开发带属性的标签库实战

一 开发自定义标签库

package lee;

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


public class QueryTag extends SimpleTagSupport
{
    // 定义成员变量来代表标签的属性
    private String driver;
    private String url;
    private String user;
    private String pass;
    private String sql;

    // driver的setter和getter方法
    public void setDriver(String driver)
    {
        this.driver = driver;
    }
    public String getDriver()
    {
        return this.driver;
    }

    // url的setter和getter方法
    public void setUrl(String url)
    {
        this.url = url;
    }
    public String getUrl()
    {
        return this.url;
    }

    // user的setter和getter方法
    public void setUser(String user)
    {
        this.user = user;
    }
    public String getUser()
    {
        return this.user;
    }

    // pass的setter和getter方法
    public void setPass(String pass)
    {
        this.pass = pass;
    }
    public String getPass()
    {
        return this.pass;
    }

    // sql的setter和getter方法
    public void setSql(String sql)
    {
        this.sql = sql;
    }
    public String getSql()
    {
        return this.sql;
    }

    // conn的setter和getter方法
    public void setConn(Connection conn)
    {
        this.conn = conn;
    }
    public Connection getConn()
    {
        return this.conn;
    }

    // stmt的setter和getter方法
    public void setStmt(Statement stmt)
    {
        this.stmt = stmt;
    }
    public Statement getStmt()
    {
        return this.stmt;
    }

    // rs的setter和getter方法
    public void setRs(ResultSet rs)
    {
        this.rs = rs;
    }
    public ResultSet getRs()
    {
        return this.rs;
    }

    // rsmd的setter和getter方法
    public void setRsmd(ResultSetMetaData rsmd)
    {
        this.rsmd = rsmd;
    }
    public ResultSetMetaData getRsmd()
    {
        return this.rsmd;
    }
    // 执行数据库访问的对象
    private Connection conn = null;
    private Statement stmt = null;
    private ResultSet rs = null;
    private ResultSetMetaData rsmd = null;
    public void doTag()throws JspException,
        IOException
    {
           try
        {
            // 注册驱动
            Class.forName(driver);
            // 获取数据库连接
            conn = DriverManager.getConnection(url,user,pass);
            // 创建Statement对象
            stmt = conn.createStatement();
            // 执行查询
            rs = stmt.executeQuery(sql);
            rsmd = rs.getMetaData();
            // 获取列数目
            int columnCount = rsmd.getColumnCount();
            // 获取页面输出流
            Writer out = getJspContext().getOut();
            // 在页面输出表格
            out.write("<table border='1' bgColor='#9999cc' width='400'>");
            // 遍历结果集
            while (rs.next())
            {
                out.write("<tr>");
                // 逐列输出查询到的数据
                for (int i = 1 ; i <= columnCount ; i++ )
                {
                    out.write("<td>");
                    out.write(rs.getString(i));
                    out.write("</td>");
                }
                out.write("</tr>");
            }
        }
        catch(ClassNotFoundException cnfe)
        {
            cnfe.printStackTrace();
            throw new JspException("自定义标签错误" + cnfe.getMessage());
        }
        catch (SQLException ex)
        {
            ex.printStackTrace();
            throw new JspException("自定义标签错误" + ex.getMessage());
        }
        finally
        {
            // 关闭结果集
            try
            {
                if (rs != null)
                    rs.close();
                if (stmt != null)
                    stmt.close();
                if (conn != null)
                    conn.close();
            }
            catch (SQLException sqle)
            {
                sqle.printStackTrace();
            }
        }
    }
}

二 建立TLD文件

<?xml version="1.0" encoding="GBK"?>

<taglib xmlns="http://xmlns.jcp.org/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
    http://xmlns.jcp.org/xml/ns/javaee/web-jsptaglibrary_2_1.xsd"
    version="2.1">
    <tlib-version>1.0</tlib-version>
    <short-name>mytaglib</short-name>
    <!-- 定义该标签库的URI -->
    <uri>http://www.crazyit.org/mytaglib</uri>


    <!-- 定义第二个标签 -->
    <tag>
        <!-- 定义标签名 -->
        <name>query</name>
        <!-- 定义标签处理类 -->
        <tag-class>lee.QueryTag</tag-class>
        <!-- 定义标签体为空 -->
        <body-content>empty</body-content>
        <!-- 配置标签属性:driver -->
        <attribute>
            <name>driver</name>
            <required>true</required>
            <fragment>true</fragment>
        </attribute>
        <!-- 配置标签属性:url -->
        <attribute>
            <name>url</name>
            <required>true</required>
            <fragment>true</fragment>
        </attribute>
        <!-- 配置标签属性:user -->
        <attribute>
            <name>user</name>
            <required>true</required>
            <fragment>true</fragment>
        </attribute>
        <!-- 配置标签属性:pass -->
        <attribute>
            <name>pass</name>
            <required>true</required>
            <fragment>true</fragment>
        </attribute>
        <!-- 配置标签属性:sql -->
        <attribute>
            <name>sql</name>
            <required>true</required>
            <fragment>true</fragment>
        </attribute>
    </tag>

</taglib>

三 使用标签

<%@ page contentType="text/html; charset=GBK" language="java" errorPage="" %>
<!-- 导入标签库，指定mytag前缀的标签，
    由http://www.crazyit.org/mytaglib的标签库处理 -->
<%@ taglib uri="http://www.crazyit.org/mytaglib" prefix="mytag"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
    <title>自定义标签示范</title>
    <meta name="website" content="http://www.crazyit.org" />
</head>
<body bgcolor="#ffffc0">
<h2>下面显示的是查询标签的结果</h2>
<!-- 使用标签 ，其中mytag是标签前缀，根据taglib的编译指令，
    mytag前缀将由http://www.crazyit.org/mytaglib的标签库处理 -->
<mytag:query
    driver="com.mysql.jdbc.Driver"
    url="jdbc:mysql://localhost:3306/javaee"
    user="root"
    pass="32147"
    sql="select * from news_inf"/><br/>
</body>
</html>

四 测试