Provide a mapping between HTTP requests and action invocation requests and vice-versa.
提供HTTP請求和Action調用映射
When given an HttpServletRequest, the ActionMapper may return null if no action invocation request matches,
or it may return an ActionMapping that describes an action invocation for the framework to try.
當有一個HttpServletRequest的化，有配置的action，就返回一個ActionMapping，否則就返回null。
The ActionMapper is not required to guarantee that the ActionMapping returned be a real action or otherwise
ensure a valid request.
Accordingly, most ActionMappers do not need to consult the Struts configuration
just to determine if a request should be mapped.
Just as requests can be mapped from HTTP to an action invocation, the opposite is true as well.
However, because HTTP requests (when shown in HTTP responses) must be in String form,
a String is returned rather than an actual request object.
DefaultActionMapper
By default, the DefaultActionMapper is used:
Default action mapper implementation, using the standard *.[ext] (where ext
usually "action") pattern. The extension is looked up from the Struts
configuration key struts.action.exection.
To help with dealing with buttons and other related requirements, this
mapper (and other ActionMappers, we hope) has the ability to name a
button with some predefined prefix and have that button name alter the
execution behaviour. The four prefixes are:
- Method prefix - method:default
- Action prefix - action:dashboard
- Redirect prefix - redirect:cancel.jsp
- Redirect-action prefix - redirect-action:cancel
In addition to these four prefixes, this mapper also understands the
action naming pattern of foo!bar in either the extension form (eg:
foo!bar.action) or in the prefix form (eg: action:foo!bar). This syntax tells
this mapper to map to the action named foo and the method bar.
Method prefix
With method-prefix, instead of calling baz action's execute() method (by
default if it isn't overriden in struts.xml to be something else), the baz
action's anotherMethod() will be called. A very elegant way determine which
button is clicked. Alternatively, one would have submit button set a
particular value on the action when clicked, and the execute() method decides
on what to do with the setted value depending on which button is clicked.
<a:form action="baz">
<a:textfield label="Enter your name" name="person.name"/>
<a:submit value="Create person"/>
<a:submit name="method:anotherMethod" value="Cancel"/>
</a:form>
Action prefix
With action-prefix, instead of executing baz action's execute() method (by
default if it isn't overriden in struts.xml to be something else), the
anotherAction action's execute() method (assuming again if it isn't overriden
with something else in struts.xml) will be executed.
<a:form action="baz">
<a:textfield label="Enter your name" name="person.name"/>
<a:submit value="Create person"/>
<a:submit name="action:anotherAction" value="Cancel"/>
</a:form>
Redirect prefix
With redirect-prefix, instead of executing baz action's execute() method (by
default it isn't overriden in struts.xml to be something else), it will get
redirected to, in this case to www.google.com. Internally it uses
ServletRedirectResult to do the task.
<a:form action="baz">
<a:textfield label="Enter your name" name="person.name"/>
<a:submit value="Create person"/>
<a:submit name="redirect:www.google.com" value="Cancel"/>
</a:form>
Redirect-action prefix
With redirect-action-prefix, instead of executing baz action's execute()
method (by default it isn't overriden in struts.xml to be something else), it
will get redirected to, in this case 'dashboard.action'. Internally it uses
ServletRedirectResult to do the task and read off the extension from the
struts.properties.
<a:form action="baz">
<a:textfield label="Enter your name" name="person.name"/>
<a:submit value="Create person"/>
<a:submit name="redirect-action:dashboard" value="Cancel"/>
</a:form>
Custom ActionMapper
You can define your own ActionMapper by implementing org.apache.struts2.dispatcher.mapper.ActionMapper then configuring Struts 2 to use the new class in struts.xml
<bean type="org.apache.struts2.dispatcher.mapper.ActionMapper" name="struts" class="com.mycompany.myapp.MyActionMapper" />
Possible uses of the ActionMapper include defining your own, cleaner namespaces, such as URLs like /person/1, which would be similar to a request to /getPerson.action?personID=1 using the DefaultActionMapper.
CompositeActionMapper
A composite action mapper that is capable of delegating to a series of ActionMapper if the former
failed to obtained a valid ActionMapping or uri.
如果前面的在獲得一個有效的ActionMapper或Uri失敗，一個復合的映射器能委托一系列的ActionMapper。
It is configured through struts.properties.
For example, with the following entries in struts.properties
<bean type="org.apache.struts2.dispatcher.mapper.ActionMapper" name="struts"
class="org.apache.struts2.dispatcher.mapper.CompositeActionMapper" />
<constant name="struts.mapper.composite"
value="org.apache.struts2.dispatcher.mapper.DefaultActionMapper,org.apache.struts2.dispatcher.mapper.RestfulActionMapperorg.apache.struts2.dispatcher.mapper.Restful2ActionMapper" />
When CompositeActionMapper#getMapping(HttpServletRequest, ConfigurationManager) or
CompositeActionMapper#getUriFromActionMapping(ActionMapping) is invoked,
CompositeActionMapper would go through these ActionMappers in sequence
starting from ActionMapper identified by 'struts.mapper.composite.1', followed by
'struts.mapper.composite.2' and finally 'struts.mapper.composite.3' (in this case) until either
one of the ActionMapper return a valid result (not null) or it runs out of ActionMapper
in which case it will just return null for both CompositeActionMapper#getMapping(HttpServletRequest, ConfigurationManager) and
CompositeActionMapper#getUriFromActionMapping(ActionMapping) methods.
For example with the following in struts-*.xml :-
<bean type="org.apache.struts2.dispatcher.mapper.ActionMapper" name="struts"
class="org.apache.struts2.dispatcher.mapper.CompositeActionMapper" />
<constant name="struts.mapper.composite"
value="org.apache.struts2.dispatcher.mapper.DefaultActionMapper,foo.bar.MyActionMapper,foo.bar.MyAnotherActionMapper" />
CompositeActionMapper will be configured with 3 ActionMapper, namely
"DefaultActionMapper", "MyActionMapper" and "MyAnotherActionMapper".
CompositeActionMapper would consult each of them in order described above.
ActionMapper and ActionMapping objets
The ActionMapper fetches the ActionMapping object corresponding to a
given request. Essentially, the ActionMapping is a data transfer object
that collects together details such as the Action class and method to
execute. The mapping is utilized by the Dispatcher and various user
interface components. It is customizable through struts.mapper.class entry in struts.properties.
Customize
 |
Custom ActionMapper must implement ActionMapper interface and have a default constructor. |
struts.mapper.class=foo.bar.MyCustomActionMapper
public class MyCustomActionMapper implements ActionMapper {
public ActionMapping getMapping(HttpServletRequest request,
ConfigurationManager configManager) {
....
}
public String getUriFromActionMapping(ActionMapping mapping) {
....
}
}
See also: RestfulActionMapper