* nsfix | validate | write ( stdout )* *
In this syntax, the tokens are always separated by whitespace, and each * stage of the pipeline may optionally have a parameter (which can be a * pipeline) in parentheses. Interior stages are called filters, and the * rightmost end of a pipeline is called a terminus. * *
Stages are usually implemented by a single class, which may not be * able to act as both a filter and a terminus; but any terminus can be * automatically turned into a filter, through use of a {@link TeeConsumer}. * The stage identifiers are either class names, or are one of the following * short identifiers built into this class. (Most of these identifiers are * no more than aliases for classes.) The built-in identifiers include:
| Stage | Parameter | Terminus | Description |
|---|---|---|---|
| dom | none | yes | Applications code can access a DOM Document built from the input event stream. When used as a filter, this buffers data up to an endDocument call, and then uses a DOM parser to report everything that has been recorded (which can easily be less than what was reported to it). |
| nsfix | none | no | This stage ensures that the XML element and attribute names in its output use namespace prefixes and declarations correctly. That is, so that they match the "Namespace plus LocalName" naming data with which each XML element and attribute is already associated. |
| null | none | yes | This stage ignores all input event data. |
| server | required server URL |
no | Sends its input as XML request to a remote server, normally a web application server using the HTTP or HTTPS protocols. The output of this stage is the parsed response from that server. |
| tee | required first pipeline |
no | This sends its events down two paths; its parameter is a pipeline descriptor for the first path, and the second path is the output of this stage. |
| validate | none | yes | This checks for validity errors, and reports them through its error handler. The input must include declaration events and some lexical events. |
| wf | none | yes | This class provides some basic "well formedness" tests on the input event stream, and reports a fatal error if any of them fail. One example: start/end calls for elements must match. No SAX parser is permitted to produce malformed output, but other components can easily do so. |
| write | required "stdout", "stderr", or filename |
yes | Writes its input to the specified output, as pretty printed XML text encoded using UTF-8. Input events must be well formed and "namespace fixed", else the output won't be XML (or possibly namespace) conformant. The symbolic names represent System.out and System.err respectively; names must correspond to files which don't yet exist. |
| xhtml | required "stdout", "stderr", or filename |
yes | Like write (above), except that XHTML rules are followed. The XHTML 1.0 Transitional document type is declared, and only ASCII characters are written (for interoperability). Other characters are written as entity or character references; the text is pretty printed. |
| xinclude | none | no | This stage handles XInclude processing. This is like entity inclusion, except that the included content is declared in-line rather than in the DTD at the beginning of a document. |
| xslt | required XSLT stylesheet URI |
no | This stage handles XSLT transformation according to a stylesheet. The implementation of the transformation may not actually stream data, although if such an XSLT engine is in use then that can happen. |
Note that {@link EventFilter#bind} can automatically eliminate * some filters by setting SAX2 parser features appropriately. This means * that you can routinely put filters like "nsfix", "validate", or "wf" at the * front of a pipeline (for components that need inputs conditioned to match * that level of correctness), and know that it won't actually be used unless * it's absolutely necessary. * * @author David Brownell */ public class PipelineFactory { /** * Creates a simple pipeline according to the description string passed in. */ public static EventConsumer createPipeline (String description) throws IOException { return createPipeline (description, null); } /** * Extends an existing pipeline by prepending the filter pipeline to the * specified consumer. Some pipelines need more customization than can * be done through this simplified syntax. When they are set up with * direct API calls, use this method to merge more complex pipeline * segments with easily configured ones. */ public static EventConsumer createPipeline ( String description, EventConsumer next ) throws IOException { // tokens are (for now) what's separated by whitespace; // very easy to parse, but IDs never have spaces. StringTokenizer tokenizer; String tokens []; tokenizer = new StringTokenizer (description); tokens = new String [tokenizer.countTokens ()]; for (int i = 0; i < tokens.length; i++) tokens [i] = tokenizer.nextToken (); PipelineFactory factory = new PipelineFactory (); Pipeline pipeline = factory.parsePipeline (tokens, next); return pipeline.createPipeline (); } private PipelineFactory () { /* NYET */ } /** * Extends an existing pipeline by prepending a pre-tokenized filter * pipeline to the specified consumer. Tokens are class names (or the * predefined aliases) left and right parenthesis, and the vertical bar. */ public static EventConsumer createPipeline ( String tokens [], EventConsumer next ) throws IOException { PipelineFactory factory = new PipelineFactory (); Pipeline pipeline = factory.parsePipeline (tokens, next); return pipeline.createPipeline (); } private String tokens []; private int index; private Pipeline parsePipeline (String toks [], EventConsumer next) { tokens = toks; index = 0; Pipeline retval = parsePipeline (next); if (index != toks.length) throw new ArrayIndexOutOfBoundsException ( "extra token: " + tokens [index]); return retval; } // pipeline ::= stage | stage '|' pipeline private Pipeline parsePipeline (EventConsumer next) { Pipeline retval = new Pipeline (parseStage ()); // minimal pipelines: "stage" and "... | id" if (index > (tokens.length - 2) || !"