eclipse birt qr code JAVA ASPECT COMPONENTS in Font

Creator ECC200 in Font JAVA ASPECT COMPONENTS

This aspect-configuration file calls the setAttributesOrder method and then calls the display method. The first call takes the value Customer for the classname parameter, and it takes the values lastName, firstName, phone, and email for the attributeNames array. No parameters are defined for the call to the display method.

Grouping parameters introduces some so-called syntactic sugar into aspect-configuration files. The syntax for grouping parameters is as follows: group <value> { <method> [ <parameter> ... ] ; ... } When a group is used, the given value is added as the first parameter for every call that is specified between the curly brackets. Grouping parameters can be used to avoid redundancies especially in cases that use the same value for several successive calls. The following configuration file, named presentation2.acc, is equivalent to presentation.acc: group Customer { setAttributesOrder { lastName, firstName, phone, email }; setCategory { lastName, firstName } main; } display ; Strictly speaking, group is not a keyword; it is an identifier that you can freely choose. Any identifier that is not a method name and that is defined in the aspect can be chosen for defining a group. Definitions that use the grouping mechanism can be nested. For example, the aspectconfiguration file group Customer { attribute lastName { setCategory General ; } } is equivalent to setCategory Customer lastName General ; Definitions that use the grouping mechanism can be factored. For example, the aspectconfiguration file group Customer,Employee { setAttributesOrder { lastName, firstName, phone, email }; } is equivalent to

setAttributesOrder Customer { lastName, firstName, phone, email }; setAttributesOrder Employee { lastName, firstName, phone, email

A JAC application-descriptor file is a text file that provides information about launching the application. It defines a set of property names and values that is loaded by JAC when the end user starts the application. The extension .jac is commonly used for application-descriptor files. Each line in an application-descriptor file starts with the name of a property followed by a colon and ends with the property value. The backslash character (\) can be used to continue the definition of the value to next line. For example, the application-descriptor file applicationName: Order management launchingClass: \ aop.jac.Customer defines the values "Order management" and "aop.jac.Customer" for the applicationName and launchingClass properties, respectively. Lines starting with the pound-sign character (#) are interpreted as comments. Table 4-1 presents the list of properties that can be used in an application-descriptor file.

The application name The main class name A series of three values for defining the aspect identifiers, the aspect-configuration files, and the Boolean values that specify whether the aspects are initially woven A series of two values for defining the aspect identifiers and the classes that implement those aspects The weaving order when several wrappers apply to the same joinpoint For distributed applications, the names of the hosts where the application is deployed

You can extend the structure of an application by using the introduction feature to add new code elements. JAC can introduce, or add, two categories of these elements: role methods and exception handlers.

You introduce a role method to define new behaviors. A role method is defined in a wrapper class. You can choose the name, signature, and return type of the method. However, the first parameter must be org.objectweb.jac.core.Wrappee. This parameter corresponds to the application object where the method will be introduced. The wrapper shown in Listing 4-9 illustrates the definition of a role method. Listing 4-9. The Definition of a Role Method package aop.jac; import import import import import org.aopalliance.intercept.ConstructorInvocation; org.aopalliance.intercept.MethodInvocation; org.objectweb.jac.core.AspectComponent; org.objectweb.jac.core.Wrappee; org.objectweb.jac.core.Wrapper;

public class TraceWrapper4 extends Wrapper { public TraceWrapper4(AspectComponent ac) { super(ac); } public void computeAmountAndPrint( Wrappee o, String header ) { double amount = ((Order)o).computeAmount(); System.out.println(header+amount); } public Object construct(ConstructorInvocation ci) throws Throwable { return proceed(ci); } public Object invoke(MethodInvocation mi) throws Throwable { return proceed(mi); } } The computeAmountAndPrint method can be introduced in the Order class to compute and print the amount of an order. The first parameter, o, is the instance of the Order class where the role method is invoked. The second parameter, header, is a string that is printed before the amount. A role method can be called by the invokeRoleMethod method, which is defined in the org.objectweb.jac.core.Wrappee class. This method takes three parameters: the instance that receives the call, the name of the role method, and the array of objects to pass as parameters to the method. For example, the code block Wrapping.invokeRoleMethod( (Wrappee)o, "computeAmountAndPrint", new Object[]{">> "});