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Web Component Certification (OCEJWCD)

Tag attributes and the setter method

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posted 19 years ago

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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

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posted 19 years ago

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<% 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

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Posts: 162

posted 19 years ago

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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

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Posts: 48

posted 19 years ago

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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

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Posts: 162

posted 19 years ago

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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

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Posts: 48

posted 19 years ago

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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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