JSTL+EL表达式+JSP自定义框架案例

不会框架不要紧，我带你自定义框架

前言：这标题说的有点大了，当一回标题党，之前在学JSP的时候提到了JSTL和EL表达式，由于一直钟情于Servlet,迟迟没有更新别的，这回算是跳出来了。这回放个大招，用Spring+SpringMVC+Spring Jdbc Template，实现一个增删改查加分页，但重点不在这，我的重心在于JSTL和EL表达式，标题虽然有点大，但话糙理不糙，我真的是要自定义框架，当然，这个框架可大可小，大的我不敢说，用JSTL自定义标签封装个分页还是可以的，也算补上JSTL和EL表达式的学习吧。对于那些一直跟着我跟新博客脚步的朋友，我提醒你们不要着急，你要是好奇就可以先试着跟着我的案例试试手，不要看到SSM框架就说还没学，不会啥的，哈哈，开玩笑，都没学怎么可能会呢，我说了，这篇的重点在于JSTL和EL表达式，重要的话说了不下三遍了，至于附加的SSM，我会持续跟新，会手把手带你理解的，别急，别急，就当先认识一下SSM吧。

环境准备

我用的开发工具是IDEA，如果有不会用IDEA的朋友可以看之前写过的博客《IDEA新手使用教程》，我建的这是一个Maven项目，如果有朋友不知道Maven，可以先看一下我之前写的介绍Maven的博客《Maven》,不知道如何配置Maven环境的可以看《Maven的安装与配置》https://www.cnblogs.com/zyx110/p/10801666.html不知道如何在IDEA中建Maven项目的朋友可以看《IDEA为新手专业打造》，此案例还会用到Tomcat,同样，不会在IDEA中配置Tomcat的朋友可以看《IDEA为新手专业打造》，好，完成这些，就可以开始敲代码了。

用JSTL封装框架

写之前先简单介绍一下JSTL和EL表达式：

JSTL简介及环境搭建

什么是JSTL

JSTL是Java中的一个定制标记库集

为什么要使用JSTL

实现了JSP页面中的代码复用，基于标签库原理，重复率较高的代码块支持复用，提高效率

书写JSP页面时可读性更强，长得很像XML，方便前端查看和参与开发

举例：

不同角色用户登录时显示不同提示信息

需要导入的JSTL模块

<!-- https://mvnrepository.com/artifact/javax.servlet/jstl -->
<dependency>
  <groupId>javax.servlet</groupId>
  <artifactId>jstl</artifactId>
  <version>1.2</version>
</dependency>

　　

EL表达式配合使用JSTL

第一个JSTL小程序

在JSP页面中导入JSTL标签库

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>

　　

使用out标签输出

<c:out value="Hello JSTL"></c:out>

　　

JSTL标签的四大分类：核心标签、格式化标签、SQL标签、XML标签EL表达式

• EL表达式全名为Expression Language，经常与JSTL配合使用，使得JSP页面更直观，写法更简单。

普通表达式的写法： <%=session.getValue("name") %>

EL表达式写法：  <c:out value="${sessionScope.name}" />

• EL表达式的格式

用美元符号“$”定界，内容包括在花括号“{ }”中；

• "."与"[ ]"运算符

²  通常情况是通用的${user.sex}或${user["sex"]}

²  "[ ]"还可以用来进行集合元素中的定位${booklist[0].price}

²  当包含特殊字符时，必须使用"[ ]"，例如：${user["first-name"]}

²  通过变量动态取值：${user[param]}，例如：param可以是name/sex/others

EL变量

EL自动类型转换

EL隐式对象

EL运算符

JSP自定义标签

什么是自定义标签

在实际开发过程中不能出现大量的html+java代码相混合的jsp页面，但是有时候jsp标签和第三方标签满足不了正常的开发工作，这就需要开发人员将业务逻辑封装到符合jsp规范的类或接口中，来自己定义标签从而满足不同的开发需求。这样做的缺点是会加重开发的工作量，但在开发过程中简化了前后端的沟通，便于后期的维护，这点工作量也是微不足道的。我们可以自己定义一套标签机制，让完全不懂写代码的人开发一套网站出来。

开发第一个自定义标签

案例场景：

在页面中显示当前时间，格式：“当前时间为：2017年8月1日 10:30:50”

• 如果使用传统的jsp脚本开发，代码如下：

<%

SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日 HH:mm:ss");

String date = sdf.format(new Date());

%>

当前时间为：<%=date %>

　　

显示结果：

• 下面使用自定义标签库来实现这个案例

第一步：编写自定义标签的业务逻辑处理类

DateTag

package utils;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.TagSupport;
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class DateTag extends TagSupport {
    private String format="yyyy-MM-dd HH:mm:ss";
    private String color="blue";
    private String fontSize="12px";

    public void setFormat(String format) {
        this.format = format;
    }

    public void setColor(String color) {
        this.color = color;
    }

    public void setFontSize(String fontSize) {
        this.fontSize = fontSize;
    }

    public int doStartTag() throws JspException {
        //自定义业务
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat(format);
        String date = simpleDateFormat.format(new Date());

        String htmlshow = "<p class='' style='font-size:"+fontSize+";color:"+color+"'>"+date+"</p>";

        try {
            pageContext.getOut().print(htmlshow);
        } catch (IOException e) {
            e.printStackTrace();
        }

        return super.doStartTag();
    }
}

　　

第二步：在WEB-INF目录下编写*.tld文件注册标签

格式模板

datetag.tld

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

<taglib 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"
        version="2.1">

    <tlib-version>1.0</tlib-version>
    <short-name>myshortname</short-name>
    <uri>http://mycompany.com</uri>

    <tag>
        <name>date</name>
        <tag-class>utils.DateTag</tag-class>
        <body-content>empty</body-content>
        <attribute>
            <name>format</name>
            <required>false</required>
        </attribute>
        <attribute>
            <name>color</name>
            <required>false</required>
        </attribute>
        <attribute>
            <name>fontSize</name>
            <required>false</required>
        </attribute>

    </tag>

</taglib>

　　

JSP显示

<%@ page contentType="text/html;charset=UTF-8" language="java" isELIgnored="false" %>
<%@ taglib prefix="z" uri="http://mycompany.com" %>
<%@ taglib prefix="c" uri="http://mycompany.com" %>
<html>
<head>
    <title>显示时间</title>
</head>
<body>
<h1>index.jsp</h1>
<c:date/>
</body>
</html>

　　

Spring+SpringMVC+Spring Jdbc Template

数据库结构

项目结构

Pom.xml

<dependencies>
  <dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>4.11</version>
    <scope>test</scope>
  </dependency>
  <!-- https://mvnrepository.com/artifact/javax.servlet/javax.servlet-api -->
  <dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>javax.servlet-api</artifactId>
    <version>3.1.0</version>
  </dependency>
  <dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>5.1.38</version>
  </dependency>
  <dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>jstl</artifactId>
    <version>1.2</version>
  </dependency>
  <!--Spring核心基础依赖-->
  <dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-core</artifactId>
    <version>5.0.2.RELEASE</version>
  </dependency>
  <dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-context</artifactId>
    <version>5.0.2.RELEASE</version>
  </dependency>
  <dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-beans</artifactId>
    <version>5.0.2.RELEASE</version>
  </dependency>
  <dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-expression</artifactId>
    <version>5.0.2.RELEASE</version>
  </dependency>
  <dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-aop</artifactId>
    <version>5.0.2.RELEASE</version>
  </dependency>
  <dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-jdbc</artifactId>
    <version>5.0.2.RELEASE</version>
  </dependency>
  <dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-tx</artifactId>
    <version>5.0.2.RELEASE</version>
  </dependency>
  <dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-web</artifactId>
    <version>5.0.2.RELEASE</version>
  </dependency>
  <dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-webmvc</artifactId>
    <version>5.0.2.RELEASE</version>
  </dependency>
  <!--日志相关-->
  <dependency>
    <groupId>commons-logging</groupId>
    <artifactId>commons-logging</artifactId>
    <version>1.2</version>
  </dependency>
</dependencies>

　　

Web.xml

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

  <servlet>
    <servlet-name>springmvc</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <load-on-startup>1</load-on-startup>
    <init-param>
      <param-name>contextConfigLocation</param-name>
      <param-value>classpath:applicationContext.xml</param-value>
    </init-param>
  </servlet>
  <servlet-mapping>
    <servlet-name>springmvc</servlet-name>
    <url-pattern>/</url-pattern>
  </servlet-mapping>

  <!--处理中文乱码-->
  <filter>
    <filter-name>encodingFilter</filter-name>
    <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
    <init-param>
      <param-name>encoding</param-name>
      <param-value>UTF-8</param-value>
    </init-param>
    <init-param>
      <param-name>forceEncoding</param-name>
      <param-value>true</param-value>
    </init-param>
  </filter>
  <filter-mapping>
    <filter-name>encodingFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>

  <!--设置访问静态资源-->
  <servlet-mapping>
    <servlet-name>default</servlet-name>
    <url-pattern>*.css</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>default</servlet-name>
    <url-pattern>*.js</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>default</servlet-name>
    <url-pattern>*.jpg</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>default</servlet-name>
    <url-pattern>*.png</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>default</servlet-name>
    <url-pattern>*.gif</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>default</servlet-name>
    <url-pattern>*.mp3</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>default</servlet-name>
    <url-pattern>*.mp4</url-pattern>
  </servlet-mapping>

</web-app>

　　

applicationContext.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:tx="http://www.springframework.org/schema/tx"
       xmlns:mvc="http://www.springframework.org/schema/mvc"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd
       http://www.springframework.org/schema/context
       http://www.springframework.org/schema/context/spring-context.xsd
       http://www.springframework.org/schema/tx
       http://www.springframework.org/schema/tx/spring-tx.xsd
       http://www.springframework.org/schema/mvc
       http://www.springframework.org/schema/mvc/spring-mvc.xsd
        ">

    <!--配置注解要扫描的包-->
    <context:component-scan base-package="controller"></context:component-scan>
    <context:component-scan base-package="dao"></context:component-scan>
    <context:component-scan base-package="Service"></context:component-scan>
    <context:component-scan base-package="pojo"></context:component-scan>
    <context:component-scan base-package="utils"></context:component-scan>
    <context:component-scan base-package="test"></context:component-scan>
    <mvc:annotation-driven></mvc:annotation-driven>

    <!--配置spring-jdbcTemplate-->
    <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
        <property name="driverClassName" value="com.mysql.jdbc.Driver"></property>
        <property name="url" value="jdbc:mysql://localhost:3306/bbb?useUnicode=true&characterEncoding=UTF-8"></property>
        <property name="username" value="root"></property>
        <property name="password" value="root"></property>
    </bean>
    <bean id="jdbcTemplate" class="org.springframework.jdbc.core.JdbcTemplate">
        <property name="dataSource" ref="dataSource"></property>
    </bean>
    <!--配置事务-->
    <bean id="txManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
        <property name="dataSource" ref="dataSource"></property>
    </bean>
    <!--注册事务注解驱动-->
    <tx:annotation-driven transaction-manager="txManager"></tx:annotation-driven>

    <!--配置访问静态资源-->
    <mvc:resources mapping="/js/**" location="/js/"></mvc:resources>
    <mvc:resources mapping="/css/**" location="/css/"></mvc:resources>
    <mvc:resources mapping="/img/**" location="/img/"></mvc:resources>

    <!--配置视图解析器-->
    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <!--配置前缀-->
        <property name="prefix" value="/"></property>
        <!--配置后缀-->
        <property name="suffix" value=".jsp"></property>
    </bean>

    <!--创建文件上传组件对象-->
    <bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver"></bean>
</beans>

Book

package pojo;

public class Book {
    @Override
    public String toString() {
        return "Book{" +
                "id=" + id +
                ", bookname='" + bookname + '\'' +
                ", price=" + price +
                '}';
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getBookname() {
        return bookname;
    }

    public void setBookname(String bookname) {
        this.bookname = bookname;
    }

    public int getPrice() {
        return price;
    }

    public void setPrice(int price) {
        this.price = price;
    }

    private int id;
    private String bookname;
    private int price;

}

 　

PageBean

package pojo;

import java.util.List;

public class PageBean<T> {

    private int pageCode;//当前页码
    private int totalPage;//总页数
    private int count;//总记录数
    private int pageSize;//每页记录数
    private List<T> pageList;//每页的数据

    public PageBean(int pageCode, int pageSize, int count, List<T> pageList) {
        this.pageCode = pageCode;
        this.count = count;
        this.pageSize = pageSize;
        this.pageList = pageList;
    }

    public PageBean() {
    }

    public int getPageCode() {
        return pageCode;
    }

    public void setPageCode(int pageCode) {
        this.pageCode = pageCode;
    }

    public int getTotalPage() {
        int tp = count/pageSize;
        return count%pageSize==0 ? tp : tp+1;
    }

    public int getCount() {
        return count;
    }

    public void setCount(int count) {
        this.count = count;
    }

    public int getPageSize() {
        return pageSize;
    }

    public void setPageSize(int pageSize) {
        this.pageSize = pageSize;
    }

    public List<T> getPageList() {
        return pageList;
    }

    public void setPageList(List<T> pageList) {
        this.pageList = pageList;
    }
}

BookDao

package dao;

import pojo.Book;

import java.util.List;

public interface BookDao {
    public List<Book> findByPage(int pageCode,int pageSize);
    public int count();
}

BookDaoImpl

package dao;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.jdbc.core.BeanPropertyRowMapper;
import org.springframework.jdbc.core.JdbcTemplate;
import org.springframework.stereotype.Repository;
import pojo.Book;

import java.util.List;
@Repository
public class BookDaoImpl implements BookDao {
    @Autowired
    private JdbcTemplate jdbcTemplate;
    @Override
    public List<Book> findByPage(int pageCode, int pageSize) {
        String sql = "select * from book limit ?,?";
        Object[] param = {(pageCode-1)*pageSize,pageSize};
        return jdbcTemplate.query(sql,new BeanPropertyRowMapper<Book>(Book.class),param);
    }

    @Override
    public int count() {
        String sql = "select count(*) from book";
        return jdbcTemplate.queryForObject(sql,Integer.class);
    }
} 

BookService

package Service;

import pojo.Book;
import pojo.PageBean;

public interface BookService {
    public PageBean<Book> findByPage(int pageCode,int pageSize);
}

　　

BookServiceImpl

package Service;

import dao.BookDao;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import pojo.Book;
import pojo.PageBean;
@Service
public class BookServiceImpl implements BookService {

    @Autowired
    private BookDao bookDao;

    @Override
    public PageBean<Book> findByPage(int pageCode, int pageSize) {
        return new PageBean<Book>(pageCode,pageSize,bookDao.count(),bookDao.findByPage(pageCode,pageSize));
    }
}

BookController

package controller;

import Service.BookService;
import com.sun.org.apache.xml.internal.resolver.readers.XCatalogReader;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;
import pojo.Book;
import pojo.PageBean;
import utils.RequestPage;

@Controller
@RequestMapping("/book")
public class BookController {
    @Autowired
    private BookService bookService;

    @RequestMapping("/query")
    public String findByPage(Integer page, Model model){
        page = RequestPage.getPage(page);//判断是否为空
        PageBean<Book> pageBean = bookService.findByPage(page,RequestPage.PAGE_SIZE);
        model.addAttribute("pageBean",pageBean);

        return "book";
    }

}

DateTag

package utils;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.TagSupport;
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class DateTag extends TagSupport {
    private String format="yyyy-MM-dd HH:mm:ss";
    private String color="blue";
    private String fontSize="12px";

    public void setFormat(String format) {
        this.format = format;
    }

    public void setColor(String color) {
        this.color = color;
    }

    public void setFontSize(String fontSize) {
        this.fontSize = fontSize;
    }

    public int doStartTag() throws JspException {
        //自定义业务
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat(format);
        String date = simpleDateFormat.format(new Date());

        String htmlshow = "<p class='' style='font-size:"+fontSize+";color:"+color+"'>"+date+"</p>";

        try {
            pageContext.getOut().print(htmlshow);
        } catch (IOException e) {
            e.printStackTrace();
        }

        return super.doStartTag();
    }
}

　　

PageTag

package utils;

import pojo.PageBean;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.TagSupport;
import java.io.IOException;

public class PageTag extends TagSupport {

    private PageBean pageBean;
    private String url;

    public void setUrl(String url) {
        this.url = url;
    }

    public void setPageBean(PageBean pageBean) {
        this.pageBean = pageBean;
    }

    @Override
    public int doStartTag() throws JspException {

        try {
            StringBuffer sb = new StringBuffer();
            //首页
            sb.append("<a href=\"" + url + "?page=1\">首页</a> ");
            //上一页
            if (pageBean.getPageCode() <= 1) {
                sb.append("<span style=\"color: #555;\">上一页</span> ");
            } else {
                sb.append("<a href=\"" + url + "?page=" + (pageBean.getPageCode() - 1) + "\">上一页</a> ");
            }

            //显示页码
            int begin, end;
            if (pageBean.getTotalPage() <= 10) {
                begin = 1;
                end = pageBean.getTotalPage();
            } else {
                begin = pageBean.getPageCode() - 5;
                end = pageBean.getPageCode() + 4;
                if (begin < 1) {
                    begin = 1;
                    end = 10;
                } else if (end > pageBean.getTotalPage()) {
                    begin = pageBean.getTotalPage() - 9;
                    end = pageBean.getTotalPage();
                }
            }

            for (int i = begin; i <= end; i++) {
                if (i == pageBean.getPageCode()) {
                    sb.append("<span style=\"color:red;\">" + i + "</span> ");
                } else {
                    sb.append("<a href=\"" + url + "?page=" + i + "\">[" + i + "]</a> ");
                }
            }

            //下一页
            if (pageBean.getPageCode() >= pageBean.getTotalPage()) {
                sb.append("<span style=\"color: #555;\">下一页</span>");
            } else {
                sb.append("<a href=\"" + url + "?page=" + (pageBean.getPageCode() + 1) + "\">下一页</a> ");
            }
            //尾页
            sb.append("<a href=\"" + url + "?page=" + pageBean.getTotalPage() + "\">尾页</a> \n" +
                    "    页码" + pageBean.getPageCode() + "/" + pageBean.getTotalPage());

            pageContext.getOut().print(sb.toString());
        } catch (IOException e) {
            e.printStackTrace();
        }

        return super.doStartTag();
    }
}

RequestPage
package utils;

public class RequestPage {
    public static final int PAGE_SIZE =5;

    public static Integer getPage(Integer page){
        if (page==null||page<1){
            page=1;
        }

        return page;
    }

}

　　

datetag.tld

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

<taglib 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"
        version="2.1">

    <tlib-version>1.0</tlib-version>
    <short-name>myshortname</short-name>
    <uri>http://mycompany.com</uri>

    <tag>
        <name>date</name>
        <tag-class>utils.DateTag</tag-class>
        <body-content>empty</body-content>
        <attribute>
            <name>format</name>
            <required>false</required>
        </attribute>
        <attribute>
            <name>color</name>
            <required>false</required>
        </attribute>
        <attribute>
            <name>fontSize</name>
            <required>false</required>
        </attribute>

    </tag>
    <tag>
        <name>page</name>
        <tag-class>utils.PageTag</tag-class>
        <body-content>empty</body-content>
        <attribute>
            <name>pageBean</name>
            <required>false</required>
            <rtexprvalue>true</rtexprvalue>
        </attribute>
        <attribute>
            <name>url</name>
            <required>false</required>
            <rtexprvalue>true</rtexprvalue>
        </attribute>
    </tag>

</taglib>

　　

book.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" isELIgnored="false" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%@ taglib prefix="z" uri="http://mycompany.com" %>
<link rel="stylesheet" href="${pageContext.request.contextPath}/css/book.css">
<html>
<head>
    <title>图书</title>
</head>
<body>
<h1 align="center">图书列表</h1>
<hr>
<table>
    <tr>
        <th>ID</th>
        <th>书名</th>
        <th>价格</th>

    </tr>
    <c:forEach var="book" items="${pageBean.pageList}">
        <tr>
            <td>${book.id}</td>
            <td>${book.bookname}</td>
            <td>${book.price}</td>
        </tr>
    </c:forEach>
</table>
<div id="page">
    <z:page url="${pageContext.request.contextPath}/book/query" pageBean="${pageBean}"></z:page>
</div>
</body>
</html>

运行显示

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