Struts2 Interceptor *after* JSP is rendered - how? - struts2

I was wondering if I can capture the result of an action after the result returns and the JSP is rendered. I want to be able to take the entire result (generated HTML) and push it into memcached so I can bring it via Nginx with-out hitting the application server. Any ideas?
PS: I know I can run the interceptor after the action executes but before the result returns and the JSP is rendered, but not after the JSP is rendered.

I haven't found a way to do this inside of struts2, your best bet it to create a servlet Filter and have it modify the OutputStream.
http://onjava.com/pub/a/onjava/2003/11/19/filters.html

Hey I know its quite late now to answer you might have already found out the answer, however for others to benefit I am posting the answer.
One thing that is very similar to what you are doing is done by sitemesh filter.
Yes, filter comes before and after the Struts2 filter itself, so you can mess with the inputs and outputs easily.
But struts does evaluate JSP/freemarker/velocity and generate the final html which is passed to the user. JSP is a bit trickey because internally a servlet is called but check out org.apache.struts2.views.freemarker.FreemarkerResult class, you can see the actual html getting generated in template.process(model, writer);. This writer is actually ServletActionContext.getResponse().getWriter();
Now to get the html all you need to do is
ServletActionContext.getResponse().getWriter().toString() //This does not work out of box. To get the toString() to work you need to use a ResponseWrapper - which is the same method to get result html in Filters. See- Programming Customized Requests and Responses.
Listing to modify resulting html in struts 2. This is not tested, but it is extracted from my code I have written earlier for custom template engine. I will probably post full description in Custom template engine for struts2
public class DecoratorInterceptor implements Interceptor {
public String intercept(ActionInvocation invocation) throws Exception {
final ActionContext context = invocation.getInvocationContext ();
HttpServletResponse responseParent = (HttpServletResponse)
context.get(ServletActionContext.HTTP_RESPONSE);
CharResponseWrapper wrapper = new CharResponseWrapper(responseParent);
ServletActionContext.setResponse(wrapper);
//Actual Action called
String result = invocation.invoke();
String htmlReturned = wrapper.toString();
//play with htmlReturned ...
String modifiedhtml = pushintoMemCache(htmlReturned );
CharArrayWriter car = new CharArrayWriter();
car.write(modifiedhtml );
PrintWriter out = responseParent.getWriter();
out.write(car.toString());
out.flush();
}
#Override
public void destroy() {
// TODO Auto-generated method stub
}
#Override
public void init() {
// TODO Auto-generated method stub
}
}

Read this article - http://struts.apache.org/2.0.6/docs/interceptors.html
SUMMARY:When you request a resource
that maps to an "action", the
framework invokes the Action object.
But, before the Action is executed,
the invocation can be intercepted by
another object. After the Action
executes, the invocation could be
intercepted again. Unsurprisingly, we
call these objects "Interceptors."

Question: How do you determine if the view has been generated? Do you set a request header or an some sort of a flag to determine if the view has been generated?
You could try throwing a MemCachedException to indicate that it is time to load into a mem cache. Your interceptor code could read
try {
return invocation.invoke();
} catch (MemCachedException mce) {
// Your code to upload to MemCache.
} finally {
// blah blah clean up.
}

Within your interceptor's intercept() method, the ActionInvocation parameter has a getResult() method which returns null before Action execution (i. e. before you call invocation.invoke() in your intercept() method) and contains an implementation of Result afterwards. That object should give you some way to access the data you need, but how this is done probably depends on the class that is actually used.
See also my somewhat related question and the answer I posted after figuring it out.

Related

How spring handle calling the customed method passed in the #PreAuthorize annotation

I am new to spring security, and recently worked on a project that require to do method level security.
I managed to handle it like below:
#Repository
public class EmployeeDaoImpl{
#PreAuthorize("#mySecurityService.canAdd('ROLE_ADMIN') ")
public void addEmployee(EmployeeEntity employee) {
try{
this.sessionFactory.getCurrentSession().save(employee);
}catch(AccessDeniedException e){
}
}
}
#Component
public class MySecurityService {
public boolean canAdd(String user) {
System.out.println("Entered has permission..........");
if(user.equals("ROLE_ADMIN")){
return false;
}
return false;
}
}
so far so good, everthing is working fine and smoothly.
My question here is about performance, how spring behind the scenes handle calling the method in the #PreAuthorize(), do spring do any kind of object/method caching or proxy-ing, or every time call the method by reflection, and how this will affect the performance?
I've did a lot of search and only found this link, it helped me, but do you have any further explaination specific to #PreAuthorize case.
http://spring.io/blog/2007/07/19/debunking-myths-proxies-impact-performance/
Hope my question is clear, Thanks.
First, the expression needs to be parsed, and only then it can be evaluated.
As a result of parsing, the expression is converted into a tree of SpelNodes. In particular, MethodReference is a SpelNode responsible for method calling.
The parsing part is cached well in PreInvocationAuthorizationAdvice.
The details of the implementation of MethodReferencecan be found here:
org.springframework.expression.spel.ast.MethodReference
org.springframework.expression.spel.ast.MethodReference#getValueInternal(...)
org.springframework.expression.spel.support.ReflectiveMethodExecutor
There is caching and the java.lang.reflect.Method reference is evaluated only once (if the target object remains the same type).
So this is pretty the most that could have been done by Spring. Further improvements require byte code generation, which would be an overkill in my opinion.

