new AbortProcessingException(t);

}

}

};
return getter;

}

public GetObjMap<Integer> getAsInteger() {

GetObjMap<Integer> getter = new GetObjMap<Integer>() {

@Override
public String get(final Object key) {

try {

if (null == key) {

return null;

}
if (o instanceof String) {

return Integer.parseInt((String)key);

} if (Number.class.isAssignableFrom(key.getClass())) {

return new Integer(((Number)key).intValue());

}
throw new IllegalArgumentException("Value cannot be converted");

} catch (Throwable t) {

throw new AbortProcessingException(t);

}

}

};
return getter;

}

}

We now need to register this in faces-config.xml. Since it is stateless, there is no need to make it Serializable. I'll put it in ApplicationScope so that it is always available.

<managed-bean>

<managed-bean-name>converter</managed-bean-name>
<managed-bean-class>org.package.XspObjectConverter</managed-bean-class>
<managed-bean-scope>application</managed-bean-scope>

</managed-bean>

Now that this groundwork is laid, we can simply create our selection items like this:

<xp:selectItem

itemLabel="20"
itemValue="${converter.asInteger[20]}" />

Now everything works!!