Class Filter


public abstract class Filter extends Object
A filter used to pre- and post-process incoming requests. Pre-processing occurs before the application's exchange handler is invoked, and post-processing occurs after the exchange handler returns. Filters are organised in chains, and are associated with HttpContext instances.

Each Filter in the chain, invokes the next filter within its own doFilter(HttpExchange, Chain) implementation. The final Filter in the chain invokes the applications exchange handler.

  • Constructor Details

    • Filter

      protected Filter()
      Constructor for subclasses to call.
  • Method Details

    • doFilter

      public abstract void doFilter(HttpExchange exchange, Filter.Chain chain) throws IOException
      Asks this filter to pre/post-process the given exchange. The filter can:
      • Examine or modify the request headers.
      • Filter the request body or the response body, by creating suitable filter streams and calling HttpExchange.setStreams(InputStream, OutputStream).
      • Set attribute objects in the exchange, which other filters or the exchange handler can access.
      • Decide to either:
        1. Invoke the next filter in the chain, by calling Filter.Chain.doFilter(HttpExchange).
        2. Terminate the chain of invocation, by not calling Filter.Chain.doFilter(HttpExchange).
      • If option 1. above is taken, then when doFilter() returns all subsequent filters in the Chain have been called, and the response headers can be examined or modified.
      • If option 2. above is taken, then this Filter must use the HttpExchange to send back an appropriate response.
      exchange - the HttpExchange to be filtered
      chain - the Chain which allows the next filter to be invoked
      IOException - may be thrown by any filter module, and if caught, must be rethrown again
      NullPointerException - if either exchange or chain are null
    • description

      public abstract String description()
      Returns a short description of this Filter.
      a String describing the Filter