|".equals (tokens [index]) ) { retval.next = next; return retval; } index++; retval.rest = parsePipeline (next); return retval; } // stage ::= id | id '(' pipeline ')' private Stage parseStage () { Stage retval = new Stage (tokens [index++]); // minimal stages: "id" and "id ( id )" if (index > (tokens.length - 2) || !"(".equals (tokens [index]) /*)*/ ) return retval; index++; retval.param = parsePipeline (null); if (index >= tokens.length) throw new ArrayIndexOutOfBoundsException ( "missing right paren"); if (/*(*/ !")".equals (tokens [index++])) throw new ArrayIndexOutOfBoundsException ( "required right paren, not: " + tokens [index - 1]); return retval; } // // these classes obey the conventions for constructors, so they're // only built in to this table of shortnames // // - filter (one or two types of arglist) // * last constructor is 'next' element // * optional (first) string parameter // // - terminus (one or types of arglist) // * optional (only) string parameter // // terminus stages are transformed into filters if needed, by // creating a "tee". filter stages aren't turned to terminus // stages though; either eliminate such stages, or add some // terminus explicitly. // private static final String builtinStages [][] = { { "dom", "gnu.xml.dom.Consumer" }, { "nsfix", "gnu.xml.pipeline.NSFilter" }, { "null", "gnu.xml.pipeline.EventFilter" }, { "server", "gnu.xml.pipeline.CallFilter" }, { "tee", "gnu.xml.pipeline.TeeConsumer" }, { "validate", "gnu.xml.pipeline.ValidationConsumer" }, { "wf", "gnu.xml.pipeline.WellFormednessFilter" }, { "xinclude", "gnu.xml.pipeline.XIncludeFilter" }, { "xslt", "gnu.xml.pipeline.XsltFilter" }, // XXX want: option for validate, to preload external part of a DTD // xhtml, write ... nyet generic-ready }; private static class Stage { String id; Pipeline param; Stage (String name) { id = name; } public String toString () { if (param == null) return id; return id + " ( " + param + " )"; } private void fail (String message) throws IOException { throw new IOException ("in '" + id + "' stage of pipeline, " + message); } EventConsumer createStage (EventConsumer next) throws IOException { String name = id; // most builtins are just class aliases for (int i = 0; i < builtinStages.length; i++) { if (id.equals (builtinStages [i][0])) { name = builtinStages [i][1]; break; } } // Save output as XML or XHTML text if ("write".equals (name) || "xhtml".equals (name)) { String filename; boolean isXhtml = "xhtml".equals (name); OutputStream out = null; TextConsumer consumer; if (param == null) fail ("parameter is required"); filename = param.toString (); if ("stdout".equals (filename)) out = System.out; else if ("stderr".equals (filename)) out = System.err; else { File f = new File (filename); /* if (!f.isAbsolute ()) fail ("require absolute file paths"); */ if (f.exists ()) fail ("file already exists: " + f.getName ()); // XXX this races against the existence test out = new FileOutputStream (f); } if (!isXhtml) consumer = new TextConsumer (out); else consumer = new TextConsumer ( new OutputStreamWriter (out, "8859_1"), true); consumer.setPrettyPrinting (true); if (next == null) return consumer; return new TeeConsumer (consumer, next); } else { // // Here go all the builtins that are just aliases for // classes, and all stage IDs that started out as such // class names. The following logic relies on several // documented conventions for constructor invocation. // String msg = null; try { Class klass = Class.forName (name); Class argTypes [] = null; Constructor constructor = null; boolean filter = false; Object params [] = null; Object obj = null; // do we need a filter stage? if (next != null) { // "next" consumer is always passed, with // or without the optional string param if (param == null) { argTypes = new Class [1]; argTypes [0] = EventConsumer.class; params = new Object [1]; params [0] = next; msg = "no-param filter"; } else { argTypes = new Class [2]; argTypes [0] = String.class; argTypes [1] = EventConsumer.class; params = new Object [2]; params [0] = param.toString (); params [1] = next; msg = "one-param filter"; } try { constructor = klass.getConstructor (argTypes); } catch (NoSuchMethodException e) { // try creating a filter from a // terminus and a tee filter = true; msg += " built from "; } } // build from a terminus stage, with or // without the optional string param if (constructor == null) { String tmp; if (param == null) { argTypes = new Class [0]; params = new Object [0]; tmp = "no-param terminus"; } else { argTypes = new Class [1]; argTypes [0] = String.class; params = new Object [1]; params [0] = param.toString (); tmp = "one-param terminus"; } if (msg == null) msg = tmp; else msg += tmp; constructor = klass.getConstructor (argTypes); // NOT creating terminus by dead-ending // filters ... users should think about // that one, something's likely wrong } obj = constructor.newInstance (params); // return EventConsumers directly, perhaps after // turning them into a filter