Организация кода по функционалу, а не по слоям

Package by feature, not layer

The first question in building an application is "How do I divide it up into packages?". For typical business applications, there seems to be two ways of answering this question.

Package By Feature

Package-by-feature uses packages to reflect the feature set. It places all items related to a single feature (and only that feature) into a single directory/package. This results in packages with high cohesion and high modularity, with minimal coupling between packages. Items that work closely together are placed next to each other. They aren't spread out all over the application. It's also interesting to note that, in some cases, deleting a feature can reduce to a single operation - deleting a directory. (Deletion operations might be thought of as a good test for maximum modularity: an item has maximum modularity only if it can be deleted in a single operation.)

In package-by-feature, the package names correspond to important, high-level aspects of the problem domain. For example, a drug prescription application might have these packages:

- com.app.doctor;

- com.app.drug;

- com.app.patient;

- com.app.presription;

- com.app.report;

- com.app.security;

- com.app.webmaster;

- com.app.util;

- and so on...

Within each package are all (or most) items related to that particular feature (and only that feature). For example, the com.app.doctor package might contain these items:

- DoctorAction.java - an action or controller object

- Doctor.java - a Model Object

- DoctorDAO.java - Data Access Object

- database items

- user interface items (perhaps a JSP, in the case of a web app)

It's important to note that a package can contain not just Java code, but other files as well. Indeed, in order for package-by-feature to really work as desired, all items related to a given feature - from user interface, to Java code, to database items - must be placed in a single directory dedicated to that feature (and only that feature).

In some cases, a feature/package will not be used by any other feature in the application. If that's the case, it may be removed simply by deleting the directory. If it is indeed used by some other feature, then its removal will not be as simple as a single delete operation.