Intercept getter method

[kantorn]

Newbie at AOP

Task: A string stored in a MySQL DB contains newlines, which however isn't diplayed in the webpage by <c:out value="">-tag.

I was thinking on intercepting the getXXX-methods of a POJO in order to inject <br>-tags instead of newlines. For different reasons, I don' want to store HTML in datastore.

How do I do this?
First problem is to get the return value of the getXXX-method, second is where I'm supposed to return it. 'invocation.proceed()' isn't optional, is it?

My code so far:

public class AddHtmlBreakInterceptor implements MethodInterceptor {
	
	public Object invoke(MethodInvocation invocation) throws Throwable{
		String out = (String) invocation.getMethod().invoke(invocation.getThis(), new Object[0]);
		//Do injection of <br> tags
		return invocation.proceed&#40;&#41;;
		// How to return the <br>-injected string???
	&#125; 		
&#125;

Thanks!

[Rod Johnson]

You can use code like this:

String fromDb = (String) invocation.proceed();
String massagedString = doMySubstitution(fromDb);

return massagedString;

You are responsible for calling proceed() in interception around advice; it's up to you if you want to massage the return value.

You can use a Pointcut to target this interceptor to only the appropriate getters.

HTH,
Rod

[kantorn]

Thanks for the quick and clarifying response!!

About Pointcut: is it possible to target multiple getXXX-methods with only one pointcut, or do one need one Pointcut per method?

[kantorn]

I don't seem to be able to 'fire' the advice

Here's a part of my setup

<bean id="breakInjector" class="ks.rah.avik2.web.form.support.AddHtmlBreakInterceptor"/>
	
	<bean id="breakInjectorTarget" class="ks.rah.avik2.domain.Event"/>

	<!-- Interceptor to inject <br>-tags into output -->
	<bean id="breakInjectorPointcut" class="org.springframework.aop.support.RegexpMethodPointcutAdvisor">
		<property name="advice"><ref local="breakInjector"/></property>
		<property name="patterns">
			<list>
				<value>^ks.rah.avik2.domain.Event.getEventDescr.*</value>
				<value>^ks.rah.avik2.domain.Event.getWhyComment.*</value>
				<value>^ks.rah.avik2.domain.Event.getConseqComment.*</value>
				<value>^ks.rah.avik2.domain.Event.getPreventComment.*</value>
				<value>^ks.rah.avik2.domain.Event.getAuxComment.*</value>
				<value>^ks.rah.avik2.domain.support.TextEntry.getText.*</value>
			</list>
		</property>
	</bean>
	
	
	<bean id="breakInjectorProxy" class="org.springframework.aop.framework.ProxyFactoryBean">
		<property name="target"><ref local="breakInjectorTarget"/></property>
		<property name="interceptorNames">
			<list>
				<value>breakInjector</value>
			</list>		
		</property>
	</bean>

The interceptor:

public class AddHtmlBreakInterceptor implements MethodInterceptor {
	
	public static Logger log = Logger.getLogger(AddHtmlBreakInterceptor.class.getName());
	
	public Object invoke(MethodInvocation invocation) throws Throwable{
		log.debug("AddHtmlBreakInterceptor invoked");
		String out =  (String) invocation.proceed();
		log.debug("Instring = " + out);
		String returnthis = replaceWithBrakes( out );
		log.debug("Instring massaged = " + returnthis);
		return  returnthis;
	}
	
	public String replaceWithBrakes(String instr){
		if&#40; instr == null || instr.length&#40;&#41; < 1 &#41;&#123;
			return "";	
		&#125;
		StringBuffer sb = new StringBuffer&#40;instr&#41;;
		int cursor = 0;
		for&#40;int i = 0; i < sb.length&#40;&#41; && cursor != -1;i = cursor&#41;&#123;
			cursor = sb.indexOf&#40;"\n", cursor&#41;;
			sb.insert&#40;cursor, "<br/>"&#41;;
		&#125;
		return sb.toString&#40;&#41;;
	&#125; 			
&#125;

I don't know what I'm doing wrong here...

Thanks!

[kantorn]

I don't know if it's relevant, but the Event object is a POJO persisted to a datastore. I want the advice to fire when I display certain get-methods in the web layer, but perhaps this is not an applicable use of Spring AOP?

Any suggestions?

[Rod Johnson]

About Pointcut: is it possible to target multiple getXXX-methods with only one pointcut, or do one need one Pointcut per method?

A pointcut will typically define a set of methods.

[kantorn]

OK.

Does this look alright?
I cannot get it to fire... no log trace... nothing

<bean id="breakInjector" class="ks.rah.avik2.web.form.support.AddHtmlBreakInterceptor"/>
   
   <bean id="breakInjectorTarget" class="ks.rah.avik2.domain.Event"/>

   <!-- Interceptor to inject <br>-tags into output -->
   <bean id="breakInjectorPointcut" class="org.springframework.aop.support.RegexpMethodPointcutAdvisor">
      <property name="advice"><ref local="breakInjector"/></property>
      <property name="patterns">
         <list>
            <value>^ks.rah.avik2.domain.Event.getEventDescr.*</value>
            <value>^ks.rah.avik2.domain.Event.getWhyComment.*</value>
            <value>^ks.rah.avik2.domain.Event.getConseqComment.*</value>
            <value>^ks.rah.avik2.domain.Event.getPreventComment.*</value>
            <value>^ks.rah.avik2.domain.Event.getAuxComment.*</value>
            <value>^ks.rah.avik2.domain.support.TextEntry.getText.*</value>
         </list>
      </property>
   </bean>
   
   
   <bean id="breakInjectorProxy" class="org.springframework.aop.framework.ProxyFactoryBean">
      <property name="target"><ref local="breakInjectorTarget"/></property>
      <property name="interceptorNames">
         <list>
            <value>breakInjector</value>
         </list>      
      </property>
   </bean>

[kantorn]

This particular problem was successfully solved with the HTML

<PRE></PRE>

tag.