java操作xml和json

1. XML

1.1 XML简介

XML, 可扩展标记语言(extensible markup language), 是一种数据表示格式, 可以藐视非常复制的数据结构, 用于传输和存储数据

特点:

纯文本, 默认UTF-8编码可嵌套, 适合表示结构化数据一般以文件形式, 如:book.xml

1.2 Dom

java解析XML:

Document: 代表整个XML文档Element: 元素Attribute: 属性Text: 文本内容Comment: 注释

Java Dom核心API:

DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance(); DocumentBuilder db = dbf.newDocumentBuilder(); Document doc = db.parse("/Users/lingjing/IdeaProjects/hadooptest/pom.xml"); Element root = doc.getDocumentElement();

java DOM API:

将XML解析为DOM可在内存中完整标识XML数据结构解析速度慢, 内存占用大

Dom示例

import javax.xml.parsers.DocumentBuilder; import javax.xml.parsers.DocumentBuilderFactory; import org.w3c.dom.Document; import org.w3c.dom.Node; public class DOMTest { static final String XML_URL = "http://rss.sina.com.cn/tech/internet/home28.xml"; public static void main(String[] args) throws Exception { DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance(); DocumentBuilder db = dbf.newDocumentBuilder(); Document doc = db.parse("/Users/lingjing/IdeaProjects/hadooptest/pom.xml"); printNode(doc, 0); } static void printNode(Node n, int indent) { String tab = ""; for (int i = 0; i < indent; i++) { // System.out.print(' '); tab += "\t"; } System.out.print(tab); switch (n.getNodeType()) { case Node.DOCUMENT_NODE: System.out.println("Document: " + n.getNodeName()); break; case Node.ELEMENT_NODE: System.out.println("Element: " + n.getNodeName()); break; case Node.TEXT_NODE: System.out.println("Text: " + n.getNodeName() + " = " + n.getNodeValue()); break; case Node.ATTRIBUTE_NODE: System.out.println("Attr: " + n.getNodeName() + " = " + n.getNodeValue()); break; case Node.CDATA_SECTION_NODE: System.out.println("CDATA: " + n.getNodeName() + " = " + n.getNodeValue()); break; case Node.COMMENT_NODE: System.out.println("Comment: " + n.getNodeName() + " = " + n.getNodeValue()); break; default: System.out.println("NodeType: " + n.getNodeType() + ", NodeName: " + n.getNodeName()); } for (Node child = n.getFirstChild(); child != null; child = child.getNextSibling()) { printNode(child, indent + 1); } } }

1.3 SAX

SAX: Simple Api for XML, 基于事件的API

SAX解析会触发一系列事件:

startDocumentstartElementCharacters: 文本endElementendDocument

SAX解析XML:

一种流式解析XML的API通过事件触发, 速度快调用方通过回调方法获取数据

SAX示例:

import javax.xml.parsers.SAXParser; import javax.xml.parsers.SAXParserFactory; public class SAXSample { static final String XML_URL = "http://rss.sina.com.cn/tech/internet/home28.xml"; public static void main(String[] args) throws Exception { SAXParserFactory spf = SAXParserFactory.newInstance(); SAXParser saxParser = spf.newSAXParser(); saxParser.parse("/Users/lingjing/IdeaProjects/hadooptest/pom.xml", new MyHandler()); } } import org.xml.sax.Attributes; import org.xml.sax.SAXException; import org.xml.sax.SAXParseException; import org.xml.sax.helpers.DefaultHandler; public class MyHandler extends DefaultHandler { void print(Object... objs) { for (Object obj : objs) { System.out.print(obj); System.out.print(" "); } System.out.println(); } @Override public void startDocument() throws SAXException { print("start document"); } @Override public void endDocument() throws SAXException { print("end document"); } @Override public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException { print("start element:", localName, qName); } @Override public void endElement(String uri, String localName, String qName) throws SAXException { print("end element:", localName, qName); } @Override public void characters(char[] ch, int start, int length) throws SAXException { print("characters:", new String(ch, start, length)); } @Override public void error(SAXParseException e) throws SAXException { print("error:", e); } }

1.4 Jackson

使用Jackson:

开源XML读写工具可在XML和JavaBean之间相互转换API接口简单可定制序列化

maven依赖地址:

<dependency> <groupId>com.fasterxml.jackson.dataformat</groupId> <artifactId>jackson-dataformat-xml</artifactId> <version>2.9.0</version> </dependency> <dependency> <groupId>org.codehaus.woodstox</groupId> <artifactId>woodstox-core-asl</artifactId> <version>4.4.1</version> </dependency>

读取XML:把xml变成java对象

XmlMapper mapper = new XmlMapper(); Book book = mapper.readValue(xml, Book.class);

写入XML:把java对象变成xml文件, 并返回字符串

XmlMapper mapper = new XmlMapper(); String xml = mapper.writeValueAsString(book);

2. fastjson

maven配置

<dependency> <groupId>com.alibaba</groupId> <artifactId>fastjson</artifactId> <version>1.2.46</version> </dependency>

代码测试:

import lombok.Data; @Data public class User { private String name; private int age; } public class TestUser { public static void main(String[] args) { User user = new User(); user.setAge(20); user.setName("ajing"); // 把User对象变成json字符串 String jstr = JSON.toJSONString(user); System.out.println(jstr); // 把字符串变成User对象 User u1 = JSON.parseObject(jstr, User.class); System.out.println(u1 instanceof User); System.out.println(u1.getAge()); System.out.println(u1.getName()); } }

转载于:https://www.cnblogs.com/lingshang/p/10984627.html