Leggere il file XML in Java è molto diverso dalla lettura di altri file come .docx e .txt perché il file XML contiene dati tra i tag. Java offre molti modi per analizzare un file XML. Esistono due parser in Java che analizzano un file XML:
- Giava DOM Analizzatore
- Giava CORRETTO Analizzatore
Analizzatore DOM Java
IL API DOM fornisce le classi per leggere e scrivere un file XML. Possiamo creare, eliminare, modificare e riorganizzare il nodo utilizzando l'API DOM. Il parser DOM analizza l'intero file XML e crea un file DOM oggetto nella memoria. Modella un file XML in a struttura ad albero per un facile attraversamento e manipolazione. In DOM tutto in un file XML è un file nodo . Il nodo rappresenta un componente di un file XML. Il parser DOM è lento in corso e occupa molta memoria quando carica un file XML in memoria.
bash diviso in corde
Dobbiamo aver seguito il processo per leggere un file XML in Java:
Passaggi per leggere il file XML in Java utilizzando Eclipse
Passo 1: Crea un semplice Giava progetto.
Passo 2: Creare un file di classe e fornire un nome file di classe. Abbiamo creato il file di classe con il nome LeggiFileXMLEsempio1 .
Passaggio 3: Scrivi il seguente codice.
Passaggio 4: Scaricamento dom-2.3.0-jaxb-1.0.6.jar file: Clicca qui...
Passaggio 5: Creare un lib cartella nel progetto.
Passaggio 6: copia dom-2.3.0-jaxb-1.0.6.jar file e incollalo nella cartella lib.
Passaggio 7: Impostare il percorso di classe :
Fare clic con il pulsante destro del mouse sul progetto->Percorso di creazione->Configura percorso di creazione->Aggiungi JAR esterni->Seleziona il file JAR->fai clic sul pulsante Apri->Applica e chiudi.
Passaggio 8: Creare un XML file. Abbiamo creato un file XML con il nome XMLFile.xml e scrivici i seguenti dati.
cos'è un file system linux
Passaggio 9: Esegui il progetto.
Creazione del file XML: XMLFile.xml
101 Naman Kumar Math 83 102 Kapil Kumar Chemistry 60 103 Harsh Singh English 70 104 Jitesh Singh Physics 76
Esempio di lettura di file XML utilizzando 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();>
Vediamo un altro esempio di lettura di file xml.
urfi javed
Esempio di lettura di file XML utilizzando DOM Parser
L'esempio seguente legge lo stesso file XML XMLFile.xml e mostrando come eseguire il loop del nodo uno per uno. Stampa il valore del nodo, il nome e l'eventuale attributo.
Esempio
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();>
Analizzatore Java SAX
Il parser Java SAX sta per API semplice per XML . Il parser SAX analizza un file XML linea per linea . Attiva eventi quando incontra il tag di apertura, il tag di chiusura e i dati dei caratteri in un file xml. Il parser SAX è anche chiamato parser basato su eventi .
Il parser SAX non carica alcun file XML in memoria. Non crea alcuna rappresentazione dell'oggetto del documento XML. Il parser SAX utilizza la funzione di call back per informare i client della struttura del documento XML. È Più veloce e usi meno memoria rispetto al parser DOM.
SAX è un interfaccia di streaming per XML, il che significa che il file XML viene analizzato in ordine sequenziale iniziando dalla parte superiore del documento e terminando con la chiusura dell'elemento root.
Esempio di lettura di file XML utilizzando il parser SAX
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(); } } }
Produzione:
ipconfig su Ubuntu
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