如何使用SAX方法在java中解析xml文档?

i want to parse a file which is similar to a HTML file . Its not exactly a html file.It can contain some user defined tags. I dont know in advance how the tags are nested in one another in advance.The tags may also have attributes. I think i shold use a SAX parser. Does java have a inbuilt SAX . Can i call a function when i encounter each tag?i want to parse a file which is similar to a HT