Using EL to generate attribute/value pairs inside of an XHTML element

I'm trying to remove all scriptlets from my JSP file. Since I'm working on getting my SCWCD certification, I thought I would ask the question here.

The following JSP code works:

But Eclipse gives me the following warnings:

Description Resource Path Location Type
Undefined attribute name (:). ephemeris.jsp /servlet/WebContent line 244 JSP Problem
Undefined attribute name (:). ephemeris.jsp /servlet/WebContent line 246 JSP Problem
Undefined attribute name (:). ephemeris.jsp /servlet/WebContent line 248 JSP Problem
Undefined attribute name (DE200). ephemeris.jsp /servlet/WebContent line 244 JSP Problem
Undefined attribute name (DE405). ephemeris.jsp /servlet/WebContent line 246 JSP Problem
Undefined attribute name (DE406). ephemeris.jsp /servlet/WebContent line 248 JSP Problem
Undefined attribute name (ephemeris.catalog). ephemeris.jsp /servlet/WebContent line 244 JSP Problem
Undefined attribute name (ephemeris.catalog). ephemeris.jsp /servlet/WebContent line 246 JSP Problem
Undefined attribute name (ephemeris.catalog). ephemeris.jsp /servlet/WebContent line 248 JSP Problem

Here's the result of the HTML rendering ("view source" on web browser). This is the correct result after selecting "DE405".

Is there something wrong with the way I use the expression?

I coded up a tag so I can avoid getting the warning messages.

This is what I coded in my JSP ("ephemeris.jsp"):

This is what gets rendered to output after selecting "DE405" ("View Source" from browser client):

*****************************************************************************************

How did I implement my tag?

Here's my Java code that writes the replacement XHTML code ("Radio.java"):

package net.jsemler.utility.jsptags;

import java.io.IOException;
import java.io.Serializable;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspTagException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.PageContext;
import javax.servlet.jsp.tagext.Tag;

public class Radio implements Tag, Serializable {    
    private static final long serialVersionUID = 1L;
    private PageContext pc;
    private Tag parent;
    private String classes, name, value, compare;

public void setPageContext(PageContext p) { pc = p; }
    public void setParent(Tag t) { parent = t; }
    public Tag getParent() { return parent; }

// My setters
    public void setClasses (String s) { classes = s; }    
    public void setName    (String s) { name = s;    }
    public void setValue   (String s) { value = s;   }
    public void setCompare (String s) { compare = s; }

public int doStartTag() throws JspException {
        try {
            JspWriter out = pc.getOut();
            out.write("<input");
            out.write(" class=\"" + classes + "\"");
            out.write(" type=\"radio\"");
            out.write(" name=\"" + name + "\"");
            out.write(" value=\"" + value + "\"");
            out.write(" onclick=\"this.form.submit()\"");
            
            if (compare.equals(value)) {
                out.write(" checked=\"checked\"");
            }
            
            out.write("/>");
        } catch (IOException e) {
            throw new JspTagException("An IOException occurred.");
        }

return SKIP_BODY;
    }

public int doEndTag() throws JspException {
        return EVAL_PAGE;
    }

public void release() {
        pc = null;
        parent = null;
        classes = name = value = compare = null;
    }
}

Here's my tag library descriptor ("RadioTag.tld"):

*****************************************************************************************

If anybody can come up with an explanation as to what was wrong with the orignal coding, I'd still be interested in knowing.

Just saw the Dynamic Attrribute tutorial for tag programming, Java Ranch is a great resource!

Hi John,

If have looked at your code twice and I couldn't find a reason why Eclipse was giving warnings.

Your solution by using dynamic attributes is a good one.

