OGNL表达式struts2标签“%，#，$”

OGNL表达式struts2标签“%，#，$”

1. 一、什么是OGNL，有什么特点？ <wbr><wbr></wbr></wbr>
2. <wbr><wbr></wbr></wbr>
3. OGNL（Object-Graph<wbr>Navigation<wbr>Language），大概可以理解为：对象图形化导航语言。是一种可以方便地操作对象属性的开源表达式语言。OGNL有如下特点：<wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr>
4. <wbr><wbr></wbr></wbr>
5. 1、支持对象方法调用，形式如：objName.methodName()； <wbr><wbr></wbr></wbr>
6. <wbr><wbr></wbr></wbr>
7. 2、支持类静态的方法调用和值访问，表达式的格式为@[类全名（包括包路）]@[方法名<wbr>|<wbr><wbr>值名]，例如： <wbr><wbr></wbr></wbr></wbr></wbr></wbr>
8. <wbr><wbr></wbr></wbr>
9. @java.lang.String@format('foo<wbr>%s'</wbr>,<wbr><span style="color:#0000ff">'bar'</span>)或<span style="color:#646464">@tutorial</span>.MyConstant<span style="color:#646464">@APP_NAME</span>； <wbr><wbr></wbr></wbr></wbr>
10. <wbr><wbr></wbr></wbr>
11. 3、支持赋值操作和表达式串联，例如： <wbr><wbr></wbr></wbr>
12. <wbr><wbr></wbr></wbr>
13. price=100,<wbr>discount=<span style="color:#c00000">0.8</span>,<wbr>calculatePrice()，这个表达式会返回<span style="color:#c00000">80</span>； <wbr><wbr></wbr></wbr></wbr></wbr>
14. <wbr><wbr></wbr></wbr>
15. 4、访问OGNL上下文（OGNL<wbr>context）和ActionContext； <wbr><wbr></wbr></wbr></wbr>
16. <wbr><wbr></wbr></wbr>
17. 5、操作集合对象。 <wbr><wbr></wbr></wbr>
18. <wbr><wbr></wbr></wbr>
19. <wbr><wbr><wbr></wbr></wbr></wbr>
20. <wbr><wbr></wbr></wbr>
21. 二、使用OGNL表达式 <wbr><wbr></wbr></wbr>
22. <wbr><wbr></wbr></wbr>
23. OGNL要结合struts标签来使用。由于比较灵活，也容易把人给弄晕，尤其是“%”、“#”、“$”这三个符号的使用。由于$广泛应用于EL中，这里重点写%和#符号的用法。 <wbr><wbr></wbr></wbr>
24. <wbr><wbr></wbr></wbr>
25. 1、“#”符号有三种用途： <wbr><wbr></wbr></wbr>
26. <wbr><wbr></wbr></wbr>
27. (1)、访问非根对象（struts中值栈为根对象）如OGNL上下文和Action上下文，#相当于ActionContext.getContext()；下表有几个ActionContext中有用的属性： <wbr><wbr></wbr></wbr>
28. <wbr><wbr></wbr></wbr>
29. <wbr><wbr><wbr></wbr></wbr></wbr>
30. <wbr><wbr></wbr></wbr>
31. 名称 <wbr><wbr></wbr></wbr>
32. <wbr>作用 <wbr><wbr></wbr></wbr></wbr>
33. <wbr>例子 <wbr><wbr></wbr></wbr></wbr>
34. <wbr><wbr><wbr></wbr></wbr></wbr>
35. parameters <wbr><wbr></wbr></wbr>
36. <wbr>包含当前HTTP请求参数的Map <wbr><wbr></wbr></wbr></wbr>
37. <wbr>#parameters.id[<span style="color:#c00000">0</span>]作用相当于request.getParameter(<span style="color:#0000ff">"id"</span>)<wbr><wbr><wbr></wbr></wbr></wbr></wbr>
38. <wbr><wbr><wbr></wbr></wbr></wbr>
39. request <wbr><wbr></wbr></wbr>
40. <wbr>包含当前HttpServletRequest的属性（attribute)的Map <wbr><wbr></wbr></wbr></wbr>
41. <wbr>#request.userName相当于request.getAttribute(<span style="color:#0000ff">"userName"</span>)<wbr><wbr><wbr></wbr></wbr></wbr></wbr>
42. <wbr><wbr><wbr></wbr></wbr></wbr>
43. session <wbr><wbr></wbr></wbr>
44. <wbr>包含当前HttpSession的属性（attribute）的Map <wbr><wbr></wbr></wbr></wbr>
45. <wbr>#session.userName相当于session.getAttribute(<span style="color:#0000ff">"userName"</span>)<wbr><wbr><wbr></wbr></wbr></wbr></wbr>
46. <wbr><wbr><wbr></wbr></wbr></wbr>
47. application <wbr><wbr></wbr></wbr>
48. <wbr>包含当前应用的ServletContext的属性（attribute）的Map <wbr><wbr></wbr></wbr></wbr>
