useridtag.java

Servlet与JSP核心编程原码,适合刚做软件开发的程序员参考！

package examples;

import javax.servlet.jsp.tagext.*;
import javax.servlet.jsp.*;
import java.io.Writer;

/**
 * Example2: A connection/query tag.
 * This is the userid entry.
 *
 * The data is stored up into the containing <connection> tag.
 * It is an error (currently only detected at run-time) not to have
 * a containing <connection> tag instance.
 *
 * <userId><%= some expr...%></userId>
 */

public class UserIdTag extends BodyTagSupport {

    /**
     * Create a new UserIdTag
     */
    public UserIdTag() {
	super();
    }

    /**
     * Attributes for this action:
     * NONE
     */

    /**
     * Process a start tag.
     * Find the enclosing connection tag and keep a reference aside.
     *
     * @return evaluate the body
     */
    public int doStartTag() throws JspTagException {
	myConnection
	    = (ConnectionTag) findAncestorWithClass(this,
						    ConnectionTag.class);
	if (myConnection == null) {
	    throw new JspTagException("userid must be inside a connection");
	}
	return EVAL_BODY_TAG;
    }

    /**
     * After body evaluation.
     * Extract a string from the nested stream.
     *
     * @param body the BodyContent for this tag
     * @return SKIP_BODY
     */

    public int doAfterBody() {
	BodyContent body = getBodyContent();

	// Convert to String for use
	myConnection.setUserId(body.getString());

	// Clean up
	body.clearBody();
	
	// Do not reevaluate the body
	return SKIP_BODY;
    }

    // variables
    private ConnectionTag myConnection; 
}