Skip to main content

Revisiting passing Parameters through EL - this time with functional techniques

The strangest thing about being a developer, to me, is that every time I think I have perfected my technique for something, I revisit it after some time away and find a better way of doing things. So this is my 4th iteration of how to pass and accept parameters through Expression Language. Allow me to introduce... the Mapper. (Quick side note: my old GetMap was based on the Map interface. Mapper is based on DataObject just because it is smaller. Mapper could just as easily implement Map if you prefer.

Just as a quick reminder, the goal is to accept a parameter through Expression Language, like so:
styleClass="#{MyViewBean.buttonStyle['MyButton']}"

public class Mapper implements DataObject, Serializable {
public static interface Function {
Object map(Object in);
}
private final Function func; //This will be an anonymous implementation

public Mapper(Function func) {
this.func = func;
}
public Object getValue(Object key){
return func.map(key); // Call the anonymous Function method
}
public void setValue(Object key, Object value){
throw new UnsupportedOperationException();
}
public Class<?> getType(Object key) {
throw new UnsupportedOperationException();
}
public boolean isReadOnly(Object key) {
return true;
}
}

This came from studying functional programming concepts and I believe this is a vast improvement on my earlier versions. It is certainly much easier to read and implement, and the most flexible. It works like this:

public class MyViewBean {
private String activeButton = "MyButton";

private final Mapper btnStyleMapper = new Mapper(
new Mapper.Function(){ // define the translation function
public Object map(Object in) {
return getActiveButton().equalsIgnoreCase(in.toString()) ? " active" : "";
}
}
);

public String getActiveButton() {
return this.activeButton;
}

public void setActiveButton(String activeButton) {
this.activeButton = activeButton;
}

public Object getButtonStyle() {
return btnStyleMapper;
}
}
One thing this version does sacrifice is strongly-typed objects due to the DataObject interface. You could use Map for better typing, but the endpoints are still going to be Objects, so it might be best to just validate the input and be on your way.

Comments

Popular posts from this blog

Rows per page selection: Part 1

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. First, lets start at the beginning. I went through the relevant design elements and set row="#{viewScope.tableRows}" , and I created an xp:comboBox with value="#{viewScope.tableRows}" and added items for 20, 30, 50, and 100, and I assigned it an onChange event handler that did a partial execution and partial refresh of a div containing the combo box, pager and the table. Then I started fixing all the problems. Problem 1: The combobox value was a string, but the rows parameter requires an integer. This was causing IllegalArgumentException / java.lang.String incompatible with java.lang.Integer. I added a NumberConverter, but this only slightly changed the exception message to java.lang.Long incompatible with java.lang....

Pass data between XPages and existing LS scripts

I'm working on modernizing a fairly hefty application with a lot of existing script libraries which we want to leverage within the XPages environment. Here is a technique that works very well. First, create an in-memory document in SSJS. We can set any input values needed for the back end. Then we pass that document to a LS Agent which can work it's magic using the values set in SSJS and use the same document to return values back to the XPage. Here is how it works in detail:

XPages Application Framework (Part 1?)

Note: I changed projects and priorities after my last POI article, resulting in a long hiatus. I anticipate using that framework on my current project and will likely refine and complete my related article series. For the past several months, I've been fortunate enough to lead a project overhaul from traditional Domino Webapp to XPages. I had a few goals in mind, but the top three were integrating Bootstrap, embracing MVC principles, and eliminating all SSJS . I imagine the motivation for Bootstrap integration is self-explanatory. There is an OpenNTF project out there called Bootstrap4XPages. I didn't use that for a number of reasons - the main being a policy in the current environment. But you may ask yourself (if you didn't follow that link), why so much hatred for SSJS? I have a litany of reasons. It impacts readability of the XPage source; it hurts maintainability when logic is scattered across dozens of XPages, custom controls, and script libraries; it mixes log...