49. <wbr>#application.userName相当于application.getAttribute(<span style="color:#0000ff">"userName"</span>)<wbr><wbr><wbr></wbr></wbr></wbr></wbr>
50. <wbr><wbr><wbr></wbr></wbr></wbr>
51. <wbr><wbr></wbr></wbr>
52. 注：attr<wbr>用于按request<wbr>&gt;<wbr>session<wbr>&gt;<wbr>application顺序访问其属性（attribute），#attr.userName相当于按顺序在以上三个范围（scope）内读取userName属性，直到找到为止。用于过滤和投影（projecting)集合，如books.{?#<strong><span style="color:#7f0055">this</span></strong>.price&lt;<span style="color:#c00000">100</span>}；构造Map，如#{<span style="color:#0000ff">'foo1'</span>:<span style="color:#0000ff">'bar1'</span>,<wbr><span style="color:#0000ff">'foo2'</span>:<span style="color:#0000ff">'bar2'</span>}。 <wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
53. <wbr><wbr></wbr></wbr>
54. <wbr><wbr><wbr></wbr></wbr></wbr>
55. <wbr><wbr></wbr></wbr>
56. (2)、用于过滤和投影（projecting)集合，如:<wbr>books.{?#<strong><span style="color:#7f0055">this</span></strong>.price&gt;<span style="color:#c00000">35</span>}<wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr>
57. <wbr><wbr></wbr></wbr>
58. books.{?#this.price>35} <wbr><wbr></wbr></wbr>
59. <wbr><wbr></wbr></wbr>
60. (3)、构造Map，如:<wbr>#{<span style="color:#0000ff">'foo1'</span>:<span style="color:#0000ff">'bar1'</span>,<wbr><span style="color:#0000ff">'foo2'</span>:<span style="color:#0000ff">'bar2'</span>}<wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr>
61. <wbr><wbr></wbr></wbr>
62. #{'foo1':'bar1',<wbr><span style="color:#0000ff">'foo2'</span>:<span style="color:#0000ff">'bar2'</span>}这种方式常用在给radio或select、checkbox等标签赋值上。如果要在页面中取一个map的值可以这样写：<wbr><wbr><wbr></wbr></wbr></wbr></wbr>
63. <wbr><wbr></wbr></wbr>
64. <s:property<wbr>value=<span style="color:#0000ff">"#myMap['foo1']"</span>/&gt;<wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr>
65. <wbr><wbr></wbr></wbr>
66. <s:property<wbr>value=<span style="color:#0000ff">"#myMap['foo1']"</span>/&gt; <wbr><wbr></wbr></wbr></wbr>
67. <wbr><wbr></wbr></wbr>
68. 2、“%”符号的用途是在标签的属性值被理解为字符串类型时，告诉执行环境%{}里的是OGNL表达式。 <wbr><wbr></wbr></wbr>
69. <wbr><wbr></wbr></wbr>
70. 这是一开始最让我不能理解的符号，原因是一些相关资源在表述时不太准备，经过一翻痛苦的探索，终于明白了它的用途。实际上就是让被理解为字符串的表达式，被真正当成ognl来执行。很有点类似javascript里面的eval_r()功能，例如<wbr>： <wbr><wbr></wbr></wbr></wbr>
71. <wbr><wbr></wbr></wbr>
72. var<wbr>oDiv<wbr>=<wbr>eval_r(<span style="color:#0000ff">"document.all.div"</span>+index)<wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
73. <wbr><wbr></wbr></wbr>
74. var<wbr>oDiv<wbr>=<wbr>eval_r(<span style="color:#0000ff">"document.all.div"</span>+index) <wbr><wbr></wbr></wbr></wbr></wbr></wbr>
75. <wbr><wbr></wbr></wbr>
76. 当index变量为1时，语句就会被当作var<wbr>oDiv<wbr>=<wbr>document.all.div1<wbr><wbr>var<wbr>oDiv<wbr>=<wbr>document.all.div1来执行。%{}就是起这个作用。举例：<wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
77. <wbr><wbr></wbr></wbr>
78. <s:set<wbr>name=<span style="color:#0000ff">"myMap"</span><wbr>value=<span style="color:#0000ff">"#{'key1':'value1','key2':'value2'}"</span>/&gt;<wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
79. <wbr><wbr></wbr></wbr>
