JSP custom tags: missing DTD/XML Schema

Question

I've written my JSP custom tag with the following TLD:

<?xml version="1.0" encoding="UTF-8"?>
<taglib
  xsi:schemaLocation="http://java.sun.com/xml/ns/javaee web-jsptaglibrary_2_1.xsd"
  xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  version="2.1">
  <tlibversion>1.0</tlibversion> 
  <jspversion>2.1</jspversion>
  ...

Now Eclipse Helios complains that "No grammar constraints (DTD or XML schema) detected for the document."

I know how to disable the warning, I was instead wondering how to solve the problem by providing DTD or schema information.

By the way in the above piece of XML I have:

xsi:schemaLocation="http://java.sun.com/xml/ns/javaee web-jsptaglibrary_2_1.xsd"

but it doesn't seem to help.

UPDATE on Peter's suggestion I went to check in my Window > Preferences > XML > XML Catalog and I found the following that may fit:

Entry element:  Public
Location:   dtdsAndSchemas/web-jsptaglibrary_1_2.dtd in jar file 
usr/local/eclipse/plugins/org.eclipse.jst.standard.schemas_1.1.0.v201003031644.jar
URI:       jar:file:/usr/local/eclipse/plugins/org
  .eclipse.jst.standard.schemas_1.1.0.v201003031644.jar!/dtdsAndSchemas
  /web-jsptaglibrary_1_2.dtd
Key type:   Public ID
Key:    -//Sun Microsystems, Inc.//DTD JSP Tag Library 1.2//EN

So I tried to add the following to my tld:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE taglib PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag Library 1.2//EN" 
"http://java.sun.com/j2ee/dtds/web-jsptaglibrary_1_2.dtd">

Now I've the following errors:

Multiple annotations found at this line:

• Attribute "xsi:schemaLocation" must be declared for element type "taglib".
• Attribute "version" must be declared for element type "taglib".

• Attribute "xmlns" with value "http://java.sun.com/xml/ns/javaee" must have a value of "http://java.sun.com/JSP/ TagLibraryDescriptor".

• schema_reference.4: Failed to read schema document 'web-jsptaglibrary_2_1.xsd', because

  1) could not find the document; 2) the document could not be read; 3) the root element of the document is not .

• The content of element type "taglib" must match "(tlib-version,jsp-version,short-name,uri?,display-name?,small-icon?,large-icon?,description?,validator?,listener*,tag+)".

• Attribute "xmlns:xsi" must be declared for element type "taglib".

Answer 1

I didn't bother looking at this problem for over a month, because anyway everything was working in Tomcat. Recently I tried GlassFish and JBoss. While GlassFish 3.1.1 didn't complain, JBoss 7.0 refused to run the application, because of tld problems. In the meantime I've also updated Eclipse Helios to Indigo.

I figured out that I was using DTD and Schema at the same time, which can't be good. I ditched the DTD and kept only the Schema. I had to rename a few tags, such as tlibversion to tlib-version, shortname to short-name, bodycontent to body-content, tagclass to tag-class, remove the info tag, which I substituted with XML comments. I guess it's probably a newer version of the specs, because in the example I followed they were named without hyphens.

After that everything worked: Eclipse didn't give any warning any more, JBoss ran the application perfectly. For reference here is the working tld:

<?xml version="1.0" encoding="UTF-8"?>
<taglib
        xsi:schemaLocation="
            http://java.sun.com/xml/ns/javaee 
            http://java.sun.com/xml/ns/javaee/web-jsptaglibrary_2_1.xsd"
        xmlns="http://java.sun.com/xml/ns/javaee" 
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        version="2.1">
    <tlib-version>1.0</tlib-version> 
    <short-name>StivloTags</short-name>
    <uri>http://www.stefanolocati.it/</uri>

    <!-- Example from http://www.stardeveloper.com/articles/display.html?article=2001081301&amp;page=1 -->
    <tag> 
        <name>firstTag</name> 
        <tag-class>obliquid.tag.FirstTag</tag-class>
        <body-content>empty</body-content> 
        <attribute>
            <name>name</name>
            <required>false</required>
        </attribute>
    </tag> 

    <!-- Truncate text after maxLength or 80 chars, adding "&amp;hellip;" if the the text was longer -->
    <tag>
        <name>ellipsis</name>
        <tag-class>obliquid.tag.Ellipsis</tag-class>
        <body-content>scriptless</body-content>
        <attribute>
             <name>maxLength</name>
             <required>false</required>
        </attribute>
    </tag>

</taglib>

Answer 2

If Eclipse doesn't automatically pick up the XSD from the library, you can always add it manually: Window > Preferences > XML > XML Catalog

In my case it was already present in the plugin section. It probably came with one of the Eclipse Java EE plugins.