Java String Buffer Treated As String In ColdFusion (When Needed)
Posted September 27, 2007 at 8:29 AM by Ben Nadel
Just a tiny discovery here: ColdFusion will automatically convert a Java String Buffer to a string when it is required for a method call. Here's a little demo:
- <!--- Create a Java String Buffer. --->
- <cfset objBuffer = CreateObject(
- <!--- Add some XML tags to the String Buffer. --->
- <cfset objBuffer.Append(
- "<foo>" &
- "<bar>blam</bar>" &
- ) />
- Parse the string buffer contents into a
- ColdFusion XML document object.
- <cfset xmlDoc = XmlParse( objBuffer ) />
- <!--- Write string buffer to screen. --->
- <cfset WriteOutput(
- HtmlEditFormat( objBuffer )
- ) />
Here we are storing the contents of an XML document inside the Java String Buffer. Then, we try passing it as an argument to two ColdFusion functions, XmlParse() and HtmlEditFormat(), both of which require a parameter of type String. This code works perfectly well, no ColdFusion errors get thrown.
At first, I assumed that the code is attempting to call the ToString() method on the object or something? But this doesn't exactly make sense because any Java object that extends the java.lang.Object class has a ToString() method, and this auto-string-conversion does NOT work for all data types.
Take, for example, the array. You can call the .ToString() method on a ColdFusion array:
- #ListToArray( "1,2,3" ).ToString()#
... and it will output:
[1, 2, 3]
However, if you were to pass in the array to the WriteOutput() method, ColdFusion would throw the following error:
Complex object types cannot be converted to simple values. The expression has requested a variable or an intermediate expression result as a simple value, however, the result cannot be converted to a simple value. Simple values are strings, numbers, boolean values, and date/time values. Queries, arrays, and COM objects are examples of complex values.
So, this leads me to believe that ColdFusion isn't just calling .ToString() behind the scenes. I wonder if there is special code in these methods to check for String Buffers.
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My guess would be that you are correct in your guess, that CF is calling toString() as a default. I would guess that when known 'complex' objects are passed in, that CF is throwing an error instead of calling the toString() method. If you attempt to output any object in Java, the complier will by default call the toString() method, which is what I would guess is happening here.
My 2 cents of a guess.
I am thinking your are correct. I tried to create an Object instance (the root Java object) and write that to the output:
<cfset objJava = CreateObject( "java", "java.lang.Object" ).Init() />
<cfset WriteOutput( objJava ) />
And it works fine, outputting:
So, it looks like it will call ToString() all the object UNLESS it encounters a known complext structure.