Java web进阶笔记（2）

el表达式
EL是为了使JSP写起来更加简单，使代码更加简化。
用于从域对象里面取得数据（page request session application四大域对象，都可以通过setAttribute来存入数据）
写在页面部分的，不是写在java代码部分
例：el.jsp

<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>







<%
request.setAttribute("number", 2000);
session.setAttribute("user", "QP");
application.setAttribute("count", "ahodfhaif");
%>


在线人数为：${requestScope.number }


${sessionScope.user }


${applicationScope.count }

在login.jsp里用el表达式进行优化

<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>







<%-- <% --%>


<%-- %> --%>
${msg } 


	用户名：

	密码：

	
	

el表达式从map集合和对象中取得数据
注：el表达式是可以和java代码混合使用的
index.jsp

<%@page import="model.User"%>
<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>







<%
Object user=session.getAttribute("user");
if(user==null){
	%>
	登录
	注册
	<% 
}else{
	%>
	当前登录用户名：${user.username }
	<%
// 	out.println("当前登录用户名："+((User)user).getUsername());
}
%>




各种商品的展示

el.jsp

<%@page import="model.User"%>
<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>







<%
request.setAttribute("number", 2000);
session.setAttribute("users", "QP");
application.setAttribute("count", "ahodfhaif");
%>
<%
User u=new User("中国","123",20,"男",false);
request.setAttribute("user", u);
%>


${user.username }
${user.password }

map就是键值对，list是集合
添加元素时候map是put方法，list是add方法

Map map =new HashMap();
List list=new ArrayList();

用el表达式从list中取值

<%@page import="java.util.Map"%>
<%@page import="java.util.ArrayList"%>
<%@page import="java.util.List"%>
<%@page import="java.util.HashMap"%>
<%@page import="model.User"%>
<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>







<%
request.setAttribute("number", 2000);
session.setAttribute("users", "QP");
application.setAttribute("count", "ahodfhaif");
%>
<%
List list=new ArrayList();
list.add(new User("中国","123",90,"男",false));
list.add(new User("中国1","123",90,"男",false));
list.add(new User("中国2","123",90,"男",false));
list.add(new User("中国3","123",90,"男",false));
request.setAttribute("list",list);
%>
${list[0].username }
${list[2].username }

el表达式还可以进行一些运算
${90+90 }
${90>80 }
${empty list }
${empty list2 }

empty用于判断一些attribute是否为空
返回值
180 true false true

el表达式不能直接访问request的，可以通过内置对象pageContext来访问request

${pageContext.request.contextPath }
<%--=request.getContextPath()--%> 

引入jstl
jstl可以理解为就是一个标签库
先导入jstl的jar包
链接：https://pan.baidu.com/s/1JpVh0rCoxMwOUohR3-zaUA
提取码：02ag


引入方式，在开头加上

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

jstl用于存储相关的标签

jstl的if else语句

<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>
    


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









<%-- 18 --%>



你是成年人


你还未成年

jstl和el连用，其中取值基本都是el

jstl的循环

${i }



${u.username }:${u.password }:${u.age }

结果

1 2 3 4 5 6 7 8 9 10 中国:123:90
中国1:123:90
中国2:123:90
中国3:123:90

使用jstl和el来修改原来的页面
index.jsp

<%@page import="model.User"%>
<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>









登录
注册

当前登录用户名：${user.username }




各种商品的展示

goods_list.jsp

<%@page import="model.Goods"%>
<%@page import="java.util.List"%>
<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>
    <%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>








商品管理

添加



商品名
描述
价格
库存
操作


	
${g.name }
${g.des }
${g.price }
${g.inventory }
删除 修改

json
用于数据传输

数据格式基本和js一样

重点 对象和数组

对象：
{
	"name":"QP",
	"age":20,
	"sex":"男"
} 

数组
[1,2,3,4,5]

