The problem
So you are really doing well for yourself and have many new customers for your application! Good job, but with many customers, come plenty of headaches.
As a simple example, let’s examine user names. You have a UserService that contains a function that accepts a user and returns the user name. There are many ways to do it, and different customers may prefer to display it in different ways. You can choose to display:
- last name, first name
- first name, last initial
- last name (user ID)
To complicate things, a new customer has requested that user names be displayed only for active users. Otherwise, they want it to display as “Temp-user-${userId}”.
A poor solution
Let’s first implement this using a simple approach:
public String getUserName(User usr) {
String customer = Utils.getCustomer();
//for some, if not active, return "Temp-user-${userId}"
if( ("CUST1".equals(customer) || "CUST2".equals(customer)) && !usr.isActive()) {
return "Temp-user-(" + usr.getId() + ")";
}
if("CUST3".equals(customer)) {
//last name, first name
return usr.getLastName() + ", " + usr.getFirstName();
}
if("CUST4".equals(customer) || "CUST6".equals(customer)) {
//first name, last initial
return usr.getFirstName() + ", " + usr.getLastName().charAt(0);
}
if("CUST7".equals(customer)) {
//last name (user ID)
return usr.getLastName() + "(" + usr.getId() + ")";
}
return null;
}
As you can see this approach can quickly get out of hand! As the number of customers increases, and more customizations are needed, this function will become very hard to maintain and become error prone. It’s also difficult to quickly gather the differences between customers just by glancing at the code. But we can do better!
A better solution
Using the techniques we learned in the previous blog post, we can create an enumeration that will define all the customizations available to our customers, and then use property files to allow each customer to override the default behavior.
Let’s say we want our application to, by default, display users as “last name, first name” and to not take into account the user’s status. We can define this in the below enumeration SiteConfig:
public enum SiteConfig {
SHOW_INACTIVE_USERS_AS_TEMP("no"),
USER_DISPLAY_TYPE("LAST_FIRST")
;
private String value;
SiteConfig(String value) {
this.value = value;
}
public boolean getBoolean() {
return BooleanUtils.toBoolean(value);
}
public <T extends Enum<T>> T getEnum(final Class<T> enumType) {
return Enum.valueOf(enumType, value);
}
static {
String customer = Utils.getCustomer();
if (customer != null) {
loadFromProperties(Utils.loadProperties("site_config_" + customer + ".properties"));
}
}
private static void loadFromProperties(Properties customerProps) {
if (customerProps != null) {
SiteConfig[] arr = SiteConfig.values();
for (SiteConfig s : arr) {
if (customerProps.containsKey(s.name())) {
s.value = customerProps.getProperty(s.name());
}
}
}
}
}
SiteConfig defines two customizations available to customers, and we can add others as needed. The default behaviors are passed into the constructor and they can be overridden by each customer by creating a properties file such as site_config_CUST1.properties
SHOW_INACTIVE_USERS_AS_TEMP=yes
USER_DISPLAY_TYPE=LAST_USERID
Now let’s re-implement our getUserName method, to make use of SiteConfig:
public String getUserName(User usr) {
//for some, if not active, return "Temp-user-${userId}"
if(!usr.isActive() && SiteConfig.SHOW_INACTIVE_USERS_AS_TEMP.getBoolean()) {
return "Temp-user-(" + usr.getId() + ")";
}
UsernameDisplayType displayType = SiteConfig.USER_DISPLAY_TYPE.getEnum(UsernameDisplayType.class);
if(UsernameDisplayType.LAST_FIRST == displayType) {
//last name, first name
return usr.getLastName() + ", " + usr.getFirstName();
} else if(UsernameDisplayType.FIRST_LAST_INITIAL == displayType) {
//first name, last initial
return usr.getFirstName() + ", " + usr.getLastName().charAt(0);
} else if(UsernameDisplayType.LAST_USERID == displayType) {
//last name (user ID)
return usr.getLastName() + "(" + usr.getId() + ")";
}
return null;
}
The new method makes it easy to add other display types and associated logic without having any knowledge of customers. It also doesn’t need to be modified as customers are added or existing customers choose a different display type.
Check out the full code and simple app below!
https://github.com/RomanSery/codesnippets
