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java.lang.Object org.mortbay.servlet.ThrottlingFilter
This filter protects a web application from having to handle an unmanageable load.
For servers where there is 1 application with standardized resource restrictions, then this affect can be easily
controlled by limiting the size of the server thread pool
, however
where there are multiple applications, or a single application has different resource requirements for different
URLs, then this filter can assist in managing the number of requests being services at any point in time.
The filter has 3 configurable values, which may be set as init parameters:
maximum
determines the maxmimum number of requests that may be on the filter chain at any point in time.
(See below for a more detailed explanation)block
determines how long (in milliseconds) a request will be queued before it is rejected.
Set this to -1 to block indefinately.queue
determines how many requests can be queued simultaneously - any additional requests will be rejected.
Set this to 0 to turn off queueing.<filter><filter-name>throttle1</filter-name> <filter-class>org.adjective.spiral.filter.ThrottlingFilter</filter-class> <filter><filter-name>throttle2</filter-name> <filter-class>org.adjective.spiral.filter.ThrottlingFilter</filter-class>creates 2 separate filters with individual request counts.
Queueing: When the number of active requests exceed the maximum
requests will be queued. This queue regulates
the flow of connections. Once the number of requests on the queue reached the queue
threshold, then any new requests
will be rejected. Requests are queued for a maximum of block
milliseconds - is no capacity is made available in this
time then the request will be rejected. The oldest pending request is removed from the queue and processed as soon as the number
of pending requests falls below the maximum
value (i.e. when a request is completed)
Rejection: Requests are rejected when the number of requests in progress has reached maximum and either the queue
is full; or a request has been queued for more than block
milliseconds. The rejection is performed by calling the
method rejectRequest(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse)
. By default this method sends the HTTP status code 503
,
but this may be over-ridden in derived classes.
This filter works best with the SelectChannelConnector
, as RetryRequest
based
Continuation
s can be used to free the thread and other resources associated with the queued requests.
Constructor Summary | |
ThrottlingFilter()
|
Method Summary | |
void |
destroy()
Called by the web container to indicate to a filter that it is being taken out of service. |
void |
doFilter(HttpServletRequest request,
HttpServletResponse response,
FilterChain chain)
|
void |
doFilter(ServletRequest request,
ServletResponse response,
FilterChain chain)
The doFilter method of the Filter is called by the container
each time a request/response pair is passed through the chain due
to a client request for a resource at the end of the chain. |
void |
init(FilterConfig filterConfig)
Called by the web container to indicate to a filter that it is being placed into service. |
protected void |
rejectRequest(HttpServletRequest request,
HttpServletResponse response)
|
Methods inherited from class java.lang.Object |
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Constructor Detail |
public ThrottlingFilter()
Method Detail |
public void init(FilterConfig filterConfig) throws ServletException
Filter
init
in interface Filter
ServletException
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException
Filter
doFilter
method of the Filter is called by the container
each time a request/response pair is passed through the chain due
to a client request for a resource at the end of the chain. The FilterChain passed in to this
method allows the Filter to pass on the request and response to the next entity in the
chain.
A typical implementation of this method would follow the following pattern:-
1. Examine the request
2. Optionally wrap the request object with a custom implementation to
filter content or headers for input filtering
3. Optionally wrap the response object with a custom implementation to
filter content or headers for output filtering
4. a) Either invoke the next entity in the chain using the FilterChain object (chain.doFilter()
),
4. b) or not pass on the request/response pair to the next entity in the filter chain to block the request processing
5. Directly set headers on the response after invocation of the next entity in the filter chain.
doFilter
in interface Filter
IOException
ServletException
public void doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain chain) throws IOException, ServletException
IOException
ServletException
protected void rejectRequest(HttpServletRequest request, HttpServletResponse response) throws IOException
IOException
public void destroy()
Filter
destroy
in interface Filter
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