This is the documentation for the Apache Daffodil Scala API.
Provides the classes necessary to compile DFDL schemas, parse and unparse files using the compiled objects, and retrieve results and parsing diagnostics
Provides the classes necessary to compile DFDL schemas, parse and unparse files using the compiled objects, and retrieve results and parsing diagnostics
The Daffodil object is a factory object to create a Compiler. The Compiler provides a method to compile a provided DFDL schema into a ProcessorFactory, which creates a DataProcessor:
val c = Daffodil.compiler() val pf = c.compileFile(file) val dp = pf.onPath("/")
The DataProcessor provides the necessary functions to parse and unparse data, returning a ParseResult or UnparseResult, respectively. These contain information about the parse/unparse, such as whether or not the processing succeeded with any diagnostic information.
The DataProcessor also provides two functions that can be used to perform parsing/unparsing via the SAX API. The first creates a DaffodilParseXMLReader which is used for parsing, and the second creates a DaffodilUnparseContentHandler which is used for unparsing.
val xmlReader = dp.newXMLReaderInstance val unparseContentHandler = dp.newContentHandlerInstance(output)
The DaffodilParseXMLReader has several methods that allow one to set properties and handlers (such as ContentHandlers or ErrorHandlers) for the reader. One can use any contentHandler/errorHandler as long as they extend the org.xml.sax.ContentHandler and org.xml.sax.ErrorHandler interfaces respectively. One can also set properties for the DaffodilParseXMLReader using DaffodilParseXMLReader.setProperty.
The following properties can be set as follows:
The constants below have literal values starting with "urn:ogf:dfdl:2013:imp:daffodil.apache.org:2018:sax:" and ending with "BlobDirectory", "BlobPrefix" and "BlobSuffix" respectively.
xmlReader.setProperty(DaffodilParseXMLReader.DAFFODIL_SAX_URN_BLOBDIRECTORY, Paths.get(System.getProperty("java.io.tmpdir"))) // value type: java.nio.file.Paths xmlReader.setProperty(DaffodilParseXMLReader.DAFFODIL_SAX_URN_BLOBPREFIX, "daffodil-sax-") // value type String xmlReader.setProperty(DaffodilParseXMLReader.DAFFODIL_SAX_URN_BLOBSUFFIX, ".bin") // value type String
The properties can be retrieved using the same variables with DaffodilParseXMLReader.getProperty and casting to the appropriate type as listed above.
The following handlers can be set as follows:
xmlReader.setContentHandler(contentHandler) xmlReader.setErrorHandler(errorHandler)
The handlers above must implement the following interfaces respectively:
org.xml.sax.ContentHandler org.xml.sax.ErrorHandler
The ParseResult can be found as a property within the DaffodilParseXMLReader using this uri: "urn:ogf:dfdl:2013:imp:daffodil.apache.org:2018:sax:ParseResult" or DaffodilParseXMLReader.DAFFODIL_SAX_URN_PARSERESULT
In order for a successful unparse to happen, the SAX API requires the unparse to be kicked off by a parse call to any org.xml.sax.XMLReader implementation that has the DaffodilUnparseContentHandler registered as its content handler. To retrieve the UnparseResult, one can use DaffodilUnparseContentHandler.getUnparseResult once the XMLReader.parse run is complete.
The DataProcessor.parse method accepts input data to parse in the form of a InputSourceDataInputStream and an InfosetOutputter to determine the output representation of the infoset (e.g. Scala XML Nodes, JDOM2 Documents, etc.):
val scalaOutputter = new ScalaXMLInfosetOutputter() val is = new InputSourceDataInputStream(data) val pr = dp.parse(is, scalaOutputter) val node = scalaOutputter.getResult
The DataProcessor.parse method is thread-safe and may be called multiple times without the need to create other data processors. However, InfosetOutputter's are not thread safe, requiring a unique instance per thread. An InfosetOutputter should call InfosetOutputter.reset before reuse (or a new one should be allocated). For example:
val scalaOutputter = new ScalaXMLInfosetOutputter() files.foreach { f => { outputter.reset val is = new InputSourceDataInputStream(new FileInputStream(f)) val pr = dp.parse(is, scalaOutputter) val node = scalaOutputter.getResult }
One can repeat calls to parse() using the same InputSourceDataInputStream to continue parsing where the previous parse ended. For example:
val is = new InputSourceDataInputStream(dataStream) val scalaOutputter = new ScalaXMLInfosetOutputter() val keepParsing = true while (keepParsing && is.hasData()) { scalaOutputter.reset() val pr = dp.parse(is, jdomOutputter) ... keepParsing = !pr.isError() }
The DaffodilParseXMLReader.parse method accepts input data to parse in the form of a InputSourceDataInputStream. The output representation of the infoset, as well as how parse errors are handled, are dependent on the content handler and the error handler provided to the DaffodilParseXMLReader. For example, the org.jdom2.input.sax.SAXHandler provides a JDOM representation, whereas other ContentHandlers may output directly to a java.io.OutputStream or java.io.Writer.
val contentHandler = new SAXHandler() xmlReader.setContentHandler(contentHandler) val is = new InputSourceDataInputStream(data) xmlReader.parse(is) val pr = xmlReader.getProperty(DaffodilParseXMLReader.DAFFODIL_SAX_URN_PARSERESULT) val doc = saxHandler.getDocument
The DaffodilParseXMLReader.parse method is not thread-safe and may only be called again/reused once a parse operation is completed. This can be done multiple times without the need to create new DaffodilParseXMLReaders, ContentHandlers or ErrorHandlers. It might be necessary to reset whatever ContentHandler is used (or allocate a new one). A thread-safe implementation would require unique instances of the DaffodilParseXMLReader and its components. For example:
val contentHandler = new SAXHandler() xmlReader.setContentHandler(contentHandler) files.foreach { f => { contentHandler.reset val is = new InputSourceDataInputStream(new FileInputStream(f)) xmlReader.parse(is) val pr = xmlReader.getProperty(DaffodilParseXMLReader.DAFFODIL_SAX_URN_PARSERESULT) val doc = saxHandler.getDocument }
The value of the supported features cannot be changed during a parse, and the parse will run with the value of the features as they were when the parse was kicked off. To run a parse with different feature values, one must wait until the running parse finishes, set the feature values using the XMLReader's setFeature and run the parse again.
One can repeat calls to parse() using the same InputSourceDataInputStream to continue parsing where the previous parse ended. For example:
val is = new InputSourceDataInputStream(dataStream) val contentHandler = new SAXHandler() xmlReader.setContentHandler(contentHandler) val keepParsing = true while (keepParsing && is.hasData()) { contentHandler.reset() xmlReader.parse(is) val pr = xmlReader.getProperty(DaffodilParseXMLReader.DAFFODIL_SAX_URN_PARSERESULT) ... keepParsing = !pr.isError() }
The same DataProcessor used for parse can be used to unparse an infoset via the DataProcessor.unparse method. An InfosetInputter provides the infoset to unparse, with the unparsed data written to the provided java.nio.channels.WritableByteChannel. For example:
val inputter = new ScalaXMLInfosetInputter(node) val ur = dp.unparse(inputter, wbc)
In order to kick off an unparse via the SAX API, one must register the DaffodilUnparseContentHandler as the contentHandler for an XMLReader implementation. The call to the DataProcessor.newContentHandlerInstance method must be provided with the java.nio.channels.WritableByteChannel, where the unparsed data ought to be written to. Any XMLReader implementation is permissible, as long as they have XML Namespace support.
val is = new ByteArrayInputStream(data) val os = new ByteArrayOutputStream() val wbc = java.nio.channels.Channels.newChannel(os) val unparseContentHandler = dp.newContentHandlerInstance(wbc) val xmlReader = SAXParserFactory.newInstance.newSAXParser.getXMLReader xmlReader.setContentHandler(unparseContentHandler) try { xmlReader.parse(is) } catch { case _: DaffodilUnparseErrorSAXException => ... case _: DaffodilUnhandledSAXException => ... }
The call to the XMLReader.parse method must be wrapped in a try/catch, as DaffodilUnparseContentHandler relies on throwing an exception to end processing in the case of anyerrors/failures. There are two kinds of errors to expect: DaffodilUnparseErrorSAXException, for the case when the UnparseResult.isError, and DaffodilUnhandledSAXException, for any other errors.
In the case of an DaffodilUnhandledSAXException,DaffodilUnparseContentHandler.getUnparseResult will return null.
try { xmlReader.parse(new InputSource(is)) } catch { case _: DaffodilUnhandledSAXException => ... case _: DaffodilUnparseErrorSAXException => ... } val ur = unparseContentHandler.getUnparseResult
It is possible that failures could occur during the creation of the ProcessorFactory, DataProcessor, or ParseResult. However, rather than throwing an exception on error (e.g. invalid DFDL schema, parse error, etc), these classes extend WithDiagnostics, which is used to determine if an error occurred, and any diagnostic information (see Diagnostic) related to the step. Thus, before continuing, one must check WithDiagnostics.isError. For example:
val pf = c.compile(file) if (pf.isError()) { val diags = pf.getDiagnostics() diags.foreach { d => System.out.println(d.toString()) } return -1; }
In some cases, it may be beneficial to save a parser and reload it. For example, when starting up, it may be quicker to reload an already compiled parser than to compile it from scratch. To save a DataProcessor:
val dp = pf.onPath("/") dp.save(saveFile);
And to restore a saved DataProcessor:
val dp = Daffodil.reload(saveFile);And use like below:
val pr = dp.parse(data);or
val xmlReader = dp.newXMLReaderInstance ... // setting appropriate handlers xmlReader.parse(data) val pr = xmlReader.getProperty("...ParseResult")
This is the documentation for the Apache Daffodil Scala API.
Package structure
org.apache.daffodil.sapi - Provides the classes necessary to compile DFDL schemas, parse and unparse files using the compiled objects, and retrieve results and parsing diagnostics
org.apache.daffodil.udf - Provides the classes necessary to create User Defined Functions to extend the DFDL expression language
org.apache.daffodil.runtime1.layers.api - Provides the classes necessary to create custom Layer extensions to DFDL.