You can use
AspectJ to do many things, but its potential arise when you use it in order to apply the
SoC paradigm.
In this post I will show you how to use it to perform custom validation in the presentation layer of a
JSF webapp. Later I will show how to use spring to define more generic pointcuts in your application.
Note: I'll asume you already have basic knowledge of AOP in general and AspectJ in particular. I will not get into syntax and terminology details here. You can consult
AspectJ site for documentation and resources. You can also find some terms definitions used here in
Captain Debug's Blog.
It is very straightforward to configure AspectJ when you are using
maven in your project. All you have to do is to add the
aspectj-maven-plugin in the
build section of your pom.xml:
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>aspectj-maven-plugin</artifactId>
<version>1.2</version>
<executions>
<execution>
<goals>
<goal>compile</goal>
<goal>test-compile</goal>
</goals>
</execution>
</executions>
<dependencies>
<dependency>
<groupId>org.aspectj</groupId>
<artifactId>aspectjrt</artifactId>
<version>1.6.1</version>
</dependency>
<dependency>
<groupId>org.aspectj</groupId>
<artifactId>aspectjtools</artifactId>
<version>1.6.1</version>
</dependency>
</dependencies>
</plugin>
You have to add the
aspectjrt and
aspectjtools dependencies to the plugin in order to let maven find the necessary to compile the AspectJ source.
Then you can code the validation AspectJ advice
BackingBeanValidatorAdvice.aj as a normal source file:
import javax.faces.application.FacesMessage;
import javax.faces.context.FacesContext;
...
public aspect BackingBeanValidatorAdvice {
pointcut doSaveChanges() : execution(* com.foo.beans.BackingBean.saveChanges(..));
void around() : doSaveChanges() {
FacesContext context = FacesContext.getCurrentInstance();
BBean bbean = context.getApplication().evaluateExpressionGet(context, "#{bBean.selected}", BBean.class);
// perform custom validation
// if validation fails
if (..) {
String sum = "...";
String det = "...";
context.addMessage("error", new FacesMessage(FacesMessage.SEVERITY_ERROR, sum, det);
return;
}
proceed();
}
}
Doing this, when your backing bean's
saveChanges(..) method is invoked, the pointcut is reached and the advice performing the custom validation is executed. Then, back to the jsf page, you can show the error's custom message as usual using <h:messages ... />
As you can see, you can apply this mechanism also to perform logging, database audits, notifications, etc. That's precisely the potential of AspectJ used in conjunction with SoC design principle.
Automatic pointcut configuracion using Spring
In this article, you had to add the pointcut manually in your advice's source. If you are using
springframework, you can configure the pointcuts in the application-context.xml. Here is an example of using AOP in spring to implement a database logging concern without modifying a single line of code in your existing application. In your application-context.xml file add the following:
...
<bean id="databaseAuditAutoProxy" class="org.springframework.aop.framework.autoproxy.BeanNameAutoProxyCreator">
<property name="beanNames">
<list>
<value>*Dao</value>
</list>
</property>
<property name="interceptorNames">
<list>
<value>regexpAdvisor</value>
</list>
</property>
</bean>
<bean id="regexpAdvisor" class="org.springframework.aop.support.DefaultPointcutAdvisor">
<property name="advice">
<ref local="databaseLoggerAuditAdvisor"/>
</property>
<property name="pointcut">
<bean class="org.springframework.aop.support.JdkRegexpMethodPointcut">
<property name="patterns">
<value>.*read.*,.*load.*,.*get.*,.*save.*,.*Username.*</value>
</property>
<property name="excludedPatterns">
<value>.*find.*,.*History.*</value>
</property>
</bean>
</property>
</bean>
<bean id="databaseLoggerAuditAdvisor" class="com.foo.aspects.DatabaseLoggerAuditAdvice">
<property name="auditService" ref="auditService"/>
</bean>
...
The
databaseAuditAutoProxy automatically create proxies for the beans names that match
beanNames attribute. The
regexpAdvisor references the advisor implementation itself and defines a
pointcut that uses regular expressions to define method names to intercept.
Then you have to code the
DatabaseLoggerAuditAdvice.aj class:
public class DatabaseLoggerAuditAdvice implements MethodBeforeAdvice, AfterReturningAdvice, ThrowsAdvice {
private AuditService auditService;
public LoggerAuditAdvice() {
}
/**
* @see org.springframework.aop.MethodBeforeAdvice#before(java.lang.reflect.Method,
* java.lang.Object[], java.lang.Object)
*/
public void before(Method method, Object[] args, Object target) throws Throwable {
log = LogFactory.getLog(target.getClass());
if (log.isInfoEnabled()) {
Audit audit = new Audit();
audit.setUsername(SecurityHelper.getUserName());
audit.setTime(new Date());
audit.setMethodName(method.getName());
audit.setMethodArgumentsValue(ArrayUtils.toString(args, "null"));
log.info(" [[[BEFORE]]] " + audit);
}
}
/**
* @see org.springframework.aop.AfterReturningAdvice#afterReturning(java.lang.Object,
* java.lang.reflect.Method, java.lang.Object[], java.lang.Object)
*/
public void afterReturning(Object returnValue, Method method, Object[] args, Object target) throws Throwable {
log = LogFactory.getLog(target.getClass());
if (log.isInfoEnabled()) {
Audit audit = new Audit();
audit.setUsername(SecurityHelper.getUserName());
audit.setTime(new Date());
audit.setMethodName(method.getName());
audit.setMethodArgumentsValue(ArrayUtils.toString(args, "null"));
audit.setTarget(target.getClass().getSimpleName());
log.info(" [[[AFTER]]] " + audit);
this.getAuditService().save(audit);
}
}
public void afterThrowing(Method m, Object[] args, Object target, Throwable ex) {
log = LogFactory.getLog(target.getClass());
log.error("Exception in method: " + m.getName() + " Exception is: " + ex.getMessage() + " for user "
+ SecurityHelper.getUserName());
}
public AuditService getAuditService() {
return auditService;
}
public void setAuditService(AuditService auditServiceToSet) {
this.auditService = auditServiceToSet;
}
}
Hope it helps, comment and give feedback.
PS: If you get errors in your project, you have to make sure you have added *.aj as source files, and to make the project as a "AspectJ Project", ie, add the AspectJ runtime. The method may vary depending on the IDE you are using. In
Eclipse, you have to configure the project as an AspectJ Project (right click on the project, Configure > Convert to AspectJ Project..) and add *.aj fileset mapping to the source code in the Java Build Path of your project.
