XML faila lasīšana Java programmā daudz atšķiras no citu failu, piemēram, .docx un .txt, lasīšanas, jo XML fails satur datus starp tagiem. Java nodrošina daudzus veidus, kā parsēt XML failu. Java ir divi parsētāji, kas parsē XML failu:
java sugas
- Java DOM Parsētājs
- Java PAREIZI Parsētājs
Java DOM parsētājs
The DOM API nodrošina klases XML failu lasīšanai un rakstīšanai. Mēs varam izveidot, dzēst, modificēt un pārkārtot mezglu, izmantojot DOM API. DOM parsētājs parsē visu XML failu un izveido a DOM objekts atmiņā. Tas modelē XML failu a koka struktūra ērtai pārvietošanai un manipulācijām. DOM viss XML failā ir a mezgls . Mezgls ir XML faila sastāvdaļa. DOM parsētājs ir lēns procesā un aizņem daudz atmiņas kad tas ielādē XML failu atmiņā.
Mums ir jāievēro process, lai lasītu XML failu Java:
Darbības, lai lasītu XML failu Java, izmantojot eclipse
1. darbība: Izveidojiet vienkāršu Java projektu.
2. darbība: Izveidojiet klases failu un norādiet klases faila nosaukumu. Mēs esam izveidojuši klases failu ar nosaukumu ReadXMLFileExample1 .
3. darbība: Uzrakstiet šādu kodu.
4. darbība: Lejupielādēt dom-2.3.0-jaxb-1.0.6.jar fails: Noklikšķiniet šeit...
5. darbība: Izveidot a lib mapi projektā.
6. darbība: Kopēt dom-2.3.0-jaxb-1.0.6.jar failu un ielīmējiet mapē lib.
7. darbība: Iestatiet klases ceļš :
Ar peles labo pogu noklikšķiniet uz projekta-> Veidošanas ceļš-> Konfigurēt būvēšanas ceļu-> Pievienot ārējos JAR-> Atlasiet JAR failu-> noklikšķiniet uz pogas Atvērt-> Lietot un aizvērt.
8. darbība: Izveidojiet an XML failu. Mēs esam izveidojuši XML failu ar nosaukumu XMLFile.xml un ierakstiet tajā šādus datus.
9. darbība: Palaidiet projektu.
XML faila izveide: XMLFile.xml
101 Naman Kumar Math 83 102 Kapil Kumar Chemistry 60 103 Harsh Singh English 70 104 Jitesh Singh Physics 76
XML faila lasīšanas piemērs, izmantojot DOM Parser
import javax.xml.parsers.DocumentBuilderFactory; import javax.xml.parsers.DocumentBuilder; import org.w3c.dom.Document; import org.w3c.dom.NodeList; import org.w3c.dom.Node; import org.w3c.dom.Element; import java.io.File; public class ReadXMLFileExample1 { public static void main(String argv[]) { try { //creating a constructor of file class and parsing an XML file File file = new File('F:\XMLFile.xml'); //an instance of factory that gives a document builder DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance(); //an instance of builder to parse the specified xml file DocumentBuilder db = dbf.newDocumentBuilder(); Document doc = db.parse(file); doc.getDocumentElement().normalize(); System.out.println('Root element: ' + doc.getDocumentElement().getNodeName()); NodeList nodeList = doc.getElementsByTagName('student'); // nodeList is not iterable, so we are using for loop for (int itr = 0; itr <nodelist.getlength(); itr++) { node system.out.println(' node name :' + node.getnodename()); if (node.getnodetype()="=" node.element_node) element eelement="(Element)" node; system.out.println('student id: '+ eelement.getelementsbytagname('id').item(0).gettextcontent()); system.out.println('first name: eelement.getelementsbytagname('firstname').item(0).gettextcontent()); system.out.println('last eelement.getelementsbytagname('lastname').item(0).gettextcontent()); system.out.println('subject: eelement.getelementsbytagname('subject').item(0).gettextcontent()); system.out.println('marks: eelement.getelementsbytagname('marks').item(0).gettextcontent()); } catch (exception e) e.printstacktrace(); < pre> <p> <strong>Output:</strong> </p> <pre> Root element: class Node Name: student Student id: 101 First Name: Naman Last Name: Kumar Subject: Math Marks: 83 Node Name: student Student id: 102 First Name: Kapil Last Name: Kumar Subject: Chemistry Marks: 60 Node Name: student Student id: 103 First Name: Harsh Last Name: Singh Subject: English Marks: 70 Node Name: student Student id: 104 First Name: Jitesh Last Name: Singh Subject: Physics Marks: 76 </pre> <p>Let's see another example of reading xml file.</p> <p> <strong>Example of reading XML file using DOM Parser</strong> </p> <p>The following example reads the same XML file <strong>XMLFile.xml</strong> , and showing that how to loop the node one by one. It prints the node value, name and attribute if any.</p> <p> <strong>Example</strong> </p> <pre> import java.io.File; import javax.xml.parsers.DocumentBuilder; import javax.xml.parsers.DocumentBuilderFactory; import org.w3c.dom.Document; import org.w3c.dom.NamedNodeMap; import org.w3c.dom.Node; import org.w3c.dom.NodeList; public class ReadXMLFileExample2 { public static void main(String[] args) { try { File file = new File('F:\XMLFile.xml'); DocumentBuilder documentBuilder = DocumentBuilderFactory.newInstance().newDocumentBuilder(); Document document = documentBuilder.parse(file); System.out.println('Root element: '+ document.getDocumentElement().getNodeName()); if (document.hasChildNodes()) { printNodeList(document.getChildNodes()); } } catch (Exception e) { System.out.println(e.getMessage()); } } private static void printNodeList(NodeList nodeList) { for (int count = 0; count <nodelist.getlength(); count++) { node elemnode="nodeList.item(count);" if (elemnode.getnodetype()="=" node.element_node) get name and value system.out.println(' node [open]'); system.out.println('node content=" + elemNode.getTextContent()); if (elemNode.hasAttributes()) { NamedNodeMap nodeMap = elemNode.getAttributes(); for (int i = 0; i < nodeMap.getLength(); i++) { Node node = nodeMap.item(i); System.out.println(" attr : ' + node.getnodename()); system.out.println('attr node.getnodevalue()); } (elemnode.haschildnodes()) recursive call the has child nodes printnodelist(elemnode.getchildnodes()); [close]'); < pre> <p> <strong>Output:</strong> </p> <pre> Root element: class Node Name =class [OPEN] Node Content = 101 Naman Kumar Maths 83 102 Kapil Kumar Chemistry 60 103 Harsh Singh English 70 104 Jitesh Singh Physics 76 Node Name =student [OPEN] Node Content = 101 Naman Kumar Maths 83 Node Name =id [OPEN] Node Content =101 Node Name =id [CLOSE] Node Name =firstname [OPEN] Node Content =Naman Node Name =firstname [CLOSE] Node Name =lastname [OPEN] Node Content =Kumar Node Name =lastname [CLOSE] Node Name =subject [OPEN] Node Content =Math Node Name =subject [CLOSE] Node Name =marks [OPEN] Node Content =83 Node Name =marks [CLOSE] Node Name =student [CLOSE] Node Name =student [OPEN] Node Content = 102 Kapil Kumar Chemistry 60 Node Name =id [OPEN] Node Content =102 Node Name =id [CLOSE] Node Name =firstname [OPEN] Node Content =Kapil Node Name =firstname [CLOSE] Node Name =lastname [OPEN] Node Content =Kumar Node Name =lastname [CLOSE] Node Name =subject [OPEN] Node Content =Chemistry Node Name =subject [CLOSE] Node Name =marks [OPEN] Node Content =60 Node Name =marks [CLOSE] Node Name =student [CLOSE] Node Name =student [OPEN] Node Content = 103 Harsh Singh English 70 Node Name =id [OPEN] Node Content =103 Node Name =id [CLOSE] Node Name =firstname [OPEN] Node Content =Harsh Node Name =firstname [CLOSE] Node Name =lastname [OPEN] Node Content =Singh Node Name =lastname [CLOSE] Node Name =subject [OPEN] Node Content =English Node Name =subject [CLOSE] Node Name =marks [OPEN] Node Content =70 Node Name =marks [CLOSE] Node Name =student [CLOSE] Node Name =student [OPEN] Node Content = 104 Jitesh Singh Physics 76 Node Name =id [OPEN] Node Content =104 Node Name =id [CLOSE] Node Name =firstname [OPEN] Node Content =Jitesh Node Name =firstname [CLOSE] Node Name =lastname [OPEN] Node Content =Singh Node Name =lastname [CLOSE] Node Name =subject [OPEN] Node Content =Physics Node Name =subject [CLOSE] Node Name =marks [OPEN] Node Content =76 Node Name =marks [CLOSE] Node Name =student [CLOSE] Node Name =class [CLOSE] </pre> <h2>Java SAX Parser</h2> <p>Java SAX parser stands for <strong>Simple API</strong> for <strong>XML</strong> . SAX parser parses an XML file <strong>line by line</strong> . It triggers events when it encounters the opening tag, closing tag, and character data in an xml file. SAX parser is also called the <strong>event-based parser</strong> .