Where can I put formatting logic?

Question

I have several classes with raw data, for example:

public interface Transaction {
   public double getAmount();
   public Date getDate();
}

I need to output formatted versions of this data in several places. For example, I can display the amount either $1,000on a web page or 1000.00when loading Excel. I also want to be able to reuse the same formatting code in different places. Some of them will be simple (for example, displaying a date in a specific format), but some of them will be more complex (for example, displaying different values ​​for one field depending on the value of another field).

My question is: where should I put the formatting code? I can think of several places:

• Add methods to the data object, such as getAmountHTML()or getAmountExcel(). Convenient, but does it make the model too tightly coupled?

• Format in the template when displaying data. Flexible, but since it is not in the method, I cannot easily reuse the same formatting in different places.

• Create a formatting class for each data class and give it a link to the source data object.

I will have many data objects to format, so I would suggest a good approach. Is there anyone who has the relevant experience?

Answer 1

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public String getFormattedString(Formatter f);

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Answer 2

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