org.apache.velocity.runtime.directive
Class VMProxyArg

java.lang.Object
  org.apache.velocity.runtime.directive.VMProxyArg

public class VMProxyArg
extends Object

The function of this class is to proxy for the calling parameter to the VM. This class is designed to be used in conjunction with the VMContext class which knows how to get and set values via it, rather than a simple get() or put() from a hashtable-like object. There is probably a lot of undocumented subtlty here, so step lightly. We rely on the observation that an instance of this object has a constant state throughout its lifetime as it's bound to the use-instance of a VM. In other words, it's created by the VelocimacroProxy class, to represent one of the arguments to a VM in a specific template. Since the template is fixed (it's a file...), we don't have to worry that the args to the VM will change. Yes, the VM will be called in other templates, or in other places on the same template, bit those are different use-instances. These arguments can be, in the lingo of the parser, one of :

• Reference() : anything that starts with '$'
• StringLiteral() : something like "$foo" or "hello geir"
• IntegerLiteral() : 1, 2 etc
• FloatingPointLiteral() : 1.2, 2e5 etc
• IntegerRange() : [ 1..2] or [$foo .. $bar]
• ObjectArray() : [ "a", "b", "c"]
• True() : true
• False() : false
• Word() : not likely - this is simply allowed by the parser so we can have syntactical sugar like #foreach($a in $b) where 'in' is the Word

Now, Reference(), StringLit, IntegerLiteral, IntRange, ObjArr are all dynamic things, so their value is gotten with the use of a context. The others are constants. The trick we rely on is that the context rather than this class really represents the state of the argument. We are simply proxying for the thing, returning the proper value when asked, and storing the proper value in the appropriate context when asked. So, the hope here, so an instance of this can be shared across threads, is to keep any dynamic stuff out of it, relying on trick of having the appropriate context handed to us, and when a constant argument, letting VMContext punch that into a local context.

Version:

$Id: VMProxyArg.java 151591 2005-02-06 15:42:19Z wglass $

Author:

Geir Magnusson Jr.

Constructor Summary

VMProxyArg(RuntimeServices rs, String contextRef, String callerRef, int t)
ctor for current impl takes the reference literal we are proxying for, the literal the VM we are for is called with...

VMProxyArg(VMProxyArg model, InternalContextAdapter c)
not used in current impl Constructor for alternate impl where VelProxy class would make new VMProxyArg objects, and use this contructor to avoid reparsing the reference args that impl also had the VMProxyArg carry it's context

Method Summary

String	getCallerReference()
String	getContextReference()
SimpleNode	getNodeTree()
Object	getObject(InternalContextAdapter context) returns the value of the reference.
Object	getStaticObject()
int	getType()
boolean	isConstant() tells if arg we are poxying for is dynamic or constant.
Object	setObject(InternalContextAdapter context, Object o) Invoked by VMContext when Context.put() is called for a proxied reference.

Methods inherited from class java.lang.Object

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

Constructor Detail

VMProxyArg

public VMProxyArg(RuntimeServices rs,
                  String contextRef,
                  String callerRef,
                  int t)

ctor for current impl takes the reference literal we are proxying for, the literal the VM we are for is called with...

Parameters:

contextRef - reference arg in the definition of the VM, used in the VM

callerRef - reference used by the caller as an arg to the VM

t - type of arg : JJTREFERENCE, JJTTRUE, etc

VMProxyArg

public VMProxyArg(VMProxyArg model,
                  InternalContextAdapter c)

not used in current impl Constructor for alternate impl where VelProxy class would make new VMProxyArg objects, and use this contructor to avoid reparsing the reference args that impl also had the VMProxyArg carry it's context

Method Detail

isConstant

public boolean isConstant()

tells if arg we are poxying for is dynamic or constant.

Returns:

true of constant, false otherwise

setObject

public Object setObject(InternalContextAdapter context,
                        Object o)

Invoked by VMContext when Context.put() is called for a proxied reference.

Parameters:

context - context to modify via direct placement, or AST.setValue()

o - new value of reference

Returns:

Object currently null

getObject

public Object getObject(InternalContextAdapter context)

returns the value of the reference. Generally, this is only called for dynamic proxies, as the static ones should have been stored in the VMContext's localcontext store

Parameters:

context - Context to use for getting current value

Returns:

Object value

getCallerReference

public String getCallerReference()

getContextReference

public String getContextReference()

getNodeTree

public SimpleNode getNodeTree()

getStaticObject

public Object getStaticObject()

getType

public int getType()