Just for our viewers, this could be the solution:
taglib:

TagHandler:

package foo;

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.PageContext;
import javax.servlet.jsp.tagext.DynamicAttributes;
import javax.servlet.jsp.tagext.SimpleTagSupport;

public class Radio extends SimpleTagSupport implements DynamicAttributes {

private String value;
	private String compare;
	private Map<String, String> tagDynamicAttributes = new HashMap<String, String>();

public void doTag() throws JspException, IOException {
		System.out.println("Radio: doTag");
		PageContext pageContext = (PageContext) getJspContext();
		JspWriter out = pageContext.getOut();
		out.print("<input ");
		for (String attrName : tagDynamicAttributes.keySet()) {
			String attrValue = tagDynamicAttributes.get(attrName);
			out.print(" " + attrName + "= "  + "\"" + attrValue + "\"");
		}
        out.write(" value=\"" + value + "\"");      
        if (compare.equals(value)) {   
            out.write(" checked=\"checked\"");   
        }   
		out.println(" ></input>");
	}
	public void setDynamicAttribute(String uri, String name, Object value) {
		tagDynamicAttributes.put(name, (String)value);
		System.out.println("Radio: Setting dynamic attributes: "); 
		System.out.println(" " + name + ": " + (String)value); 
	}
	public String getValue() {
		return value;
	}
	public void setValue(String value) {
		this.value = value;
		System.out.println("Radio: Setting attribute: ");  
		System.out.println(" " + "value: " + value); 
	}
	public String getCompare() {
		return compare;
	}
	public void setCompare(String compare) {
		this.compare = compare;
		System.out.println("Radio: Setting attribute: ");  
		System.out.println(" " + "compare: " + compare); 
	}
}

jsp:

rendered into:

CATALOG: DE200<br></br>
<input name= "Catalog" onclick= "this.form.submit()" class= "radio" type= "radio" value="DE200" checked="checked" ></input>
DE200<br>
<input name= "Catalog" onclick= "this.form.submit()" class= "radio" type= "radio" value="DE405" ></input>
DE405<br>
<input name= "Catalog" onclick= "this.form.submit()" class= "radio" type= "radio" value="DE406" ></input>
DE406<br>

Regards,
Frits

Thanks!

I've converted over to the Dynamic Attributes method. I now have 3 tags defined to take care of the similiar situations involving checkboxes and select options. I put the definitions all in one file.

EphemerisTags.tld:

<?xml version="1.0" encoding="ISO-8859-1" ?>
<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">

<tlib-version>1.0</tlib-version>
  <short-name>EphemerisTags</short-name>
  <uri>/EphemerisTags</uri>

<tag> 
    <name>radio</name> 
    <tag-class>net.jsemler.astronomy.ephemeris.webapp.taglibrary.Radio</tag-class>
    <body-content>empty</body-content>

<attribute>
      <name>value</name>
      <required>true</required>
      <rtexprvalue>true</rtexprvalue>
      <type>java.lang.String</type>   
    </attribute>

<attribute>
      <name>compare</name>
      <required>true</required>
      <rtexprvalue>true</rtexprvalue>
      <type>java.lang.String</type>   
    </attribute>
    
    <dynamic-attributes>true</dynamic-attributes>   
  </tag>
   
  <tag> 
    <name>checkbox</name> 
    <tag-class>net.jsemler.astronomy.ephemeris.webapp.taglibrary.Checkbox</tag-class>
    <body-content>empty</body-content>

<attribute>
      <name>value</name>
      <required>true</required>
      <rtexprvalue>true</rtexprvalue>
      <type>java.lang.String</type>   
    </attribute>

<attribute>
      <name>compare</name>
      <required>true</required>
      <rtexprvalue>true</rtexprvalue>
      <type>java.util.List</type>   
    </attribute>
    
    <dynamic-attributes>true</dynamic-attributes>   
  </tag>
   
  <tag> 
    <name>option</name> 
    <tag-class>net.jsemler.astronomy.ephemeris.webapp.taglibrary.Option</tag-class>
    <body-content>empty</body-content>

<attribute>
      <name>value</name>
      <required>true</required>
      <rtexprvalue>true</rtexprvalue>
      <type>java.lang.String</type>   
    </attribute>

<attribute>
      <name>compare</name>
      <required>true</required>
      <rtexprvalue>true</rtexprvalue>
      <type>java.lang.String</type>   
    </attribute>
    
