How is html page outputed when using taglib and xml ?

Question

Dear all,
          I am a newbie for taglib and xml. Today, when I read some source code of a
          website, I found that there is a entry like
          "%@ taglib uri="/tlds/taglib.tld" prefix="myprefix" %>",
          and some other entries like
          "<myprefix:Content area="<%=contentArea%>" />"
          I opened the specifized file taglib.tld and saw a tag entry named "Content",
          its tagclass is com.mycom.presentation.taglib.ContentTag. Again I opend a
          java class file "ContentTag.java" and saw some setXXX methods and doXXX
          methods. I donot know how is the webpage outputed. Can someone give me a
          detailed description about that? I will greatly appreciate your help.
          Some source code segments are listed as follows:
          test.jsp:
          <%@ taglib uri="/tlds/taglib.tld" prefix="myprefix" %>
          <td>
          <myprefix:Content body="<%=body%>" area="<%=contentArea%>"
          pageName="<%=pageName%>" />
          </td>
          taglib.tld:
          <?xml version="1.0" encoding="ISO-8859-1" ?>
          <!DOCTYPE taglib
          PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag Library 1.1//EN"
          "http://java.sun.com/j2ee/dtds/web-jsptaglibrary_1_1.dtd">
          <tag>
          <name>Content</name>
          <tagclass>com.myprefix.presentation.taglib.ContentTag</tagclass>
          <bodycontent>JSP</bodycontent>
          <info>An tag which given the screen and element does the right content
          thing!</info>
          <attribute>
          <name>id</name>
          <required>false</required>
          <rtexprvalue>true</rtexprvalue>
          <!--type>String</type-->
          </attribute>
          <attribute>
          <name>pageName</name>
          <required>false</required>
          <rtexprvalue>true</rtexprvalue>
          <!--type>String</type-->
          </attribute>
          <attribute>
          <name>area</name>
          <required>false</required>
          <rtexprvalue>true</rtexprvalue>
          <!--type>String</type-->
          </attribute>
          <attribute>
          <name>body</name>
          <required>false</required>
          <rtexprvalue>true</rtexprvalue>
          <!--type>long</type-->
          </attribute>
          </tag>
          ContentTag.java
          package com.mycom.presentation.taglib;
          import javax.servlet.*;
          import javax.servlet.http.*;
          import javax.servlet.jsp.JspTagException;
          import javax.servlet.jsp.tagext.BodyTagSupport;
          public class ContentTag extends BodyTagSupport {
          private String ......;
          public String ......;
          public ContentTag() {
          super();
          public void setPageName(String pageName) {
          this.pageName = pageName;
          public void setArea(String area) {
          this.area = area;
          public void setSegment(String segment) {
          this.segment = segment;
          if (segment!=null) // && !segment.equals("null")
          this.segment_set = true;
          public void setAdmin(String admin) {
          try{
          this.admin = Boolean.getBoolean(admin);
          } catch (Exception _) {
          debugCategory.debug("Setting admin err " + admin);
          public void setBody(String body)
          try {
          this.body = Long.parseLong(body);
          } catch (NumberFormatException ne) {
          debugCategory.debug("Setting body format err");
          public int doStartTag() {
          if (contentMap == null)
          HttpSession session = pageContext.getSession();
          if (segment==null)
          segment =
          (String)session.getAttribute(Parameters.segment_id);
          if (currentScreen==null)
          currentScreen =
          (String)session.getAttribute(Parameters.currentScreen);
          try{
          StateEngineProxy sep =
          (StateEngineProxy)session.getAttribute("stateMachine");
          ModelManager mm =
          (ModelManager)session.getAttribute("modelManager");
          if (sep == null||mm==null)
          sep = new StateEngineProxy();
          session.setAttribute("stateMachine", sep);
          mm = new ModelManager();
          mm.init(session, sep);
          session.setAttribute("modelManager", mm);
          if (body !=0)
          //content = (ContentAI)
          contentMap.get(Parameters.content_id+Long.toString(body));
          if (content==null)
          debugCategory.debug("Get by Body");
          mm.getContent(body);
          content =
          (ContentAI)session.getAttribute(Parameters.content);
          //contentMap.put(Parameters.content_id +
          Long.toString(body), content);
          file:// pageContext.setAttribute(CONTENT_MAP,
          contentMap, myScope);
          if (pageName!=null&&area!=null &&
          segment!=null&&segment!=""&&area!=""&&pageName!="")
          contentList = (Collection)
          mm.getContentBySegmentPageNameAndArea(segment,
          pageName, area);
          if(contentList!=null){
          Iterator it = contentList.iterator();
          if (it.hasNext()) {
          content = (ContentAI)it.next();
          session.setAttribute(Parameters.content,
          content);
          return EVAL_BODY_TAG;
          return EVAL_BODY_TAG;
          public int doEndTag() throws JspTagException {
          current = SUPPLIERSINFORMATION;
          pageContext.getOut().flush();
          if ( content != null
          && !currentScreen.equals(ScreenNames.CONTENT_LIST_URL)
          && !currentScreen.equals(ScreenNames.CONTENT_EDIT_URL))
          if ( !admin ){
          // include body?
