Java 操作 XML (2)--SAX 方式处理 XML
SAX 是一个用于处理XML事件驱动的“推”模型，虽然它不是W3C标准，但它却是一个得到了广泛认可的API。本文主要介绍 Java SAX 方式处理 XML，文中所使用到的软件版本：Java 1.8.0_191。
1、SAX 简介
SAX 的全称是 Simple APIs for XML，也即 XML 简单应用程序接口。与DOM不同，SAX 提供的访问模式是一种顺序模式，这是一种快速读写 XML 数据的方式。当使用 SAX 分析器对 XML 文档进行分析时，会触发一系列事件，并激活相应的事件处理函数，应用程序通过这些事件处理函数实现对XML文档的访问，因而 SAX 接口也被称作事件驱动接口。
1.1、SAX 的优点
1、顺序读入文档并产生相应事件，可以处理任何大小的XML文档。
2、适用于只需要文档的部分内容，或者只需要从文档中得到特定信息。
1.2、SAX 的缺点
1、只能对文档按顺序解析一遍，不支持对文档的随意访问。
2、只能读取XML文档内容，而不能修改。
3、开发上比较复杂，需要自己来实现事件处理器。
2、Java SAX 方式操作 XML
2.1、XML 文件
<?xml version="1.0" encoding="utf-8" ?> <school:grade xmlns:school="http://www.w3.org/TR/html4/school/"> <school:student rollno="1" school:age="10"> <school:firstname>cxx1</school:firstname> <lastname>Bob1</lastname> <nickname>stars1</nickname> <marks>85</marks> </school:student> <student rollno="2"> <firstname>cxx2</firstname> <lastname>Bob2</lastname> <nickname>stars2</nickname> <marks>85</marks> </student> <student rollno="3"> <firstname>cxx3</firstname> <lastname>Bob3</lastname> <nickname>stars3</nickname> <marks>85</marks> </student> </school:grade>
2.2、Java 代码例子
该例子演示如何使用 SAX 方式解析 XML 以及使用 SAX 方式来生成 XML。
package com.abc.demo.general.xml; import org.apache.commons.lang.StringUtils; import org.junit.Test; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import org.xml.sax.Attributes; import org.xml.sax.SAXException; import org.xml.sax.helpers.AttributesImpl; import org.xml.sax.helpers.DefaultHandler; import javax.xml.parsers.SAXParser; import javax.xml.parsers.SAXParserFactory; import javax.xml.transform.OutputKeys; import javax.xml.transform.Transformer; import javax.xml.transform.sax.SAXTransformerFactory; import javax.xml.transform.sax.TransformerHandler; import javax.xml.transform.stream.StreamResult; import java.io.ByteArrayOutputStream; import java.util.ArrayList; import java.util.List; public class SaxCase { private static Logger logger = LoggerFactory.getLogger(SaxCase.class); /** * 解析xml * @throws Exception */ @Test public void parse() throws Exception { SAXParserFactory factory = SAXParserFactory.newInstance(); SAXParser parser = factory.newSAXParser(); SaxHandler handler = new SaxHandler(); parser.parse(DomCase.class.getResourceAsStream("student.xml"), handler); logger.info(handler.getStudents().toString()); } /** * 生成xml * @throws Exception */ @Test public void toXml() throws Exception { //创建SAX转换工厂 SAXTransformerFactory factory = (SAXTransformerFactory) SAXTransformerFactory.newInstance(); TransformerHandler handler = factory.newTransformerHandler(); //创建handler转换器 Transformer transformer = handler.getTransformer(); //换行 transformer.setOutputProperty(OutputKeys.INDENT, "yes"); transformer.setOutputProperty(OutputKeys.ENCODING, "utf-8"); ByteArrayOutputStream out = new ByteArrayOutputStream(); StreamResult streamResult = new StreamResult(out); handler.setResult(streamResult); AttributesImpl attributes = new AttributesImpl(); //打开doc对象 handler.startDocument(); handler.startElement("http://www.w3.org/TR/html4/school/", "", "school:class", null); //第一个学生 attributes.clear(); attributes.addAttribute("", "", "rollno", "", "1"); attributes.addAttribute("", "", "school:age", "", "10"); handler.startElement("", "", "student", attributes); handler.startElement("", "", "school:firstname", null); handler.characters("cxx1".toCharArray(), 0, 4); handler.endElement("", "", "school:firstname"); handler.startElement("", "", "lastname", null); handler.characters("Bob1".toCharArray(), 0, 4); handler.endElement("", "", "lastname"); handler.startElement("", "", "nickname", null); handler.characters("stars1".toCharArray(), 0, 6); handler.endElement("", "", "nickname"); handler.startElement("", "", "marks", null); handler.characters("85".toCharArray(), 0, 2); handler.endElement("", "", "marks"); handler.endElement("", "", "student"); //第二个学生 attributes.clear(); attributes.addAttribute("", "", "rollno", "", "2"); handler.startElement("", "", "student", attributes); handler.startElement("", "", "firstname", null); handler.characters("cxx2".toCharArray(), 0, 4); handler.endElement("", "", "firstname"); handler.startElement("", "", "lastname", null); handler.characters("Bob2".toCharArray(), 