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Here I'd like to give some design option and my thinkings of this project. Thank you for your comment.
Wiki Markup Since valves have different levels, such as server level, engine level, host level, context level. And there are several places for the configuration: server.xml, web.xml. For server level, both server.xml and web.xml is suitable, since both of them are some kind of global. For engine and host level, I think server.xml is much more suitable. And we could also use "$CATALINA_BASE/conf/\[enginename\]/engine-filters.default" for engine level filters, "$CATALINA_BASE/conf/\[enginename\]/\[hostname\]/host-filters.default" for host level filters and "$CATALINA_BASE/conf/\[enginename\]/\[hostname\]/context.xml.default" for context levelfilters. This is the options for configuration file location that I could think about. In my opinion, we could put all these configuration in server.xml for simplicity, but keep an eye on those "$CATALINA_BASE/conf/\[enginename\]/\[hostname\]/" path just like tomcat deal with context.xml.default now. \\
markt - Are Valves going to be removed completely?
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xxd - I know the order of context level and wrapper level filters is already defined in the servlet spec. What I mean is the filters of engine and host level.
markt - Order should be:
(1) Global filters (2) Engine filters (3) Host filters (4) Context filters Where a filter is defined at multiple levels, merge the configurations using the Servlet 3.0 rules with the *lowest* level taking precedence (ie context > host > engine > global).
3. I will modify the digestor code in order to load the configuration about filters in, ContextRuleSet.java, EngineRuleSet.java, HostRuleSet.java in particular. And those filters information will be store in an order map (I'd like to choose treeMap now) – TreeMap<FilterMetaInfo, Filter>. The FilterMetaInfo class is generally like this:
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xxd - I think all the filters need to be formed as a chain, and will be invoked when the request comes in. Those engine and host level is just ordinary filters after they are added into the filter chain. But before it, they have some global attributes compared with context level filters. So, could we just add those engine and host level filters into the filter chain when the filter chain is created? But for sake of performance, I think we could cache those high level filters since they are global to some degree.
For the discussing of configuration location of those converted filters, please refer to http://wiki.apache.org/tomcat/SummerOfCode2009/LoadingFilterConfiguration.
4. Do I need to remove all the pipeline facility or can I try to remove as much logic as possible from StandardEngineValve StandardHostValve/StandardHostValve? I found that those valve just delegate to the lower level pipeline(valves), and the lowest StandardWrapperValve will actually finish the job (filterChain and/or the servlet invocation).
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- Right now I don't know. I'd like to remove all the valve code if possible. It depends how much access to Tomcat internals the filters end up needing. This question probably needs to be deferred until we have some working filters to make judgements based on.
xxd - All these jobs should be finished somewhere, if we do not use valves. Can I just override the invoke() method of Container interface for StandardEngine StandardHost/StandardContext/StandardWrapper, and high level container will call the invoke() method of the container which have a lower level than itself, for example, in invoke() method of StandardEngine, the invoke() method of StandardHost will be called. And I will move all the valve invoke() logic into the corresponding invoke() method of its container.
By the way, I'd like to added all the filters configurated in the server.xml file into the filterChain when the filterChain is created(in ApplicationFilterFactory.java line 143 or so, after "StandardContext context = (StandardContext) wrapper.getParent();") in the order of be configed in server.xml or some other configuration location. The general algorithm is like this: first, get to engine and host level through context (through getParent()); then add host and engine level filters into filter chain in the order of Engine -> Host -> Context. Is that a proper place for me to add those logic? What's the opinion of yours?
markt - The long term aim is to remove Valves entirely
5. Valve interface has a event() method which is used to process a comet event. Filters need not to worry about whether it is a comet event or not. So how can we reflect this part in our new filter-based structure?
markt - implements CometFilter interface to support comet based request.
6. Do we really need to move the logic in StandardEngine StandardHost/StandardContextValve into some filters? Since the logic of these classes is purely servlet-engine concerned, I do not think those logic could be reused by filters. Any comments?
markt - Whilst removal is the aim, it may well end up making sense to keep some internal Valves.
7. My solution now to load configuration in $CATALINA_BASE/conf/server.xml is to add a CallMapParamRule.class to collect the attribute-value pairs into a map, and this map is the initiation parameter of a filter. A method with signature – "addFilterWithConfig(Class<? extends Filter> filterClass, Map<String, String> paramMap)" will be added in StandardEngine/Host/Context to add new filters into it. The main content of CallMapParamRule is as blow:
| Wiki Markup |
|---|
public void begin(String namespace, String name, Attributes attributes)
throws Exception \{
for (int i = 0, count = attributes.getLength(); i < count; i++) \{
// here we do not deal with the className attribute, since it
// is used as the class name that will be initiated.
if("className".equalsIgnoreCase(attributes.getLocalName(i))) \{
continue;
\}
paramMap.put(attributes.getLocalName(i), attributes.getValue(i));
\}
digester.getLogger().debug(paramMap);
Object parameters\[\] = (Object\[\]) digester.peekParams();
parameters\[paramIndex\] = paramMap;
\} |
In order to add those newly added filters into the FilterChain, the ApplicationFilterFactory class also need to be altered.
Any comments about this solution? Or are there a better one?
8. I've posted the patch file of the source code for loading configuration of filters from server.xml and hacking those loaded filters into filter chain as attachment of this wiki page. Any comments are welcomed. And the source code could reduce duplicating code by altering the Container interface. But I do not know the influence of this action. So I added the corresponding code into StandardEngine, StandardHost and StandardContext respectively.
9. I've made a seperate wiki page for the configuration location of those newly added filters. Here is the link: http://wiki.apache.org/tomcat/SummerOfCode2009/LoadingFilterConfiguration
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