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JSP and filter

2022-07-03 13:13:00 【Tolerance speech】

1.JSP

1.1 summary

Java Server Pages:java Server page , And also Servlet equally , For dynamic Web technology .

The biggest feature ：

  • Write jsp It's like writing html equally
  • difference ：
    • html Only static data is provided to users .html Comments of can be displayed on the client
    • jsp Pages can be embedded java Code , Provide users with dynamic data .jsp The comment of cannot be seen on the client , But you can grab the bag .

 

1.2 principle

Work inside the server

  • tomcat There is one of them. work Catalog
  • idea Use in tomcat Will be in idea Of tomcat Produce one in work Catalog

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Found that the page was converted into a java Program ,JSP It will eventually be transformed into a Java class . Browser sends request to server , No matter what resources are accessed , In fact, they are all visiting Servlet.

JSP In essence Servlet:

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Some internal source code ：

// initialization 
public void _jspInit() {
    }
// The destruction 
public void _jspDestroy() {
    }
//JSPService
public void _jspService(HttpServletRequest request, HttpServletResponse response)

public void _jspService(HttpServletRequest request, HttpServletResponse response)

  1. Judge the request

  2. Built in some objects 

     final jakarta.servlet.jsp.PageContext pageContext;// Page context 
 final jakarta.servlet.ServletContext application; //application
 final jakarta.servlet.ServletConfig config;       //config
 jakarta.servlet.jsp.JspWriter out = null;         //out
 final java.lang.Object page = this;               //page The current page 
 HttpServletRequest request;                       // request 
 HttpServletResponse response;                     // Respond to

  3. Code added before the output page 

    response.setContentType("text/html; charset=UTF-8");// Set the page type of the response 
pageContext = _jspxFactory.getPageContext(this, request, response,
      			null, false, 8192, true);
 _jspx_page_context = pageContext;
application = pageContext.getServletContext();
config = pageContext.getServletConfig();
out = pageContext.getOut();
_jspx_out = out;

  4. These objects can be found in JSP Use directly on the page

  5. stay jsp On the page ：

    • As long as it is java The code will be output intact

    • html Code , Will be converted to the following format , Output to the front end 

      out.write("<html lang=\"en\">\r\n");

 

1.3 grammar

Every language has its own grammar ,JSP As java An application of Technology , It has some of its own extended syntax , It supports java All the grammar of .

 

1.3.1jsp expression 

<%--
 Used to convert the output of the program , Output to client 
<%=  Variables or expressions %>
--%>
<%= new java.util.Date()%>

 

1.3.2jsp Script snippets 

<%
  int sum=0;
    for (int i = 1; i < 100; i++) {
        sum+=i;
    }
    out.println("<h1>sum="+sum+"</h1>");
%>

 

1.3.3jsp Script fragment reproduction 

<%
  int x=1;
  out.println(x);
%>
<p> This is a jsp file </p>
<%
    int y=2;
    out.println(y);
%>

<hr>

<%-- Embed... In the code html Elements --%>
<%
    for (int i = 1; i <=3; i++) {
%>
<h1>hello world!<%= i%></h1>
<%
    }
%>

 

1.3.4jsp Statement

Global variables ：

<%!
 static{
     System.out.println("loading Servlet");
 }
 private int globalvar = 0;
 public void m(){
     System.out.println(" Into the method m");
 }
%>

jsp The declaration will be compiled into jsp Generated java Class , Those above will be generated to _jspService In the method .

 

1.4 Instructions 

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>    Solve the Chinese garbled code 
<%@ page errorPage="error/500.jsp" %>                                   Custom error page 
<%@page isErrorPage="true" %>

 Extract public pages ：
<%-- Three pages will be combined into one page --%>
  <%@include file="common/header.jsp"%>
  <h1> The main body of the page </h1>
  <%@include file="common/footer.jsp"%>

<%--jsp label ： Splicing pages , In essence, there are three pages --%>
<jsp:include page="/common/header.jsp"/>
<h1>1111111</h1>
<jsp:include page="/common/footer.jsp"/>

<error-page>
    <error-code>500</error-code>
    <location>/error/500.jsp</location>
</error-page>
<error-page>
    <error-code>404</error-code>
    <location>/error/404.jsp</location>
</error-page>

 

1.5 Nine built-in objects

1.5.1 summary

  • PageContext To save things
  • Request To save things
  • Response
  • Session To save things
  • Application 【ServletContext】 To save things
  • Config 【ServletConfig】
  • Out
  • Page 【 no need 】
  • Exception

Schematic diagram ： Insert picture description here

request： Client sends request to server , Generate data , It's useless for users to read it , such as ： Journalism

session： Client sends request to server , Generate data , The user will be useful after a while , such as ： The shopping cart

application： Client sends request to server , Generate data , One user runs out , Another user can also use , such as ： Chat data 

