自定义标签---数据库条件查询标签

后台代码（直接后台拼接）

package com.yydb.tag;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.TagSupport;

import com.yydb.util.DBUtil;

public class QueryTag extends TagSupport{
	private String tableName;
	private String conditionName;
	private String conditionVal;
	public String getTableName() {
		return tableName;
	}
	public void setTableName(String tableName) {
		this.tableName = tableName;
	}
	public String getConditionName() {
		return conditionName;
	}
	public void setConditionName(String conditionName) {
		this.conditionName = conditionName;
	}
	public String getConditionVal() {
		return conditionVal;
	}
	public void setConditionVal(String conditionVal) {
		this.conditionVal = conditionVal;
	}
	@Override
	public int doStartTag() throws JspException {
		
		DBUtil db = new DBUtil();
		Connection conn = db.getConn();
		PreparedStatement ps = null;
		ResultSet rs = null;
		
		String sql = "select * from "+tableName+" where "+conditionName+" = "+conditionVal;
		
		try {
			ps = conn.prepareStatement(sql);
			ResultSetMetaData rsmd = ps.getMetaData();
			int cloumn = rsmd.getColumnCount();
			JspWriter out = pageContext.getOut();
			
			out.print("<table border='1' cellspacing='1' cellpadding='1'>");
			out.print("<tr>");
			for (int i = 0; i < cloumn; i++) {
				out.print("<th>"+rsmd.getColumnName(i+1)+"</th>");
			}
			out.print("</tr>");
			
			rs = ps.executeQuery();
			
			while(rs.next()){
				out.print("<tr>");
				for (int i = 0; i < cloumn; i++) {
					out.print("<td>"+rs.getObject(i+1)+"</td>");
				}
				
				out.print("</tr>");
			}
			out.print("</table>");
			
		
		} catch (Exception e) {
			e.printStackTrace();
		}
		
		return super.SKIP_BODY;
	}
	
	
}

tld设置：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE taglib PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag Library 1.2//EN"
                        "http://java.sun.com/dtd/web-jsptaglibrary_1_2.dtd">
<taglib>
	 <tlib-version>1.0</tlib-version>
	 <jsp-version>1.2</jsp-version>
	 <short-name>mt</short-name>
	 <uri>www.yydb</uri>
	 <tag>
	 	<name>QueryTag</name>
	 	<tag-class>com.yydb.tag.QueryTag</tag-class>
	 	<body-content>jsp</body-content>
	 	<attribute>
	 		<name>tableName</name>
	 		<required>true</required>
	 		<rtexprvalue>true</rtexprvalue>
	 	</attribute>
	 	<attribute>
	 		<name>conditionName</name>
	 		<required>true</required>
	 		<rtexprvalue>true</rtexprvalue>
	 	</attribute>
	 	<attribute>
	 		<name>conditionVal</name>
	 		<required>true</required>
	 		<rtexprvalue>true</rtexprvalue>
	 	</attribute>
	 </tag>
 </taglib>

jsp中引入标签库

<%@ taglib uri="www.yydb" prefix="mt" %>

jsp中引入自定义标签

<mt:QueryTag tableName="admin" conditionName="username" conditionVal="23786"></mt:QueryTag>