自定义标签

Writer out=getJspContext().getOut();

编写标签类继承SimpleTagSupport,定义标签属性的get和set方法

package com.chinaebi.test;

import java.io.IOException;
import java.io.Writer;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.sql.Statement;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.SimpleTagSupport;

public class QueryTag extends SimpleTagSupport{
   private Connection conn=null;
   private String driver;
   private String url;
   private String user;
   private String sql;
   private Statement stmt=null;
   private ResultSet rs=null;
   private ResultSetMetaData rsmd;
public Connection getConn() {
    return conn;
}
public void setConn(Connection conn) {
    this.conn = conn;
}
public String getDriver() {
    return driver;
}
public void setDriver(String driver) {
    this.driver = driver;
}
public String getUrl() {
    return url;
}
public void setUrl(String url) {
    this.url = url;
}
public String getUser() {
    return user;
}
public void setUser(String user) {
    this.user = user;
}
public String getSql() {
    return sql;
}
public void setSql(String sql) {
    this.sql = sql;
}
   @Override
    public void doTag() throws JspException, IOException {
       try {
        Class.forName(driver);
           conn=DriverManager.getConnection(url, user, null);
           stmt=conn.createStatement();
           rs=stmt.executeQuery(sql);
           rsmd=rs.getMetaData();
           Writer out=getJspContext().getOut();
           out.write("<table border='1' width='400' cellpadding='0'>");
           while(rs.next()){
               out.write("<tr>");
               for(int i=1;i<=rsmd.getColumnCount();i++){
                   //System.out.println(rs.getString(i));
                   out.write("<td>"+rs.getString(i)+"<td>");
               }
               out.write("</tr>");
           }
    } catch (ClassNotFoundException e) {
        e.printStackTrace();
    } catch (SQLException e) {
        e.printStackTrace();
    }finally{
        try {
            if (rs!=null) {
                rs.close();
            }
            if (stmt!=null) {
                stmt.close();
            }
            if (conn!=null) {
                conn.close();
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
    }
}

在WEB_INF下的任意路径建一个标签配置文件.tld文件，具体配置如下

<?xml version="1.0" encoding="UTF-8" ?>

<taglib xmlns="http://java.sun.com/xml/ns/j2ee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd"
    version="2.0">
    <description>A tag library exercising SimpleTag handlers.</description>
    <tlib-version>1.0</tlib-version>
    <short-name>myTaglib</short-name>
    <uri>http://www.chinaebi.org/myTaglib</uri>
    <tag>
    <description>Outputs Hello, World</description>
        <name>helloWorld</name>
    <tag-class>com.chinaebi.test.HelloWordTag</tag-class>
    <body-content>empty</body-content>
    </tag>
    <tag>
        <name>query</name>
        <tag-class>com.chinaebi.test.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>sql</name>
            <required>true</required>
            <fragment>true</fragment>
        </attribute>
    </tag>