foreachtag.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.sql.*;
import java.io.*;

/**
 * Example3:  A foreach tag.  Will iterate over a table doing some binding
 *
 * <!-- assume a connection and a query previously defined into "query0" -->
 * <foreach row="row0" in="query0">
 *  this is some string to do
 *  This may include <%=some expression involving row0 %>
 * </foreach>
 */

public class ForEachTag extends BodyTagSupport {

    /**
     * Construct a ForEachTag
     */
    public ForEachTag() {
	super();
    }

    /**
     * Attributes for this action:
     *   row
     *   in
     */

    /**
     * Attribute: row
     * setter and getter
     */
    public void setRow(String s) {
	rowId = s;
    }
    public String getRow() {
	return rowId;
    }

    /**
     * Attribute: in
     * setter and getter
     */
    public void setIn(String s) {
	inId = s;
    }
    public String getIn() {
	return inId;
    }


    /**
     * Process a start tag
     * Locate the desired result object.
     *
     * @return whether there are any rows in the result object
     */
    public int doStartTag() throws JspTagException
    {
	result = (ResultSet) pageContext.getAttribute(inId);

	try {
	    if (result.next()) {
		// resultset is non-empty, we just moved to next row
		pageContext.setAttribute(rowId, result);
		return EVAL_BODY_TAG;
	    } else {
		return SKIP_BODY;
	    }
	} catch (SQLException ex) {
	    throw new JspTagException("error processing an SQL request ---");
	}
    }

    /**
     * After body evaluation
     *
     * @return whether the body should be reevaluated
     */

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

	try {
	    // write evaluation on the output Writer
	    body.writeOut(getPreviousOut());
	} catch (IOException ex) {
	    throw new JspTagException("unexpected IO error");
	}

	// clear up so the next time we get here we are afresh.
	body.clearBody();

	try {
	    if (result.next()) {
		// resultset has more row, move over
		return EVAL_BODY_TAG;
	    } else {
		return SKIP_BODY;
	    }
	} catch (SQLException ex) {
	    throw new JspTagException("error processing an SQL request ---");
	}
    }

    /**
     * Process a tag end.
     */
    public int doEndTag() {
	return EVAL_PAGE;
    }


    /**
     * Release
     * Clean up.
     */
    public void release() {
	rowId = null;
	result = null;
	super.release();
    }

    // variables
    private String rowId;	// the id of the row object
    private String inId;	// the id of the in object
    private ResultSet result;	// the result set from the query
}