XML String encoding - anyone have the the code?

Question

I need to encode strings for use in XML (node values) and replace
items like ampersands, < and > symbols, etc with the proper escaped strings.
My code will be installed on systems where I CANNOT add additional libraries to whatever they may already have.
So, I cannot use JAXP, for example.
Does anyone have the actual Java code for making strings XML compatible ?
I am particularly concerned that the if the string already contains a valid encoding that it is NOT 're-processed' so that this (excuse the extra -'s):
'Hello &-amp-;'
does not become this:
'Hello &-amp-;-amp-;'
Thanks.

Answer 1

It isn't especially difficult code. Here's what you have to do:
1. Replace & by &amp;
2. Replace < by &lt;
3. Replace > by &gt;
4. Replace " by &quot;
5. Replace &apos; by &apos;
Note that it's important that #1 come first, otherwise you will be incorrectly processing things twice. The order of the rest doesn't matter. (Technically you don't have to do all of these things in all situations -- for example attribute values have different escaping rules than text nodes do -- but it isn't wrong to do them all.)
And note that this is called "escaping", not "encoding".
I am particularly concerned that the if the string already contains a valid encoding that it is NOT 're-processed'This isn't a valid design criterion. You have to set up your design so that you have unescaped strings and you are creating escaped strings, or vice versa. If you have a string and you don't know if it has already been escaped or not, then that's a design failure.