jsp下拉列表—自定义标签

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

   然后编写Dao类：

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

最后是tld的配置

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

html的调用:

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