使用SAX解析常见的XML元素 [英] Using SAX to parse common XML elements

问题描述

我目前正在使用SAX（Java）来解析一些不同的XML文档，每个文档代表不同的数据并且结构略有不同。因此，每个XML文档都由不同的SAX类处理（子类化 DefaultHandler ）。

I'm currently using SAX (Java) to parse a a handful of different XML documents, with each document representing different data and having slightly different structures. For this reason, each XML document is handled by a different SAX class (subclassing DefaultHandler).

但是，那里是一些可以出现在所有这些不同文档中的XML结构。理想情况下，我想告诉解析器嘿，当你到达 complex_node 元素时，只需使用 ComplexNodeHandler 即可阅读它，然后给我回复结果。如果你到达 some_other_node ，请使用 OtherNodeHandler 阅读并给我回到那个结果。

However, there are some XML structures that can appear in all these different documents. Ideally, I'd like to tell the parser "Hey, when you reach a complex_node element, just use ComplexNodeHandler to read it, and give me back the result. If you reach a some_other_node, use OtherNodeHandler to read it and give me back that result".

然而，我看不出一个明显的方法来做到这一点。

However, I can't see an obvious way to do this.

我应该只是制作一个单片处理程序类，它可以读取我拥有的所有不同文档（并根除代码重复），或者是否有一种更智能的方法来处理这个问题？

Should I simply just make a monolithic handler class that can read all the different documents I have (and eradicate duplication of code), or is there a smarter way to handle this?

推荐答案

以下是我对类似问题的回答（使用sax跳过节点。它演示了如何在XMLReader上交换内容处理程序。

Below is an answer I made to a similar question (Skipping nodes with sax). It demonstrates how to swap content handlers on an XMLReader.

在此示例中，交换的ContentHandler只是忽略所有事件，直到它放弃控制，但您可以轻松地调整概念。

In this example the swapped in ContentHandler simply ignores all events until it gives up control, but you could adapt the concept easily.

您可以执行以下操作：

import javax.xml.parsers.SAXParser; 
import javax.xml.parsers.SAXParserFactory; 
import org.xml.sax.XMLReader; 

public class Demo { 

    public static void main(String[] args) throws Exception { 
        SAXParserFactory spf = SAXParserFactory.newInstance(); 
        SAXParser sp = spf.newSAXParser(); 
        XMLReader xr = sp.getXMLReader(); 
        xr.setContentHandler(new MyContentHandler(xr)); 
        xr.parse("input.xml"); 
    } 
} 

MyContentHandler

此类负责处理XML文档。当您点击要忽略的节点时，您可以交换IgnoringContentHandler，它将吞下该节点的所有事件。

This class is responsible for processing your XML document. When you hit a node you want to ignore you can swap in the IgnoringContentHandler which will swallow all events for that node.

import org.xml.sax.Attributes; 
import org.xml.sax.ContentHandler; 
import org.xml.sax.Locator; 
import org.xml.sax.SAXException; 
import org.xml.sax.XMLReader; 

public class MyContentHandler implements ContentHandler { 

    private XMLReader xmlReader; 

    public MyContentHandler(XMLReader xmlReader) { 
        this.xmlReader = xmlReader; 
    } 

    public void setDocumentLocator(Locator locator) { 
    } 

    public void startDocument() throws SAXException { 
    } 

    public void endDocument() throws SAXException { 
    } 

    public void startPrefixMapping(String prefix, String uri) 
            throws SAXException { 
    } 

    public void endPrefixMapping(String prefix) throws SAXException { 
    } 

    public void startElement(String uri, String localName, String qName, 
            Attributes atts) throws SAXException { 
        if("sodium".equals(qName)) { 
            xmlReader.setContentHandler(new IgnoringContentHandler(xmlReader, this)); 
        } else { 
            System.out.println("START " + qName); 
        } 
    } 

    public void endElement(String uri, String localName, String qName) 
            throws SAXException { 
        System.out.println("END " + qName); 
    } 

    public void characters(char[] ch, int start, int length) 
            throws SAXException { 
        System.out.println(new String(ch, start, length)); 
    } 

    public void ignorableWhitespace(char[] ch, int start, int length) 
            throws SAXException { 
    } 

    public void processingInstruction(String target, String data) 
            throws SAXException { 
    } 

    public void skippedEntity(String name) throws SAXException { 
    } 

} 

IgnoringContentHandler

当IgnoringContentHandler完成吞咽事件时，它会将控制权传递给您的主ContentHandler。

When the IgnoringContentHandler is done swallowing events it passes control back to your main ContentHandler.

import org.xml.sax.Attributes; 
import org.xml.sax.ContentHandler; 
import org.xml.sax.Locator; 
import org.xml.sax.SAXException; 
import org.xml.sax.XMLReader; 

public class IgnoringContentHandler implements ContentHandler { 

    private int depth = 1; 
    private XMLReader xmlReader; 
    private ContentHandler contentHandler; 

    public IgnoringContentHandler(XMLReader xmlReader, ContentHandler contentHandler) { 
        this.contentHandler = contentHandler; 
        this.xmlReader = xmlReader; 
    } 

    public void setDocumentLocator(Locator locator) { 
    } 

    public void startDocument() throws SAXException { 
    } 

    public void endDocument() throws SAXException { 
    } 

    public void startPrefixMapping(String prefix, String uri) 
            throws SAXException { 
    } 

    public void endPrefixMapping(String prefix) throws SAXException { 
    } 

    public void startElement(String uri, String localName, String qName, 
            Attributes atts) throws SAXException { 
        depth++; 
    } 

    public void endElement(String uri, String localName, String qName) 
            throws SAXException { 
        depth--; 
        if(0 == depth) { 
           xmlReader.setContentHandler(contentHandler); 
        } 
    } 

    public void characters(char[] ch, int start, int length) 
            throws SAXException { 
    } 

    public void ignorableWhitespace(char[] ch, int start, int length) 
            throws SAXException { 
    } 

    public void processingInstruction(String target, String data) 
            throws SAXException { 
    } 

    public void skippedEntity(String name) throws SAXException { 
    } 

} 

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