if (obj instanceof EventConsumer) { if (filter) return new TeeConsumer ((EventConsumer) obj, next); return (EventConsumer) obj; } // if it's not a handler, it's an error // we can wrap handlers in a filter EventFilter retval = new EventFilter (); boolean updated = false; if (obj instanceof ContentHandler) { retval.setContentHandler ((ContentHandler) obj); updated = true; } if (obj instanceof DTDHandler) { retval.setDTDHandler ((DTDHandler) obj); updated = true; } if (obj instanceof LexicalHandler) { retval.setProperty ( EventFilter.PROPERTY_URI + "lexical-handler", obj); updated = true; } if (obj instanceof DeclHandler) { retval.setProperty ( EventFilter.PROPERTY_URI + "declaration-handler", obj); updated = true; } if (!updated) fail ("class is neither Consumer nor Handler"); if (filter) return new TeeConsumer (retval, next); return retval; } catch (IOException e) { throw e; } catch (NoSuchMethodException e) { fail (name + " constructor missing -- " + msg); } catch (ClassNotFoundException e) { fail (name + " class not found"); } catch (Exception e) { // e.printStackTrace (); fail ("stage not available: " + e.getMessage ()); } } // NOTREACHED return null; } } private static class Pipeline { Stage stage; // rest may be null Pipeline rest; EventConsumer next; Pipeline (Stage s) { stage = s; } public String toString () { if (rest == null && next == null) return stage.toString (); if (rest != null) return stage + " | " + rest; throw new IllegalArgumentException ("next"); } EventConsumer createPipeline () throws IOException { if (next == null) { if (rest == null) next = stage.createStage (null); else next = stage.createStage (rest.createPipeline ()); } return next; } } /* public static void main (String argv []) { try { // three basic terminus cases createPipeline ("null"); createPipeline ("validate"); createPipeline ("write ( stdout )"); // four basic filters createPipeline ("nsfix | write ( stderr )"); createPipeline ("wf | null"); createPipeline ("null | null"); createPipeline ( "call ( http://www.example.com/services/xml-1a ) | xhtml ( stdout )"); // tee junctions createPipeline ("tee ( validate ) | write ( stdout )"); createPipeline ("tee ( nsfix | write ( stdout ) ) | validate"); // longer pipeline createPipeline ("nsfix | tee ( validate ) | write ( stdout )"); createPipeline ( "null | wf | nsfix | tee ( validate ) | write ( stdout )"); // try some parsing error cases try { createPipeline ("null ("); // extra token '(' System.err.println ("** didn't report error"); } catch (Exception e) { System.err.println ("== err: " + e.getMessage ()); } try { createPipeline ("nsfix |"); // extra token '|' System.err.println ("** didn't report error"); } catch (Exception e) { System.err.println ("== err: " + e.getMessage ()); } try { createPipeline ("xhtml ( foo"); // missing right paren System.err.println ("** didn't report error"); } catch (Exception e) { System.err.println ("== err: " + e.getMessage ()); } try { createPipeline ("xhtml ( foo bar"); // required right paren System.err.println ("** didn't report error"); } catch (Exception e) { System.err.println ("== err: " + e.getMessage ()); } try { createPipeline ("tee ( nsfix | validate");// missing right paren System.err.println ("** didn't report error"); } catch (Exception e) { System.err.println ("== err: " + e.getMessage ()); } // try some construction error cases try { createPipeline ("call"); // missing param System.err.println ("** didn't report error"); } catch (Exception e) { System.err.println ("== err: " + e.getMessage ()); } try { createPipeline ("call ( foobar )"); // broken param System.err.println ("** didn't report error"); } catch (Exception e) { System.err.println ("== err: " + e.getMessage ()); } try { createPipeline ("nsfix ( foobar )"); // illegal param System.err.println ("** didn't report error"); } catch (Exception e) { System.err.println ("== err: " + e.getMessage ()); } try { createPipeline ("null ( foobar )"); // illegal param System.err.println ("** didn't report error"); } catch (Exception e) { System.err.println ("== err: " + e.getMessage ()); } try { createPipeline ("wf ( foobar )"); // illegal param System.err.println ("** didn't report error"); } catch (Exception e) { System.err.println ("== err: " + e.getMessage ()); } try { createPipeline ("xhtml ( foobar.html )"); new File ("foobar.html").delete (); // now supported } catch (Exception e) { System.err.println ("** err: " + e.getMessage ()); } try { createPipeline ("xhtml"); // missing param System.err.println ("** didn't report error"); } catch (Exception e) { System.err.println ("== err: " + e.getMessage ()); } try { createPipeline ("write ( stdout ) | null"); // nonterminal System.err.println ("** didn't report error"); } catch (Exception e) { System.err.println ("== err: " + e.getMessage ()); } try { createPipeline ("validate | null"); // now supported } catch (Exception e) { System.err.println ("** err: " + e.getMessage ()); } try { createPipeline ("validate ( foo )"); // illegal param System.err.println ("** didn't report error"); } catch (Exception e) { System.err.println ("== err: " + e.getMessage ()); } try { createPipeline ("tee"); // missing param System.err.println ("** didn't report error"); } catch (Exception e) { System.err.println ("== err: " + e.getMessage ()); } try { // only builtins so far createPipeline ("com.example.xml.FilterClass"); System.err.println ("** didn't report error"); } catch (Exception e) { System.err.println ("== err: " + e.getMessage ()); } } catch (Exception e) { e.printStackTrace (); } } /**/ }