ActionServlet Design Guidelines

1. Create reusable components!

• Do not use Context for retrieving HTTP parameter values, if possible. Use parameter passing provided by ActionServlet instead.

  Example: non-reusable component

  public MyComponent {
     public void someMethod(Context context) {
        String parameter = context.get("someParameter");
        // do something...
     }
  }

  Example: reusable component

  public MyComponent {
     public void someMethod(String parameter) {
        // do something...
     }
  }

  Advantage: You can map any HTTP parameter of any name to the formal parameter of the method - in ActionConfig by <action> element:

  <action name="ActionName" method="someMethod(String HTTPParameterName)"/>

• Do not use Context for assigning $variables.

  Example: non-reusable component

  public MyComponent {
     public void someMethod(Context context) {
        // do something...
        context.put("variable", someValue);
     }
  }

  Example: reusable component

  public MyComponent {
     public int someMethod() {
        // do something...
        return someValue;
     }
  }

  Advantage: You can map return value to any $variable without changing the component's code in ActionConfig by <on-return> element:

  <on-return value="*" assign-to="variable" show-template="..."/>

  Note: <output-variable> element can be also used to set $variables.

2. Use <properties> to setup your components!

public DbComponent {
   private int maxDbConnections;
   
   public DbComponent() {
      maxDbConnections = Integer.parseInt(System.getProperty("max.db.connections"));
   }
}

public DbComponent {
   private int maxDbConnections;
   
   public void setMaxDbConnections(int value) {
      maxDbConnections = value;
   }
}

<properties>
   <property component="DbComponent" name="MaxDbConnections" value="5"/>
</properties>

<components>
   <component class="DbComponent" name="DbComponent"/>
</components>

Note: Custom initialization (of Corba object, EJBs etc.) can be done by instantiators (see Specification).

3. Use type handlers for conversions to custom types!

public MyComponent {
   public void someMethod(String email) {
      // parse string to get recipient name and his/her address, ...
      // (this must be done by each component class handling email)
   }
}

public class EmailHandler implements SimpleTypeHandler {
   public Object convert(Context context, String email) 
   throws ConversionException {
      return new Email(email);   // Email does parsing
   }
}

public MyComponent {
   public void someMethod(Email email) {
      String recipient = email.getRecipient();
      String address = email.getAddress();
      // ...
   }
}

Note: You must bind type handler to its type in ActionConfig:

<type-handler target-type="Email" class="EmailHandler"/>