我需要读取和写入XML文件,使用Java读写XML文件最简单的方法是什么?
我需要读取和写入XML文件,使用Java读写XML文件最简单的方法是什么?
这是一个快速的DOM示例,展示了如何读写一个带有DTD的简单XML文件:
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE roles SYSTEM "roles.dtd">
<roles>
<role1>User</role1>
<role2>Author</role2>
<role3>Admin</role3>
<role4/>
</roles>
还有DTD:
<?xml version="1.0" encoding="UTF-8"?>
<!ELEMENT roles (role1,role2,role3,role4)>
<!ELEMENT role1 (#PCDATA)>
<!ELEMENT role2 (#PCDATA)>
<!ELEMENT role3 (#PCDATA)>
<!ELEMENT role4 (#PCDATA)>
首先导入这些:
import javax.xml.parsers.*;
import javax.xml.transform.*;
import javax.xml.transform.dom.*;
import javax.xml.transform.stream.*;
import org.xml.sax.*;
import org.w3c.dom.*;
以下是您需要的几个变量:
private String role1 = null;
private String role2 = null;
private String role3 = null;
private String role4 = null;
private ArrayList<String> rolev;
这是一个读取器(String xml是您的xml文件名):
public boolean readXML(String xml) {
rolev = new ArrayList<String>();
Document dom;
// Make an instance of the DocumentBuilderFactory
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
try {
// use the factory to take an instance of the document builder
DocumentBuilder db = dbf.newDocumentBuilder();
// parse using the builder to get the DOM mapping of the
// XML file
dom = db.parse(xml);
Element doc = dom.getDocumentElement();
role1 = getTextValue(role1, doc, "role1");
if (role1 != null) {
if (!role1.isEmpty())
rolev.add(role1);
}
role2 = getTextValue(role2, doc, "role2");
if (role2 != null) {
if (!role2.isEmpty())
rolev.add(role2);
}
role3 = getTextValue(role3, doc, "role3");
if (role3 != null) {
if (!role3.isEmpty())
rolev.add(role3);
}
role4 = getTextValue(role4, doc, "role4");
if ( role4 != null) {
if (!role4.isEmpty())
rolev.add(role4);
}
return true;
} catch (ParserConfigurationException pce) {
System.out.println(pce.getMessage());
} catch (SAXException se) {
System.out.println(se.getMessage());
} catch (IOException ioe) {
System.err.println(ioe.getMessage());
}
return false;
}
这里是一个作家:
public void saveToXML(String xml) {
Document dom;
Element e = null;
// instance of a DocumentBuilderFactory
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
try {
// use factory to get an instance of document builder
DocumentBuilder db = dbf.newDocumentBuilder();
// create instance of DOM
dom = db.newDocument();
// create the root element
Element rootEle = dom.createElement("roles");
// create data elements and place them under root
e = dom.createElement("role1");
e.appendChild(dom.createTextNode(role1));
rootEle.appendChild(e);
e = dom.createElement("role2");
e.appendChild(dom.createTextNode(role2));
rootEle.appendChild(e);
e = dom.createElement("role3");
e.appendChild(dom.createTextNode(role3));
rootEle.appendChild(e);
e = dom.createElement("role4");
e.appendChild(dom.createTextNode(role4));
rootEle.appendChild(e);
dom.appendChild(rootEle);
try {
Transformer tr = TransformerFactory.newInstance().newTransformer();
tr.setOutputProperty(OutputKeys.INDENT, "yes");
tr.setOutputProperty(OutputKeys.METHOD, "xml");
tr.setOutputProperty(OutputKeys.ENCODING, "UTF-8");
tr.setOutputProperty(OutputKeys.DOCTYPE_SYSTEM, "roles.dtd");
tr.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", "4");
// send DOM to file
tr.transform(new DOMSource(dom),
new StreamResult(new FileOutputStream(xml)));
} catch (TransformerException te) {
System.out.println(te.getMessage());
} catch (IOException ioe) {
System.out.println(ioe.getMessage());
}
} catch (ParserConfigurationException pce) {
System.out.println("UsersXML: Error trying to instantiate DocumentBuilder " + pce);
}
}
这里是getTextValue的取值:private String getTextValue(String def, Element doc, String tag) {
String value = def;
NodeList nl;
nl = doc.getElementsByTagName(tag);
if (nl.getLength() > 0 && nl.item(0).hasChildNodes()) {
value = nl.item(0).getFirstChild().getNodeValue();
}
return value;
}
添加一些访问器和修改器,你就完成了!
