TLD

Tag Library declarations in the Webapp DD

taglib*, <taglib (taglib-uri, taglib-location)>
ex:
<web-app>
    <taglib>
        <taglib-uri> http://www.jspinsider.com/jspkit/javascript </taglib-uri>
        <taglib-location> /WEB-INF/JavaScriptExampleTag.tld </taglib-location>
    </taglib>
</web-app>

Tag Library Descriptor

Interface/Class	Method	Return	body-content	NOTE
Tag	doStartTag()	SKIP_BODY	Must be “empty”
		EVAL_BODY_INCLUDE	JSP
		EVAL_BODY_BUFFERED	tagdependent	Tag Handler must implement BodyTag
	doEndTag()	SKIP_PAGE
		EVAL_PAGE
	setPageContext()			First method to be called by container
	setParent()			Second method to be called
	setter methods			If present then third call
	getParent()	Tag
	release()			Called in end, must be called , to release state
IterationTag extends Tag	doAfterBody()	EVAL_BODY_AGAIN	JSP	Body is again evaluated till it return SKIP_BODY.
		SKIP_BODY	JSP
BodyTag extends IterationTag	doInitBody()	EVAL_BODY_BUFFERED	tagdependent	This is called after setBodyContent() and before the first time body is evaluated.It will be called only if doST() returns EVAL_BODY_BUFFERED

Identify properly formatted custom tag usage in a JSP page.
Uses include:
·    An empty custom tag - <msgBean:message/>
·    A custom tag with attributes - <msgBean:message attrName=”value” />
·    A custom tag that surrounds other JSP code - <msgBean:message> <h1>This is the title</h1> </msgBean:message>
·    Nested custom tags- <msgBean:message> <helloBean:sayHello/> </msgBean:message>

Identify valid return values for the following methods:
·    doStartTag - Tag.EVAL_BODY_INCLUDE, BodyTag.EVAL_BODY_BUFFERED, Tag.SKIP_BODY
·    doAfterBody – IterationTag.EVAL_BODY_AGAIN, Tag.SKIP_BODY
·    doEndTag – Tag.EVAL_PAGE, Tag.SKIP_PAGE
·    PageContext.getOut - javax.servlet.jsp.JspWriter

Identify the method in the custom tag handler that accesses:
·    A given JSP page's implicit variable
·    The JSP page's attributes

A PageContext instance provides access to all the namespaces associated with a JSP page, provides access to several page attributes, as well as a layer above the implementation details.
The following methods provide convenient access to implicit objects:
getOut(), getException(), getPage() getRequest(), getResponse(), getSession(),
getServletConfig() and getServletContext().

The following methods provide support for forwarding, inclusion and error handling:
forward(), include(), and handlePageException().

The methods related to attributes are:
setAttribute(), getAttribute(), removeAttribute() – deals page scope
findAttribute(), - looks in all scopes
int getAttributesScope() and getAttributeNamesInScope(int scope)

Note:
TagSupport implements IterationTag which extends Tag.
BodyTagSupport implements BodyTag which extends IterationTag.

getPreviousOut(), getBodyContent(), setBodyContent(), doInitBody() methods are defined in BodyTagSupport.

Identify methods that return an outer tag handler from within an inner tag handler.
Tag Tag.getParent()
Tag TagSupport.getParent()
Tag TagSupport.findAncestorWithClass(Tag from, java.lang.Class class) (A static method)

