-
Notifications
You must be signed in to change notification settings - Fork 16
/
chap-snippets.lyx
5231 lines (3744 loc) · 83.4 KB
/
chap-snippets.lyx
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
#LyX 1.6.7 created this file. For more info see http://www.lyx.org/
\lyxformat 345
\begin_document
\begin_header
\textclass book
\use_default_options true
\language english
\inputencoding auto
\font_roman palatino
\font_sans helvet
\font_typewriter courier
\font_default_family default
\font_sc false
\font_osf false
\font_sf_scale 100
\font_tt_scale 100
\graphics default
\paperfontsize default
\spacing single
\use_hyperref false
\papersize default
\use_geometry false
\use_amsmath 1
\use_esint 1
\cite_engine basic
\use_bibtopic false
\paperorientation portrait
\secnumdepth 3
\tocdepth 3
\paragraph_separation indent
\defskip medskip
\quotes_language english
\papercolumns 1
\papersides 1
\paperpagestyle default
\tracking_changes false
\output_changes false
\author ""
\author ""
\end_header
\begin_body
\begin_layout Chapter
Snippets
\begin_inset Index
status open
\begin_layout Plain Layout
Snippets
\end_layout
\end_inset
\begin_inset CommandInset label
LatexCommand label
name "cha:Snippets"
\end_inset
\end_layout
\begin_layout Standard
Put simply, a snippet is a Scala method that transforms input XML into output
XML
\begin_inset Index
status open
\begin_layout Plain Layout
XML
\end_layout
\end_inset
.
Snippets act as independent (or dependent, if you want) pieces of logic
that you insert into your page to perform rendering.
As such, snippets form the backbone of Lift's View-First
\begin_inset Index
status open
\begin_layout Plain Layout
View-First
\end_layout
\end_inset
rendering architecture.
Although snippets aren't the only mechanism Lift has for rendering page
views (see Views, Section
\begin_inset CommandInset ref
LatexCommand vref
reference "sec:Views"
\end_inset
, Custom Dispatch, Section
\begin_inset CommandInset ref
LatexCommand vref
reference "sec:Custom-dispatch-func"
\end_inset
, or even the REST API, Chapter
\begin_inset CommandInset ref
LatexCommand ref
reference "cha:Web-Services"
\end_inset
), they're so widely used and so important that we feel they warrant their
own chapter.
\end_layout
\begin_layout Standard
In this chapter we will cover the ins and outs of snippets, from the snippet
tag that you place in your templates, through how the snippet method is
resolved, to the snippet method definition itself.
We'll also cover related topics and some advanced functionality in snippets
for those looking to push Lift's boundaries.
\end_layout
\begin_layout Section
The Snippet Tag
\begin_inset Index
status open
\begin_layout Plain Layout
snippet
\end_layout
\end_inset
\begin_inset Index
status open
\begin_layout Plain Layout
Tags ! snippet
\end_layout
\end_inset
\begin_inset CommandInset label
LatexCommand label
name "sec:The-Snippet-Tag"
\end_inset
\begin_inset CommandInset label
LatexCommand label
name "sub:snippet-tag"
\end_inset
\end_layout
\begin_layout LyX-Code
\family typewriter
Usage: <lift:snippet type="snippetName" ...options...
/>
\end_layout
\begin_layout LyX-Code
<lift:snippetName ...options...
/>
\end_layout
\begin_layout LyX-Code
<div class=
\begin_inset Quotes erd
\end_inset
lift:snippetName?opt1=...;opt2=...;opt3=...
\begin_inset Quotes erd
\end_inset
/>
\end_layout
\begin_layout Standard
The snippet tag is what you use to tell Lift where and how to invoke a snippet
method on given XML content.
The most important part of the tag is the snippet name, which is used to
resolve which snippet method will process the snippet tag contents.
We'll cover how the snippet name is resolved to a concrete method in section
\begin_inset CommandInset ref
LatexCommand ref
reference "sub:Snippet-Dispatch"
\end_inset
.
\end_layout
\begin_layout Standard
\align center
\begin_inset Box Shadowbox
position "t"
hor_pos "c"
has_inner_box 1
inner_pos "t"
use_parbox 0
width "75col%"
special "none"
height "1in"
height_special "totalheight"
status open
\begin_layout Plain Layout
Note that there is a shorthand for the
\family typewriter
type
\family default
attribute simply by appending the snippet name after the
\family typewriter
lift:
\family default
prefix.