使用JAXB(Java Architecture for XML Binding)编写XML:
http://www.mkyong.com/java/jaxb-hello-world-example/
package com.mkyong.core;
import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.XmlElement;
import javax.xml.bind.annotation.XmlRootElement;
@XmlRootElement
public class Customer {
String name;
int age;
int id;
public String getName() {
return name;
}
@XmlElement
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
@XmlElement
public void setAge(int age) {
this.age = age;
}
public int getId() {
return id;
}
@XmlAttribute
public void setId(int id) {
this.id = id;
}
}
package com.mkyong.core;
import java.io.File;
import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Marshaller;
public class JAXBExample {
public static void main(String[] args) {
Customer customer = new Customer();
customer.setId(100);
customer.setName("mkyong");
customer.setAge(29);
try {
File file = new File("C:\\file.xml");
JAXBContext jaxbContext = JAXBContext.newInstance(Customer.class);
Marshaller jaxbMarshaller = jaxbContext.createMarshaller();
// output pretty printed
jaxbMarshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
jaxbMarshaller.marshal(customer, file);
jaxbMarshaller.marshal(customer, System.out);
} catch (JAXBException e) {
e.printStackTrace();
}
}
}
main
方法中完成,其余代码只是生成一些测试对象并向其填充一些数据。
配置xStream
实例非常简单,并且编组/取消编组每个都只需要一行代码。import java.math.BigDecimal;
import java.util.ArrayList;
import java.util.List;
import com.thoughtworks.xstream.XStream;
public class XStreamIsGreat {
public static void main(String[] args) {
XStream xStream = new XStream();
xStream.alias("good", Good.class);
xStream.alias("pRoDuCeR", Producer.class);
xStream.alias("customer", Customer.class);
Producer a = new Producer("Apple");
Producer s = new Producer("Samsung");
Customer c = new Customer("Someone").add(new Good("S4", 10, new BigDecimal(600), s))
.add(new Good("S4 mini", 5, new BigDecimal(450), s)).add(new Good("I5S", 3, new BigDecimal(875), a));
String xml = xStream.toXML(c); // objects -> xml
System.out.println("Marshalled:\n" + xml);
Customer unmarshalledCustomer = (Customer)xStream.fromXML(xml); // xml -> objects
}
static class Good {
Producer producer;
String name;
int quantity;
BigDecimal price;
Good(String name, int quantity, BigDecimal price, Producer p) {
this.producer = p;
this.name = name;
this.quantity = quantity;
this.price = price;
}
}
static class Producer {
String name;
public Producer(String name) {
this.name = name;
}
}
static class Customer {
String name;
public Customer(String name) {
this.name = name;
}
List<Good> stock = new ArrayList<Good>();
Customer add(Good g) {
stock.add(g);
return this;
}
}
}
好的,已经在答案列表中提到了DOM、JaxB和XStream,但是读写XML还有一种完全不同的方式:数据投影。您可以使用一个库来提供可读和可写的视图,将XML结构和Java结构解耦为Java接口。来自教程:
给出一些真实世界的XML:
<weatherdata>
<weather
...
degreetype="F"
lat="50.5520210266113" lon="6.24060010910034"
searchlocation="Monschau, Stadt Aachen, NW, Germany"
... >
<current ... skytext="Clear" temperature="46"/>
</weather>
</weatherdata>
public interface WeatherData {
@XBRead("/weatherdata/weather/@searchlocation")
String getLocation();
@XBRead("/weatherdata/weather/current/@temperature")
int getTemperature();
@XBRead("/weatherdata/weather/@degreetype")
String getDegreeType();
@XBRead("/weatherdata/weather/current/@skytext")
String getSkytext();
/**
* This would be our "sub projection". A structure grouping two attribute
* values in one object.
