开发带属性的标签库实战

淩亂°似流年 2021-07-24 13:36 350阅读 0赞

**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>
        
        <uri>http://www.crazyit.org/mytaglib</uri>
    
    
        
        <tag>
            
            <name>query</name>
            
            <tag-class>lee.QueryTag</tag-class>
            
            <body-content>empty</body-content>
            
            <attribute>
                <name>driver</name>
                <required>true</required>
                <fragment>true</fragment>
            </attribute>
            
            <attribute>
                <name>url</name>
                <required>true</required>
                <fragment>true</fragment>
            </attribute>
            
            <attribute>
                <name>user</name>
                <required>true</required>
                <fragment>true</fragment>
            </attribute>
            
            <attribute>
                <name>pass</name>
                <required>true</required>
                <fragment>true</fragment>
            </attribute>
            
            <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="" %>
    
    <%@ 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>
    
    <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**

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5ncWl1bWluZw_size_16_color_FFFFFF_t_70][]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2NoZW5ncWl1bWluZw_size_16_color_FFFFFF_t_70]: /images/20210724/e4cb006f4146439e80cc0ae2440bb586.png