If you use this shorthand, make sure to avoid naming your snippets the
same as Lift's built-in tags, such as
\family typewriter
surround
\family default
,
\family typewriter
children
\family default
,
\family typewriter
embed
\family default
, etc.
\end_layout
\end_inset
\end_layout
\begin_layout Standard
In addition to the the
\family typewriter
type
\family default
attribute, Lift will process several other options:
\end_layout
\begin_layout Description
form If the
\family typewriter
form
\begin_inset Index
status open
\begin_layout Plain Layout
Forms ! snippet tag
\end_layout
\end_inset
\family default
attribute is included with a value of either
\begin_inset Quotes eld
\end_inset
POST
\begin_inset Quotes erd
\end_inset
or
\begin_inset Quotes eld
\end_inset
GET
\begin_inset Quotes erd
\end_inset
, then an appropriate form tag will be emitted into the XHTML using the
specified submission method.
If you omit this tag from a snippet that generates a form, the form elements
will display but the form won't submit.
\end_layout
\begin_layout Description
multipart
\begin_inset Index
status open
\begin_layout Plain Layout
Forms ! multipart
\end_layout
\end_inset
\begin_inset Index
status open
\begin_layout Plain Layout
Forms ! file upload
\end_layout
\end_inset
The
\family typewriter
multipart
\family default
attribute is a boolean (the default is false, specify
\begin_inset Quotes eld
\end_inset
yes
\begin_inset Quotes erd
\end_inset
,
\begin_inset Quotes eld
\end_inset
true
\begin_inset Quotes erd
\end_inset
or
\begin_inset Quotes eld
\end_inset
1
\begin_inset Quotes erd
\end_inset
to enable) that specifies whether a generated form tag should be set to
use multipart form submission.
This is most typically used for file uploads (Section
\begin_inset CommandInset ref
LatexCommand ref
reference "sec:File-Uploads"
\end_inset
).
If you don't also specify the
\family typewriter
form
\family default
attribute then this won't do anything.
\end_layout
\begin_layout Description
eager_eval
\begin_inset Index
status open
\begin_layout Plain Layout
Snippets ! eager_eval
\end_layout
\end_inset
The eager_eval attribute is a boolean (the default is false, specify
\begin_inset Quotes eld
\end_inset
yes
\begin_inset Quotes erd
\end_inset
,
\begin_inset Quotes eld
\end_inset
true
\begin_inset Quotes erd
\end_inset
or
\begin_inset Quotes eld
\end_inset
1
\begin_inset Quotes erd
\end_inset
to enable) that controls the order of processing for the snippet tag contents.
Normally, the snippet is processed and then the XML returned from the snippet
is further processed for Lift tags.
Enabling eager_eval reverses this order so that the contents of the snippet
tag are processed first.
We cover this in more detail with an example in Section
\begin_inset CommandInset ref
LatexCommand ref
reference "sub:Eager-Eval"
\end_inset
.
\end_layout
\begin_layout Standard
With Lift 2.2's Designer-Friendly Templates (Section
\begin_inset CommandInset ref
LatexCommand vref
reference "sec:Designer-Friendly-Templates"
\end_inset
), you can also specify a snippet tag as part of the class attribute for
a given element.
Attributes for snippets invoked in this manner are passed via a query string.
Listing
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:Invoking-Snippets-Via-Class"
\end_inset
shows an example of how we can use the standard
\family typewriter
lift:surround
\family default
processing by modiying the
\family typewriter
class
\family default
of our content element.
