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JSP basic knowledge summary

2022-04-23 01:38:00 【Love you, Bai~】

JSP Learning notes

1. brief introduction

JSP：Java Server Page, yes Java Web Server side dynamic resources .

image-20220127095402847

2. Related configuration

file —> Set up —>（ Search for ） code —> Such as UTF-8

image-20220216164532434

3. notes

image-20220127101050119

display comments ： On the client side （ Web source code ） View comments for

Implicit annotation ： Not on the client （ Web source code ） View comments for

stay jsp Your own notes in <%----%>

The shortcut key is also 

Ctrl+/

4.Scriptlet

image-20220127102218484

  1. Defining local variables — Generated code in servlet Medium service In the method body of
  2. Declare global variables — Generated code in servlet In the method body of
  3. Output expression , You can output variables or literal values — Generated code in servlet In the class body of 
<%-- The first one is ：Java Script segment , Can write Java Code for , Defining local variables , Write statements, etc --%>
<%// Defining local variables 
    String str= "Hello jsp";
    // Output content to console 
    System.out.println(str);
    // Output content to browser 
    out.print(str);
    // Output global variables 
    out.write(" Global variables "+num);
%>
<%-- The second kind ： Statement , Declare global variables , Method , Class etc. --%>
<%!
int num =10;
%>
<%-- The third kind of ： Output expression , You can output variables or literal values --%>
<%=str%>

image-20220127144636507

5. A small problem —jsp in out.println Report errors

​

  • Should be Tomcat Related to File->Project Structure->modules->Dependencies

Pictured

image-20220216164653698

choice library Then click OK

image-20220216164702962

choice tomcat Then click add selected Click OK again

6.include Static contains

Before saying include , First to speak

1.JSP Instruction label

image-20220127150212844

2.include Static inclusion

image-20220127152248713

 Format ：<%@include file=" The page address to include "%>

eg：

Master file 

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title> Static inclusion </title>
</head>
<body>
   <%@include file="04-head.jsp"%>
    <h2> Main part </h2>
    <%@include file="04-foot.jsp"%>
</body>
</html>

04-head.jsp file 

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title> Head </title>
</head>
<body>
<h2> Head content </h2>
</body>
</html>

04-foot.jsp file 

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title> The tail </title>
</head>
<body>
<h2> Tail content </h2>
</body>
</html>

The final result ：

image-20220127152029106

characteristic ：

  1. Replace the content directly
  2. Static inclusion will only generate a source file , The end is all in ispservlet In method body （ In the source code file ）
  3. Variables with the same name cannot appear （ Because in the end, the documents are spliced together ）
  4. A little bit more efficient , The coupling degree is high , inflexible

3.include Dynamic inclusion 

 Format ： <jsp:include page=" To include the page path "></jsp:include>

Master file ：

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title> Dynamic inclusion </title>
</head>
<body>
<jsp:include page="04-head.jsp"></jsp:include>
    <h2> Subject matter </h2>
    <jsp:include page="04-foot.jsp"></jsp:include>
</body>
</html>

04-head.jsp file 

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title> Head </title>
</head>
<body>
<h2> Head content </h2>
</body>
</html>

04-foot.jsp file 

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title> The tail </title>
</head>
<body>
<h2> Tail content </h2>
</body>
</html>

The final result ：
image-20220127153412580

characteristic ：

  1. Dynamic inclusion is equivalent to a call in a method
  2. Dynamic inclusion will generate multiple source files
  3. You can define variables with the same name
  4. Efficient , Low coupling

Be careful ： When dynamic inclusion does not need to pass parameters ,include There should be nothing between the two labels , Including line breaks and spaces

eg：

image-20220127153817174

stay head Add the space bar after the file

Running effect ：

image-20220127153905045
reason ：

Because when you enter spaces or special symbols , At this time, the input content will be regarded as parameters

Use dynamic inclusion to pass parameters 

<%-- Dynamic inclusion 
     Format ：
         <jsp:include page=" To include the page path "></jsp:include>

<%-- Dynamically include pass parameters 
     <jsp:include page=" Page path to include ">
        <jsp:param name=" Parameter name " value=" Parameter values "/>
    </jsp:include>
     notes ：name Property does not support expression ,value Support expression 
     To obtain parameters ：
    requset.getParameter(name); Get the parameter value through the specified parameter name 
    --%>

The main function ：

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title> Dynamic inclusion </title>
</head>
<body>

