Java：XML Parser

Question

I have a response XML something like this -

<Response> <aa> <Fromhere> <a1>Content</a1> <a2>Content</a2> </Fromhere> </aa> </Response>

I want to extract the whole content from <Fromhere> to </Fromhere> in a string. Is it possible to do that through any string function or through XML parser?

Please advice.

Answer 1

You could try an XPath approach for simpleness in XML parsing:

InputStream response = new ByteArrayInputStream("<Response> <aa> "
        + "<Fromhere> <a1>Content</a1> <a2>Content</a2> </Fromhere> "
        + "</aa> </Response>".getBytes()); /* Or whatever. */

DocumentBuilder builder = DocumentBuilderFactory
        .newInstance().newDocumentBuilder();
Document doc = builder.parse(response);

XPath xpath = XPathFactory.newInstance().newXPath();
XPathExpression expr = xpath.compile("string(/Response/aa/FromHere)");
String result = (String)expr.evaluate(doc, XPathConstants.STRING);

Note that I haven't tried this code. It may need tweaking.

Answer 2

Through an XML parser. Using string functions to parse XML is a bad idea...
Beside the Sun tutorials pointed out above, you can check the DZone Refcardz on Java and XML , I found it was a good, terse explanation how to do it.
But well, there is probably plenty of Web resources on the topic, including on this very site.

Answer 3

You can apply an XSLT stylesheet to extract the desired content.

This stylesheet should fit your example:

<?xml version="1.0" encoding="ISO-8859-1"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:template match="/Response/aa/Fromhere/*">
        <xsl:copy>
            <xsl:apply-templates/>
        </xsl:copy>
    </xsl:template>
</xsl:stylesheet>

Apply it with something like the following (exception handling not included):

String xml = "<Response> <aa> <Fromhere> <a1>Content</a1> <a2>Content</a2> </Fromhere> </aa> </Response>";
Source xsl = new StreamSource(new FileReader("/path/to/file.xsl");

TransformerFactory transformerFactory = TransformerFactory.newInstance();
Transformer transformer = transformerFactory.newTransformer(xsl);
transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");

StringWriter out = new StringWriter();
transformer.transform(new StreamSource(new StringReader(xml)), new StreamResult(out));

System.out.println(out.toString());

This should work with any version of Java starting with 1.4.

Answer 4

This should work

import java.util.regex.*

Pattern p = Pattern.compile("<Fromhere>.*</Fromhere>");
Matcher m = p.matcher(responseString);
String whatYouWant = m.group();

It would be a little more verbose to use Scanner, but that could work too.

Whether this is a good idea is for someone more experienced than I.

Answer 5

One option is to use a StreamFilter :

class MyFilter implements StreamFilter {
  private boolean on;

  @Override
  public boolean accept(XMLStreamReader reader) {
    final String element = "Fromhere";
    if (reader.isStartElement() && element.equals(reader.getLocalName())) {
      on = true;
    } else if (reader.isEndElement()
        && element.equals(reader.getLocalName())) {
      on = false;
      return true;
    }
    return on;
  }
}

Combined with a Transformer , you can use this to safely parse logically-equivalent markup like this:

<Response>
  <!-- <Fromhere></Fromhere> -->
  <aa>
    <Fromhere>
      <a1>Content</a1> <a2>Content</a2>
    </Fromhere>
  </aa>
</Response>

Demo:

StringWriter writer = new StringWriter();

XMLInputFactory inputFactory = XMLInputFactory.newInstance();
XMLStreamReader reader = inputFactory
    .createXMLStreamReader(new StringReader(xmlString));
reader = inputFactory.createFilteredReader(reader, new MyFilter());
TransformerFactory transFactory = TransformerFactory.newInstance();
Transformer transformer = transFactory.newTransformer();
transformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
transformer.transform(new StAXSource(reader), new StreamResult(writer));

System.out.println(writer.toString());

This is a programmatic variation on Massimiliano Fliri's approach.