ExprProps is a subclass of Properties that
* is "smart" in the sense that it wraps a Calculator
* object, passing get and getProperty keys to
* the Calculator for processing.
*
* Keys are first searched for in the Properties
* object. If not found, the key is passed to the getValue
* method of the wrapped Calculator object. The
* Calculator will return null if the key
* consists of only a name or Brazil token and that name/token evaluates
* to 0. In this case, a value associated with the key can not be
* "found" and the get or getpropertymethod returns
* null also.
*
* Only property names that "look" like expressions (e.g. contain
* at least one of characters in [&|*+/%=!<>-]) are passed to the calculator.
*
* @author Steve Drach <drach@sun.com>
* @version 2.3, 04/05/24
*
* @see java.util.Properties
* @see sunlabs.brazil.util.Calculator
* @see ExprPropsHandler
*/
public class ExprProps extends Properties {
private Calculator c;
private Request request;
// only keys that have at least one of these are considered
private static Regexp exp = new Regexp("[&|+*/%=!<>-]");
/**
* This constructor creates a Calculator instance with
* this instance of ExprProps as it's symbol table.
*/
public ExprProps() {
super();
c = new Calculator(this);
}
/**
*
* This constructor creates a Calculator instance with
* this instance of ExprProps as it's symbol table and
* with the Properties instance referenced by the
* parameter defaults as it's set of default values.
*
* @param defaults the defaults
*/
public ExprProps(Properties defaults) {
super(defaults);
c = new Calculator(this);
}
/**
* This constructor creates a Calculator instance with
* request.props as it's symbol table.
*
* @param request the Request instance
*/
public ExprProps(Request request) {
super();
/*
* Note that request.props may have it's value changed, by BSLTemplate
* for example, after Calculator is initialized. Save request so
* a new request.props can be passed to each call to
* Calculator.getValue().
*/
this.request = request;
c = new Calculator(request.props);
}
/**
* This constructor creates a Calculator instance with
* request.props as it's symbol table and with the
* Properties instance referenced by the parameter
* defaults as it's set of default values.
*
* @param request the Request instance
* @param defaults the defaults
*/
public ExprProps(Request request, Properties defaults) {
super(defaults);
this.request = request;
c = new Calculator(request.props);
}
/**
*
* Returns the value to which the specified key is mapped in this
* Hashtable. If the key is not found, then it's value
* is computed by treating the key as an arithmetic expression or
* statement.
*
* If, during the computation, an ArithmeticException is
* thrown, the key compute.error is set in the base
* Properties. The value associated with the key is
* an error message.
*
* @param key the Hashtable key
*
* @return the value in this table with the
* specified key or null
*/
public Object get(Object key) {
Object val = super.get(key);
if (val == null && key instanceof String &&
null != exp.match((String) key)) {
try {
remove("compute.error");
if (request != null) {
// request.props may have changed (see BSLTemplate)
val = c.getValue((String)key, request.props);
} else {
val = c.getValue((String)key);
}
} catch (ArithmeticException e) {
put("compute.error", e.getMessage());
val = null; // should be "" perhaps but that breaks things
}
}
return val;
}
private boolean calculating; // prevent infinite recursion
/**
*
* Searches for the property with the specified key in this property list.
* If the key is not found in this property list, then it's value is
* computed by treating the key as an arithmetic expression or statement.
*
* If, during the computation, an ArithmeticException is
* thrown, the key compute.error is set in the base
* Properties. The value associated with the key is
* an error message.
*
* If the result of the computation is null, the default
* property list, and its defaults, recursively, are then checked. The
* method returns null if the property is not found.
*
* @param key the property key
*
* @return the value in this property list with the
* specified key or null
*
* @see java.util.Properties#defaults
*/
public String getProperty(String key) {
String val = super.getProperty(key);
if (val == null && !calculating && null != exp.match(key)) {
try {
remove("compute.error");
calculating = true;
/*
* It's critical that keys that contain only a name
* return a value of null rather than 0 so they can
* be found in Property instances further down the
* list.
*/
if (request != null) {
// request.props may have changed (see BSLTemplate)
val = c.getValue(key, request.props);
} else {
val = c.getValue(key);
}
if (val != null) {
// System.err.println("Calculator: " + key + " -> " + val);
}
} catch (ArithmeticException e) {
put("compute.error", e.getMessage());
val = null; // should be "" perhaps but that breaks things
} finally {
calculating = false;
}
}
return ((val == null) && (defaults != null)) ? defaults.getProperty(key) : val;
}
}