</p> <p>SAX parser does not load any XML file into memory. It does not create any object representation of the XML document. SAX parser uses call back function to inform clients of the XML document structure. It is <strong>faster</strong> and uses <strong>less memory</strong> than DOM parser.</p> <p>SAX is a <strong>streaming interface</strong> for XML, which means that XML file parses in sequential order starting at the top of the document, and ending with the closing of the root element.</p> <p> <strong>Example of reading XML file using SAX parser</strong> </p> <pre> 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 ReadXMLFileExample3 { public static void main(String args[]) { try { SAXParserFactory factory = SAXParserFactory.newInstance(); SAXParser saxParser = factory.newSAXParser(); DefaultHandler handler = new DefaultHandler() { boolean id = false; boolean firstname = false; boolean lastname = false; boolean subject = false; boolean marks = false; //parser starts parsing a specific element inside the document public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException { System.out.println('Start Element :' + qName); if(qName.equalsIgnoreCase('Id')) { id=true; } if (qName.equalsIgnoreCase('FIRSTNAME')) { firstname = true; } if (qName.equalsIgnoreCase('LASTNAME')) { lastname = true; } if (qName.equalsIgnoreCase('SUBJECT')) { subject = true; } if (qName.equalsIgnoreCase('MARKS')) { marks = true; } } //parser ends parsing the specific element inside the document public void endElement(String uri, String localName, String qName) throws SAXException { System.out.println('End Element:' + qName); } //reads the text value of the currently parsed element public void characters(char ch[], int start, int length) throws SAXException { if (id) { System.out.println('ID : ' + new String(ch, start, length)); id = false; } if (firstname) { System.out.println('First Name: ' + new String(ch, start, length)); firstname = false; } if (lastname) { System.out.println('Last Name: ' + new String(ch, start, length)); lastname = false; } if (subject) { System.out.println('Subject: ' + new String(ch, start, length)); subject = false; } if (marks) { System.out.println('Marks : ' + new String(ch, start, length)); marks = false; } } }; saxParser.parse('F:\XMLFile.xml', handler); } catch (Exception e) { e.printStackTrace(); } } } </pre> <p> <strong>Output:</strong> </p> <pre> Start Element: class Start Element: student Start Element: id ID: 101 End Element: id Start Element: firstname First Name: Naman End Element: firstname Start Element: lastname Last Name: Kumar End Element: lastname Start Element: subject Subject: Math End Element: subject Start Element: marks Marks: 83 End Element: marks End Element: student Start Element: student Start Element: id ID: 102 End Element: id Start Element: firstname First Name: Kapil End Element: firstname Start Element: lastname Last Name: Kumar End Element: lastname Start Element: subject Subject: Chemistry End Element: subject Start Element: marks Marks: 60 End Element: marks End Element: student Start Element: student Start Element: id ID: 103 End Element: id Start Element: firstname First Name: Harsh End Element: firstname Start Element: lastname Last Name: Singh End Element: lastname Start Element: subject Subject: English End Element: subject Start Element: marks Marks: 70 End Element: marks End Element: student Start Element: student Start Element: id ID: 104 End Element: id Start Element: firstname First Name: Jitesh End Element: firstname Start Element: lastname Last Name: Singh End Element: lastname Start Element: subject Subject: Physics End Element: subject Start Element: marks Marks: 76 End Element: marks End Element: student End Element: class </pre> <hr></nodelist.getlength();></pre></nodelist.getlength();>
Apskatīsim vēl vienu xml faila lasīšanas piemēru.
