connectiontag.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.*;
import javax.servlet.jsp.tagext.*;
import java.io.*;
import java.sql.*;

/**
 * Example: A connection/password/userid/query set of tags.
 * All JDBC code is just to show things.
 *
 * This is the runtime representation of a connection tag
 *
 * This example is made intentionally extra complex to show how to do
 * some things
 *
 * ConnectionTag supports two programming paradigms. 
 *
 * (A) define an id to use later down.
 * <connection id="con01" ref="connection.xml">
 *  <password>....
 *  <userid>....
 * </connection> 
 * ... now the connection object is defined via "id"
 *
 * (B) implicitly define a connection that is available within the start/end tag
 * <connection ref="connection.xml">
 * <password>....</password>
 * <userid>....</userid>
 * <query....> </query>
 * </connection>
 */

public class ConnectionTag extends TagSupport {

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

    /**
     * Attributes for this action:
     *   id (inherited)
     *   ref
     */

    /**
     * ref is a reference to some connection data.
     * setter and getter methods.
     */
    public void setRef(String s) {
	this.ref = s;
    }
    public String getRef() {
	return this.ref;
    }

    /**
     * Process the start tag.
     * Extract and store away any needed TagData.
     *
     * @return evaluate the body
     */
    public int doStartTag() throws JspTagException {
	ref = getRef();
	if (ref == null) {
	  throw new JspTagException("missing ref attribute");
	}

	return EVAL_BODY_INCLUDE;
    }

    // No need to do anything before or after body evaluation

    /**
     * Process the end tag
     *
     * Define an object into the PageContect if ID is given
     */

    public int doEndTag() throws JspTagException {
	String tagId = getId();
	if (tagId != null) {
	    if (userId == null) {
	      
		throw new JspTagException("userId has not been defined yet");
	    }
	    if (password == null) {
		throw new JspTagException("password has not been defined yet");
	    }
	    if (connection == null) {
		getConnection();
	    }
	    pageContext.setAttribute(tagId, connection);
	}
	return EVAL_PAGE;
    }



    /**
     * Get the SQL connection Object.
     * A connection object requires having defined both the userid and the password
     * previous to its use.  Trying to get the connection object before the data is
     * available will produce an error
     */
    public Connection getConnection() throws JspTagException {
	if (userId == null) {
	    throw new JspTagException("userId has not been defined yet");
	}
	if (password == null) {
	    throw new JspTagException("password has not been defined yet");
	}
	// TODO -- Debugging information?  Line number?

	try {
	    // get the connection object
	    connection = DriverManager.getConnection(ref,
						     userId,
						     password);
	} catch (SQLException ex) {
	    // TODO -- revise this
	    connection = null;
	    throw new JspTagException("some error!");
	}
	return connection;
    }


    /**
     * Release data
     */
    public void release() {
	ref = null;
	super.release();
    }


    // Methods that are used by the enclosing tags

    // The methods could be package private if we wanted to

    public void setUserId(String uid) {
	userId = uid;
    }

    public void setPassword(String pass) {
	password = pass;
    }

    // For completeness
    public String getUserId() { return userId; }
    public String getPassword() { return password; }

    // class data

    private Connection connection;// the sql connection object
    private String password;	// password for the connection
    private String userId;	// userid for the connection
    private String ref;		// the ref attribute; assumed to be some URL spec
}