*/
interface Coordinates {
@XBRead("@lon")
double getLongitude();
@XBRead("@lat")
double getLatitude();
}
@XBRead("/weatherdata/weather")
Coordinates getCoordinates();
}
使用此接口的实例就像普通Java对象一样:
private void printWeatherData(String location) throws IOException {
final String BaseURL = "http://weather.service.msn.com/find.aspx?outputview=search&weasearchstr=";
// We let the projector fetch the data for us
WeatherData weatherData = new XBProjector().io().url(BaseURL + location).read(WeatherData.class);
// Print some values
System.out.println("The weather in " + weatherData.getLocation() + ":");
System.out.println(weatherData.getSkytext());
System.out.println("Temperature: " + weatherData.getTemperature() + "°"
+ weatherData.getDegreeType());
// Access our sub projection
Coordinates coordinates = weatherData.getCoordinates();
System.out.println("The place is located at " + coordinates.getLatitude() + ","
+ coordinates.getLongitude());
}
SAX
解析器与DOM
解析器的工作方式不同,它既不将任何XML
文档加载到内存中,也不创建任何XML
文档的对象表示。相反,SAX
解析器使用回调函数org.xml.sax.helpers.DefaultHandler
来通知客户端XML
文档结构。
SAX
解析器比DOM
解析器更快,使用的内存更少。
以下是SAX
回调方法:
startDocument()
和endDocument()
- 在XML文档的开头和结尾调用的方法。
startElement()
和endElement()
- 在文档元素的开头和结尾调用的方法。
characters()
- 在XML文档元素的开始和结束标记之间调用的包含文本内容的方法。
创建一个简单的XML文件。
<?xml version="1.0"?>
<company>
<staff>
<firstname>yong</firstname>
<lastname>mook kim</lastname>
<nickname>mkyong</nickname>
<salary>100000</salary>
</staff>
<staff>
<firstname>low</firstname>
<lastname>yin fong</lastname>
<nickname>fong fong</nickname>
<salary>200000</salary>
</staff>
</company>
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;
public class ReadXMLFile {
public static void main(String argv[]) {
try {
SAXParserFactory factory = SAXParserFactory.newInstance();
SAXParser saxParser = factory.newSAXParser();
DefaultHandler handler = new DefaultHandler() {
boolean bfname = false;
boolean blname = false;
boolean bnname = false;
boolean bsalary = false;
public void startElement(String uri, String localName,String qName,
Attributes attributes) throws SAXException {
System.out.println("Start Element :" + qName);
if (qName.equalsIgnoreCase("FIRSTNAME")) {
bfname = true;
}
if (qName.equalsIgnoreCase("LASTNAME")) {
blname = true;
}
if (qName.equalsIgnoreCase("NICKNAME")) {
bnname = true;
}
if (qName.equalsIgnoreCase("SALARY")) {
bsalary = true;
}
}
public void endElement(String uri, String localName,
String qName) throws SAXException {
System.out.println("End Element :" + qName);
}
public void characters(char ch[], int start, int length) throws SAXException {
if (bfname) {
System.out.println("First Name : " + new String(ch, start, length));
bfname = false;
}
if (blname) {
System.out.println("Last Name : " + new String(ch, start, length));
blname = false;
}
if (bnname) {
System.out.println("Nick Name : " + new String(ch, start, length));
bnname = false;
}
if (bsalary) {
System.out.println("Salary : " + new String(ch, start, length));
bsalary = false;
}
}
};
saxParser.parse("c:\\file.xml", handler);
} catch (Exception e) {
e.printStackTrace();
}
}
}
结果
开始元素: 公司
开始元素: 员工
开始元素: 名字
名字:勇
结束元素: 名字
开始元素: 姓
姓: Mook Kim
结束元素: 姓
开始元素: 昵称
昵称:Mkyong
结束元素: 昵称
等等...