数组里面可以包含对象
[
{
	"name":"QP",
	"age":20,
	"sex":"男"
} ,
{
	"name":"QP",
	"age":20,
	"sex":"男"
} ,
{
	"name":"QP",
	"age":20,
	"sex":"男"
} 
]

json相关jar包可以从 json.org 里面找（所有语言的json解析包都有,不过可能不是最新版
https://mvnrepository.com/open-source/cloud-computing-integration 这里可以直接用名字搜新的jar包）
链接：https://pan.baidu.com/s/1-_6IJduwFNp9b3Tf-MZUVA
提取码：z3q1

fastjson的用法

package util;

import java.util.List;

import com.alibaba.fastjson.JSON;

public class JsonTest {
	public static void main(String[] args) {
		// 序列化
//		Goods goods = new Goods("黄瓜", "好吃", 100, 400);
//		String json = JSON.toJSONString(goods);
//		System.out.println(json);

		// 反序列化
//		String s = "{\"des\":\"好吃\",\"inventory\":400,\"name\":\"黄瓜\",\"price\":100}";
//		Goods goods = JSON.parseObject(s, Goods.class);
//		System.out.println(goods.getName());

		// 元素数组的反序列化
		String s = "[" + "{" + "	\"name\":\"QP\"," + "	\"age\":20," + "	\"sex\":\"男\"" + "} ," + "{"
				+ "	\"name\":\"QP\"," + "	\"age\":21," + "	\"sex\":\"男\"" + "} ," + "{" + "	\"name\":\"QP\","
				+ "	\"age\":22," + "	\"sex\":\"男\"" + "} " + "]";
		List list = JSON.parseArray(s, UserTest.class);
		for (UserTest ut : list) {
			System.out.println(ut);
		}
	}
}

java自动将字符转义的用法：

String s=@"字符串";

会自动将冒号中的字符串转义，注意转义过将@去掉

ajax:用于向服务器发起请求,在不进行页面跳转或者向页面发起请求情况下 利用ajax向服务器发送数据服务器并相应 ajax.jsp

<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>











	用户名：

	密码：

	

	

ajaxServlet

package controller;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/ajaxrequest")
public class ajaxServlet extends HttpServlet {
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		// getParameter是获取客户端通过url传过来的数据，数据储存在data属性当中
		System.out.println("收到ajax请求" + req.getParameter("data"));
//		设置编码类型
		resp.setContentType("text/html; charset=utf-8");
		resp.getWriter().append("我是数据！");
	}
}

利用ajax来实现注册请求
register.jsp

<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>









<%
if(request.getAttribute("msg")!=null)
	out.println(request.getAttribute("msg")+"
");
%>

	用户名：
 

	密码：

	年龄：

	性别：男 女
	
	

VerifyUsernameServlet

package controller;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import service.UserService;

/**
 * Servlet implementation class VerifyUsernameServlet
 */
@WebServlet("/verifyusername")
public class VerifyUsernameServlet extends HttpServlet {

	protected void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		String username = request.getParameter("username");
		UserService service = new UserService();
		boolean isExist = service.isExist(username);
		response.getWriter().append("{\"isSuccess\":" + !isExist + "}");
	}

}

过滤器filter
用处：过滤请求，比如权限管理，中文参数，敏感词汇等。
创建filter

Test1Filter.java

package filter;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;

/**
 * Servlet Filter implementation class Test1Filter
 */
//  /*表示过滤所有页面的请求
@WebFilter("/*")
public class Test1Filter implements Filter {

	/**
	 * Default constructor.
	 */
	public Test1Filter() {
		System.out.println("构造方法");
	}

	/**
	 * @see Filter#destroy()
	 */
	public void destroy() {
		System.out.println("Destory");
	}

	/**
	 * @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain)
	 */
	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
			throws IOException, ServletException {
		System.out.println("doFilter");

		// pass the request along the filter chain
		chain.doFilter(request, response);
	}