<body>
<%-- Built-in objects --%>
<%
 pageContext.setAttribute("name1","x1");// The saved data is only valid in one page 
 request.setAttribute("name2","x2");// The saved data is only valid in one request , Please forward this data 
 session.setAttribute("name3","x3");// The saved data is valid only in one session , From open browser to close browser 
 application.setAttribute("name4","x4");// The saved data is only valid in the server , From turning on the server to turning off the server 
%>
<%-- The code in the script fragment , Will be generated intact to .jsp.java
 requirement ： The code here must guarantee java The correctness of grammar , Notes are also used java Notes // --%>
<%
    // from pageContext Remove from , We look for ways to 
    // From the lower level to the higher level page-->request-->session-->application
    String name1 = (String) pageContext.findAttribute("name1");
    String name2 = (String) pageContext.findAttribute("name2");
    String name3 = (String) pageContext.findAttribute("name3");
    String name4 = (String) pageContext.findAttribute("name4");
    String name5 = (String) pageContext.findAttribute("name5");// non-existent 
%>
<%-- Use EL Expression output result   ${} --%>
<h1> The value taken out is ：</h1>
<h2>${name1}</h2>
<h3>${name2}</h3>
<h4>${name3}</h4>
<h5>${name4}</h5>
<h6>${name5}</h6>
<h6><%= name5%></h6>
</body>

Output results ： Insert picture description here

 

1.5.2 Scope 

<%-- Scope （scope） Changes ：--%>
<%pageContext.setAttribute("a","b",pageContext.SESSION_SCOPE);%>

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 Source code ：
public void setAttribute(String name, Object attribute, int scope) {
    
        switch(scope) {
    
        case 1:
            this.mPage.put(name, attribute);
            break;
        case 2:
            this.mRequest.put(name, attribute);
            break;
        case 3:
            this.mSession.put(name, attribute);
            break;
        case 4:
            this.mApp.put(name, attribute);
            break;
        default:
            throw new IllegalArgumentException("Bad scope " + scope);
        }
}

<%-- Request forwarding --%>
<% 
   pageContext.forward("/index.jsp");
   request.getRequestDispatcher("/index.jsp").forward(request,response);
%>

 

1.6 label

1.6.1JSP label

  • jsp:include
  • jsp:forward
  • jsp:param
<%--http://localhost:8080/jsp/jsptag1.jsp？name= Xiao Ming &age=18--%>
<jsp:forward page="/jsptag2.jsp">
    <jsp:param name="name" value=" Xiao Ming "/>
    <jsp:param name="age" value="18"/>
</jsp:forward>

<%-- Take out the parameters --%>
 name ：<%= request.getParameter("name")%>
 Age ：<%= request.getParameter("age")%>

 

1.6.2JSTL label

1.6.2.1 summary

JSTL Tag library is used to make up for HTML The lack of labels ; It customizes many labels , It can be used by us , The function of tags and java code ！

Use jstl Steps of label Library ：

  • Import corresponding jstl Tag library
  • Use the method
  • stay tomcat We also need to introduce our jstl Package, otherwise it will report an error ！

pom.xml Packages that need to be imported in ：

    <!--jstl The dependency of expressions -->
    <dependency>
      <groupId>javax.servlet.jsp.jstl</groupId>
      <artifactId>jstl-api</artifactId>
      <version>1.2</version>
    </dependency>
    <!--standard Tag library -->
    <dependency>
      <groupId>taglibs</groupId>
      <artifactId>standard</artifactId>
      <version>1.1.2</version>
    </dependency>

 

1.6.2.2 Core tags

Insert picture description here

 

c:if

<%-- introduce jstl Core tag library , We can use jstl label --%>
<%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>

<h4>if test </h4>
<hr>
<form action="coretag.jsp" method="post">
    <%--EL Expression to get the data in the form  ${param. Parameter name } --%>
    <input type="text" name="username" value="${param.username}">
    <input type="submit" value=" Sign in ">
</form>
<%-- Judge if the submitted user name is administrator , Then login successfully --%>
<c:if test="${param.username == 'Admin'}" var="isAdmin">
    <c:out value=" The administrator welcomes you "></c:out>
</c:if>
<c:out value="${isAdmin}"></c:out>

