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The tags are designed to display dynamic data. To create a input field that displays the property “postalCode”, we'd pass the String “postalCode” to the textfield tag.
<s:textfield name="postalCode"/>
If there is a “postalCode” property on the value stack, its value will be set to the input field. When the field is submitted back to the framework, the value of the control will be set back to the “postalCode” property.
Sometimes, we want to pass the dynamic data to a tag. For example, we might want to display a label with the input field, and we might want to obtain the label from the application's messages resources. Accordingly, the framework will parse expressions found in the tag attributes, so that we can merge dynamic data into the tag attributes at runtime. The expression escape sequence is %{ ... }
. Any text embedded in the escape sequence is evalulated as an expression.
<s:textfield key="postalCode.label" name="postalCode"/>
The expression language (OGNL) lets us call methods and evaluate properties. The method getText
is provided by ActionSupport
, which is the base class for most Actions. Since the Action is on the stack, we can call any of its methods from an expression, including getText
.
The HTTP protocol is text-based, but some tags have non-String attribute types, like bool
or int
. To make using non-String attributes intuitative, the framework evaulates all non-String attributes as an expression. In this case, you do not need to use the escape notation. (But, if you do anyway , the framework will just strip it off.)
<s:select key="state.label" name="state" multiple="true"/>
Since the attribute multiple
maps to a boolean property, the framework does not interpret the value as a String. The value is evaluated as an expression and automtically converted to a boolean.
Since it's easy to forget which attributes are String and which are non-String, you can still use the escape notation.
<s:select key="state.label" name="state" multiple="%{true}"/>
<s:select key="state.label" name="state" multiple="allowMultiple"/>
<s:select key="state.label" name="state" multiple="%{allowMultiple}"/>
Most often, the value
attribute is set automatically, since name
attribute usually tells the framework which property to call to set the value
. But, if there is a reason to set the value
directly, be advised that value
is an Object NOT a String.
NOTE: Since
value
is not a String, whatever is passed tovalue
is evaluated as an expression - NOT a String literal.
<s:textfield key="state.label" name="state" value="ca"/>
If a textfield
is passed the value attribute ca
, the framework will look for a property named getCa
. Generally, this is not what we mean. What we mean to do is pass a literal String. In the expression language, literals are placed within quotes
<s:textfield key="state.label" name="state" value="%{'ca'}" />
Another approach would be to use the idiom value="'ca'"
, but, in this case, using the expression notation is recommended.
Boiled down, the tag attributes are evaluated using three rules.
%{ ... }
notation.%{}
, the notation is ignored as redundant, and the content evaluated.Please remember about altSyntax option that can change when value is evaluated as an expression - Alt Syntax
Username: ${user.username}
<s:textfield name="username"/>
<s:url var="es" action="Hello"> <s:param name="request_locale">es</s:param> </s:url> <s:a href="%{es}">Espanol</s:a>
put("username","trillian")
.<s:property value="#session.user.username" /> <s:select label="FooBar" name="foo" list="#{'username':'trillian', 'username':'zaphod'}" />
The following names of property are disallowed:
The below code will not work:
<s:iterator value="parameters"/>
public class MyAction { private String[] parameters; public String[] getParameters() { return parameters; } }
Since Struts 2.6 and migration to the latest Freemarker version (which enables auto-escaping by default) you should stop using ?html
in your custom tags and freemarker based pages. You can also automatically escape body of the following tags by setting escapeHtmlBody
attribute to true:
<s:a/>
<s:submit/>
<s:component/>
There is a new global flag struts.ui.escapeHtmlBody
which controls this behaviour for all the above tags. Yet the attribute escapeHtmlBody
always takes precedence over the flag.
<s:a href="%{...}" escapeHtmlBody="true"> <img src="/images/icon_waste_sml.png"/> </s:a>