XML faila lasīšanas piemērs, izmantojot DOM Parser
Šis piemērs nolasa to pašu XML failu XMLFile.xml , un parāda, kā pa vienam mezglam izveidot cilpu. Tas izdrukā mezgla vērtību, nosaukumu un atribūtu, ja tāds ir.
Piemērs
import java.io.File; import javax.xml.parsers.DocumentBuilder; import javax.xml.parsers.DocumentBuilderFactory; import org.w3c.dom.Document; import org.w3c.dom.NamedNodeMap; import org.w3c.dom.Node; import org.w3c.dom.NodeList; public class ReadXMLFileExample2 { public static void main(String[] args) { try { File file = new File('F:\XMLFile.xml'); DocumentBuilder documentBuilder = DocumentBuilderFactory.newInstance().newDocumentBuilder(); Document document = documentBuilder.parse(file); System.out.println('Root element: '+ document.getDocumentElement().getNodeName()); if (document.hasChildNodes()) { printNodeList(document.getChildNodes()); } } catch (Exception e) { System.out.println(e.getMessage()); } } private static void printNodeList(NodeList nodeList) { for (int count = 0; count <nodelist.getlength(); count++) { node elemnode="nodeList.item(count);" if (elemnode.getnodetype()="=" node.element_node) get name and value system.out.println(\' node [open]\'); system.out.println(\'node content=" + elemNode.getTextContent()); if (elemNode.hasAttributes()) { NamedNodeMap nodeMap = elemNode.getAttributes(); for (int i = 0; i < nodeMap.getLength(); i++) { Node node = nodeMap.item(i); System.out.println(" attr : \' + node.getnodename()); system.out.println(\'attr node.getnodevalue()); } (elemnode.haschildnodes()) recursive call the has child nodes printnodelist(elemnode.getchildnodes()); [close]\'); < pre> <p> <strong>Output:</strong> </p> <pre> Root element: class Node Name =class [OPEN] Node Content = 101 Naman Kumar Maths 83 102 Kapil Kumar Chemistry 60 103 Harsh Singh English 70 104 Jitesh Singh Physics 76 Node Name =student [OPEN] Node Content = 101 Naman Kumar Maths 83 Node Name =id [OPEN] Node Content =101 Node Name =id [CLOSE] Node Name =firstname [OPEN] Node Content =Naman Node Name =firstname [CLOSE] Node Name =lastname [OPEN] Node Content =Kumar Node Name =lastname [CLOSE] Node Name =subject [OPEN] Node Content =Math Node Name =subject [CLOSE] Node Name =marks [OPEN] Node Content =83 Node Name =marks [CLOSE] Node Name =student [CLOSE] Node Name =student [OPEN] Node Content = 102 Kapil Kumar Chemistry 60 Node Name =id [OPEN] Node Content =102 Node Name =id [CLOSE] Node Name =firstname [OPEN] Node Content =Kapil Node Name =firstname [CLOSE] Node Name =lastname [OPEN] Node Content =Kumar Node Name =lastname [CLOSE] Node Name =subject [OPEN] Node Content =Chemistry Node Name =subject [CLOSE] Node Name =marks [OPEN] Node Content =60 Node Name =marks [CLOSE] Node Name =student [CLOSE] Node Name =student [OPEN] Node Content = 103 Harsh Singh English 70 Node Name =id [OPEN] Node Content =103 Node Name =id [CLOSE] Node Name =firstname [OPEN] Node Content =Harsh Node Name =firstname [CLOSE] Node Name =lastname [OPEN] Node Content =Singh Node Name =lastname [CLOSE] Node Name =subject [OPEN] Node Content =English Node Name =subject [CLOSE] Node Name =marks [OPEN] Node Content =70 Node Name =marks [CLOSE] Node Name =student [CLOSE] Node Name =student [OPEN] Node Content = 104 Jitesh Singh Physics 76 Node Name =id [OPEN] Node Content =104 Node Name =id [CLOSE] Node Name =firstname [OPEN] Node Content =Jitesh Node Name =firstname [CLOSE] Node Name =lastname [OPEN] Node Content =Singh Node Name =lastname [CLOSE] Node Name =subject [OPEN] Node Content =Physics Node Name =subject [CLOSE] Node Name =marks [OPEN] Node Content =76 Node Name =marks [CLOSE] Node Name =student [CLOSE] Node Name =class [CLOSE] </pre> <h2>Java SAX Parser</h2> <p>Java SAX parser stands for <strong>Simple API</strong> for <strong>XML</strong> . SAX parser parses an XML file <strong>line by line</strong> . It triggers events when it encounters the opening tag, closing tag, and character data in an xml file. SAX parser is also called the <strong>event-based parser</strong> .