Return response object in event listener not working when triggered in controller plugin

I implemented a shared event listener that manipulates and returns the response object with an error template showing the message of the triggered error code. (I'm not talking about throwing exceptions and catching them in a dispatch.error listener!)
This works fine when I call this event in a controller action. However, when I trigger my error event in a controller plugin that is called in the onDispatch method of the controller, only the status code is set correctly. But the called action is fully executed and no error page is shown.
I have absolutely no idea why this happens and I hope, someone is able to explain me the dispatch/event triggering/short circuiting/returning response issue here.
Following extracts might give you an impression of my code:
Listener:
class SharedErrorListener implements SharedListenerAggregateInterface {
...
public myErrorFunction(EventInterface $e) {
// get error code
// set status code to injected response object
// add error template to injected view model
// return response
}
}
Random controller action (works fine):
return $this->getEventManager()->trigger('error', $this, array(
'errorCode' => my_error_code
));
onDispatch() of controller:
// call plugin, if return value given return it (response must be returned?!).
$r= $this->plugin('myplugin')->doIt();
if (isset($r)) {
return $r;
}
class myplugin doIt() where error is triggered, but error template not showing up:
return $this->getController()->getEventManager()->trigger('error', $this, array(
'errorCode' => my_error_code
));
As the code in the controller and the controller plugin ist pretty much the same, I think it must depend on some application state. I did a lot of research, but couldn't find, what the problem might be. But as the event is triggered correctly and also the right status code is set to the response, I am just very confused. I don't want to implement an ErrorController (which would allow to call a redirect), because I think the solution via EventManager is actually very nice.
I'm too busy to actually read all the above, but from what my impression is, this code-snipped may actually help you out:
$trigger = $this->getEventManager()->trigger(self::EVENT_IDENTITY_GET, $identity);
if ($trigger instanceof ResponseCollection && !is_null($trigger->last())) {
return $trigger->last();
}
I finally found the problem here. By returning the response during the onDispatch process, the onDispatch() of the AbstractActionController wasn't called. In that function the return value of the controller action, e.g. the view model, is set as "result" of the MvcEvent. I just had to set the template that was set in the listener as the result for the event:
$r = $this->plugin('my_plugin')->doIt();
if ($r instanceof ResponseCollection) {
$e->setResult($this->getServiceLocator()->get('view_manager')->getViewModel()->getChildren());
return $r;
}
Hope this helps someone.

How to clear SessionMap() in JSF without getting null in reference to this map

I use tomcat 7.0 and JSF 2.1 and I have problem when I call in my .xhtml page something like that: #{homePage.get("userName")}
I get javax.el.ELException: Caused by: java.lang.NullPointerException
at mainPacket.HomePageBean.get(HomePageBean.java:35)
I have ManagedBean like below:
#ManagedBean(name = "homePage")
#ViewScoped
public class HomePageBean {
private Map<String, Object> map;
public HomePageBean() {
map= FacesContext.getCurrentInstance().getExternalContext().getSessionMap();
//remove unnecessary values from sessionMap
FacesContext.getCurrentInstance().getExternalContext().getSessionMap().clear();
}
public String get(Object s){
return map.get(s).toString();
}
}
When I don't use clear, everything works ok. But I want to clear sessionMap. How to resolve it ?
Thanks
Java is an object oriented language. It doesn't give you a copy of the object everytime you request it. No, it gives you a reference to the object instance in memory. At the moment you invoke Map#clear() on the session map, then the map reference which you obtained just beforehand is basically also emptied, because it points to exactly the same map instance which you just emptied!
Your concrete functional requirement is nowhere mentioned in the question and the whole design in the code posted so far makes honestly no utter sense (I can't imagine any sensible real world use case for this), so it's hard to propose you the right solution. Best what you can get is the advice to add a nullcheck.
public String get(Object s){
Object value = map.get(s);
return (value != null) ? value.toString() : null;
}
You should by the way be very careful with abruptly emptying the session map this way. JSF stores view scoped and session scoped managed beans in there and it's also used by the flash scope.

Is there any way in Struts 2 by which I can get all namespaces in my app?

