1. Introduction to sax
SAX is an event-driven way of parsing XML. Sequentially reads XML files, generates events, and propagates them to user-defined callback methods to process XML files.
advantage:
Process xml in segments instead of loading the whole xml into memory at one time, with less memory usage and faster speed.
shortcoming:
Sequential access, no rollback. Coding is complex and requires users to control the data structure.
Second, the use process
1. Create a factory
SAXParserFactory saxParserFactory = SAXParserFactory.newInstance();
2. Set factory properties ( optional )
saxParserFactory.setValidating(true); // Whether to validate xml, default false saxParserFactory.setNamespaceAware(true); // Whether to display the namespace default false
3. Generate the parser
SAXParser parser = saxParserFactory.newSAXParser();
4. Set parser properties ( optional)
parser.setProperty("http://java.sun.com/xml/jaxp/properties/schemaLanguage", "http://www.w3.org/2001/XMLSchema"); // Required in validation mode
5. Get XMLReader ( optional)
XMLReader reader = parser.getXMLReader();
6. Set the XMLReader property ( optional)
reader.setContentHandler(new MyDefalutHandler()); // content handler reader.setEntityResolver(new MyEntityResolver()); // schama解析器 reader.setErrorHandler(new MyErrorHandler()); // exception handler
7. Parse the xml file
reader.parse(SaxDemo.class.getResource("/").getPath() + "/saxDemo.xml");
或者 parser.parse(SaxDemo.class.getResource("/").getPath() + "/saxDemo.xml", new DefaultHandler());
Both SAXParser and XMLReader can parse xml , but SAXParser overloads exception handling, content processing, and schema parsing into a single handler. Personally, I think the division of responsibilities is not very clear. It is recommended to use XMLReader.
3. Regular use of code examples
saxDemo.xml
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:util="http://www.springframework.org/schema/util" xmlns:aop="http://www.springframework.org/schema/cache" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util.xsd http://www.springframework.org/schema/cache http://www.springframework.org/schema/cache/spring-cache.xsd" default-autowire="byName"> <aop:annotation-driven></aop:annotation-driven> <util:map key-type="java.lang.String" value-type="java.lang.String"> <entry key="key" value="value"></entry> </util:map> <bean id="commonMap" class="java.util.HashMap"> <constructor-arg> <map> <entry key="key" value="value"></entry> </map> </constructor-arg> </bean> </beans>
MyDefalutHandler
public class MyDefalutHandler extends DefaultHandler{
@Override
public void startDocument() throws SAXException {
System.out.println("startDocument()");
}
@Override
public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {
StringBuilder builder = new StringBuilder();
int length = attributes.getLength();
if (length > 0) {
for (int i = 0; i < length; i++) {
builder.append(attributes.getLocalName(i).trim())
.append(":")
.append(attributes.getValue(i).trim())
.append(" ");
}
}
System.out.println(String.format("startElement uri=%s localName=%s qname=%s attributes=%s", uri, localName, qName, builder));
}
@Override
public void characters(char[] ch, int start, int length) throws SAXException {
String content = new String(ch, start, length);
if (StringUtils.isNotBlank(content)) {
System.out.println("characters=" + content);
}
}
@Override
public void endElement(String uri, String localName, String qName) throws SAXException {
System.out.println(String.format("startElement uri=%s localName=%s qname=%s", uri, localName, qName));
}
@Override
public void endDocument() throws SAXException {
System.out.println("endDocument()");
}
}
test class
public class SaxDemo {
public static void main(String[] args) throws Exception {
SAXParserFactory saxParserFactory = SAXParserFactory.newInstance();
SAXParser parser = saxParserFactory.newSAXParser();
XMLReader reader = parser.getXMLReader();
reader.setContentHandler(new MyDefalutHandler()); // content handler
reader.parse(SaxDemo.class.getResource("/").getPath() + "/saxDemo.xml");
}
}
Test Results
startDocument() startElement uri= localName= qname=beans attributes=xmlns:http://www.springframework.org/schema/beans xmlns:xsi:http://www.w3.org/2001/XMLSchema-instance xmlns:util:http://www.springframework.org/schema/util xmlns:aop:http://www.springframework.org/schema/cache xsi:schemaLocation:http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util.xsd http://www.springframework.org/schema/cache http://www.springframework.org/schema/cache/spring-cache.xsd default-autowire:byName startElement uri= localName= qname=aop:annotation-driven attributes= startElement uri= localName= qname=aop:annotation-driven startElement uri= localName= qname=util:map attributes=key-type:java.lang.String value-type:java.lang.String startElement uri= localName= qname=entry attributes=key:key value:value startElement uri= localName= qname=entry startElement uri= localName= qname=util:map startElement uri= localName= qname=bean attributes=id:commonMap class:java.util.HashMap startElement uri= localName= qname=constructor-arg attributes= startElement uri= localName= qname=map attributes= startElement uri= localName= qname=entry attributes=key:key value:value startElement uri= localName= qname=entry startElement uri= localName= qname=map startElement uri= localName= qname=constructor-arg startElement uri= localName= qname=bean startElement uri= localName= qname=beans endDocument()