学步园

有时一个网页中下拉列表很多，而且是动态变化的时候，这时有自定义标签就会很方便

首先是jdbc数据连接

ackage pro.shopping.util;</p> <p>import java.io.IOException;<br /> import java.sql.Connection;<br /> import java.sql.DriverManager;<br /> import java.sql.PreparedStatement;<br /> import java.sql.ResultSet;<br /> import java.sql.SQLException;<br /> import java.util.Properties;</p> <p>import com.sun.java_cup.internal.internal_error;</p> <p>/*<br /> * 该类用于连接数据库和对数据库进行操作<br /> */<br /> public class JdbcUtil {<br /> public Connection con = null; </p> <p> //连接数据库<br /> public Connection getCon(){<br /> //获取配置文件的数据<br /> Properties pro = new Properties();<br /> try {<br /> pro.load(JdbcUtil.class.getResourceAsStream("/db.properties"));<br /> String userName = pro.getProperty("userName");<br /> String userPassword = pro.getProperty("userPassword");<br /> String url = pro.getProperty("url");<br /> String driver = pro.getProperty("driver");</p> <p> Class.forName(driver);<br /> con = DriverManager.getConnection(url,userName,userPassword);<br /> } catch (Exception e) {<br /> // TODO Auto-generated catch block<br /> e.printStackTrace();<br /> }<br /> return con;</p> <p> }</p> <p> //查询操作<br /> public ResultSet gerSet(String sql,Object ...p){<br /> //连接数据库<br /> con = this.getCon();<br /> ResultSet re = null;<br /> try {<br /> PreparedStatement pre = con.prepareStatement(sql);<br /> if(p!=null){<br /> for (int i = 0; i < p.length; i++) {<br /> pre.setObject(i+1, p[i]);<br /> }<br /> re = pre.executeQuery();<br /> }<br /> } catch (SQLException e) {<br /> // TODO Auto-generated catch block<br /> e.printStackTrace();<br /> }<br /> return re;<br /> }</p> <p> //增加、删除、修改操作<br /> public int zsg(String sql,Object ...p){<br /> con = this.getCon();<br /> int j = 0;<br /> try {<br /> PreparedStatement pre = con.prepareStatement(sql);<br /> if(p!=null){<br /> for (int i = 0; i < p.length; i++) {<br /> pre.setObject(i+1, p[i]);<br /> }<br /> j = pre.executeUpdate();<br /> con.close(); //关闭数据库<br /> }<br /> } catch (SQLException e) {<br /> // TODO Auto-generated catch block<br /> e.printStackTrace();<br /> }<br /> return j;<br /> }</p> <p>}<br />

   然后编写Dao类：

 package pro.shoping.Tag;</p> <p>import java.io.IOException;<br /> import java.sql.ResultSet;<br /> import java.sql.SQLException;</p> <p>import javax.servlet.jsp.JspException;<br /> import javax.servlet.jsp.JspWriter;<br /> import javax.servlet.jsp.tagext.SimpleTagSupport;</p> <p>import pro.shopping.util.JdbcUtil;</p> <p>public class HtmlTag extends SimpleTagSupport{<br /> private JdbcUtil jUtil = new JdbcUtil();</p> <p> private String table;<br /> private String value;<br /> private String label;<br /> public void setTable(String table) {<br /> this.table = table;<br /> }<br /> public void setValue(String value) {<br /> this.value = value;<br /> }<br /> public void setLabel(String label) {<br /> this.label = label;<br /> }</p> <p> @Override<br /> public void doTag() throws JspException, IOException {<br /> // TODO Auto-generated method stub<br /> String sql = "select * from "+table;<br /> ResultSet rs = jUtil.gerSet(sql);<br /> JspWriter out = getJspContext().getOut();<br /> out.print("<select name="+table+">");<br /> out.print("<option value=-1>--请选择--</option>");<br /> try {<br /> while (rs != null && rs.next()) {<br /> String v = rs.getString(value);<br /> String l = rs.getString(label);<br /> out.print("<option value=" + v + ">" + l + "</option>");<br /> }<br /> } catch (SQLException e) {<br /> // TODO Auto-generated catch block<br /> e.printStackTrace();<br /> }<br /> out.print("</select>");<br /> super.doTag();<br /> }</p> <p>}

最后是tld的配置

<?xml version="1.0" encoding="UTF-8" ?></p> <p><taglib xmlns="http://java.sun.com/xml/ns/javaee"<br /> xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"<br /> xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-jsptaglibrary_2_1.xsd"<br /> version="2.1"></p> <p> <description>JSTL 1.1 core library</description><br /> <display-name>JSTL core</display-name><br /> <tlib-version>1.1</tlib-version><br /> <short-name>ccc</short-name><br /> <uri>http://java.sun.com/jsp/jstl/core3</uri></p> <p> <tag><br /> <name>select</name><br /> <tag-class>pro.shoping.Tag.HtmlTag</tag-class><br /> <body-content>empty</body-content></p> <p> <!-- 属性 --><br /> <attribute><br /> <name>table</name><br /> <required>true</required><br /> </attribute></p> <p> <attribute><br /> <name>value</name><br /> <required>true</required><br /> </attribute></p> <p> <attribute><br /> <name>label</name><br /> <required>true</required><br /> </attribute></p> <p> </tag></p> <p></taglib>  

html的调用:

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%><br /> <%@ taglib prefix="html" uri="/WEB-INF/html.tld" %></p> <p>部门:<html:select label="depname" table="dep" value="depid"></html:select> <br><br /> 员工:<html:select label="empname" table="emp" value="empid"></html:select>