Output results ： Insert picture description here

 
c:choose

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

<%-- Define a variable score, The value is 85--%>
<c:set var="score" value="85"></c:set>
<c:choose>
    <c:when test="${score>=90}">
        <c:out value=" good "/>
    </c:when>
    <c:when test="${score>=80}">
        commonly 
    </c:when>
    <c:when test="${score>=70}">
        <c:out value=" good "/>
    </c:when>
    <c:when test="${score>=60}">
        <c:out value=" pass "/>
    </c:when>
</c:choose>

 
c:foreach

<%
    ArrayList<String> people = new ArrayList<>();
    people.add(0," Zhao Yi ");
    people.add(1," Li Er ");
    people.add(2," That three ");
    people.add(3," The king of the four ");
    request.setAttribute("list",people);
%>

<%--
var: Variables obtained from each iteration 
items： Object to traverse 
--%>
<c:forEach var="people" items="${list}">
  <c:out value="${people}"/><br>
</c:forEach>
<hr>
<c:forEach var="people" items="${list}" begin="1" end="3" step="2">
    <c:out value="${people}"></c:out>
</c:forEach>

Output results ： Insert picture description here

 

1.6.3EL expression

${ }

  • get data
  • Perform an operation
  • obtain web Develop common objects

 

1.7JavaBean

Entity class JavaBean There is a specific way of writing ：

  • There has to be a parameterless construct
  • Property must be privatized
  • There must be a corresponding get、set Method
  • It is usually used to map the fields in the database ,ORM

ORM： Object mapping

  • surface —> class
  • Field —> attribute
  • rows —> object 
<%@ page import="moli.jsp.pojo.People" %>
<%
    People people = new People();
    people.setAddress(" heilongjiang ");
    people.setAge(18);
    people.setId(1);
    people.setName(" Xiao Ming ");
    String name = people.getName();
    out.println(name);
%>
<hr/>

<jsp:useBean id="peole" class="moli.jsp.pojo.People" scope="page"/>
<jsp:setProperty name="peole" property="address" value=" heilongjiang "/>
<jsp:setProperty name="peole" property="name" value=" Xiao Ming "/>
<jsp:setProperty name="peole" property="age" value="18"/>
<jsp:setProperty name="peole" property="id" value="1"/>
<jsp:getProperty name="peole" property="name"/>

Output results ： Insert picture description here

 
 
 

 

2.MVC Three layer architecture

MVC：model view controller Model view controller

2.1 Earlier years

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 User direct access control layer , The control layer can directly operate the database 
servlet-->CRUD--> database 
 disadvantages ： The program is very bloated , Not conducive to maintenance 
servlet In the code of ： Processing requests , Respond to , View jump , Handle JDBC, Deal with business code , Processing logic code 
 framework ： Nothing can't be solved by adding a layer 
 The programmer calls --JDBC--MySQL,Oracle,sqlServlet...

 

2.2 Now?

Insert picture description here

View

  • Display data
  • Provide connection , launch Servlet request （a,form,img……）

Controller（Servlet）

  • Accept user requests （req Request parameters ,session Information ……）
  • Give it to the business layer to process the corresponding code
  • Control view jump

Model

  • Business processing ： Business logic （Service）
  • Data persistence layer ：CRUD（Dao）
 Sign in --- Receive user login request --- Handle user requests （ Get user login parameters ,username,password）--- Give it to the business layer to handle the login business （ Determine whether the user name and password are correct ; Business ）---Dao The layer queries whether the user name and password are correct --- database

 
 
 

3.Filter And the monitor

3.1Filter

filter ： It's used to filter the data of the website

  • Solve the Chinese garbled code
  • validate logon ……

Insert picture description here

 

filter Development steps ：

  1. Guide pack （ It must be javax.servlet Under the Filter Interface ）

  2. Write filters

    chain chain , Let our request go on , So that the program can be handed over to the next part ; If you don't write , Our program will be blocked and stopped here .

    package filter;
import javax.servlet.*;
import java.io.IOException;
public class characterEncodingFilter implements Filter {
      
    // Initialization and web Start the server together , Wait for the filter object to appear at any time 
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
      
        System.out.println("characterEncodingFilter Already initialized ");
    }
    // All code in the filter will be executed when filtering specific requests 
    // The filter must be allowed to move forward chain.doFilter(request,response);
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
      
        request.setCharacterEncoding("utf-8");
        response.setCharacterEncoding("utf-8");
        response.setContentType("text/html;charset=UTF-8");
        System.out.println("characterEncodingFilter Before execution ");
        chain.doFilter(request,response);
        System.out.println("characterEncodingFilter After execution ");
    }
    // The destruction ,web When the server is down , The filter will be destroyed 
    @Override
    public void destroy() {
      
        System.out.println("characterEncodingFilter It has been destroyed ");
    }
}

    public class showServlet extends HttpServlet {
      
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
      
        resp.getWriter().write(" Hello ");
    }
}

  3. Configure filter web.xml

    <servlet>
  <servlet-name>showServlet</servlet-name>
  <servlet-class>moli.showServlet</servlet-class>
</servlet>
<servlet-mapping>
  <servlet-name>showServlet</servlet-name>
  <url-pattern>/show</url-pattern>
</servlet-mapping>
<servlet-mapping>
  <servlet-name>showServlet</servlet-name>
  <url-pattern>/moli/show</url-pattern>
</servlet-mapping>

<filter>
  <filter-name>characterEncodingFilter</filter-name>
  <filter-class>filter.characterEncodingFilter</filter-class>
</filter>
<filter-mapping>
  <filter-name>characterEncodingFilter</filter-name>
  <!-- As long as it is /moli All requests are filtered -->
  <url-pattern>/moli/*</url-pattern>
</filter-mapping>

    At this time, enter the address in the browser ：http://localhost:8080/f/show It's still garbled , But input http://localhost:8080/f/moli/show There will be no more random code .

     
     

3.2 Monitor

Implement a listener interface （N Kind of ）：

// Count the number of people online ： Statistics session
public class OlinerCountListener implements HttpSessionListener {
    
    // establish session monitor ： Watch every move of the client 
    // Once created session This event will be triggered once 
    @Override
    public void sessionCreated(HttpSessionEvent se) {
    
        ServletContext sc = se.getSession().getServletContext();
        System.out.println(se.getSession().getId());
        Integer onlineCount = (Integer) sc.getAttribute("OnlineCount");
        if (onlineCount==null){
    
            onlineCount = new Integer(1);
        }else {
    
            onlineCount = new Integer(onlineCount+1);
        }
        sc.setAttribute("OnlineCount",onlineCount);
    }
    // The destruction session monitor 
    // Once destroyed session This event will be triggered once 
    @Override
    public void sessionDestroyed(HttpSessionEvent se) {
    
        ServletContext sc = se.getSession().getServletContext();
        Integer onlineCount = (Integer) sc.getAttribute("OnlineCount");
        if (onlineCount==null){
    
            onlineCount = new Integer(0);
        }else {
    
            onlineCount = new Integer(onlineCount-1);
        }
        sc.setAttribute("OnlineCount",onlineCount);
    }
}

<h1>
     The current is <span style="color: bisque">
    <%= this.getServletConfig().getServletContext().getAttribute("OnlineCount")%>
    </span> People online 
</h1>

<!-- Register listener -->
<listener>
   <listener-class>listener.OlinerCountListener</listener-class>
</listener>

Output results ： Insert picture description here

 

Application of monitoring ：

public class TestPanel {
    
    public static void main(String[] args) {
    
        Frame frame = new Frame(" Primordial winter ");// Create a new form 
        Panel panel = new Panel(null);// panel 
        frame.setLayout(null);
        frame.setBounds(300,300,500,500);
        frame.setBackground(new Color(0,99,23));
        panel.setBounds(50,50,300,300);
        panel.setBackground(new Color(100,0,0));
        frame.add(panel);
        frame.setVisible(true);
        // Listen for off events 
        frame.addWindowListener(new WindowAdapter() {
    
            @Override
            public void windowClosing(WindowEvent e) {
    
                System.exit(0);
            }
        });
    }
}

Insert picture description here

 
 

3.3 application

Users can enter the home page only after logging in , After the user logs off, he can't enter the home page .

The login page ：

<form action="/moli/login" method="post">
    <input type="text" name="username">
    <input type="submit">

public class LoginServlet extends HttpServlet {
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
       // Get the parameters of the front-end request 
        String username = req.getParameter("username");
        if (username.equals("admin")){
    
            req.getSession().setAttribute("USER_SESSION",req.getSession().getId());
            resp.sendRedirect("/sys/success.jsp");
        }else {
    
            resp.sendRedirect("/error.jsp");
        }
    }
}

Login success page 

<h1> Home page </h1>
<p><a href="/moli/logout"> Cancellation </a></p>

logout 

public class logoutServlet extends HttpServlet {
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
        Object user_session = req.getSession().getAttribute("USER_SESSION");
        if (user_session!=null){
    
            req.getSession().removeAttribute("user_session");
            resp.sendRedirect("/login.jsp");
        }
    }
}

Login failure page 

<h1> error </h1>
<h2> No permission or wrong user name </h2>
<a href="/login.jsp"> Return to landing page </a>

filter 

public class SysFilter implements Filter {
    
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
    }
    @Override
    public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws IOException, ServletException {
    
        HttpServletRequest request = (HttpServletRequest) req;
        HttpServletResponse response = (HttpServletResponse) resp;
        if (request.getSession().getAttribute("user_session") == null) {
    
            response.sendRedirect("/error.jsp");
        }
        chain.doFilter(req,resp);
    }
    @Override
    public void destroy() {
    }
}
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