1XML::SAX::Base(3) User Contributed Perl Documentation XML::SAX::Base(3)
2
6 XML::SAX::Base - Base class SAX Drivers and Filters
7
9 package MyFilter;
10 use XML::SAX::Base;
11 @ISA = ('XML::SAX::Base');
12
14 This module has a very simple task - to be a base class for PerlSAX
15 drivers and filters. It's default behaviour is to pass the input
16 directly to the output unchanged. It can be useful to use this module
17 as a base class so you don't have to, for example, implement the char‐
18 acters() callback.
19 The main advantages that it provides are easy dispatching of events the
21 right way (ie it takes care for you of checking that the handler has
22 implemented that method, or has defined an AUTOLOAD), and the guarantee
23 that filters will pass along events that they aren't implementing to
24 handlers downstream that might nevertheless be interested in them.
25
27 Writing SAX Filters is tremendously easy: all you need to do is inherit
28 from this module, and define the events you want to handle. A more
29 detailed explanation can be found at
30 http://www.xml.com/pub/a/2001/10/10/sax-filters.html.
31 Writing Drivers is equally simple. The one thing you need to pay atten‐
33 tion to is NOT to call events yourself (this applies to Filters as
34 well). For instance:
35 package MyFilter;
37 use base qw(XML::SAX::Base);
38 sub start_element {
40 my $self = shift;
41 my $data = shift;
42 # do something
43 $self->{Handler}->start_element($data); # BAD
44 }
45 The above example works well as precisely that: an example. But it has
47 several faults: 1) it doesn't test to see whether the handler defines
48 start_element. Perhaps it doesn't want to see that event, in which case
49 you shouldn't throw it (otherwise it'll die). 2) it doesn't check Con‐
50 tentHandler and then Handler (ie it doesn't look to see that the user
51 hasn't requested events on a specific handler, and if not on the
52 default one), 3) if it did check all that, not only would the code be
53 cumbersome (see this module's source to get an idea) but it would also
54 probably have to check for a DocumentHandler (in case this were SAX1)
55 and for AUTOLOADs potentially defined in all these packages. As you can
56 tell, that would be fairly painful. Instead of going through that, sim‐
57 ply remember to use code similar to the following instead:
58 package MyFilter;
60 use base qw(XML::SAX::Base);
61 sub start_element {
63 my $self = shift;
64 my $data = shift;
65 # do something to filter
66 $self->SUPER::start_element($data); # GOOD (and easy) !
67 }
68 This way, once you've done your job you hand the ball back to
70 XML::SAX::Base and it takes care of all those problems for you!
71 Note that the above example doesn't apply to filters only, drivers will
73 benefit from the exact same feature.
74
76 A number of methods are defined within this class for the purpose of
77 inheritance. Some probably don't need to be overridden (eg parse_file)
78 but some clearly should be (eg parse). Options for these methods are
79 described in the PerlSAX2 specification available from
80 http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/~check‐
81 out~/perl-xml/libxml-perl/doc/sax-2.0.html?rev=HEAD&con‐
82 tent-type=text/html.
83 * parse
85 The parse method is the main entry point to parsing documents.
86 Internally the parse method will detect what type of "thing" you
87 are parsing, and call the appropriate method in your implementation
88 class. Here is the mapping table of what is in the Source options
89 (see the Perl SAX 2.0 specification for the meaning of these val‐
90 ues):
91 Source Contains parse() calls
93 =============== =============
94 CharacterStream (*) _parse_characterstream($stream, $options)
95 ByteStream _parse_bytestream($stream, $options)
96 String _parse_string($string, $options)
97 SystemId _parse_systemid($string, $options)
98 However note that these methods may not be sensible if your driver
100 class is not for parsing XML. An example might be a DBI driver that
101 generates XML/SAX from a database table. If that is the case, you
102 likely want to write your own parse() method.
103 Also note that the Source may contain both a PublicId entry, and an
105 Encoding entry. To get at these, examine $options->{Source} as
106 passed to your method.
