jsp2自定义标签+属性

前面说过jsp2自定义标签如果要加入属性需要设置属性的getter和setter方法。代码如下：

 public class GetParam extends SimpleTagSupport {
     private String driver;
     private String url;
     private String user;
     private String pwd;
     private String sql;
     private Connection conn = null;;
     private Statement stm = null;;
     private ResultSet rs = null;

     public void setDriver(String driver) {
         this.driver = driver;
     }

     public String getDriver() {
         return this.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 getPwd() {
         return pwd;
     }

     public void setPwd(String pwd) {
         this.pwd = pwd;
     }

     public String getSql() {
         return sql;
     }

     public void setSql(String sql) {
         this.sql = sql;
     }

     @Override
     public void doTag() throws JspException, IOException {
         // TODO Auto-generated method stub
         try {
             // 注册驱动
             Class.forName(driver);
             // 建立连接
             conn = DriverManager.getConnection(url, user, pwd);
             stm = conn.createStatement();
             rs = stm.executeQuery(sql);
             // 获取页面输出流
             Writer out = getJspContext().getOut();
             // 设置表格
             out.write("<table border='1' width='300'>");
             // 遍历
             while (rs.next()) {
                 out.write("<tr>");
                 for (int i = 1; i < rs.getMetaData().getColumnCount(); i++) {
                     out.write("<td>");
                     out.write(rs.getString(i));
                     out.write("</td>");
                 }
                 out.write("</tr>");
             }
             out.write("</table>");

         } catch (SQLException | ClassNotFoundException ex) {

             // TODO: handle exception
             ex.printStackTrace();
             throw new JspException("自定义标签错误" + ex.getMessage());
         } finally {
             try {
                 if (rs != null) {
                     rs.close();
                 }
                 if (stm != null) {
                     stm.close();
                 }
                 if (conn != null) {
                     conn.close();
                 }
             } catch (SQLException e) {
                 // TODO: handle exception
                 e.printStackTrace();
             }
         }
     }
 }

接下来配置tld文件，对于有属性的标签，需要在<tag>元素下增加<attribute>子元素。在<attribute>下有三个元素，

第一个是name:设置属性名，第二个是required：该属性是否为必须属性，第三个是fragment：该属性是否支持JSP脚本，表达式等动态内容。

在配置<attribute>下面的name时候，一定要和属性名对应，不然会报错"Unable to find setter method for attribute: XXX"，tld文件完整代码如下：

 <?xml version="1.0" encoding="GBK" ?>
 <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">
     <!-- 描述 -->
     <description>A tag library exercising SimpleTag handlers.</description>
     <!-- 版本 -->
     <tlib-version>1.0</tlib-version>
     <!-- 短名 -->
     <short-name>gotparam</short-name>
     <!-- 指定标签库URI -->
     <uri>http://tomcat.apache.org/gotparam</uri>
     <tag>
         <description>Outputs Hello, World</description>
         <!-- 标签库名字 -->
         <name>GetParam</name>
         <!-- 标签处理类 -->
         <tag-class>lee.GetParam</tag-class>
         <!-- 标签体内容 -->
         <body-content>empty</body-content>
         <!-- 标签属性:driver -->
         <attribute>
             <name>driver</name>
             <required>true</required>
             <fragment>true</fragment>
         </attribute>
         <!-- 标签属性:url -->
         <attribute>
             <name>url</name>
             <required>true</required>
             <fragment>true</fragment>
         </attribute>
         <!-- 标签属性:user -->
         <attribute>
             <name>user</name>
             <required>true</required>
             <fragment>true</fragment>
         </attribute>
         <!-- 标签属性:pwd -->
         <attribute>
             <name>pwd</name>
             <required>true</required>
             <fragment>true</fragment>
         </attribute>
         <!-- 标签属性:sql -->
         <attribute>
             <name>sql</name>
             <required>true</required>
             <fragment>true</fragment>
         </attribute>
     </tag>
 </taglib>

最后新建一个jsp文件测试标签，代码如下：

 <%@ page language="java" contentType="text/html; charset=UTF-8"
     pageEncoding="UTF-8"%>
 <%@ taglib uri="http://tomcat.apache.org/gotparam" prefix="gotparam"%>
 <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
 <html>
 <head>
 <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
 <title>Insert title here</title>
 </head>
 <body>
     <gotparam:GetParam user="root" url="jdbc:mysql://localhost:3306/house"
         driver="com.mysql.jdbc.Driver" pwd="123456" sql="select * from house" />
 </body>
 </html>