来源(MyKong) - http://www.mkyong.com/java/how-to-read-xml-file-in-java-sax-parser/
public void save(String tableName, List<Customer> customers) {
File f = new File(FileUtil.getTableFileName(tableName));
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
try {
// make the xml tree
// use factory to get the instance of document builder
DocumentBuilder db = dbf.newDocumentBuilder();
Document doc = db.newDocument();
// Root element <customers>
Element rootElem = doc.createElement(Customer.KEY_ROOT);
doc.appendChild(rootElem);
for (Customer customer : customers) {
Element customerElem = doc.createElement(Customer.KEY_ELEMENT);
rootElem.appendChild(customerElem);
// child element <ID> under <customer>
Element cid = doc.createElement(Customer.KEY_ID);
cid.appendChild(doc.createTextNode(Integer.toString(customer.getId())));
customerElem.appendChild(cid);
if (customer.getName() != null) {
Element name = doc.createElement(Customer.KEY_NAME);
name.appendChild(doc.createTextNode(customer.getName()));
customerElem.appendChild(name);
}
if (customer.getAddress() != null) {
Element address = doc.createElement(Customer.KEY_ADDRESS);
address.appendChild(doc.createTextNode(customer.getAddress()));
customerElem.appendChild(address);
}
if (customer.getCity() != null) {
Element city = doc.createElement(Customer.KEY_CITY);
city.appendChild(doc.createTextNode(customer.getCity()));
customerElem.appendChild(city);
}
if (customer.getPostCode() != null) {
Element postCode = doc.createElement(Customer.KEY_POSTCODE);
postCode.appendChild(doc.createTextNode(customer.getPostCode()));
customerElem.appendChild(postCode);
}
if (customer.getCountry() != null) {
Element country = doc.createElement(Customer.KEY_COUNTRY);
country.appendChild(doc.createTextNode(customer.getCountry()));
customerElem.appendChild(country);
}
}
// save the xml file
// Transformer is for process XML from a variety of sources and write the
// transformation
// output to a variety of sinks
Transformer transformer = TransformerFactory.newInstance().newTransformer();
// set xml encoding to utf-8
transformer.setOutputProperty(OutputKeys.ENCODING, "utf-8");
// pretty print
transformer.setOutputProperty(OutputKeys.INDENT, "yes");
DOMSource source = new DOMSource(doc);
StreamResult result = new StreamResult(f);
transformer.transform(source, result);
} catch (Exception e) {
e.printStackTrace();
}
}
public static List<List<String>> read(String fileName) {
List<List<String>> result = new ArrayList<>();
File f = new File(fileName);
if (!f.exists()) {
return result;
}
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
DocumentBuilder db;
try {
db = dbf.newDocumentBuilder();
Document doc = db.parse(f);
doc.getDocumentElement().normalize();
NodeList StatesNodes = doc.getElementsByTagName(STATE_ROOT_ELEMENT);
List<String> keys = new ArrayList<>();
List<String> states = new ArrayList<>();
for (int i = 0; i < StatesNodes.getLength(); i++) {
NodeList children = StatesNodes.item(i).getChildNodes();
for (int j = 0; j < children.getLength(); j++) {
Node child = children.item(j);
String childName = child.getNodeName();
if (child.getNodeType() == Node.ELEMENT_NODE) {
keys.add(childName);
states.add(child.getTextContent());
}
}
}
result.add(keys);
result.add(states);
} catch (Exception e) {
e.printStackTrace();
}
return result;
}