80. <s:property<wbr>value=<span style="color:#0000ff">"#myMap['key1']"</span>/&gt;<wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr>
81. <wbr><wbr></wbr></wbr>
82. <s:url<wbr>value=<span style="color:#0000ff">"#myMap['key1']"</span><wbr>/&gt;<wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr>
83. <wbr><wbr></wbr></wbr>
84. <s:set<wbr>name=<span style="color:#0000ff">"myMap"</span><wbr>value=<span style="color:#0000ff">"#{'key1':'value1','key2':'value2'}"</span>/&gt; <wbr><wbr></wbr></wbr></wbr></wbr>
85. <wbr><wbr></wbr></wbr>
86. <s:property<wbr>value=<span style="color:#0000ff">"#myMap['key1']"</span>/&gt; <wbr><wbr></wbr></wbr></wbr>
87. <wbr><wbr></wbr></wbr>
88. <s:url<wbr>value=<span style="color:#0000ff">"#myMap['key1']"</span>/&gt; <wbr><wbr></wbr></wbr></wbr>
89. <wbr><wbr></wbr></wbr>
90. 上面的代码第2行会在页面上输出“value1”，而第3行则会输出"#myMap['key1']"这么一个字符串。<wbr>如果将第<span style="color:#c00000">3</span>行改写成这样：<wbr><wbr><wbr></wbr></wbr></wbr></wbr>
91. <wbr><wbr></wbr></wbr>
92. <s:url<wbr>value=<span style="color:#0000ff">"%{#myMap['key1']}"</span>/&gt;<wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr>
93. <wbr><wbr></wbr></wbr>
94. <s:url<wbr>value=<span style="color:#0000ff">"%{#myMap['key1']}"</span>/&gt; <wbr><wbr></wbr></wbr></wbr>
95. <wbr><wbr></wbr></wbr>
96. 则输出为“value1”。 <wbr><wbr></wbr></wbr>
97. <wbr><wbr></wbr></wbr>
98. <wbr><wbr><wbr></wbr></wbr></wbr>
99. <wbr><wbr></wbr></wbr>
100. <wbr><wbr><wbr></wbr></wbr></wbr>
101. <wbr><wbr></wbr></wbr>
102. 这说明struts2里不同的标签对ognl的表达式的理解是不一样的。如果当有的标签“看不懂”类似“#myMap['key1']”的语句时，就要用%{}来把这括进去，“翻译”一下了。 <wbr><wbr></wbr></wbr>
103. <wbr><wbr></wbr></wbr>
104. 3、“$”有两种用途 <wbr><wbr></wbr></wbr>
105. <wbr><wbr></wbr></wbr>
106. (1)、在国际化资源文件中，引用OGNL表达式。 <wbr><wbr></wbr></wbr>
107. <wbr><wbr></wbr></wbr>
108. (2)、在Struts<wbr><span style="color:#c00000">2</span>配置文件中，引用OGNL表达式：<wbr><wbr><wbr></wbr></wbr></wbr></wbr>
109. <wbr><wbr></wbr></wbr>
110. <action<wbr>name=<span style="color:#0000ff">"saveUser"</span><wbr><strong><span style="color:#7f0055">class</span></strong>=<span style="color:#0000ff">"userAction"</span><wbr>method=<span style="color:#0000ff">"save"</span>&gt; <wbr><wbr></wbr></wbr></wbr></wbr></wbr>
111. <wbr><wbr></wbr></wbr>
112. <result<wbr>type=<span style="color:#0000ff">"redirect"</span>&gt;listUser.action?msg=${msg}&lt;/result&gt; <wbr><wbr></wbr></wbr></wbr>
113. <wbr><wbr></wbr></wbr>
114. </action> <wbr><wbr></wbr></wbr>
115. <wbr><wbr></wbr></wbr>
116. <action<wbr>name=<span style="color:#0000ff">"saveUser"</span><wbr><strong><span style="color:#7f0055">class</span></strong>=<span style="color:#0000ff">"userAction"</span><wbr>method=<span style="color:#0000ff">"save"</span>&gt;<wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>
117. <wbr><wbr></wbr></wbr>
118. <result<wbr>type=<span style="color:#0000ff">"redirect"</span>&gt;listUser.action?msg=${msg}&lt;/result&gt; <wbr><wbr></wbr></wbr></wbr>
119. <wbr><wbr></wbr></wbr>
120. </action><wbr></wbr>