</p> <p>SAX parser does not load any XML file into memory. It does not create any object representation of the XML document. SAX parser uses call back function to inform clients of the XML document structure. It is <strong>faster</strong> and uses <strong>less memory</strong> than DOM parser.</p> <p>SAX is a <strong>streaming interface</strong> for XML, which means that XML file parses in sequential order starting at the top of the document, and ending with the closing of the root element.</p> <p> <strong>Example of reading XML file using SAX parser</strong> </p> <pre> 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 ReadXMLFileExample3 { public static void main(String args[]) { try { SAXParserFactory factory = SAXParserFactory.newInstance(); SAXParser saxParser = factory.newSAXParser(); DefaultHandler handler = new DefaultHandler() { boolean id = false; boolean firstname = false; boolean lastname = false; boolean subject = false; boolean marks = false; //parser starts parsing a specific element inside the document public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException { System.out.println('Start Element :' + qName); if(qName.equalsIgnoreCase('Id')) { id=true; } if (qName.equalsIgnoreCase('FIRSTNAME')) { firstname = true; } if (qName.equalsIgnoreCase('LASTNAME')) { lastname = true; } if (qName.equalsIgnoreCase('SUBJECT')) { subject = true; } if (qName.equalsIgnoreCase('MARKS')) { marks = true; } } //parser ends parsing the specific element inside the document public void endElement(String uri, String localName, String qName) throws SAXException { System.out.println('End Element:' + qName); } //reads the text value of the currently parsed element public void characters(char ch[], int start, int length) throws SAXException { if (id) { System.out.println('ID : ' + new String(ch, start, length)); id = false; } if (firstname) { System.out.println('First Name: ' + new String(ch, start, length)); firstname = false; } if (lastname) { System.out.println('Last Name: ' + new String(ch, start, length)); lastname = false; } if (subject) { System.out.println('Subject: ' + new String(ch, start, length)); subject = false; } if (marks) { System.out.println('Marks : ' + new String(ch, start, length)); marks = false; } } }; saxParser.parse('F:\XMLFile.xml', handler); } catch (Exception e) { e.printStackTrace(); } } } </pre> <p> <strong>Output:</strong> </p> <pre> Start Element: class Start Element: student Start Element: id ID: 101 End Element: id Start Element: firstname First Name: Naman End Element: firstname Start Element: lastname Last Name: Kumar End Element: lastname Start Element: subject Subject: Math End Element: subject Start Element: marks Marks: 83 End Element: marks End Element: student Start Element: student Start Element: id ID: 102 End Element: id Start Element: firstname First Name: Kapil End Element: firstname Start Element: lastname Last Name: Kumar End Element: lastname Start Element: subject Subject: Chemistry End Element: subject Start Element: marks Marks: 60 End Element: marks End Element: student Start Element: student Start Element: id ID: 103 End Element: id Start Element: firstname First Name: Harsh End Element: firstname Start Element: lastname Last Name: Singh End Element: lastname Start Element: subject Subject: English End Element: subject Start Element: marks Marks: 70 End Element: marks End Element: student Start Element: student Start Element: id ID: 104 End Element: id Start Element: firstname First Name: Jitesh End Element: firstname Start Element: lastname Last Name: Singh End Element: lastname Start Element: subject Subject: Physics End Element: subject Start Element: marks Marks: 76 End Element: marks End Element: student End Element: class </pre> <hr></nodelist.getlength();>
Java SAX parsētājs
Java SAX parsētājs apzīmē Vienkārša API priekš XML . SAX parsētājs parsē XML failu rindu pēc rindas . Tas aktivizē notikumus, saskaroties ar sākuma tagu, beigu tagu un rakstzīmju datiem xml failā. SAX parsētājs tiek saukts arī par uz notikumiem balstīts parsētājs .