    <dynamic-attributes>true</dynamic-attributes>   
  </tag>

</taglib>

Checkbox.java:

package net.jsemler.astronomy.ephemeris.webapp.taglibrary;

import java.io.IOException;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.DynamicAttributes;
import javax.servlet.jsp.tagext.SimpleTagSupport;

public class Checkbox extends SimpleTagSupport implements DynamicAttributes {    
    private String value;
    private List<String> compareList;
    private Map<String, Object> attrMap = new HashMap<String, Object>();

// Required tag attributes
    public void setCompare (List<String> cl) { compareList = cl; }
    public void setValue   (String s) { value = s; }

// Optional tag attributes
    public void setDynamicAttribute(String uri, String name, Object value) {
        attrMap.put(name, value);
    }

public void doTag() throws IOException {
        JspWriter out = getJspContext().getOut();
        out.print("<input");

for (String name: attrMap.keySet()) {
            out.print(" " + name + "=\"" + attrMap.get(name) + "\"");
        }

out.print(" value=\"" + value + "\"");
        out.print(" type=\"checkbox\"");
        out.print(" onclick=\"this.form.submit()\"");

if (compareList.contains(value)) {
            out.print(" checked=\"checked\"");
        }

out.print("/>" + value);
    }
}

Option.java:

package net.jsemler.astronomy.ephemeris.webapp.taglibrary;

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.DynamicAttributes;
import javax.servlet.jsp.tagext.SimpleTagSupport;

public class Option extends SimpleTagSupport implements DynamicAttributes {    
    private String compare, value;
    private Map<String, Object> attrMap = new HashMap<String,Object>();

// Required tag attributes
    public void setCompare (String s) { compare = s; }
    public void setValue   (String s) { value = s;   }

// Optional tag attributes
    public void setDynamicAttribute(String uri, String name, Object object) {
        attrMap.put(name, object);
    }

public void doTag() throws IOException {
        JspWriter out = getJspContext().getOut();
        out.print("<option");

for (String name: attrMap.keySet()) {
            out.print(" " + name + "=\"" + attrMap.get(name) + "\"");
        }

out.print(" value=\"" + value + "\"");

if (compare.equals(value)) {
            out.print(" selected=\"selected\"");
        }

out.print(">" + value + "</option>");
    }
}

Radio.java:

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.DynamicAttributes;
import javax.servlet.jsp.tagext.SimpleTagSupport;

public class Radio extends SimpleTagSupport implements DynamicAttributes {
    private String compare, value;
    private Map<String, Object> attrMap = new HashMap<String, Object>();

// Required tag attributes
    public void setCompare (String s) { compare = s; }
    public void setValue   (String s) { value = s;   }

// Optional tag attributes
    public void setDynamicAttribute(String uri, String name, Object value) {
        attrMap.put(name, value);
    }

public void doTag() throws IOException {
        JspWriter out = getJspContext().getOut();
        out.print("<input");

for (String name: attrMap.keySet()) {
            out.print(" " + name + "=\"" + attrMap.get(name)+ "\"");
        }

out.print(" value=\"" + value + "\"");
        out.print(" type=\"radio\"");
        out.print(" onclick=\"this.form.submit()\"");

if (compare.equals(value)) {
            out.print(" checked=\"checked\"");
        }

out.print("/>" + value);
    }
}

Here are my code fragments that shows how I use my tags to simplify my programming of checkboxes, radio, and select options (I maintain a name list of checked items for my check box group in the EL expresion "ephemeris.reductions"):

ephemeris.jsp:

