Servlet与JSP核心编程原码.zip_law5x6

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 }