org.apache.velocity.runtime.directive

Class VMProxyArg


public class VMProxyArg
extends java.lang.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 : Now, Reference(), StringLit, NumberLit, 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,v 1.13.4.1 2004/03/03 23:22:56 geirm Exp $

Author:
Geir Magnusson Jr.

Field Summary

private int
GENERALSTATIC
in the event our type is switched - we don't care really what it is
private String
callerReference
the reference we are proxying for
private boolean
constant
by default, we are dynamic.
private String
contextReference
our identity in the current context
private SimpleNode
nodeTree
the AST if the type is such that it's dynamic (ex.
private int
numTreeChildren
number of children in our tree if a reference
private RuntimeServices
rsvc
private String
singleLevelRef
the 'de-dollared' reference if we are a ref but don't have a method attached
private Object
staticObject
reference for the object if we proxy for a static arg like an NumberLiteral
private int
type
type of arg I will have
private InternalContextAdapter
usercontext
not used in this impl : carries the appropriate user context

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.
private void
setup()
does the housekeeping upon creationg.

Field Details

GENERALSTATIC

private final int GENERALSTATIC
in the event our type is switched - we don't care really what it is


callerReference

private String callerReference
the reference we are proxying for


constant

private boolean constant
by default, we are dynamic. safest


contextReference

private String contextReference
our identity in the current context


nodeTree

private SimpleNode nodeTree
the AST if the type is such that it's dynamic (ex. JJTREFERENCE )


numTreeChildren

private int numTreeChildren
number of children in our tree if a reference


rsvc

private RuntimeServices rsvc


singleLevelRef

private String singleLevelRef
the 'de-dollared' reference if we are a ref but don't have a method attached


staticObject

private Object staticObject
reference for the object if we proxy for a static arg like an NumberLiteral


type

private int type
type of arg I will have


usercontext

private InternalContextAdapter usercontext
not used in this impl : carries the appropriate user context

Constructor Details

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 Details

getCallerReference

public String getCallerReference()


getContextReference

public String getContextReference()


getNodeTree

public SimpleNode getNodeTree()


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


getStaticObject

public Object getStaticObject()


getType

public int getType()


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


setup

private void setup()
does the housekeeping upon creationg. If a dynamic type it needs to make an AST for further get()/set() operations Anything else is constant.


Copyright B) 2002 Apache Software Foundation. All Rights Reserved.