[pre] java.lang.object
|
- javax.servlet.jsp.tagext.tagsupport
|
- org.apache.struts.taglib.formtag [/ pre]
First, technical preparation
TAG interface
1. Tagsupport implements the javax.servlet.jsp.tagext.tag interface, the TAG interface defines the basic protocol between the Tag Handler and JSP implementation classes. The life cycle is defined and the method to be called at the beginning of the Tag. The TAG interface defines the following methods:
DostartTag ()
doendtag ()
RELEASE ()
getParent (), SetParent (TAG)
SetPageContext (PageContext)
JSP Page Implements the object first calls the setPageContext, Separent method, and initializes other properties; then, you can call the Tag Handler's dostartTAG (), and DOENDTAG () method.
2. Lifecycle
[img] /members/srx81/formtag-1.jpg [img]
? [1] Call release () Releases all properties
? [2] TAG ended normally
? [3] Check the trycatchfinally interface for additional details related to exception handling and resources management
Tagsupport class
Javax.Servlet.jsp.tagext.tagsupport is the basic class of Tag Handler that implements Tag, IterationTag interface. ITerationTag inherits to the TAG interface and adds a way to DOAFTERBODY (). You only need to inherit tagsupport, redefine several methods to generate a new Tag Handler. Tagsupport has two Protected properties:
? Id? D? D protected string
? PageContext? D? Dprotected pageContext
? VALUES? D? D Private Hashtable
? Parent - Private Tag
There are other constants that inherit from Tag, IterationTAG, such as Eval_Body_InClude, etc.
The subclass of Tagsupport also needs to define a non-arranging configuration method of a public in which a PUBLIC is unfolded.
Tagsupport has the following methods:
• Tag, IterationTAG interface definition method;
• Attribute ID, PageContext, Parent's setter / getter method;
• Key value pair method, SETVALUE (String, Object), getValues (), getValue (string), RemoveValue (String) method.
Second, work mechanism
First, look at how a servlet container receives a .jsp request, how to resolve similar
Taking Tomcat 4.0.3 parsing the logon.jsp in Struts-Example as an example, if you have already accessed the link:
Http: // localhost: 8080 / struts-example / logon.jsp
In $ Tomcat / Work / LocalHost / Struts-Example, you can find a file called Logon $ Jsp.java, which is Tomcat to resolve the corresponding Java source file obtained by Logon.JSP. You can find
The Java source code corresponding to the label,
Org.apache.struts.taglib.html.formTag_jspx_th_html_form_0 =
New org.apache.struts.taglib.html.formtag ();
_jspx_th_html_form_0.setpageContext (PageContext);
_jspx_th_html_form_0.setparent (_jspx_th_html_html_0);
_jspx_th_html_form_0.setAction
"/ logon");
_jspx_th_html_form_0.setfocus
"Username");
Try {
INT _JSPX_EVAL_HTML_FORM_0 = _jspx_th_html_form_0.dostarttag ();
IF (_jspx_eval_html_form_0 ==
Javax.servlet.jsp.tagext.bodytag.eval_body_buffered)
Throw
NEW JSptagexception
"Since Tag Handler"
"Class Org.apache.struts.taglib.html.FormTag Does Not IMPLEMENT"
"Bodytag, IT can't returnral");
......
IF (_jspx_th_html_form_0.doendtag () == javax.servlet.jsp.tagext.tag.skip_page)
Return;
}
Finally {
_jspx_th_html_form_0.release ();
}
Note that
Main attribute
protected string action = null;
// This form should be submitted by the action URL
protected string name = null;
//
protected string type = null;
// Form bean class name
protected string scope = null;
// Form Bean visible range
protected
Static MessageResources Messages =
MessageResources.getMessageResources (Constants.Package, ".localestrings");
Main method
1, dostarttag
/ / Find the Form Bean's Name, Scope, Type properties
LOOKUP ();
2, Lookup
protected
Void Lookup ()
Throws JSPEXCEPTION {
// Check if the value required is set
IF (name! = null) {
IF (scope == null)
SCOPE = "session";
IF (Type == Null) {
// Error handling model
JSPEXCEPTION E =
NEW JSPEXCEXCE ("FORMTAG.NAMETYPE"); pageContext.setttribute (action.exception_key, e,
PageContext.Request_scope);
Throw e;
}
Return;
}
/ / Find a collection instance of the required Application range, mappings, and instantiated in the Action Servlet and placed in servletContext.
ActionMAppings mappings = (pageContext)
PageContext.getattribute (action.mappings_key,
PageContext.Application_scope);
ActionformBeans FormBeans = ...
IF ((mappings == null) || (FORMBEANS == Null) ...
/ / Find this formally associated actionMApping
String mappingname = getActionMappingname ();
/ / Emphasize mapping name from Action
ActionMapping mapping = mappings.findmapping (mappingname);