<%@ taglib prefix="util" uri="/WEB-INF/tlds/EphemerisTags.tld" %>
...
<jsp:useBean id="ephemeris" class="net.jsemler.astronomy.ephemeris.webapp.EphemerisSelect" scope="request"/>
...
              <div class="calendar_month">
                <select class="option" name="Month" size="1" onchange="this.form.submit()">
                  <util:option compare="${ephemeris.month}" value="January"/>
                  <util:option compare="${ephemeris.month}" value="February"/>
                  <util:option compare="${ephemeris.month}" value="March"/>
                  <util:option compare="${ephemeris.month}" value="April"/>
                  <util:option compare="${ephemeris.month}" value="May"/>
                  <util:option compare="${ephemeris.month}" value="June"/>
                  <util:option compare="${ephemeris.month}" value="July"/>
                  <util:option compare="${ephemeris.month}" value="August"/>
                  <util:option compare="${ephemeris.month}" value="September"/>
                  <util:option compare="${ephemeris.month}" value="October"/>
                  <util:option compare="${ephemeris.month}" value="November"/>
                  <util:option compare="${ephemeris.month}" value="December"/>
                </select>
               </div>
...
            <fieldset class="reductions">
              <legend>Reductions</legend> 
              <div style="float:left;width:50%">
                <util:checkbox class="checkbox" name="Reductions" compare="${ephemeris.reductions}" value="Nutation"/><br/>
                <util:checkbox class="checkbox" name="Reductions" compare="${ephemeris.reductions}" value="Light Time"/><br/>
                <util:checkbox class="checkbox" name="Reductions" compare="${ephemeris.reductions}" value="Light Deflection"/><br/>
              </div>
              <div style="float:left;width:50%">
                <util:checkbox class="checkbox" name="Reductions" compare="${ephemeris.reductions}" value="Light Aberration"/><br/>
                <util:checkbox class="checkbox" name="Reductions" compare="${ephemeris.reductions}" value="Split Earth/Moon"/><br/>
              </div>
            </fieldset>
...
            <fieldset class="catalog">
              <legend>Catalog</legend>
              <util:radio class="radio" name="Catalog" compare="${ephemeris.catalog}" value="DE200"/><br/>
              <util:radio class="radio" name="Catalog" compare="${ephemeris.catalog}" value="DE405"/><br/>
              <util:radio class="radio" name="Catalog" compare="${ephemeris.catalog}" value="DE406"/><br/>
            </fieldset>
...

With Month drop down box set to "December", Reduction checkboxes all checked, and Catalog DE200 radio button selected, it renders as:

...
                <select class="option" name="Month" size="1" onchange="this.form.submit()">
                  <option value="January">January</option>
                  <option value="February">February</option>
                  <option value="March">March</option>
                  <option value="April">April</option>
                  <option value="May">May</option>
                  <option value="June">June</option>
                  <option value="July">July</option>
                  <option value="August">August</option>
                  <option value="September">September</option>
                  <option value="October">October</option>
                  <option value="November">November</option>
                  <option value="December" selected="selected">December</option>
                </select>
 ...
            <fieldset class="reductions">
              <legend>Reductions</legend> 
              <div style="float:left;width:50%">
                <input name="Reductions" class="checkbox" value="Nutation" type="checkbox" onclick="this.form.submit()" checked="checked"/>Nutation<br/>
                <input name="Reductions" class="checkbox" value="Light Time" type="checkbox" onclick="this.form.submit()" checked="checked"/>Light Time<br/>
                <input name="Reductions" class="checkbox" value="Light Deflection" type="checkbox" onclick="this.form.submit()" checked="checked"/>Light Deflection<br/>
              </div>
              <div style="float:left;width:50%">
                <input name="Reductions" class="checkbox" value="Light Aberration" type="checkbox" onclick="this.form.submit()" checked="checked"/>Light Aberration<br/>
                <input name="Reductions" class="checkbox" value="Split Earth/Moon" type="checkbox" onclick="this.form.submit()" checked="checked"/>Split Earth/Moon<br/>
              </div>
            </fieldset>
...
            <fieldset class="catalog">
              <legend>Catalog</legend>
              <input name="Catalog" class="radio" value="DE200" type="radio" onclick="this.form.submit()" checked="checked"/>DE200<br/>
              <input name="Catalog" class="radio" value="DE405" type="radio" onclick="this.form.submit()"/>DE405<br/>
              <input name="Catalog" class="radio" value="DE406" type="radio" onclick="this.form.submit()"/>DE406<br/>
            </fieldset>
...