Learning Notes (vi) custom labels and relative path absolute paths

2. Custom Labels

1). HelloWorld

①. Create a label processor class: Implement the Simpletag interface.
②. In the Web-inf folder, create a new. TLD (Tag library profile) as an XML file with an extension. and copy into the fixed part: and the
Description, Display-name, tlib-version, Short-name, Uri make changes

<taglib xmlns= "HTTP://JAVA.SUN.COM/XML/NS/J2EE"
Xmlns:xsi= "Http://www.w3.org/2001/XMLSchema-instance"
xsi:schemalocation= "Http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd"
version= "2.0" >

<DESCRIPTION>JSTL 1.1 Core Library</description>
<display-name>jstl core</display-name>
<tlib-version>1.1</tlib-version>
<short-name>c</short-name>
<uri>http://java.sun.com/jsp/jstl/core</uri>

</taglib>

③. Describe the custom label in the TLD file:

<!--describe your custom Hellosimpletag label--
<tag>
<!--tag name: The name of the tag when using it on a JSP page--
<name>hello</name>

<!--the full-class name of the tag
<tag-class>com.atguigu.javaweb.tag.HelloSimpleTag</tag-class>
<!--label body type--
<body-content>empty</body-content>
</tag>

④. Using a custom label on a JSP page:

> Importing tag Library profiles using taglib directives: <% @taglib uri= "Http://www.atguigu.com/mytag/core" prefix= "Atguigu"%>

> Using a custom tag: <atguigu:hello/>

2). Setjspcontext: Must be called by the JSP engine, before Dotag, the PageContext representing the JSP engine to the label processor class.

Private PageContext PageContext;

@Override
public void Setjspcontext (Jspcontext arg0) {
System.out.println (arg0 instanceof PageContext);
This.pagecontext = (PageContext) arg0;
}

3). Custom Labels with attributes:

①. The setter method is defined in the label processor class first. It is recommended that all property types be set to String types.

private String value;
Private String count;

public void SetValue (String value) {
This.value = value;
}

public void SetCount (String count) {
This.count = count;
}

②. To describe the attribute in the TLD description file:

<!--describe the properties of the current label--
<attribute>
<!--property name, as defined by the setter method of the label processor class, and
<name>value</name>
<!--whether the property is required--
<required>true</required>
<!--rtexprvalue:runtime expression value
Whether the current property can accept dynamic values for run-time expressions--
<rtexprvalue>true</rtexprvalue>
</attribute>

③. Using attributes in the page, the property name is the name defined in the TLD file.

<atguigu:hello value= "${param.name}" count= "Ten"/>

4). Usually the development of simple tags directly inherit simpletagsupport. can call its corresponding getter method to get the corresponding API

public class Simpletagsupport implements simpletag{

public void Dotag ()
Throws Jspexception, ioexception{}

Private Jsptag Parenttag;

public void SetParent (Jsptag parent) {
This.parenttag = parent;
}

Public Jsptag getParent () {
return this.parenttag;
}

Private Jspcontext Jspcontext;

public void Setjspcontext (Jspcontext pc) {
This.jspcontext = PC;
}

Protected Jspcontext Getjspcontext () {
return this.jspcontext;
}

Private Jspfragment jspbody;

public void Setjspbody (Jspfragment jspbody) {
This.jspbody = Jspbody;
}

Protected Jspfragment Getjspbody () {
return this.jspbody;
}
}

1. Relative path and absolute path:

1). Why solve the problem of relative paths: in the case of a Servlet forwarding page, the relative path can be confused.

a.jsp: <a href= "Tobservlet" >to B page2</a>
ToBServlet:request.getRequestDispatcher ("/dir/b.jsp"). Forward (request, response);

Note that at this point the value of the address bar of the browser after clicking to B Page2 hyperlink: Http://localhost:8989/day_36/ToBServlet, the actual display is
Dir-Path b.jsp

The b.jsp page has a hyperlink: <a href= "c.jsp" >to c Page</a>. By default, c.jsp should be under the same path as b.jsp. Click on the hyperlink now
will be displayed in the browser address bar: http://localhost:8989/day_36/c.jsp. However, there is no c.jsp in the root directory, so there is a problem with path confusion.

2). Using an absolute path will solve the above problem:

Absolute path: The path relative to the root directory of the current WEB site.

http://localhost:8989/day_36/c.jsp:http://localhost:8989/is the root directory of the WEB site,/day_36 is ContextPath,
/c.jsp is a file path relative to the current WEB application. We need to add the ContextPath to the current WEB application under any path.

Like what:
<a href= "Tobservlet" >to B page2</a> need to be changed to: <a href= "<%= request.getcontextpath ()%>/ToBServlet" > To B page2</a>
Response.sendredirect ("a.jsp"); Should be changed to: Response.sendredirect (Request.getcontextpath () + "/a.jsp");
<form action= "Addservlet" ></form> need to change to: <form action= "<%= request.getcontextpath ()%>/addservlet "></form>

3). In the Javaweb app/representative: sometimes represents the root of the current WEB app, sometimes representing the root directory of the site.

/represents the root path of the current web app: if/where the command or method needs to be parsed by the Web server, rather than directly to the browser, then/represents the root path of the web App. Write at this time
The absolute path does not need to be added ContextPath.
When you do a serlvet mapping path in the Web. xml file,
On request Forwarding: Request.getrequestdispatcher ("/dir/b.jsp"). Forward (request, response);

/represents the root directory of the site: if/directly to the browser parsing,/represents the site's root path, at this time must be added ContextPath
<form action= "/addservlet" ></form>
Response.sendredirect ("/a.jsp");

4). How to obtain ContextPath:
Servletcontext:getcontextpath ()
Httpservletrequest:getcontextpath ()

Learning Notes (vi) custom labels and relative path absolute paths