Processing existing XML
Groovy provides special XML processing support through the following classes:
| Technology | When/Why to use | Requirements |
|---|---|---|
| XmlParser | supports GPath expressions for XML documents and allows updating | - |
| XmlSlurper | lower overheads than XmlParser due to lazy evaluation but only supports read operations | - |
| DOMCategory | low-level tree-based processing where you want some syntactic sugar | place use(DOMCategory) around your code |
If you have special needs, you can use one of the many available Java APIs for XML processing. You should consult the documentation of individual APIs for the details, but some examples to get you started are included here:
| Technology | When/Why to use | Requirements |
|---|---|---|
| DOM | low-level tree-based processing | - |
| SAX | event-based push-style parsing can be useful for streaming large files | - |
| StAX | event-based pull-style parsing can be useful for streaming large files | requires stax.jar |
| DOM4J | nicer syntax over DOM processing plus can be useful for large files if you use prune capability | requires dom4j.jar |
| XOM | nicer syntax over DOM processing plus a strong emphasis on compliancy | requires xom.jar |
| JDOM | nicer syntax over DOM processing | requires jdom.jar |
| XPath | use XPath expressions | requires Java 5+ or JAXP 1.3+ or xalan.jar or jaxen.jar |
| XSLT | when your transformation is more easily expressed using XSLT than code | - |
| XQuery | when your transformation is more easily expressed using XQuery than other alternatives | mxquery.jar or alternative |
Creating new XML
The most commonly used approach for creating XML with Groovy is to use a builder, i.e. one of:
| Technology | When/Why to use | Requirements |
|---|---|---|
| MarkupBuilder | supports Groovy's builder pattern with XML/HTML | - |
| StreamingMarkupBuilder | for larger files | - |
Groovy also has some low-level helper classes you typically won't need to use directly but you may sometimes see in older examples of using XML with Groovy.
| Technology | When/Why to use | Requirements |
|---|---|---|
| SAXBuilder | support class when using SAX | - |
| StreamingSAXBuilder | streaming version of SAXBuilder | - |
| DOMBuilder | support class when using DOM | - |
| StreamingDOMBuilder | streaming version of DOMBuilder | - |
You can also use Java API's which support XML document creation:
| Technology | When/Why to use | Requirements |
|---|---|---|
| DOM | low-level creation mechanism | - |
| JDOM | if you are an existing JDOM user | requires jdom.jar |
| DOM4J | if you are an existing DOM4J user | requires dom4j.jar |
| XOM | if you are an existing XOM user | requires xom.jar |
Troubleshooting
Some of the following Jira issues may indicate solutions or workarounds to problems other users faced while using XML.
| Issue | Description |
|---|---|
| GROOVY-2126 | ClassCastException when using java.util.prefs package |
More Information
For some more discussion of the pro's and con's of your XML Processing options and some additional details, see the following books:
The following articles may also be of interest:
- Getting Groovy with XML by Jack Herrington.
- XML and Java technologies: Document models, Part 1: Performance
- DOM, DOM4J, JDOM, XOM Comparison (slightly outdated)
- Dom4J performance versus Xerces / Xalan
- Hints for parsing XHTML with DOM4J
You may also be interested in how XML is applied in other parts of Groovy:
