javax.servlet.jsp.tagext.BodyTag Maven / Gradle / Ivy
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package javax.servlet.jsp.tagext;
import javax.servlet.jsp.*;
/**
* The BodyTag interface extends IterationTag by defining additional
* methods that let a tag handler manipulate the content of evaluating its body.
*
*
* It is the responsibility of the tag handler to manipulate the body
* content. For example the tag handler may take the body content,
* convert it into a String using the bodyContent.getString
* method and then use it. Or the tag handler may take the body
* content and write it out into its enclosing JspWriter using
* the bodyContent.writeOut method.
*
*
A tag handler that implements BodyTag is treated as one that
* implements IterationTag, except that the doStartTag method can
* return SKIP_BODY, EVAL_BODY_INCLUDE or EVAL_BODY_BUFFERED.
*
*
* If EVAL_BODY_INCLUDE is returned, then evaluation happens
* as in IterationTag.
*
*
* If EVAL_BODY_BUFFERED is returned, then a BodyContent object will be
* created (by code generated by the JSP compiler) to capture the body
* evaluation.
* The code generated by the JSP compiler obtains the BodyContent object by
* calling the pushBody method of the current pageContext, which
* additionally has the effect of saving the previous out value.
* The page compiler returns this object by calling the popBody
* method of the PageContext class;
* the call also restores the value of out.
*
*
* The interface provides one new property with a setter method and one
* new action method.
*
*
Properties
*
There is a new property: bodyContent, to contain the BodyContent
* object, where the JSP Page implementation object will place the
* evaluation (and reevaluation, if appropriate) of the body. The setter
* method (setBodyContent) will only be invoked if doStartTag() returns
* EVAL_BODY_BUFFERED and the corresponding action element does not have
* an empty body.
*
*
Methods
*
In addition to the setter method for the bodyContent property, there
* is a new action method: doInitBody(), which is invoked right after
* setBodyContent() and before the body evaluation. This method is only
* invoked if doStartTag() returns EVAL_BODY_BUFFERED.
*
*
Lifecycle
*
Lifecycle details are described by the transition diagram below.
* Exceptions that are thrown during the computation of doStartTag(),
* setBodyContent(), doInitBody(), BODY, doAfterBody() interrupt the
* execution sequence and are propagated up the stack, unless the
* tag handler implements the TryCatchFinally interface; see that
* interface for details.
*
* 
*
*
Empty and Non-Empty Action
*
If the TagLibraryDescriptor file indicates that the action must
* always have an empty element body, by an <body-content> entry
* of "empty", then the doStartTag() method must return SKIP_BODY.
* Otherwise, the doStartTag() method may return SKIP_BODY,
* EVAL_BODY_INCLUDE, or EVAL_BODY_BUFFERED.
*
*
Note that which methods are invoked after the doStartTag() depends on
* both the return value and on if the custom action element is empty
* or not in the JSP page, not how it's declared in the TLD.
*
*
* If SKIP_BODY is returned the body is not evaluated, and doEndTag() is
* invoked.
*
*
* If EVAL_BODY_INCLUDE is returned, and the custom action element is not
* empty, setBodyContent() is not invoked,
* doInitBody() is not invoked, the body is evaluated and
* "passed through" to the current out, doAfterBody() is invoked
* and then, after zero or more iterations, doEndTag() is invoked.
* If the custom action element is empty, only doStart() and
* doEndTag() are invoked.
*
*
* If EVAL_BODY_BUFFERED is returned, and the custom action element is not
* empty, setBodyContent() is invoked,
* doInitBody() is invoked, the body is evaluated, doAfterBody() is
* invoked, and then, after zero or more iterations, doEndTag() is invoked.
* If the custom action element is empty, only doStart() and doEndTag()
* are invoked.
*/
public interface BodyTag extends IterationTag {
/**
* Deprecated constant that has the same value as EVAL_BODY_BUFFERED
* and EVAL_BODY_AGAIN. This name has been marked as deprecated
* to encourage the use of the two different terms, which are much
* more descriptive.
*
* @deprecated As of Java JSP API 1.2, use BodyTag.EVAL_BODY_BUFFERED
* or IterationTag.EVAL_BODY_AGAIN.
*/
public final static int EVAL_BODY_TAG = 2;
/**
* Request the creation of new buffer, a BodyContent on which to
* evaluate the body of this tag.
*
* Returned from doStartTag when it implements BodyTag.
* This is an illegal return value for doStartTag when the class
* does not implement BodyTag.
*/
public final static int EVAL_BODY_BUFFERED = 2;
/**
* Set the bodyContent property.
* This method is invoked by the JSP page implementation object at
* most once per action invocation.
* This method will be invoked before doInitBody.
* This method will not be invoked for empty tags or for non-empty
* tags whose doStartTag() method returns SKIP_BODY or EVAL_BODY_INCLUDE.
*
*
* When setBodyContent is invoked, the value of the implicit object out
* has already been changed in the pageContext object. The BodyContent
* object passed will have not data on it but may have been reused
* (and cleared) from some previous invocation.
*
*
* The BodyContent object is available and with the appropriate content
* until after the invocation of the doEndTag method, at which case it
* may be reused.
*
* @param b the BodyContent
* @see #doInitBody
* @see #doAfterBody
*/
void setBodyContent(BodyContent b);
/**
* Prepare for evaluation of the body.
* This method is invoked by the JSP page implementation object
* after setBodyContent and before the first time
* the body is to be evaluated.
* This method will not be invoked for empty tags or for non-empty
* tags whose doStartTag() method returns SKIP_BODY or EVAL_BODY_INCLUDE.
*
*
* The JSP container will resynchronize the values of any AT_BEGIN and
* NESTED variables (defined by the associated TagExtraInfo or TLD) after
* the invocation of doInitBody().
*
* @throws JspException if an error occurred while processing this tag
* @see #doAfterBody
*/
void doInitBody() throws JspException;
}