在 Freemarker 中处理 null

Question

Situation:

• Old java project using freemarker has many finished templates working great.
• Every template is using data form Transaction object.
• This transaction object is very large, because wraps all data about transaction.
• In templates is a lot of expression like this: get("object1").getNestedObject2().getNestedObject3().getValue();

Problem: New requirements appear: All templates have to be process for preview with no real data. All numbers should be Zero and all string should be ---.

Unsatisfactory solutions:

1. Remake all templates to check null values. (Lot of work and not safe)
2. Create Transaction object that contains all default value. (Lot of work)

Well my question is: Can I say to Freemarker, that if he finds null or finds null along the way, that he should use 0 instead if he was expecting number or --- if he was expecting String.

Or do you see any better solution?

Answer 1

If you need to show a dummy data model to the templates, your best bet is probably a custom ObjectWrapper (see Configuration.setObjectWrapper ). Everything that reads the data model runs through the TemplateModel -s, and the root TemplateModel is made by the ObjectWrapper , thus it can control what values the templates get for what names. But the question is, when you have to return a dummy value for a name, how can you tell what its type will be? It's not just about finding out if it will be a string or a number, but also if it will be a method (like getNestedObject2 ) or a hash (something that can be followed by . ). What can help there is that FreeMarker allows a value to have multiple types, so you can return a value that can be used as a method and as a hash and as a string, for example. Depending on the application that hack is might be good enough, except, you still have to decide if the value is a string or a number, because ${} will print the numerical value if the value both a string and a number.