          if
          rentScreen.equals(ScreenNames.CONTENT_NEWS_URL)){ 
          pageContext.getOut().println("<h3>" + content.getSubject() + "<br></h3>");
          pageContext.getOut().println("<!-- Subject[" + content.getSubject() + "]");
          pageContext.getOut().println("OrgID[" + content.getOrgId() + "]");
          pageContext.getOut().println("LogoPath[" + content.getLogoPath() + "]");
          pageContext.getOut().println("PageName[" + content.getPageName() + "]");
          pageContext.getOut().println("Area[" + content.getArea() + "]");
          pageContext.getOut().println("Segment[" + content.getSegment() + "]");
          pageContext.getOut().println("<!--Body[-->" + "<br>" + content.getBody() + "<!--]-->");
          return EVAL_PAGE;
          public int doAfterBody() throws JspTagException {
          return SKIP_BODY;
          public static String shortenLink(String link)
          

Answer 1

Hi Andy,
          The sequence of operations that happen when a JSP page encounters a Custome Tag are
          1. Find the class associated with the custom tag from the tld.
          2. The set and get methods that u find are for passing  the values for the tag attributes that u may need
          to pass.
          3. The Tag Lib class performs the operation specified and flushes the output to the jsp.
          For further understanding ..u can refer to these sites !!!
          http://java.sun.com/products/jsp/tutorial/TagLibrariesTOC.html
          http://www.weblogic.com/docs51/classdocs/API_taglib.html#intro
          Regards,
          Sundhar Subramanian
          Andy Ping wrote:
          > Dear all,
          >
          > I am a newbie for taglib and xml.  Today, when I read some source code of a
          > website, I found that there is a entry like
          >     "%@ taglib uri="/tlds/taglib.tld" prefix="myprefix" %>",
          > and some other entries like
          >     "<myprefix:Content  area="<%=contentArea%>"  />"
          > I opened the specifized file taglib.tld and saw a tag entry named "Content",
          > its tagclass is com.mycom.presentation.taglib.ContentTag.  Again I opend a
          > java class file "ContentTag.java" and saw some setXXX methods and doXXX
          > methods.  I donot know how is the webpage outputed.  Can someone give me a
          > detailed description about that?   I will greatly appreciate your help.
          > Some source code segments are listed as follows:
          >
          > ----------------
          > test.jsp:
          > ----------------
          > ...
          > <%@ taglib uri="/tlds/taglib.tld" prefix="myprefix" %>
          > ...
          > <td>
          >     <myprefix:Content body="<%=body%>" area="<%=contentArea%>"
          > pageName="<%=pageName%>" />
          > </td>
          > ...
          >
          > ----------------
          > taglib.tld:
          > ----------------
          > <?xml version="1.0" encoding="ISO-8859-1" ?>
          > <!DOCTYPE taglib
          >         PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag Library 1.1//EN"
          >  "http://java.sun.com/j2ee/dtds/web-jsptaglibrary_1_1.dtd">
          > ......
          >   <tag>
          >     <name>Content</name>
          >     <tagclass>com.myprefix.presentation.taglib.ContentTag</tagclass>
          >     <bodycontent>JSP</bodycontent>
          >     <info>An tag which given the screen and element does the right content
          > thing!</info>
          >     <attribute>
          >       <name>id</name>
          >       <required>false</required>
          >       <rtexprvalue>true</rtexprvalue>
          >       <!--type>String</type-->
          >     </attribute>
          >     <attribute>
          >       <name>pageName</name>
          >       <required>false</required>
          >       <rtexprvalue>true</rtexprvalue>
          >       <!--type>String</type-->
          >     </attribute>
          >     <attribute>
          >       <name>area</name>
          >       <required>false</required>
          >       <rtexprvalue>true</rtexprvalue>
          >       <!--type>String</type-->
          >     </attribute>
          >     <attribute>
          >       <name>body</name>
          >    <required>false</required>
          >    <rtexprvalue>true</rtexprvalue>
          >       <!--type>long</type-->
          >     </attribute>
          >   </tag>
          > ......
          >
          > ----------------
          > ContentTag.java
          > ----------------
          > package com.mycom.presentation.taglib;
          >
          > import javax.servlet.*;
          > import javax.servlet.http.*;
          > import javax.servlet.jsp.JspTagException;
          > import javax.servlet.jsp.tagext.BodyTagSupport;
          > ...
