sunlabs.brazil.properties
Class ExprPropsHandler

java.lang.Object
  sunlabs.brazil.properties.ExprPropsHandler (view source)

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".

See Also:

ExprProps, Request

Constructor Summary

ExprPropsHandler()

Method Summary

boolean	init(Server server, String prefix) Initializes the handler.
boolean	respond(Request request) Creates an instance of ExprProps that uses request.props for the wrapped Calculator's symbol table.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

ExprPropsHandler

public ExprPropsHandler()

Method Detail

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:

Calculator