Class ExprPropsHandler

java.lang.Object
sunlabs.brazil.properties.ExprPropsHandler
All Implemented Interfaces:
Handler
public class ExprPropsHandler extends Object implements Handler
The ExprPropsHandler installs an expression evaluator as a "smart properties" into the current request object, enabling arithmetic and logical expression evaluation in property name lookups.

The following configuration parameters are used:

prefix, suffix, glob, match
Only URL's that match are allowed. (See MatchString).

Using the expression evaluator can be a bit tricky, as the evaluator works by interpreting a property name as an expression, and using its the expression result as its value. For example, the construct: 

"${x + 4 == 3}"
will evaluate to either "1" or "0", depending upon the value of "x". For use with the <if> constuct of the BSLTemplate, the following construct: 
<if name="${x + 4 == 3}"> ... [if expression] ... </if>
Will take (or not take) the "if expression" if there is a property named "1" that is set (to anything but 0 or false), but a property named "0" is not set. An entry in a server configuration file: 
1=true
will do the trick.

alternately, the construct: 

<if name=true value="${x + 4 == 3}"> ... [if expression] ... </if>
Will work as expected only if there is a configuration property: 
true=1
The choice of the name "true" is arbitrary, it could be any valiable whose value is "1".
Version:
2.5, 06/11/13
Author:
Steve Drach <drach@sun.com>
See Also:

  • Constructor Details

    • ExprPropsHandler

      public ExprPropsHandler()

  • Method Details

    • init

      public boolean init(Server server, String prefix)
      Description copied from interface: Handler
      Initializes the handler.
      Specified by:
      init in interface Handler
      Parameters:
      server - The HTTP server that created this Handler. Typical Handlers will use Server.props to obtain run-time configuration information.
      prefix - The handlers name. The string this Handler may prepend to all of the keys that it uses to extract configuration information from Server.props. This is set (by the Server and ChainHandler) to help avoid configuration parameter namespace collisions.
      Returns:
      true if this Handler initialized successfully, false otherwise. If false is returned, this Handler should not be used.

    • respond

      public boolean respond(Request request) throws IOException
      Creates an instance of ExprProps that uses request.props for the wrapped Calculator's symbol table.
      Specified by:
      respond in interface Handler
      Parameters:
      request - The Request object that represents the HTTP request.
      Returns:
      false
      Throws:
      IOException - if there was an I/O error while sending the response to the client. Typically, in that case, the Server will (try to) send an error message to the client and then close the client's connection.

      The IOException should not be used to silently ignore problems such as being unable to access some server-side resource (for example getting a FileNotFoundException due to not being able to open a file). In that case, the Handler's duty is to turn that IOException into a HTTP response indicating, in this case, that a file could not be found.

      See Also: