Java custom simple tag example

The following will take permission control as an example to customize a tag:
1. Tag type

<wxt:per uri="${pageContext.request.contextPath }/privilege/list"></wxt:per>

Steps:
1. Customize a class PerssionTag that inherits SimpleTagSupport (custom tags generally Inherit this class)

package cn.com.liveuc.privilege.tag;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Set;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.PageContext;
import javax.servlet.jsp.tagext.SimpleTagSupport;
import cn.com.liveuc.privilege.model.Privilege;
import cn.com.liveuc.privilege.model.Resource;
import cn.com.liveuc.privilege.model.Role;
import cn.com.liveuc.privilege.model.User;
/**
 * 
 * @说明   自定义标签
 */
public class PerssionTag extends SimpleTagSupport {

 //自定义标签属性，用于标签传入参数
 private String uri;

 //接收标签传入的参数
 public void setUri(String uri) {
  this.uri = uri;
 }
 @Override
 public void doTag() throws JspException, IOException {
  //获取用户登陆后保存的Session
  PageContext page = (PageContext) this.getJspContext();
  User user = (User) page.getSession().getAttribute("login");
  //如果用户登陆
  if(user != null) {
   //用户登陆判断用户权限
   List<String> list = new ArrayList<String>();
   //获取用户的角色
   Set<Role> role = user.getRole();
   for(Role r:role) {
    //获取角色对应的权限
    Set<Privilege> privilege = r.getPrivilege();
    for(Privilege p:privilege) {
     //获取权限对应的资源
     Set<Resource> res = p.getResource();
     for(Resource re:res) {
      list.add(re.getUri());
     }
    }
   }
   for(String ur:list) {
    //判断用户的权限
    if(ur.equals(uri)) {
     this.getJspBody().invoke(null); //有权限输出标签体内容
    }
   }
  }
 }
}

2. Create a tld file description tag under WEB-INF.

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<taglib xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 version="2.0"
 xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd">
 <description><![CDATA["To make it easier to access dynamic data;
                    the Apache Struts framework includes a library of custom tags.
                    The tags interact with the framework&#39;s validation and internationalization features;
                    to ensure that input is correct and output is localized.
                    The Struts Tags can be used with JSP FreeMarker or Velocity."]]></description>
 <display-name>"Struts Tags"</display-name>
 <tlib-version>2.2.3</tlib-version>
 <short-name>s</short-name>
 <uri>/wxt</uri>
 <tag>
  <name>per</name><!-- 标签名 -->
  <tag-class>cn.com.liveuc.privilege.tag.PerssionTag</tag-class>
  <body-content>scriptless</body-content>
  <!-- 标签属性 -->
  <attribute>
   <name>uri</name><!-- 属性名称 -->
   <required>true</required><!-- 是否必须 -->
   <rtexprvalue>true</rtexprvalue><!-- 是否为动态标签 -->
  </attribute>
 </tag>
</taglib>

3. Use tags
Import tags in Jsp pages:
% @taglib prefix="wxt" uri="/wxt" %
Use tag:
     User Management

User permissions that include uri resources will output the tag content.

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