\end_layout
\begin_layout Standard
\begin_inset listings
inline false
status open
\begin_layout Plain Layout
\begin_inset Caption
\begin_layout Plain Layout
Invoking Snippets Via the Class Attribute
\begin_inset CommandInset label
LatexCommand label
name "lst:Invoking-Snippets-Via-Class"
\end_inset
\end_layout
\end_inset
\end_layout
\begin_layout Plain Layout
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
\end_layout
\begin_layout Plain Layout
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
\end_layout
\begin_layout Plain Layout
<html xmlns="http://www.w3.org/1999/xhtml">
\end_layout
\begin_layout Plain Layout
<head>
\end_layout
\begin_layout Plain Layout
<title>Not really</title>
\end_layout
\begin_layout Plain Layout
</head>
\end_layout
\begin_layout Plain Layout
<body class="lift:content_id=real_content">
\end_layout
\begin_layout Plain Layout
<div class="lift:surround?with=default;at=content" id="real_content">
\end_layout
\begin_layout Plain Layout
<h1>Welcome to your project!</h1>
\end_layout
\begin_layout Plain Layout
</div>
\end_layout
\begin_layout Plain Layout
</body>
\end_layout
\begin_layout Plain Layout
</html>
\end_layout
\end_inset
\end_layout
\begin_layout Section
Snippet Dispatch
\begin_inset CommandInset label
LatexCommand label
name "sub:Snippet-Dispatch"
\end_inset
\begin_inset Index
status open
\begin_layout Plain Layout
Snippets ! Dispatch
\end_layout
\end_inset
\end_layout
\begin_layout Standard
The first step taken by Lift when evaluating a snippet tag is to resolve
what snippet method will actually process the content.
There are several mechanisms that are used to resolve the method, but they
can be broken down into two main approaches: dispatch via reflection and
explicit dispatch.
In addition, Lift allows per-request remapping of snippet names via
\family typewriter
S.mapSnippet
\family default
\begin_inset Index
status open
\begin_layout Plain Layout
mapSnippet
\end_layout
\end_inset
.
We'll cover each in the following sections.
\end_layout
\begin_layout Subsection
Implicit Dispatch Via Reflection
\begin_inset Index
status open
\begin_layout Plain Layout
Reflection
\end_layout
\end_inset
\begin_inset Index
status open
\begin_layout Plain Layout
Snippets ! Implicit dispatch
\end_layout
\end_inset
\begin_inset CommandInset label
LatexCommand label
name "sub:Implicit-Dispatch-Via"
\end_inset
\end_layout
\begin_layout Standard
The simplest, and default, approach to resolving snippet names is to use
implicit dispatch via reflection.
When using implicit dispatch, Lift will use the snippet name specified
in the snippet tag to first locate a class.
Lift will then either instantiate a class, or if it's a stateful snippet
(we'll cover stateful snippets in Section
\begin_inset CommandInset ref
LatexCommand ref
reference "sub:Stateless-versus-Stateful"
\end_inset
), retrieve the current instance.
One Lift has a class instance, it uses the snippet name to further determine
which method in the class to execute.
There are three ways to specify this:
\end_layout
\begin_layout Enumerate
Via the
\family typewriter
type
\family default
attribute on the snippet tag.
The value should be
\begin_inset Quotes eld
\end_inset
\family typewriter
ClassName
\family default
:
\family typewriter
method
\family default
\begin_inset Quotes erd
\end_inset
for the particular snippet method you want to have handle the tag
\end_layout
\begin_layout Enumerate
Via a tag suffix of
\family typewriter
Class.method
\family default
.
This is the same as specifying the
\family typewriter
type=
\begin_inset Quotes erd
\end_inset
Class:method
\begin_inset Quotes erd
\end_inset
\family default
attribute
\end_layout
\begin_layout Enumerate
Via a tag suffix of just
\family typewriter
Class
\family default
.
This will use the
\family typewriter
render
\family default
method on the specified class to handle the tag
\end_layout
\begin_layout Standard
Classes are resolved as specified in Section
\begin_inset CommandInset ref
LatexCommand ref
reference "sub:Class-Resolution"
\end_inset
.
\end_layout
\begin_layout Standard
\align center
\begin_inset Box Shadowbox
position "t"
hor_pos "c"
has_inner_box 1
inner_pos "t"
use_parbox 0
width "75col%"
special "none"
height "1in"
height_special "totalheight"
status open
\begin_layout Plain Layout
The most important thing to remember when using implicit dispatch is that
your snippet classes must be members of a
\family typewriter
snippet
\family default
subpackage as registered by
\family typewriter
LiftRules.addToPackages
\family default
.
For example, if you have
\family typewriter
LiftRules.addToPackages(
\begin_inset Quotes eld
\end_inset
com.foo
\begin_inset Quotes erd
\end_inset
)
\family default
in your
\family typewriter
Boot.boot
\family default
method, snippets should be members of
\family typewriter
com.foo.snippet
\family default
.