Is there any way in Struts2 by which I can get list of namespaces in my App ?
I want this as set or list at runtime .
I am using Struts2 RestActionMapper plugin.
When there invalid namespace is specified for valid action, Struts is throwing namespace error.
But I could not redirected to standard error page when this error occurs. I tried almost all options e.g.global error mapping default namespace etc . Nothing worked. So thought it would be great if I could get list of namespaces in my app, thus i could have checked invalid namespace against my list of valid namespaces and accordingly I could have thrown generic error which would finally result in my standard error page.
I am looking for how to get list of all namespaces in my project.
So basically I want to do something like this.
validNamespaces = getNamespaces();
if(validNamespaces.contains(namespaceRetrivedFromRestPlugin))
{Sysout("This is valid namespace.")}
else
{Sysout("Invalid namespace");}
This is possible, though like Steven has pretty much stated, I'm not convinced that this is the right approach to the problem you state of redirecting to an error page. But, I'll leave that part up to you and use this space to answer the namespace question.
This code will have to be in a Struts2-created object for the injection to work.
private Configuration configuration;
#Inject
public void setConfiguration(Configuration config) {
this.configuration = config;
}
protected Set<String> getNamespaces() {
Set<String> namespaces = Collections.emptySet();
Map<String, Map<String, ActionConfig>> allActionConfigs = this.configuration.getRuntimeConfiguration().getActionConfigs();
if (allActionConfigs != null) {
namespaces = allActionConfigs.keySet();
}
return namespaces;
}
The configuration can also be obtained from a ConfigurationManager. Also, you would obviously want to store these in a variable rather than calling above method over and over. If your object is, say, an interceptor, then you could call this method from the init() method and store it in a class-level variable.

Streaming text output for long-running action?

I have a few utility actions that return text output via return Content("my text","text/plain").
Sometimes these methods take a few minutes to run (i.e. log parsing, database maintenance).
I would like to modify my action method so that instead of returning all of the output at once, the text is instead streamed to the client when it is ready.
Here's a contrived example:
public ActionResult SlowText()
{
var sb = new System.Text.StringBuilder();
sb.AppendLine("This happens quickly...");
sb.AppendLine("Starting a slow 10 second process...");
System.Threading.Thread.Sleep(10000);
sb.AppendLine("All done with 10 second process!");
return Content(sb.ToString(), "text/plain");
}
As written, this action will return three lines of text after 10 seconds. What I want is a way to keep the response stream open, and return the first two lines immediately, and then the third line after 10 seconds.
I remember doing this 10+ years ago in Classic ASP 3.0 using the Response object. Is there an official, MVC-friendly way to accomplish this?
--
Update: using Razor .cshtml in the app; but not using any views (just ContentResult) for these actions.
Writing directly to the Response object should work, but only in some simple cases. Many MVC features depend on output writer substitution (e.g. partial views, Razor view engine, and others) and if you write directly to the Response your result will be out of order.
However, if you don't use a view and instead write straight in the controller then you should be fine (assuming your action is not being called as a child action).
I would skip the MVC controller entirely since you are going to break encapsulation anyway. In it's place I'd use a barenaked IHttpHandler implementation, streaming directly to the aforementioned output stream.
You are exposing yourself to a browser timeout if the process takes longer than originally intended. Then you don't have a way to recover what happened / unless you implement a separate method that gives the information on the long running process.
Given that you want the other method anyway, you can start a long running process and return immediately. Have the browser check the other method that gives the latest information on the long running process. On the last time I had to do this, I kept it simple and just set the refresh header from the controller before returning the view.
As for starting a long running process, you can do something like this:
// in the controller class
delegate void MyLongProcess();
//...
// in the method that starts the action
MyLongProcess processTask = new MyLongProcess(_someInstance.TheLongRunningImplementation);
processTask.BeginInvoke(new AsyncCallback(EndMyLongProcess), processTask);
//...
public void EndMyLongProcess(IAsyncResult result)
{
try{
MyLongProcess processTask = (MyLongProcess)result.AsyncState;
processTask.EndInvoke(result);
// anything you needed at the end of the process
} catch(Exception ex) {
// an error happened, make sure to log this
// as it won't hit the global.asax error handler
}
}
As for where do you put the log of the actions that happened, it's up to you to how long lived you want it to be. It can be as simple as a static field/class where you add the info of the ongoing process, or instead saving it to a data store where it can survive an application recycle.
The above assume this is all about a long running process that goes on reporting the actions that has been done. Streaming is a different subject, but the above might still play a role in keeping the operations in your controller & only the piece responsible of streaming what becomes available to the client in the action result.
You can implement your custom ActionResult like ContentStreamingResult and use HttpContext, HttpRequest and HttpResponse in the ExecuteResult method.
public class ContentStreamingResult : ActionResult
{
private readonly TextReader _reader;
public ContentStreamingResult(TextReader reader)
{
_reader = reader;
}
public override void ExecuteResult(ControllerContext context)
{
var httpContext = context.HttpContext;
//Read text from the reader and write to the response
}
}
public class YourController : Controller
{
public ContentStreamingResult DownloadText()
{
string text = "text text text";
return new ContentStreamingResult(new System.IO.StringReader(text));
}
}
Try Response.Flush and BufferOutput to false. Note it would work with the different action results, you have to directly write into the response object. Probably you can use it with conjunction with AsyncController.

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