bodytag.java

使用java语言编写的小应用程序

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package javax.servlet.jsp.tagext;

import javax.servlet.jsp.*;

/**
 * The BodyTag interface extends Tag by defining additional methods that let
 * a Tag handler access its body.
 * <p>
 * The interface provides two new methods: one is to be invoked with the BodyContent
 * for the evaluation of the body, the other is to be reevaluated after every body
 * evaluation.
 * <p>
 * Without repeating the portions described in Tag.java, a typical invocation sequence is:
 *
 * <pre>
 * <code>
 *
 * -- we are picking up after all the setters have been done
 * t.doStartTag();
 * out = pageContext.pushBody();
 * -- prepare for body
 * t.setBodyContent(out);
 * -- preamble
 * t.doBodyInit();
 * -- BODY evaluation into out
 * t.doAfterBody();
 * -- while doAfterBody returns EVAL_BODY_TAG we iterate
 * -- BODY evaluation into out
 * t.doAfterBody()
 * -- done
 * t.doEndTag()
 *
 * </code>
 * </pre>
 */

public interface BodyTag extends Tag {

    /**
     * Request the creation of new BodyContent on which to evaluate the
     * body of this tag.
     * Returned from doStartTag and doAfterBody.
     * This is an illegal return value for doStartTag when the class does not
     * implement BodyTag, since BodyTag is needed to manipulate the new Writer.
     */
 
    public final static int EVAL_BODY_TAG = 2;

    /**
     * Setter method for the bodyContent property.
     * <p>
     * This method will not be invoked if there is no body evaluation.
     *
     * @param b the BodyContent
     * @seealso #doInitBody
     * @seealso #doAfterBody
     */

    void setBodyContent(BodyContent b);

    /**
     * Prepare for evaluation of the body.
     * <p>
     * The method will be invoked once per action invocation by the page implementation
     * after a new BodyContent has been obtained and set on the tag handler
     * via the setBodyContent() method and before the evaluation
     * of the tag's body into that BodyContent.
     * <p>
     * This method will not be invoked if there is no body evaluation.
     *
     * @seealso #doAfterBody
     */

    void doInitBody() throws JspException;

    /**
     * Actions after some body has been evaluated.
     * <p>
     * Not invoked in empty tags or in tags returning SKIP_BODY in doStartTag()
     * This method is invoked after every body evaluation.
     * The pair "BODY -- doAfterBody()" is invoked initially if doStartTag()
     * returned EVAL_BODY_TAG, and it is repeated as long
     * as the doAfterBody() evaluation returns EVAL_BODY_TAG
     * <p>
     * The method re-invocations may be lead to different actions because
     * there might have been some changes to shared state, or because
     * of external computation.
     *
     * @returns whether additional evaluations of the body are desired
     * @seealso #doInitBody
     */

    int doAfterBody() throws JspException;
}