DOM方式与SAX方式的比较

DOM方式

package tigers;

import java.util.*;

import javax.xml.parsers.*;
import org.w3c.dom.*;
import java.io.*;

public class Tiger23 {
static class Bean23 {
Map<String, String> attrs; //标记属性
String name, value; //标记名称和文本内容
public Bean23(String name, String value, Map<String, String> attrs) {
this.name = name;
this.value = value;
this.attrs = attrs;
}

public Map<String, String> getAttrs() {
return attrs;
}

public void setAttrs(Map<String, String> attrs) {
this.attrs = attrs;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public String getValue() {
return value;
}

public void setValue(String value) {
this.value = value;
}
public String toString() {
Set<String> keySet = attrs.keySet();
String str = "";
for (String key : keySet) {
String value = attrs.get(key);
str += " " + key + "='" + value + "'";
}
return "\nElement:<" + name + ", <" + value + ">" + ",(" + str + ")>";
}
}
static Map<String, String> getElementAttrs(Element element) {
Map<String, String> attrs = new HashMap<String, String>();
if (element.hasAttributes()) {
NamedNodeMap maps = element.getAttributes();
for (int i = 0; i < maps.getLength(); i++) {
Attr attr = (Attr) maps.item(i);
attrs.put(attr.getName(), attr.getValue());
}
}
return attrs;
}
static Collection<Bean23> getElements(Document doc) {
Collection<Bean23> elements = new ArrayList<Bean23> ();
Element rootElement = doc.getDocumentElement();
elements = circle(rootElement, elements);
return elements;
}
static Collection<Bean23> circle(Element element, Collection<Bean23> elements) {
String name = element.getTagName();
String value = "";
Map<String, String> attrs = getElementAttrs(element);
Bean23 bean = new Bean23(name, value, attrs);
elements.add(bean);
NodeList list = element.getChildNodes();
for (int i = 0; i < list.getLength(); i++) {
Node node = list.item(i);
if (node.hasChildNodes()) {
Element childElement = (Element) node;
elements = circle(childElement, elements);
continue;
} else if (node.getNodeType() != Node.COMMENT_NODE && (node.getNodeValue() != null)) {
value += node.getNodeValue().trim();
}
bean.setValue(value);
}
return elements;
}
static Collection<Bean23> parse(String xmlFile) {
Collection<Bean23> elements = null;
try {
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
Document doc = builder.parse(new File(xmlFile));
elements = getElements(doc);
} catch (Exception e) {
e.printStackTrace();
}
return elements;
}
public static void main(String[] args) {
Collection<Bean23> elements = new ArrayList<Bean23> ();
long start = System.currentTimeMillis();
for (int i = 0; i < 100; i++) {
elements = parse("c:/test.xml");
System.gc();
}
long end = System.currentTimeMillis();
System.out.println("<DOM方式>past time: " + (end - start));
System.out.println(elements);
}
}

SAX方式

package tigers;

import java.util.*;

import org.xml.sax.helpers.DefaultHandler;
import org.xml.sax.Attributes;
import org.xml.sax.XMLReader;

import java.io.*;
import org.xml.sax.InputSource;

public class Tiger22 {
static class Bean22 { //代表XML中的一个标记。
private String uri, localName, qName, value = "";
private Map<String, String> attrs = new HashMap<String, String> (); //当前标记的属性集合
public Bean22(String uri, String localName, String qName, Map<String, String> attrs) {
this.uri = uri;
this.localName = localName;
this.qName = qName;
this.attrs = attrs;
}

public String getValue() {
return value;
}

public void setValue(String value) {
this.value = value;
}

public Map getAttrs() {
return attrs;
}

public String getLocalName() {
return localName;
}

public String getQName() {
return qName;
}

public String getUri() {
return uri;
}
public String toString() {
Set<String> keySet = attrs.keySet();
String str = "";
for (String key : keySet) {
String value = attrs.get(key);
str += " " + key + "='" + value + "'";
}
return "\nElement:<" + localName + ", <" + value + ">" + ",(" + str + ")>";
}
}
static class Inner extends DefaultHandler {
private Bean22 currentElement; //当前标记
private String text; //当前标记的文本内容
private Collection<Bean22> elements = new ArrayList<Bean22> (); //存放所有的标记
public Collection<Bean22> parse(String xmlFile) {
try {
XMLReader reader = org.xml.sax.helpers.XMLReaderFactory.createXMLReader();
reader.setContentHandler(this);
reader.parse(new InputSource(new FileReader(xmlFile)));
} catch (Exception e) {
e.printStackTrace();
}
return elements;
}

/*这里使用java.util.Map存放属性信息。注意：org.xml.sax.Attributes原本就是集合类型，但由于SAX工作的方式，决定了如果直接使用Attributes存放属性信息，后来解析的标记的属性信息可能覆盖先前解析的标记的属性信息，导致问题出现。所以这里使用Map替代Attributes存放属性信息，可以很好地避免上述问题的发生。*/
public void startElement(String uri, String localName, String qName, Attributes attrs) {
Map<String, String> mapAttrs = new HashMap<String, String> ();
for (int i = 0; i < attrs.getLength(); i++) {
mapAttrs.put(attrs.getQName(i), attrs.getValue(i));
}
currentElement = new Bean22(uri, localName, qName, mapAttrs);
elements.add(currentElement);
text = new String();
}

public void characters(char[] ch, int start, int end) {
text += new String(ch, start, end).trim();
currentElement.setValue(text);
}
public void endElement(String uri, String localName, String qName) {
//不需要实现任何代码。
}
}
public static void main(String[] args) {
Collection<Bean22> elements = new ArrayList<Bean22> ();
long start = System.currentTimeMillis();
for (int i = 0; i < 100; i++) {
Inner in = new Inner();
elements = in.parse("c:/test.xml");
System.gc();
}
long end = System.currentTimeMillis();
System.out.println("<SAX方式>past time: " + (end - start));
System.out.println(elements);
}
}

测试文件及测试结果

c:/test.xml

<?xml version="1.0" encoding="UTF-8"?>
<root>
<elements id="001">
<!-- element Comment -->
<element name="aaaa">
AAAAAAAAA
</element>
<element name="bbbb">
BBBBBBBBB
</element>
</elements>
<mappings>
<mapping id="1234" elementName="aaaa">
11223344
</mapping>
<mapping id="5678" elementName="aaaa">
55667788
</mapping>
</mappings>
</root>

结果：

<SAX方式>past time: 5750
[
Element:<root, <>,()>,
Element:<elements, <>,( id='001')>,
Element:<element, <AAAAAAAAA>,( name='aaaa')>,
Element:<element, <BBBBBBBBB>,( name='bbbb')>,
Element:<mappings, <>,()>,
Element:<mapping, <11223344>,( elementName='aaaa' id='1234')>,
Element:<mapping, <55667788>,( elementName='aaaa' id='5678')>]

结果：

<DOM方式>past time: 5907
[
Element:<root, <>,()>,
Element:<elements, <>,( id='001')>,
Element:<element, <AAAAAAAAA>,( name='aaaa')>,
Element:<element, <BBBBBBBBB>,( name='bbbb')>,
Element:<mappings, <>,()>,
Element:<mapping, <11223344>,( elementName='aaaa' id='1234')>,
Element:<mapping, <55667788>,( elementName='aaaa' id='5678')>]

结论：

1、使用任何一种方式，第一次解析时都比较耗时，连续解析多次后平均所用时间有很大减少。

2、对于小文件，两者看不出很大差别，SAX甚至比DOM更耗时；文件越大，SAX的优势越大。

3、就编程难度而言，SAX比DOM更容易实现。