在不更改 XML 的情况下用 Java 解析包含 HTML 实体的

问题描述

I have to parse a bunch of XML files in Java that sometimes -- and invalidly -- contain HTML entities such as —, > and so forth. I understand the correct way of dealing with this is to add suitable entity declarations to the XML file before parsing. However, I can't do that as I have no control over those XML files.

Is there some kind of callback I can override that is invoked whenever the Java XML parser encounters such an entity? I haven't been able to find one in the API.

I'd like to use:

DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();

DocumentBuilder parser = dbf.newDocumentBuilder();
Document        doc    = parser.parse( stream );

I found that I can override resolveEntity in org.xml.sax.helpers.DefaultHandler, but how do I use this with the higher-level API?

Here's a full example:

public class Main {
    public static void main( String [] args ) throws Exception {
        DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
        DocumentBuilder parser = dbf.newDocumentBuilder();
        Document        doc    = parser.parse( new FileInputStream( "test.xml" ));
    }

}

with test.xml:

<?xml version="1.0" encoding="UTF-8"?>
<foo>
    <bar>Some&nbsp;text &mdash; invalid!</bar>
</foo>

Produces:

[Fatal Error] :3:20: The entity "nbsp" was referenced, but not declared.
Exception in thread "main" org.xml.sax.SAXParseException; lineNumber: 3; columnNumber: 20; The entity "nbsp" was referenced, but not declared.

Update: I have been poking around in the JDK source code with a debugger, and boy, what an amount of spaghetti. I have no idea what the design is there, or whether there is one. Just how many layers of an onion can one layer on top of each other?

They key class seems to be com.sun.org.apache.xerces.internal.impl.XMLEntityManager, but I cannot find any code that either lets me add stuff into it before it gets used, or that attempts to resolve entities without going through that class.

I would use a library like Jsoup for this purpose. I tested the following below and it works. I don't know if this helps. It can be located here: http://jsoup.org/download

public static void main(String args[]){


    String html = "<?xml version="1.0" encoding="UTF-8"?><foo>" + 
                  "<bar>Some&nbsp;text &mdash; invalid!</bar></foo>";
    Document doc = Jsoup.parse(html, "", Parser.xmlParser());

    for (Element e : doc.select("bar")) {
        System.out.println(e);
    }   


}

Result:

<bar>
 Some&nbsp;text — invalid!
</bar>

Loading from a file can be found here:

http://jsoup.org/cookbook/input/load-document-from-file

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