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The XmlWriter class

Summary:

• Syntax
• Methods
• Usage
  • Create a SaxDocumentHandler object writing to a file
  • Create a SaxDocumentHandler object writing to a pipe
  • Create a SaxDocumentHandler object writing to a socket
• Examples

See also: Classes and Objects, XML Utilities, SaxDocumentHandler

Syntax

The XmlWriter class allows you to write XML documents to different types of output, following the SAX standards.

Syntax:

om.XmlWriter

Methods:

Usage:

This class is only used to create a SaxDocumentHandler object, by using one of the class methods described in the above table.

First, define a variable of type om.SaxDocumentHander and create the object with one of the "create" methods, according to the output destination:

• The method om.XmlWriter.createFileWriter(filename) creates an object writing to the file identified by filename.
• The method om.XmlWriter.createPipeWriter(progname) creates an object writing to a pipe opened by a sub-process identified by progname.
• The method om.XmlWriter.createSocketWriter(hostname,portnum) creates an object writing to the TCP socket identified by the host hostname and the TCP port portnum.

To handle element attributes, define a variable of type om.SaxAttributes.

Create the SaxAttributes object with om.SaxAttributes.create() class method. See the class definition for more details about attributes definition.

Use SaxDocumentHandler methods

Use the method startDocument() to start writing to the output. From this point, the order of method calls defines the structure of the XML document.

To write an element, fill the SaxAttributes object with attributes. Then, initiate the element output with the method startElement(name,attset), where name is the tag name of the element and attset is the SaxAttributes object defining element attributes. After this call, you can write text nodes with the characters() method. You can write an entity node with the entity() method. Finish element output with a call to the endElement() method. Repeat these steps as many times as you have elements to write.

Instead of using the startElement() method, you can generate processing instruction elements with processingInstruction(name,attset), where name is the name of the application. The resulting XML output is in the form: <?name attribute="value1" ... ?>

Finally, you must finish the document output with a endDocument() call.

Examples

Example 1:

The following code writes an HTML page to a file using the XmlWriter class:

01 MAIN
02   DEFINE w om.SaxDocumentHandler
03   DEFINE a,n om.SaxAttributes
04 
05   LET w = om.XmlWriter.createFileWriter("sample.html")
06   LET a = om.SaxAttributes.create()
07   LET n = om.SaxAttributes.create()
08 
09   CALL n.clear()
10 
11   CALL w.startDocument()
12 
13     CALL w.startElement("HTML",n)
14 
15       CALL w.startElement("HEAD",n)
16 
17         CALL w.startElement("TITLE",n)
18         CALL w.characters("HTML page generated with XmlWriter")
19         CALL w.endElement("TITLE")
20 
21         CALL a.clear()
22         CALL a.addAttribute("type","text/css")
23         CALL w.startElement("STYLE",a)
24         CALL w.characters("\nBODY { background-color:#c0c0c0; }\n")  
25         CALL w.endElement("STYLE")
26 
27       CALL w.endElement("HEAD")
28 
29       CALL w.startElement("BODY",n)
30 
31         CALL addHLine(w)
32         CALL addTitle(w,"What is XML?",1,"55ff55")
33         CALL addParagraph(w,"XML = eXtensible Markup Language ...")
34 
35         CALL addHLine(w)
36         CALL addTitle(w,"What is SAX?",1,"55ff55")
37         CALL addParagraph(w,"SAX = Simple Api for XML ...")
38 
39       CALL w.endElement("BODY")
40 
41     CALL w.endElement("HTML")
42 
43   CALL w.endDocument()
44 
45 END MAIN
46 
47 FUNCTION addHLine(w)
48   DEFINE w om.SaxDocumentHandler
49   DEFINE a om.SaxAttributes
50   LET a = om.SaxAttributes.create()
51   CALL a.clear()
52   CALL a.addAttribute("width","100%")
53   CALL w.startElement("HR",a)
54   CALL w.endElement("HR")
55 END FUNCTION
56 
57 FUNCTION addTitle(w,t,x,c)
58   DEFINE w om.SaxDocumentHandler
59   DEFINE t VARCHAR(100)
60   DEFINE x INTEGER
61   DEFINE c VARCHAR(20)
62   DEFINE a om.SaxAttributes
63   DEFINE n varchar(10)
64   LET a = om.SaxAttributes.create()
65   LET n = "h" || x
66   CALL a.clear()
67   CALL w.startElement(n,a)
68   IF c IS NOT NULL THEN
69     CALL a.addAttribute("color",c)
70   END IF
71   CALL w.startElement("FONT",a)
72   CALL w.characters(t)
73   CALL w.endElement("FONT")
74   CALL w.endElement(n)
75 END FUNCTION
76 
77 FUNCTION addParagraph(w,t)
78   DEFINE w om.SaxDocumentHandler
79   DEFINE t VARCHAR(2000)
80   DEFINE a om.SaxAttributes
81   LET a = om.SaxAttributes.create()
82   CALL a.clear()
83   CALL w.startElement("P",a)
84   CALL w.characters("Text is:")
84   CALL w.skippedEntity("nbsp")         # Add a non breaking space :  
84   CALL w.characters("is")
84   CALL w.characters(t)
85   CALL w.endElement("P")
86 END FUNCTION