	/**
	 * @see Filter#init(FilterConfig)
	 */
	public void init(FilterConfig fConfig) throws ServletException {
		System.out.println("init");
	}
}

@WebFilter("/login.jsp")
//表示只对login.jsp进行过滤

利用web.xml来配置filter的过滤路径
web.xml

  web05
  
    index.html
    index.htm
    index.jsp
    default.html
    default.htm
    default.jsp
  
  
  
  	Test1Filter
  	filter.Test1Filter
  
  
  	Test1Filter
  	/*
  

filter 工作流程

这里filter的执行顺序是和web.xml里面配置的先后顺序有关的
先配置的先执行
Test2Filter.java

package filter;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;

@WebFilter("/login.jsp")
public class Test2Filter implements Filter {

	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
			throws IOException, ServletException {
		System.out.println("test2 Filter brfore");
		chain.doFilter(request, response);
		System.out.println("test2 Filter after");
	}

	public void init(FilterConfig fConfig) throws ServletException {

	}

	public void destroy() {
		// TODO Auto-generated method stub
	}
}

一般都是请求时候做过滤，响应的时候一般是不做过滤的，但也有情况需要用到响应过滤。

用过滤解决编码问题
EncodeFilter

package filter;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;

/**
 * Servlet Filter implementation class EncodeFilter
 */
@WebFilter("/EncodeFilter")
public class EncodeFilter implements Filter {
	public void destroy() {
		// TODO Auto-generated method stub
	}

	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
			throws IOException, ServletException {
		request.setCharacterEncoding("utf-8");
		chain.doFilter(request, response);
	}

	public void init(FilterConfig fConfig) throws ServletException {
		// TODO Auto-generated method stub
	}
}

也可以直接设置初始化编码格式（在web.xml中设置）
web.xml

    EncodeFilter
    filter.EncodeFilter
    
    Encoding
    UTF-8
    
  

EncodeFilter

package filter;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;

//@WebFilter("/EncodeFilter")
public class EncodeFilter implements Filter {
	private String encoding;

	public void destroy() {
		// TODO Auto-generated method stub
	}

	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
			throws IOException, ServletException {
		request.setCharacterEncoding(encoding);
		chain.doFilter(request, response);
	}

	public void init(FilterConfig fConfig) throws ServletException {
//		这里是从web.xml配置文件中获取名为Encoding的配置信息
		encoding = fConfig.getInitParameter("Encoding");
	}
}

权限管理（所有跟后台有关的页面我们规定都放在admin下面）
web.xml

    AdminFilter
    filter.AdminFilter
  
  
    AdminFilter
    /admin/*
  

AdminFilter

package filter;

import java.io.IOException;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import model.User;

/**
 * Servlet Filter implementation class AdminFilter
 */
@WebFilter("/AdminFilter")
public class AdminFilter implements Filter {

	public void destroy() {
		// TODO Auto-generated method stub
	}

	public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
			throws IOException, ServletException {
		HttpServletRequest httpReq = (HttpServletRequest) request;
		HttpServletResponse httpResp = (HttpServletResponse) response;
		Object o = httpReq.getSession().getAttribute("user");
		if (o == null) {
			// 重定向的时候要加上项目名
			httpResp.sendRedirect(httpReq.getContextPath() + "/index.jsp");
		} else {
			User u = (User) o;
			if (u.isAdmin()) {
				chain.doFilter(request, response);
			} else {
				httpResp.sendRedirect(httpReq.getContextPath() + "/index.jsp");
			}
		}
	}
	public void init(FilterConfig fConfig) throws ServletException {
		// TODO Auto-generated method stub
	}
}

设置过滤的请求类型
REQUEST 是普通请求
FORWORD 是转发过来的请求
INCLUDE 是用jsp标签里面include内含页面的那种请求（只有被包含那种才会被调用）
ERROR 是当页面来了一个错误的请求（比如404）
ERROR page配置
例：
web.xml