Tag Extension Classes

public abstract class BodyContent extends JspWriter {
// Constructor
protected BodyContent(JspWriter e);
// Methods
public void clearBody( );
public void flush( ) throws java.io.IOException;
public JspWriter getEnclosingWriter( );
public abstract java.io.Reader getReader( );
public abstract String getString( );
public abstract void writeOut(java.io.Writer out)
    throws java.io.IOException;
}

public interface BodyTag extends Tag {
// Constants
public static final int EVAL_BODY_TAG;
// Methods
public int doAfterBody( ) throws JspException;
public void doInitBody( ) throws JspException;
public void setBodyContent(BodyContent b);
}

public class BodyTagSupport extends TagSupport implements BodyTag {
// Constructor
public BodyTagSupport( );
// Methods
public int doAfterBody( ) throws JspException;
public int doEndTag( ) throws JspException;
public void doInitBody( );
public BodyContent getBodyContent( );
public JspWriter getPreviousOut( );
public void release( );
public void setBodyContent(BodyContent b);
}

public interface Tag {
// Constants
public static final int EVAL_BODY_INCLUDE;
public static final int EVAL_PAGE;
public static final int SKIP_BODY;
public static final int SKIP_PAGE;
// Methods
public int doEndTag( ) throws JspException;
public int doStartTag( ) throws JspException;
public Tag getParent( );
public void release( );
public void setPageContext(PageContext pc);
public void setParent(Tag t)
}

public class TagAttributeInfo {
// Constructor
public TagAttributeInfo(String name, boolean required,
    boolean rtexprvalue, String type, boolean reqTime);
// Methods
public boolean canBeRequestTime( );
public static TagAttributeInfo getIdAttribute(TagAttributeInfo[] a);
public String getName( );
public String getTypeName( );
public boolean isRequired( );
public String toString( );
}

public class TagData implements Cloneable {
// Constants
public static final Object REQUEST_TIME_VALUE;
// Constructor
public TagData(Object[][] atts);
public TagData(java.util.Hashtable attrs);
// Methods
public Object getAttribute(String attName);
public String getAttributeString(String attName);
public String getId( );
public void setAttribute(String attName, Object value);
}

public abstract class TagExtraInfo {
// Constructor
public TagExtraInfo( );
// Methods
public TagInfo getTagInfo( );
public VariableInfo[] getVariableInfo(TagData data);
public boolean isValid(TagData data);
public void setTagInfo(TagInfo tagInfo);
}

public class TagInfo {
// Constants
public static final String BODY_CONTENT_EMPTY;
public static final String BODY_CONTENT_JSP;
public static final String BODY_CONTENT_TAG_DEPENDENT;
// Constructor
public TagInfo(String tagName, String tagClassName,
    String bodycontent, String infoString, TagLibraryInfo taglib,
    TagExtraInfo tagExtraInfo, TagAttributeInfo[] attributeInfo);
// Methods
public TagAttributeInfo[] getAttributes( );
public String getBodyContent( );
public String getInfoString( );
public String getTagClassName( );
public TagExtraInfo getTagExtraInfo( );
public TagLibraryInfo getTagLibrary( );
public String getTagName( );
public VariableInfo[] getVariableInfo(TagData data);
public boolean isValid(TagData data);
public String toString( );
}

public abstract class TagLibraryInfo {
// Constructor
protected TagLibraryInfo(String prefix, String uri);
// Methods
public String getInfoString( );
public String getPrefixString( );
public String getReliableURN( );
public String getRequiredVersion( );
public String getShortName( );
public TagInfo getTag(String shortname);
public TagInfo[] getTags( );
public String getURI( );
}

public class TagSupport implements Tag, java.io.Serializable {
// Constructor
public TagSupport( );
// Methods
public int doEndTag( ) throws JspException;
public int doStartTag( ) throws JspException;
public static final Tag findAncestorWithClass(Tag from, Class klass);
public String getId( );
public Tag getParent( );
public Object getValue(String k);
public java.util.Enumeration getValues( );
public void release( );
public void removeValue(String k);
public void setPageContext(PageContext pageContext);
public void setId(String id);
public void setParent(Tag t);
public void setValue(String k, Object o);
}

public class VariableInfo {
// Constants
public static final int AT_BEGIN;
public static final int AT_END;
public static final int NESTED;
// Constructor
public VariableInfo(String varName, String className,
    boolean declare, int scope);
// Methods
public String getClassName( );
public boolean getDeclare( );
public int getScope( );
public String getVarName( );
}