Java XML 转换为字符串 – 将 XML 对象写入文件的示例

原文： https://howtodoinjava.com/xml/xml-to-string-write-xml-file/

Java 示例读取 XML 文件，打印 XML 字符串进行控制台，或将 XML 写入文件。

1）将 XML 转换为字符串

要将 XML 对象（即org.w3c.dom.Document）转换为字符串，您需要以下类：

• javax.xml.transform.Transformer：此类的实例可以使用其transform()方法将源树转换为结果树。
• javax.xml.transform.TransformerFactory：创建Transformer实例的工厂。
• javax.xml.transform.dom.DOMSource：文档树（DOM）树形式的源树。
• javax.xml.transform.stream.StreamResult：转换结果树的持有人，可以是 XML，纯文本，HTML 或其他某种形式的标记。

1.1）将 XML 打印到控制台或日志文件

private static void writeXmlDocumentToXmlFile(Document xmlDocument)
{
    TransformerFactory tf = TransformerFactory.newInstance();
    Transformer transformer;
    try {
        transformer = tf.newTransformer();
        // Uncomment if you do not require XML declaration
        // transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
        //A character stream that collects its output in a string buffer, 
        //which can then be used to construct a string.
        StringWriter writer = new StringWriter();
        //transform document to string 
        transformer.transform(new DOMSource(xmlDocument), new StreamResult(writer));
        String xmlString = writer.getBuffer().toString();    
        System.out.println(xmlString);                        //Print to console or logs
    } 
    catch (TransformerException e) 
    {
        e.printStackTrace();
    }
    catch (Exception e) 
    {
        e.printStackTrace();
    }
}

1.2）将 XML 写入文件

private static void writeXmlDocumentToXmlFile(Document xmlDocument, String fileName)
{
    TransformerFactory tf = TransformerFactory.newInstance();
    Transformer transformer;
    try {
        transformer = tf.newTransformer();
        //Uncomment if you do not require XML declaration
        //transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
        //Write XML to file
        FileOutputStream outStream = new FileOutputStream(new File(fileName)); 
        transformer.transform(new DOMSource(xmlDocument), new StreamResult(outStream));
    } 
    catch (TransformerException e) 
    {
        e.printStackTrace();
    }
    catch (Exception e) 
    {
        e.printStackTrace();
    }
}

2）从文件读取 XML

将 XML 从.xml文件读取到Document对象的示例。

private static Document convertXMLFileToXMLDocument(String filePath) 
{
    //Parser that produces DOM object trees from XML content
    DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
    //API to obtain DOM Document instance
    DocumentBuilder builder = null;
    try 
    {
        //Create DocumentBuilder with default configuration
        builder = factory.newDocumentBuilder();
        //Parse the content to Document object
        Document xmlDocument = builder.parse(new File(filePath));
        return xmlDocument;
    } 
    catch (Exception e) 
    {
        e.printStackTrace();
    }
    return null;
}

3）完整的例子

用于运行示例的完整代码。

package com.howtodoinjava.demo;
import java.io.File;
import java.io.FileOutputStream;
import java.io.StringWriter;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import org.w3c.dom.Document;
public class XmlToStringExample 
{
    public static void main(String[] args) 
    {
        final String xmlFilePath = "employees.xml";
        //Use method to convert XML string content to XML Document object
        Document xmlDocument = convertXMLFileToXMLDocument( xmlFilePath );
        //Write to file or print XML
        writeXmlDocumentToXmlFile(xmlDocument, "newEmployees.xml");
    }
    private static Document convertXMLFileToXMLDocument(String filePath) 
    {
        //Parser that produces DOM object trees from XML content
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        //API to obtain DOM Document instance
        DocumentBuilder builder = null;
        try 
        {
            //Create DocumentBuilder with default configuration
            builder = factory.newDocumentBuilder();
            //Parse the content to Document object
            Document xmlDocument = builder.parse(new File(filePath));
            return xmlDocument;
        } 
        catch (Exception e) 
        {
            e.printStackTrace();
        }
        return null;
    }
    private static void writeXmlDocumentToXmlFile(Document xmlDocument, String fileName)
    {
        TransformerFactory tf = TransformerFactory.newInstance();
        Transformer transformer;
        try {
            transformer = tf.newTransformer();
            // Uncomment if you do not require XML declaration
            // transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
            //Print XML or Logs or Console
            StringWriter writer = new StringWriter();
            transformer.transform(new DOMSource(xmlDocument), new StreamResult(writer));
            String xmlString = writer.getBuffer().toString();    
            System.out.println(xmlString);            
            //Write XML to file
            FileOutputStream outStream = new FileOutputStream(new File(fileName)); 
            transformer.transform(new DOMSource(xmlDocument), new StreamResult(outStream));
        } 
        catch (TransformerException e) 
        {
            e.printStackTrace();
        }
        catch (Exception e) 
        {
            e.printStackTrace();
        }
    }
}

输入文件。

<employees>
    <employee id="101">
         <name>Lokesh Gupta</name>
        <title>Author</title>
    </employee>
    <employee id="102">
         <name>Brian Lara</name>
        <title>Cricketer</title>
    </employee>
</employees>

输出文件。

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<employees>
    <employee id="101">
         <name>Lokesh Gupta</name>
        <title>Author</title>
    </employee>
    <employee id="102">
         <name>Brian Lara</name>
        <title>Cricketer</title>
    </employee>
</employees>

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