SAX parsētājs neielādē atmiņā nevienu XML failu. Tas nerada nekādu XML dokumenta objekta attēlojumu. SAX parsētājs izmanto atzvanīšanas funkciju, lai informētu klientus par XML dokumenta struktūru. Tas ir ātrāk un lietojumiem mazāk atmiņas nekā DOM parsētājs.
saraksta virkne java
SAX ir a straumēšanas interfeiss XML, kas nozīmē, ka XML fails tiek parsēts secīgā secībā, sākot no dokumenta augšdaļas un beidzot ar saknes elementa aizvēršanu.
XML faila lasīšanas piemērs, izmantojot SAX parsētāju
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 ReadXMLFileExample3 { public static void main(String args[]) { try { SAXParserFactory factory = SAXParserFactory.newInstance(); SAXParser saxParser = factory.newSAXParser(); DefaultHandler handler = new DefaultHandler() { boolean id = false; boolean firstname = false; boolean lastname = false; boolean subject = false; boolean marks = false; //parser starts parsing a specific element inside the document public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException { System.out.println('Start Element :' + qName); if(qName.equalsIgnoreCase('Id')) { id=true; } if (qName.equalsIgnoreCase('FIRSTNAME')) { firstname = true; } if (qName.equalsIgnoreCase('LASTNAME')) { lastname = true; } if (qName.equalsIgnoreCase('SUBJECT')) { subject = true; } if (qName.equalsIgnoreCase('MARKS')) { marks = true; } } //parser ends parsing the specific element inside the document public void endElement(String uri, String localName, String qName) throws SAXException { System.out.println('End Element:' + qName); } //reads the text value of the currently parsed element public void characters(char ch[], int start, int length) throws SAXException { if (id) { System.out.println('ID : ' + new String(ch, start, length)); id = false; } if (firstname) { System.out.println('First Name: ' + new String(ch, start, length)); firstname = false; } if (lastname) { System.out.println('Last Name: ' + new String(ch, start, length)); lastname = false; } if (subject) { System.out.println('Subject: ' + new String(ch, start, length)); subject = false; } if (marks) { System.out.println('Marks : ' + new String(ch, start, length)); marks = false; } } }; saxParser.parse('F:\XMLFile.xml', handler); } catch (Exception e) { e.printStackTrace(); } } }
Izvade:
Start Element: class Start Element: student Start Element: id ID: 101 End Element: id Start Element: firstname First Name: Naman End Element: firstname Start Element: lastname Last Name: Kumar End Element: lastname Start Element: subject Subject: Math End Element: subject Start Element: marks Marks: 83 End Element: marks End Element: student Start Element: student Start Element: id ID: 102 End Element: id Start Element: firstname First Name: Kapil End Element: firstname Start Element: lastname Last Name: Kumar End Element: lastname Start Element: subject Subject: Chemistry End Element: subject Start Element: marks Marks: 60 End Element: marks End Element: student Start Element: student Start Element: id ID: 103 End Element: id Start Element: firstname First Name: Harsh End Element: firstname Start Element: lastname Last Name: Singh End Element: lastname Start Element: subject Subject: English End Element: subject Start Element: marks Marks: 70 End Element: marks End Element: student Start Element: student Start Element: id ID: 104 End Element: id Start Element: firstname First Name: Jitesh End Element: firstname Start Element: lastname Last Name: Singh End Element: lastname Start Element: subject Subject: Physics End Element: subject Start Element: marks Marks: 76 End Element: marks End Element: student End Element: class