    <jsp:include page="04-head.jsp"></jsp:include>
    <h2> Subject matter </h2>
    <%
        int a = 1;
    %>
    <jsp:include page="04-foot.jsp"></jsp:include>

    <%
        String str = "HEELO";
    %>
    <jsp:include page="04-foot.jsp">
        <jsp:param name="uname" value="admin"/>
        <jsp:param name="msg" value="<%=str%>"/>
    </jsp:include>
    </body>
</html>

04-foot.jsp file 

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title> The tail </title>
</head>
<body>
<h2> Tail content </h2>
<%
    int a = 10;
    // Get the parameters passed dynamically 
    String uname = request.getParameter("uname");
    String msg =request.getParameter("msg");
    out.print(uname+","+msg);
%>
</body>
</html>

04-head.jsp file 

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title> Head </title>
</head>
<body>
<h2> Head content </h2>
</body>
</html>

image-20220127162226981

7.JSP Four domain objects of

image-20220127162516743

The scope of attribute validation

image-20220127162615205

image-20220127162700268

JSP Four domain objects of 
  page Scope 
     Jump valid on the current page , Invalid after jump 
  request Scope 
     Valid in a request , Server side jump is valid , Invalid client jump 
  session Scope 
     Effective in a conversation , Server and client jumps are valid 
  qpplication Scope 
     The whole application works 

  JSP Server jump 
  1. Server jump 
  <jsp:forward page=" Jump to the page address "></jsp:forward>
  2. Server jump 
   Hyperlinks <a href=" Jump to the page address "> Jump </a>

( Hyperlink jump ) Master file ：

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>JSP Four domain objects of </title>
</head>
<body>
    <%
  // Set up page Domain object of scope 
  pageContext.setAttribute("name1"," Zhang San ");
  // Set up request object 
  request.setAttribute("name2"," Li Si ");
  // Set up session Scope object 
  session.setAttribute("name3"," Wang Wu ");
  // Set up application Domain object of scope 
  application.setAttribute("name4"," Zhao Liu ");
%>
        <a href="06-JSP Four domain objects of -02.jsp"> Jump </a>
</body>
</html>

06-JSP Four domain objects of -02.jsp file 

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>JSP Four domain objects of </title>
</head>
<body>
  // Get the value in the object 
  out.print("page Range :"+pageContext.getAttribute("name1")+"<br>");
  out.print("page Range :"+request.getAttribute("name2")+"<br>");
  out.print("page Range :"+session.getAttribute("name3")+"<br>");
  out.print("page Range :"+application.getAttribute("name4")+"<br>");

%>
</body>
</html>

Running results :

image-20220127193900686

image-20220127193907482

( Server jump ) Master file ：

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>JSP Four domain objects of </title>
</head>
<body>
    <%
  // Set up page Domain object of scope 
  pageContext.setAttribute("name1"," Zhang San ");
  // Set up request object 
  request.setAttribute("name2"," Li Si ");
  // Set up session Scope object 
  session.setAttribute("name3"," Wang Wu ");
  // Set up application Domain object of scope 
  application.setAttribute("name4"," Zhao Liu ");
%>

<jsp:forward page="06-JSP Four domain objects of -02.jsp"></jsp:forward>
</body>
</html>

06-JSP Four domain objects of -02.jsp file 

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>JSP Four domain objects of </title>
</head>
<body>
  // Get the value in the object 
  out.print("page Range :"+pageContext.getAttribute("name1")+"<br>");
  out.print("page Range :"+request.getAttribute("name2")+"<br>");
  out.print("page Range :"+session.getAttribute("name3")+"<br>");
  out.print("page Range :"+application.getAttribute("name4")+"<br>");

%>
</body>
</html>

Running results :

image-20220127194030010

8. Simple user login function

login.jsp：

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title> The user login </title>
</head>
<body>
    <form action="loginServlet" method="post">
         full name : <input type="text" name="uname"> <br>
         password : <input type="password" name="upwd"> <br>
        <button> Sign in </button>   <span style="color: red;font-size: 12px"><%=request.getAttribute("msg")%></span>
    </form>
</body>
</html>

index.jsp：

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
  <head>
    <title>$Title$</title>
  </head>
  <body>
    <h2> welcome <%=session.getAttribute("uname")%> Sign in </h2>
  </body>
</html>

