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Data Types for Your Action Form’s Properties
There are two points to ponder when choosing data types for an action form’s properties.
- The Struts action servlet populates the properties of an action form with the current HttpServletRequest object’s parameter values. These parameter values are strings.
- In an action class, there are two tasks you often perform: populate a transfer object with an action form’s properties or populate an action form with a transfer object’s properties. This means that you need to perform data conversion if the data type of each of the action form’s properties is not compatible with the data type of the corresponding property in the transfer object.
Because request parameters are strings, populating an action form’s properties with request parameters will be easiest if each of the action form’s properties is a string. Struts does convert a request parameter value to a data type suitable for the corresponding property of an action form prior to populating the property. However, it can only convert string values to java.lang.String or Java primitive types (boolean, int, long, etc) and their Java object equivalents (Boolean, Integer, Long, etc). If you are using a java.util.Date for an action form’s property, for example, Struts will invariably throw an exception when trying to convert the corresponding request parameter to the Date property, regardless whether or not the request parameter has the correct date pattern. This is to say, you can choose String, primitives or their Java equivalents as the data types of your action form’s properties, but not other types such as java.util.Date.
What data types should you use for an action form’s properties? Here are some suggestions.
- The boolean type is the best type for a property that is mapped to a check box in an HTML page. Struts handles String to Boolean conversion perfectly.
- The int type is good for properties mapped to pre-defined options, such as in a select box or multibox. However, you can also use String.
- The numeric types (int, short, long, float, etc) are not always suitable for properties mapped to a text box, password, and text area, even for HTML input fields that accept numeric values. This is because if the user enters a non-numeric value (such as “abc”) to an HTML input field mapped to a numeric property, the conversion from the string (“abc”) to a numeric type will fail and the corresponding action form’s property will have the previous value (which is initially a 0). As a result, when the HTML form is redisplayed (because input validation failed), the user will see the value of the action form’s property (0), and not the incorrect value entered earlier (“abc”). This could be confusing for the user. Moreover, when the HTML form is displayed for the first time, the user will see a 0 in every input field mapped to a numeric type property. Blank fields are the norm.
There is a dilemma here. On the one hand, choosing String as the data type of an action form’s properties makes data conversion from the HttpServletRequest object’s parameters easier. On the other hand, for easier data conversion from an action form to a transfer object, you want the action form’s properties to have compatible data types with those of the transfer object.
Let’s see how to tackle this problem in the sample applications.