\end_layout
\end_inset
\end_layout
\begin_layout Standard
Listing
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:Snippet-tag-equivalence"
\end_inset
shows three equivalent snippet tags.
Note: these are only equivalent because the method name is
\begin_inset Quotes eld
\end_inset
render.
\begin_inset Quotes erd
\end_inset
If we had chosen a different method, e.g.,
\begin_inset Quotes eld
\end_inset
list,
\begin_inset Quotes erd
\end_inset
then the third example below will still call a
\begin_inset Quotes eld
\end_inset
render
\begin_inset Quotes erd
\end_inset
method.
\end_layout
\begin_layout Standard
\align center
\family typewriter
\begin_inset Box Shadowbox
position "t"
hor_pos "c"
has_inner_box 1
inner_pos "t"
use_parbox 0
width "75col%"
special "none"
height "1in"
height_special "totalheight"
status open
\begin_layout Plain Layout
It's important to note that with pure implicit dispatch, Java's reflection
allows access to
\emph on
any
\emph default
method on the enclosing class, no matter what the protection on the method
is set to (e.g.
private, protected).
Because of this, it's possible to invoke private and protected methods
via implicit dispatch, which could be a security concern.This is one reason
that we recommend using either DispatchSnippet or explicit dispatch for
production sites.
We'll cover both of these approaches momentarily.
\end_layout
\begin_layout Plain Layout
Another important note is that lookup via reflection is relatively expensive
\begin_inset Foot
status open
\begin_layout Plain Layout
See
\begin_inset Flex URL
status collapsed
\begin_layout Plain Layout
http://www.jguru.com/faq/view.jsp?EID=246569
\end_layout
\end_inset
for a more thorough explanation
\end_layout
\end_inset
operation, yet another reason that we recommend explicit dispatch for productio
n sites.
\end_layout
\end_inset
\end_layout
\begin_layout Standard
\begin_inset listings
inline false
status open
\begin_layout Plain Layout
\begin_inset Caption
\begin_layout Plain Layout
Snippet Tag Equivalence
\begin_inset CommandInset label
LatexCommand label
name "lst:Snippet-tag-equivalence"
\end_inset
\end_layout
\end_inset
\end_layout
\begin_layout Plain Layout
<lift:snippet type="MyClass:render" />
\end_layout
\begin_layout Plain Layout
<lift:MyClass.render />
\end_layout
\begin_layout Plain Layout
<lift:MyClass />
\end_layout
\end_inset
\end_layout
\begin_layout Standard
In addition to
\begin_inset Quotes eld
\end_inset
pure
\begin_inset Quotes erd
\end_inset
implicit dispatch, you can exert a little more control on which method
in a given class handles a snippet by implementing the
\family typewriter
net.liftweb.http.DispatchSnippet
\begin_inset Index
status open
\begin_layout Plain Layout
DispatchSnippet
\end_layout
\end_inset
\family default
trait.
This trait contains a single method, dispatch, of type
\begin_inset Formula $PartialFunction[String,NodeSeq\Rightarrow NodeSeq]$
\end_inset
that maps the method name (the
\begin_inset Quotes eld
\end_inset
method
\begin_inset Quotes erd
\end_inset
part of
\begin_inset Quotes eld
\end_inset
Class.method
\begin_inset Quotes erd
\end_inset
or
\begin_inset Quotes eld
\end_inset
Class:method
\begin_inset Quotes erd
\end_inset
as described above) to a particular method.
Only method names defined in the dispatch PartialFunction can be executed;
any methods that aren't covered by the partial function will result in
a snippet failure.
Listing
\begin_inset CommandInset ref
LatexCommand ref
reference "lst:Using-DispatchSnippet-to-select"
\end_inset
shows how you can control the dispatch by providing a custom
\family typewriter
dispatch
\family default
def.
\end_layout
\begin_layout Standard
\begin_inset listings
inline false
status open
\begin_layout Plain Layout
\begin_inset Caption
\begin_layout Plain Layout
Using DispatchSnippet to Control Snippet Method Selection
\begin_inset CommandInset label
LatexCommand label
name "lst:Using-DispatchSnippet-to-select"
\end_inset
\end_layout
\end_inset
\end_layout
\begin_layout Plain Layout
package com.foo.snippet
\end_layout
\begin_layout Plain Layout
\end_layout
\begin_layout Plain Layout