          >
          > public class ContentTag extends  BodyTagSupport {
          >     private String ......;
          >     public String ......;
          >     ......
          >
          >     public ContentTag() {
          >         super();
          >     }
          >
          >     public void setPageName(String pageName) {
          >         this.pageName = pageName;
          >     }
          >
          >     public void setArea(String area) {
          >         this.area = area;
          >     }
          >
          >     public void setSegment(String segment) {
          >         this.segment = segment;
          >         if (segment!=null) // && !segment.equals("null")
          >         {
          >             this.segment_set = true;
          >         }
          >     }
          >
          >     public void setAdmin(String admin) {
          >         try{
          >             this.admin = Boolean.getBoolean(admin);
          >         } catch (Exception _) {
          >             debugCategory.debug("Setting admin err " + admin);
          >         }
          >
          >     }
          >     public void setBody(String body)
          >     {
          >         try {
          >          this.body = Long.parseLong(body);
          >         } catch (NumberFormatException ne) {
          >             debugCategory.debug("Setting body format err");
          >         }
          >     }
          >
          >     public int doStartTag() {
          >             if (contentMap == null)
          >             {
          >             }
          >    HttpSession session = pageContext.getSession();
          >             if (segment==null)
          >             {
          >                 segment =
          > (String)session.getAttribute(Parameters.segment_id);
          >             }
          >             if (currentScreen==null)
          >             {
          >                 currentScreen =
          > (String)session.getAttribute(Parameters.currentScreen);
          >             }
          >             try{
          >                 StateEngineProxy sep =
          >                     (StateEngineProxy)session.getAttribute("stateMachine");
          >                 ModelManager mm =
          > (ModelManager)session.getAttribute("modelManager");
          >                 if (sep == null||mm==null)
          >                 {
          >                     sep = new StateEngineProxy();
          >                     session.setAttribute("stateMachine", sep);
          >                     mm = new ModelManager();
          >                     mm.init(session, sep);
          >
          >                     session.setAttribute("modelManager", mm);
          >                 }
          >                 if (body !=0)
          >                 {
          >                     //content = (ContentAI)
          >                     //
          > contentMap.get(Parameters.content_id+Long.toString(body));
          >                     if (content==null)
          >                     {
          >                     debugCategory.debug("Get by Body");
          >                     mm.getContent(body);
          >                     content =
          > (ContentAI)session.getAttribute(Parameters.content);
          >
          >                     //contentMap.put(Parameters.content_id +
          > Long.toString(body), content);
          >                     file:// pageContext.setAttribute(CONTENT_MAP,
          > contentMap, myScope);
          >                     }
          >                 }
          >                 if (pageName!=null&&area!=null &&
          >                     segment!=null&&segment!=""&&area!=""&&pageName!="")
          >                 {
          >                      contentList = (Collection)
          >                          mm.getContentBySegmentPageNameAndArea(segment,
          > pageName, area);
          >                      if(contentList!=null){
          >                         Iterator it = contentList.iterator();
          >                         if (it.hasNext()) {
          >                             content = (ContentAI)it.next();
          >                             session.setAttribute(Parameters.content,
          > content);
          >                             return EVAL_BODY_TAG;
          >                         }
          >                      }
          >                 }
          >                 ...
          >            }
          >   return EVAL_BODY_TAG;
          >     }
          >
          >     public int doEndTag() throws JspTagException {
          >         current = SUPPLIERSINFORMATION;
          >         pageContext.getOut().flush();
          >         if ( content != null
          >             && !currentScreen.equals(ScreenNames.CONTENT_LIST_URL)
          >             && !currentScreen.equals(ScreenNames.CONTENT_EDIT_URL))
          >         {
          >             if ( !admin  ){
          >             // include body?
          >                 if
          > rentScreen.equals(ScreenNames.CONTENT_NEWS_URL)){
          >                     pageContext.getOut().println("<h3>" + content.getSubject() + "<br></h3>");
          >                 }
          >                 pageContext.getOut().println("<!-- Subject[" + content.getSubject() + "]");
          >                 pageContext.getOut().println("OrgID[" + content.getOrgId() + "]");
          >                 pageContext.getOut().println("LogoPath[" + content.getLogoPath() + "]");
          >                 pageContext.getOut().println("PageName[" + content.getPageName() + "]");
          >                 pageContext.getOut().println("Area[" + content.getArea() + "]");
          >                 pageContext.getOut().println("Segment[" + content.getSegment() + "]");
          >                 pageContext.getOut().println("<!--Body[-->" + "<br>" + content.getBody() + "<!--]-->");
          >             }
          >         }
          >  return EVAL_PAGE;
          >     }
          >
          >     public int doAfterBody() throws JspTagException {
          >         return SKIP_BODY;
          >     }
          >
          >     public static String shortenLink(String link)
          >     {
          >        ...
          >     }
          > }