SAX解析XML,为什么会报内存溢出？

用下面的SAX方式，解析一个450M的xml文件时，会报内存溢出？
为什么？Java code:

import java.io.File;
import java.io.FileInputStream;
import java.util.*;

import javax.xml.parsers.*;
import org.xml.sax.Attributes;
import org.xml.sax.helpers.DefaultHandler;

public class SaxXml {
public SaxXml() {
}

public void readXML(String FileName) throws Exception{
SAXParserFactory spf = SAXParserFactory.newInstance();
SAXParser sp = spf.newSAXParser();
MySAXHandler handler = new MySAXHandler();
sp.parse(new FileInputStream(new File(FileName)), handler);
}

class MySAXHandler extends DefaultHandler{
java.util.Stack tagStack = new java.util.Stack();

@SuppressWarnings("unchecked")
public void startElement(String namespace,String localName,String qName,Attributes atts){
tagStack.push(qName);
System.out.println("qName:"+qName);
}
public void endElement(String namespace,String localName,String qName){

}
public void characters(char[] chs,int start,int length){

}

}


public static void main(String[] args){
String name = "f:/data/AuditBizDataDataSet2.xml";
SaxXml q = new SaxXml();
try {
q.readXML(name);
} catch (Exception e) {
e.printStackTrace();
}
}
}

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那我应该在