How to read and write xml files

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I have to read and write to and from an XML file  What is the easiest way to read and write XML files using Java

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Ok  already having DOM  JaxB and XStream in the list of answers  there is still a complete different way to read and write XML  Data projection You can decouple the XML structure and the Java structure by using a library that provides read and writeable views to the XML Data as Java interfaces  From the tutorials   Given some real world XML    lt weatherdata gt     lt weather              degreetype  F      lat  50 5520210266113  lon  6 24060010910034       searchlocation  Monschau  Stadt Aachen  NW  Germany                    gt       lt current     skytext  Clear  temperature  46   gt     lt  weather gt   lt  weatherdata gt    With data projection you can define a projection interface   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        And use instances of this interface just like POJOs   private void printWeatherData String location  throws IOException    final String BaseURL    http   weather service msn com find aspx outputview search amp 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         This works even for creating XML  the XPath expressions can be writable

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SAX parser is working differently with a DOM parser  it neither load any XML document into memory nor create any object representation of the XML document  Instead  the SAX parser use callback function org xml sax helpers DefaultHandler to informs clients of the XML document structure   SAX Parser is faster and uses less memory than DOM parser  See following SAX callback methods    startDocument   and endDocument       Method called at the start and end of an XML document  startElement   and endElement       Method called at the start and end of a document element  characters       Method called with the text contents in between the start and end tags of an XML document element    XML file   Create a simple XML file    lt  xml version  1 0   gt   lt company gt       lt staff gt           lt firstname gt yong lt  firstname gt           lt lastname gt mook kim lt  lastname gt           lt nickname gt mkyong lt  nickname gt           lt salary gt 100000 lt  salary gt       lt  staff gt       lt staff gt           lt firstname gt low lt  firstname gt           lt lastname gt yin fong lt  lastname gt           lt nickname gt fong fong lt  nickname gt           lt salary gt 200000 lt  salary gt       lt  staff gt   lt  company gt     XML parser    Java  file Use SAX parser to parse the XML file   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                          Result  Start Element  company Start Element  staff Start Element  firstname First Name   yong End Element  firstname Start Element  lastname Last Name   mook kim End Element  lastname Start Element  nickname Nick Name   mkyong End Element  nickname and so on     Source MyKong  - http   www mkyong com java how-to-read-xml-file-in-java-sax-parser

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The answers only cover DOM   SAX and a copy paste implementation of a JAXB example   However  one big area of when you are using XML is missing  In many projects   programs there is a need to store   retrieve some basic data structures  Your program has already a classes for your nice and shiny business objects   data structures  you just want a comfortable way to convert this data to a XML structure so you can do more magic on it  store  load  send  manipulate with XSLT    This is where XStream shines  You simply annotate the classes holding your data  or if you do not want to change those classes  you configure a XStream instance for marshalling  objects -  xml  or unmarshalling  xml -  objects    Internally XStream uses reflection  the readObject and readResolve methods of standard Java object serialization   You get a good and speedy tutorial here    To give a short overview of how it works  I also provide some sample code which marshalls and unmarshalls a data structure  The marshalling   unmarshalling happens all in the main method  the rest is just code to generate some test objects and populate some data to them  It is super simple to configure the xStream instance and marshalling   unmarshalling is done with one line of code each   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 - gt  xml     System out println  Marshalled  n    xml       Customer unmarshalledCustomer    Customer xStream fromXML xml      xml - gt  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 lt Good gt  stock   new ArrayList lt Good gt          Customer add Good g          stock add g         return this

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The above answer only deal with DOM parser  that normally reads the entire file in memory and parse it  what for a big file is a problem   you could use a SAX parser that uses less memory and is faster  anyway that depends on your code    SAX parser callback some functions when it find a start of element  end of element  attribute  text between elements  etc  so it can parse the document and at the same time you get what you need   Some example code   http   www mkyong com java how-to-read-xml-file-in-java-sax-parser

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Writing XML using JAXB  Java Architecture for XML Binding    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

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Here is a quick DOM example that shows how to read and write a simple xml file with its dtd    lt  xml version  1 0  encoding  UTF-8  standalone  no   gt   lt  DOCTYPE roles SYSTEM  roles dtd  gt   lt roles gt       lt role1 gt User lt  role1 gt       lt role2 gt Author lt  role2 gt       lt role3 gt Admin lt  role3 gt       lt role4  gt   lt  roles gt    and the dtd    lt  xml version  1 0  encoding  UTF-8   gt   lt  ELEMENT roles  role1 role2 role3 role4  gt   lt  ELEMENT role1   PCDATA  gt   lt  ELEMENT role2   PCDATA  gt   lt  ELEMENT role3   PCDATA  gt   lt  ELEMENT role4   PCDATA  gt    First import these   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      Here are a few variables you will need   private String role1   null  private String role2   null  private String role3   null  private String role4   null  private ArrayList lt String gt  rolev    Here is a reader  String xml is the name of your xml file    public boolean readXML String xml            rolev   new ArrayList lt String gt             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          And here a writer   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             getTextValue is here   private String getTextValue String def  Element doc  String tag        String value   def      NodeList nl      nl   doc getElementsByTagName tag       if  nl getLength    gt  0  amp  amp  nl item 0  hasChildNodes              value   nl item 0  getFirstChild   getNodeValue              return value      Add a few accessors and mutators and you are done

[java] How to read and write xml files?

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