107 (*) A CharacterStream is a filehandle that does not need any encod‐
109 ing translation done on it. This is implemented as a regular file‐
110 handle and only works under Perl 5.7.2 or higher using PerlIO. To
111 get a single character, or number of characters from it, use the
112 perl core read() function. To get a single byte from it (or number
113 of bytes), you can use sysread(). The encoding of the stream should
114 be in the Encoding entry for the Source.
115 * parse_file, parse_uri, parse_string
117 These are all convenience variations on parse(), and in fact simply
118 set up the options before calling it. You probably don't need to
119 override these.
120 * get_options
122 This is a convenience method to get options in SAX2 style, or more
123 generically either as hashes or as hashrefs (it returns a hashref).
124 You will probably want to use this method in your own implementa‐
125 tions of parse() and of new().
126 * get_feature, set_feature
128 These simply get and set features, and throw the appropriate excep‐
129 tions defined in the specification if need be.
130 If your subclass defines features not defined in this one, then you
132 should override these methods in such a way that they check for
133 your features first, and then call the base class's methods for
134 features not defined by your class. An example would be:
135 sub get_feature {
137 my $self = shift;
138 my $feat = shift;
139 if (exists $MY_FEATURES{$feat}) {
140 # handle the feature in various ways
141 }
142 else {
143 return $self->SUPER::get_feature($feat);
144 }
145 }
146 Currently this part is unimplemented.
148 * set_handler
150 This method takes a handler type (Handler, ContentHandler, etc.)
151 and a handler object as arguments, and changes the current handler
152 for that handler type, while taking care of resetting the internal
153 state that needs to be reset. This allows one to change a handler
154 during parse without running into problems (changing it on the
155 parser object directly will most likely cause trouble).
156 * set_document_handler, set_content_handler, set_dtd_handler, set_lexi‐
158 cal_handler, set_decl_handler, set_error_handler, set_entity_resolver
159 These are just simple wrappers around the former method, and take a
160 handler object as their argument. Internally they simply call
161 set_handler with the correct arguments.
162 * get_handler
164 The inverse of set_handler, this method takes a an optional string
165 containing a handler type (DTDHandler, ContentHandler, etc. 'Han‐
166 dler' is used if no type is passed). It returns a reference to the
167 object that implements that that class, or undef if that handler
168 type is not set for the current driver/filter.
169 * get_document_handler, get_content_handler, get_dtd_handler, get_lexi‐
171 cal_handler, get_decl_handler, get_error_handler, get_entity_resolver
172 These are just simple wrappers around the get_handler() method, and
173 take no arguments. Internally they simply call get_handler with the
174 correct handler type name.
175 It would be rather useless to describe all the methods that this module
177 implements here. They are all the methods supported in SAX1 and SAX2.
178 In case your memory is a little short, here is a list. The apparent
179 duplicates are there so that both versions of SAX can be supported.
180 * start_document
182 * end_document
183 * start_element
184 * start_document
185 * end_document
186 * start_element
187 * end_element
188 * characters
189 * processing_instruction
190 * ignorable_whitespace
191 * set_document_locator
192 * start_prefix_mapping
193 * end_prefix_mapping
194 * skipped_entity
195 * start_cdata
196 * end_cdata
197 * comment
198 * entity_reference
199 * notation_decl
200 * unparsed_entity_decl
201 * element_decl
202 * attlist_decl
203 * doctype_decl
204 * xml_decl
205 * entity_decl
206 * attribute_decl
207 * internal_entity_decl
208 * external_entity_decl
209 * resolve_entity
210 * start_dtd
211 * end_dtd
212 * start_entity
213 * end_entity
214 * warning
215 * error
216 * fatal_error
217
219 - more tests
220 - conform to the "SAX Filters" and "Java and DOM compatibility"
221 sections of the SAX2 document.
222
224 Kip Hampton (khampton@totalcinema.com) did most of the work, after
225 porting it from XML::Filter::Base.
226 Robin Berjon (robin@knowscape.com) pitched in with patches to make it
228 usable as a base for drivers as well as filters, along with other
229 patches.
230 Matt Sergeant (matt@sergeant.org) wrote the original XML::Filter::Base,
232 and patched a few things here and there, and imported it into the
233 XML::SAX distribution.
234
236 XML::SAX
237perl v5.8.8 2007-02-13 XML::SAX::Base(3)