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Web Component Certification (OCEJWCD)

Tag attributes and the setter method

Ranch Hand

Posts: 48

posted 14 years ago

I am trying to get the "Simple tag with attribute" example on page 511 of HFSJ working.

Here's the code . . .

<%--this is the jsp--%>
<%@ taglib prefix="myTags" uri="simpleTags" %>
<%@ page import="java.util.ArrayList" %>
 
<jsp:useBean id="movie1"  class="foo.Movie">
  <jsp:setProperty name="movie1" property="name" value="Crawlspace"  />
  <jsp:setProperty name="movie1" property="genre" value="Horror"  />
</jsp:useBean>
 
<jsp:useBean id="movie2"  class="foo.Movie">
  <jsp:setProperty name="movie2" property="name" value="Blind Swordsman" />
  <jsp:setProperty name="movie2" property="genre" value="Samurai"  />
</jsp:useBean>
 
<%
  java.util.ArrayList movieCollection = new java.util.ArrayList(2);
  movieCollection.add("${movie1}");
  movieCollection.add("${movie2}");
%>
 
<HTML>
<BODY>
<table>
  <myTags:movieTag  movieList="${movieCollection}">
    <tr>
      <td>${movie.name}</td>
      <td>${movie.genre}</td> 
    </tr>
  </myTags:movieTag>
</table>
</BODY>
</HTML>
 
*********************************************************
//Heres the .tld

<?xml version="1.0" encoding="ISO-8859-1" ?>
<!DOCTYPE taglib
  PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag Library 1.2//EN"
  "http://java.sun.com/dtd/web-jsptaglibrary_1_2.dtd">
 
<taglib>
    <tlib-version>1.2</tlib-version>
    <jspversion>2.0</jspversion>
    <uri>simpleTags</uri>
      
<tag>
   <description> to print movieList</description>
           <name>movieTag</name>
   <tag-class>foo.MovieTag</tag-class>
           <body-content>scriptless</body-content>
           <attribute>
             <name>movieList</name>
     <required>true</required>
             <rtexprvalue>true</rtexprvalue>
           </attribute>
        </tag>
</taglib>

**********************************************************
//and here's the tag handler class . . .
 
package foo;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.SimpleTagSupport;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Iterator; 
 
public class MovieTag extends SimpleTagSupport{
 
    private ArrayList movieList;
 
  public void setMovieList(ArrayList movieList){
    this.movieList=movieList;
  }//setMovieList
  
    public void doTag() throws JspException, IOException{
    
      Iterator i = movieList.iterator();
 
      while(i.hasNext()){
  
Movie movie = (Movie) i.next();
        getJspContext().setAttribute("movie", movie);
getJspBody().invoke(null);
 
      }//while

}//doTag
}//MovieTag
 
**************************************************************
//and here's the bean.
 
package foo; 
public class Movie{
 
   private String name;
   private String  genre;
 
   public void setName(String name){
this.name=name;
   }//setName
 
   public String getName(){
return this.name;
   }//getName
 
   public void setGenre(String genre){
this.genre=genre;
   }//setGenre
 
   public String getGenre(){
return this.genre;
   }//getGenre
 
}

The tag handler class and the bean are in $CATALINA_HOME/webapps/simple_tag/WEB-INF/classes/foo.

The .tld is in /WEB-INF.

When I run it, in Tomcat 5.5.12, I get a NullPointer exception at the line where the iterator is declared in the tag handler.

Any thoughts will be greatly appreciated.

Thank you,

Marc Peabody

pie sneak

Posts: 4727

I like...

posted 14 years ago

<% java.util.ArrayList movieCollection = new java.util.ArrayList(2); movieCollection.add("${movie1}"); movieCollection.add("${movie2}");%> <HTML><BODY><table> <myTags:movieTag movieList="${movieCollection}">

Two big things here.
1) I don't think movieCollection.add("${movie1}"); will work because I don't think EL works inside of scriptlets.

2) <myTags:movieTag movieList="${movieCollection}"> won't find your collection because your never added it to any scope. Try ending the scriptlet with a:
request.setAttribute("movieCollection", movieCollection);
Fixing this second part alone will solve the NullPointer.

A good workman is known by his tools.

Chandra Sagi

Ranch Hand

Posts: 162

posted 14 years ago

Two big things here.
1) I don't think movieCollection.add("${movie1}"); will work because I don't think EL works inside of scriptlets.

2) <myTags:movieTag movieList="${movieCollection}"> won't find your collection because your never added it to any scope. Try ending the scriptlet with a:
request.setAttribute("movieCollection", movieCollection);
Fixing this second part alone will solve the NullPointer.

I guess these should not be a problem.

Micheal,

I have given it a try but with no luck. I used

SimpleTagSupport to implement DynamicAttributes and also tried to add <dynamic-attributes> in tld. It was mentioned in HFJS on pg562 Q7. Try using this, may be it would solve your problem. Please let me know if you solve it.

Thanks
Chandu

Joseph Clark

Ranch Hand

Posts: 48

posted 14 years ago

Well, this works . . .

<%@ taglib prefix="myTags" uri="simpleTags" %>
<%@ page import="java.util.ArrayList" %>
 
<%--
<jsp:useBean id="movie1"  class="foo.Movie">
  <jsp:setProperty name="movie1" property="name" value="Crawlspace"  />
  <jsp:setProperty name="movie1" property="genre" value="Horror"  />
</jsp:useBean>
<jsp:useBean id="movie2"  class="foo.Movie">
  <jsp:setProperty name="movie2" property="name" value="Blind Swordsman" />
  <jsp:setProperty name="movie2" property="genre" value="Samurai"  />
</jsp:useBean>
--%>
 
 
<%
  java.util.ArrayList movieCollection = new java.util.ArrayList(2);
  foo.Movie m1=new foo.Movie();
  foo.Movie m2 = new foo.Movie();
  m1.setName("Seven Days In May");
  m1.setGenre("Drama");
  m2.setName("The High and the Mighty");
  m2.setGenre("Airplane");
  movieCollection.add(m1);
  movieCollection.add(m2);
  request.setAttribute("movieCollection", movieCollection);
%>
 
<HTML>
<BODY>
<table>
  <myTags:movieTag  movieList="${movieCollection}">
    <tr>
      <td>${movie.name}</td>
      <td>${movie.genre}</td> 
    </tr>
  </myTags:movieTag>
</table>
</BODY>
</HTML>

Thanks for the tip Marc.
No telling when it would have occured to me to give the thing a scope.
[ March 03, 2006: Message edited by: Michael Clark ]

Chandra Sagi

Ranch Hand

Posts: 162

posted 14 years ago

Marc,

No offense. You are correct. Could any of you explain me about Question 7 in HFJS on pg562.

Thanks in Advance.
Chandu

Joseph Clark

Ranch Hand

Posts: 48

posted 14 years ago

I didn't get to dynamic att's yet, Chandu.

Did you read Bryan Basham's tutorial?:

https://coderanch.com/t/170429/java-Web-Component-SCWCD/certification/Tutorial-Dynamic-Attributes

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