	404
	/dispatche1.jsp
  

设置过滤的请求类型
web.xml

    DispatcherFilter
    filter.DispatcherFilter
  
  
    DispatcherFilter
    /dispatcher1.jsp
    REQUEST
  

监听器（用来监听request、session 和 application）
request 所属的类 HttpServletRequest
session 。。。 HTTPSession
application 。。。 ServletContext

监听器主要分为两大类
第一大类：监听这三个对象的创建和销毁
第二大类：监听这三个对象里面的属性

监听器也是一个类
实现监听器的接口
javax.servlet.ServletContextListener
HttpSessionListener
ServletRequestListener

ServletContextAttributeListener
HttpSessionAttributeListener
ServletRequestAttributeListener

配置



或者注解方式
@webListener

web.xml

  
    SessionListener
  

设置生命周期
web.xml

  
    1
  

Session绑定监听器
比如向model User中添加绑定监听器，则当Session中添加了User时该监听器触发
例：
在User里面绑定监听器

package model;

import javax.servlet.http.HttpSessionBindingEvent;
import javax.servlet.http.HttpSessionBindingListener;

public class User implements HttpSessionBindingListener {
	private String username;
	private String password;
	private int age;
	private String sex;
	private boolean isAdmin = false;

	public String getUsername() {
		return username;
	}

	public void setUsername(String username) {
		this.username = username;
	}

	public String getPassword() {
		return password;
	}

	public void setPassword(String password) {
		this.password = password;
	}

	public int getAge() {
		return age;
	}

	public void setAge(int age) {
		this.age = age;
	}

	public String getSex() {
		return sex;
	}

	public void setSex(String sex) {
		this.sex = sex;
	}

	public boolean isAdmin() {
		return isAdmin;
	}

	public void setAdmin(boolean isAdmin) {
		this.isAdmin = isAdmin;
	}

	public User(String username, String password, int age, String sex, boolean isAdmin) {
		super();
		this.username = username;
		this.password = password;
		this.age = age;
		this.sex = sex;
		this.isAdmin = isAdmin;
	}

	@Override
	public void valueBound(HttpSessionBindingEvent event) {
		System.out.println("valueBound:" + event.getName() + ":" + event.getValue());
	}

	@Override
	public void valueUnbound(HttpSessionBindingEvent event) {
		System.out.println("valueUnbound");
	}
}

单点登录
SessionManager.java

package util;

import java.util.HashMap;
import java.util.Map;

import javax.servlet.http.HttpSession;

public class SessionManager {
	public static Map sessionMap = new HashMap();

}

SessionAttributeListener.java

package listener;

import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;

import model.User;
import util.SessionManager;

@WebListener
public class SessionAttributeListener implements HttpSessionAttributeListener {

	public SessionAttributeListener() {
		// TODO Auto-generated constructor stub
	}

	public void attributeAdded(HttpSessionBindingEvent arg0) {
		if (arg0.getName().equals("user")) {
			User u = (User) arg0.getValue();
			// 判断是否有其他客户端已经登录
			if (SessionManager.sessionMap.containsKey(u.getUsername())) {
				// 获得另外一个客户端的session
				HttpSession session = SessionManager.sessionMap.get(u.getUsername());
				// 把登陆信息从客户端抹除
				session.removeAttribute("user");
				// 从session集合里面移除对应的用户名
				SessionManager.sessionMap.remove(u.getUsername());
			}
			SessionManager.sessionMap.put(u.getUsername(), arg0.getSession());
		}
	}

	public void attributeRemoved(HttpSessionBindingEvent arg0) {
		// TODO Auto-generated method stub
		System.out.println("attributeRemoved");
	}

	public void attributeReplaced(HttpSessionBindingEvent arg0) {
		// TODO Auto-generated method stub
		System.out.println("attributeReplaced");
	}

}