0, 4); handler.endElement("", "", "lastname"); handler.startElement("", "", "nickname", null); handler.characters("stars2".toCharArray(), 0, 6); handler.endElement("", "", "nickname"); handler.startElement("", "", "marks", null); handler.characters("85".toCharArray(), 0, 2); handler.endElement("", "", "marks"); handler.endElement("", "", "student"); //第三个学生 attributes.clear(); attributes.addAttribute("", "", "rollno", "", "3"); handler.startElement("", "", "student", attributes); handler.startElement("", "", "firstname", null); handler.characters("cxx3".toCharArray(), 0, 4); handler.endElement("", "", "firstname"); handler.startElement("", "", "lastname", null); handler.characters("Bob3".toCharArray(), 0, 4); handler.endElement("", "", "lastname"); handler.startElement("", "", "nickname", null); handler.characters("stars3".toCharArray(), 0, 6); handler.endElement("", "", "nickname"); handler.startElement("", "", "marks", null); handler.characters("85".toCharArray(), 0, 2); handler.endElement("", "", "marks"); handler.endElement("", "", "student"); handler.endElement("", "", "school:class"); handler.endDocument(); logger.info(out.toString()); } } class SaxHandler extends DefaultHandler { private String text; private static Logger logger = LoggerFactory.getLogger(SaxHandler.class); private List<Student> students = new ArrayList<>(); private Student student = null; public List<Student> getStudents() { return students; } public SaxHandler() {} @Override public void startDocument() throws SAXException { super.startDocument(); logger.info("SAX解析开始"); } @Override public void endDocument() throws SAXException { super.endDocument(); logger.info("SAX解析结束"); } @Override public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException { super.startElement(uri, localName, qName, attributes); logger.info("qName={}", qName); if (qName.equals("student") || qName.equals("school:student")) { student = new Student(); students.add(student); student.setRollno(Integer.parseInt(attributes.getValue("rollno"))); String age = attributes.getValue("school:age"); if (StringUtils.isNotBlank(age)) { student.setAge(Integer.parseInt(age)); } } } @Override public void endElement(String uri, String localName, String qName) throws SAXException { super.endElement(uri, localName, qName); if ("firstname".equals(qName) || "school:firstname".equals(qName) ) { student.setFirstname(text); } else if ("lastname".equals(qName)) { student.setLastname(text); } else if ("nickname".equals(qName)) { student.setNickname(text); } else if ("marks".equals(qName)) { student.setMarks(text); } } @Override public void characters(char[] ch, int start, int length) throws SAXException { super.characters(ch, start, length); text = new String(ch, start, length); } }
Student 实体类：
package com.abc.demo.general.xml; /** * 学生 */ public class Student { private int rollno; private int age; private String firstname; private String lastname; private String nickname; private String marks; public Student() {} public Student(int rollno, int age, String firstname, String lastname, String nickname, String marks) { this.rollno = rollno; this.age = age; this.firstname = firstname; this.lastname = lastname; this.nickname = nickname; this.marks = marks; } public int getRollno() { return rollno; } public void setRollno(int rollno) { this.rollno = rollno; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public String getFirstname() { return firstname; } public void setFirstname(String firstname) { this.firstname = firstname; } public String getLastname() { return lastname; } public void setLastname(String lastname) { this.lastname = lastname; } public String getNickname() { return nickname; } public void setNickname(String nickname) { this.nickname = nickname; } public String getMarks() { return marks; } public void setMarks(String marks) { this.marks = marks; } @Override public String toString() { return "Student{" + "rollno=" + rollno + ", age=" + age + ", firstname='" + firstname + '\'' + ", lastname='" + lastname + '\'' + ", nickname='" + nickname + '\'' + ", marks='" + marks + '\'' + '}'; } }
