吴裕雄--天生自然JAVA开发JSP-Servlet学习笔记：自定义标签-编写带有属性的标签

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 */
package le;

import javax.servlet.jsp.tagext.*;
import javax.servlet.jsp.*;
import java.io.*;
import java.sql.*;

/**
 *
 * @author Administrator
 */
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();
            }
        }
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<taglib version="2.1" 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">
    <tlib-version>1.0</tlib-version>
    <short-name>mytaglib</short-name>
    <uri>/WEB-INF/tlds/mytaglib</uri>
    <!-- A validator verifies that the tags are used correctly at JSP
          translation time. Validator entries look like this: 
       <validator>
           <validator-class>com.mycompany.TagLibValidator</validator-class>
           <init-param>
              <param-name>parameter</param-name>
              <param-value>value</param-value>
           </init-param>
       </validator>
    -->
    <!-- A tag library can register Servlet Context event listeners in
         case it needs to react to such events. Listener entries look
         like this: 
      <listener>
          <listener-class>com.mycompany.TagLibListener</listener-class> 
      </listener>
    -->
    
    <!-- 定义第一个标签 -->
    <tag>
        <!-- 定义标签名 -->
        <name>helloWorld</name>
        <!-- 定义标签处理类 -->
        <tag-class>le.HelloWorldTag</tag-class>
        <!-- 定义标签体为空 -->
        <body-content>empty</body-content>
    </tag>

    <!-- 定义第二个标签 -->
    <tag>
        <!-- 定义标签名 -->
        <name>query</name>
        <!-- 定义标签处理类 -->
        <tag-class>le.QueryTag</tag-class>
        <!-- 定义标签体为空 -->
        <body-content>empty</body-content>
        <!-- 配置标签属性:driver -->
        <attribute>
            <name>driver</name> 
            <required>true</required>
            <fragment>true</fragment>
        </attribute>
        <!-- 配置标签属性:url -->
        <attribute>
            <name>url</name> 
            <required>true</required>
            <fragment>true</fragment>
        </attribute>
        <!-- 配置标签属性:user -->
        <attribute>
            <name>user</name> 
            <required>true</required>
            <fragment>true</fragment>
        </attribute>
        <!-- 配置标签属性:pass -->
        <attribute>
            <name>pass</name> 
            <required>true</required>
            <fragment>true</fragment>
        </attribute>
        <!-- 配置标签属性:sql -->
        <attribute>
            <name>sql</name> 
            <required>true</required>
            <fragment>true</fragment>
        </attribute>
    </tag>

    <!-- 定义第三个标签 -->
    <tag>
        <!-- 定义标签名 -->
        <name>iterator</name>
        <!-- 定义标签处理类 -->
        <tag-class>le.IteratorTag</tag-class>
        <!-- 定义标签体不允许出现JSP脚本 -->
        <body-content>scriptless</body-content>
        <!-- 配置标签属性:collection -->
        <attribute>
            <name>collection</name> 
            <required>true</required>
            <fragment>true</fragment>
        </attribute>
        <!-- 配置标签属性:item -->
        <attribute>
            <name>item</name> 
            <required>true</required>
            <fragment>true</fragment>
        </attribute>
    </tag>
    <tag>
        <!-- 定义标签名 -->
        <name>fragment</name>
        <!-- 定义标签处理类 -->
        <tag-class>le.FragmentTag</tag-class>
        <!-- 指定该标签不支持标签体 -->
        <body-content>empty</body-content>
        <!-- 定义标签属性：fragment -->
        <attribute>
            <name>fragment</name>
            <required>true</required>
            <fragment>true</fragment>
        </attribute>
    </tag>
    <!-- 定义接受动态属性的标签 -->
    <tag>
        <name>dynaAttr</name>
        <tag-class>le.DynaAttributesTag</tag-class>
        <body-content>empty</body-content>
        <!-- 指定支持动态属性 -->
        <dynamic-attributes>true</dynamic-attributes>
    </tag>
    
</taglib>

<%-- 
    Document   : queryTag
    Created on : 2020-5-4, 21:40:23
    Author     : Administrator
--%>

<%@ page contentType="text/html; charset=GBK" language="java" errorPage="" %>
<!-- 导入标签库，指定mytag前缀的标签，
        由http://www.crazyit.org/mytaglib的标签库处理 -->
<%@ taglib uri="/WEB-INF/tlds/mytaglib" prefix="mytag"%>
<!DOCTYPE html>
<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>
        <!-- 使用标签 ，其中mytag是标签前缀，根据taglib的编译指令，
                mytag前缀将由http://www.crazyit.org/mytaglib的标签库处理 -->
        <mytag:query
            driver="com.mysql.cj.jdbc.Driver"
            url="jdbc:mysql://localhost:3306/taobao"
            user="root"
            pass="admin"
            sql="select * from person"/><br/>
    </body>
</html>