LoginServlet.java

@WebServlet("/loginServlet")
public class LoginServlet extends HttpServlet {
    

    @Override
    protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
    
        // Set the encoding format of the client ( Prevent confusion code )
        req.setCharacterEncoding("UTF-8");
        // Accept the parameters passed by the client 
        String uname = req.getParameter("uname");
        String upwd = req.getParameter("upwd");
        // Judge whether the parameter is empty 
        if (uname == null ||"".equals(uname.trim())) {
    
            // Prompt user information 
            req.setAttribute("msg", " User name cannot be empty ");
            // Request forwarding to jump to login.jsp
            req.getRequestDispatcher("login.jsp").forward(req, resp);
            return;
        }
        if (upwd == null||"".equals(upwd.trim())) {
    
            // Prompt user information 
            req.setAttribute("msg", " User password cannot be empty ");
            // Request forwarding to jump to login.jsp
            req.getRequestDispatcher("login.jsp").forward(req, resp);
            return;
        }
        // Determine whether the account password is correct 
        if (!"admin".equals(uname)||!"admin".equals(upwd)) {
    
            // Prompt user information 
            req.setAttribute("msg", " Login failed ");
            // Request forwarding to jump to login.jsp
            req.getRequestDispatcher("login.jsp").forward(req, resp);
            return;
        }
        // Login successful 
        // Set login information to session
        req.getSession().setAttribute("uname",uname);
        // Jump to index.jsp
        resp.sendRedirect("index.jsp");
    }
}

9.EL expression

eg：

<span style="color: red;font-size: 12px"><%=request.getAttribute("msg")%></span>

adopt EL expression , You can put what is displayed on the page in a simple user function null Change to an empty string 

<span style="color: red;font-size: 12px">${msg}</span>

1. The syntax of the expression image-20220128000421009

When getting the specified domain object 

${ The name of the object . Data name }

2. Use of expressions - get data

1. obtain list

 obtain list
     obtain list Of size ${list.size()}
     obtain list The specified subscript ：${list[ Subscript ]}
     notes ：list Represents the domain limited variable name

2. obtain Map

 obtain Map
     obtain Map Specified in the key Of value
    ${map.key}
     perhaps 
    ${map["key"]}
     notes ：Map Represents the domain limited variable name

eg：

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title> Use of expressions </title>
</head>
<body>
<%
    //list
    List<String> list = new ArrayList<>();
    list.add("aaa");
    list.add("bbb");
    list.add("ccc");
    request.setAttribute("list",list);
    //Map
    Map map = new HashMap();
    map.put("aaa","111");
    map.put("bbb","222");
    map.put("ccc","333");
    request.setAttribute("map",map);
%>
<h4> obtain list</h4>
 obtain list Of size：${
    list.size()}<br>
 obtain list The specified subscript ：${
    list[1]}<br>
<h4> obtain Map</h4>
 obtain list Of size：${
    map.aaa}<br>
 obtain list The specified subscript ：${
    map["bbb"]}<br>

</body>
</html>

image-20220128003924943

3.JavaBean

image-20220128003652768

4.empty

image-20220128003952388

1. character string

The domain object is a string

​ Nonexistent domain object ：ture

​ An empty string ：ture

​ null：ture

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title> Use of expressions </title>
</head>
<body>
<%
    request.setAttribute("str1","abc");
    request.setAttribute("str2","");
    request.setAttribute("str3",null);
%>
${empty str}<br>
${empty str1}<br>
${empty str2}<br>
${empty str3}<br>
</body>
</html>

image-20220128014025349

2.List

No length —true

null-true

<%@ page import="java.util.List" %>
<%@ page import="java.util.ArrayList" %><%--
  Created by IntelliJ IDEA. User: lenovo
  Date: 2022/1/28
  Time: 1:36
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title> Use of expressions </title>
</head>
<body>

<%
    List list1 =new ArrayList<>();
    List list2 = null;
    List list3 = new ArrayList<>();
    list3.add(1);
    request.setAttribute("list1",list1);
    request.setAttribute("list2",list2);
    request.setAttribute("list3",list3);
%>
${
    empty list1}<br>
${
    empty list2}<br>
${
    empty list3}<br>
</body>
</html>

image-20220128015250245

3.Map

null：true

empty map object ：true

<%@ page import="java.util.Map" %>
<%@ page import="java.util.HashMap" %><%--
  Created by IntelliJ IDEA.
  User: lenovo
  Date: 2022/1/28
  Time: 1:36
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title> Use of expressions </title>
</head>
<body>

<%
    Map map1 = null;
    Map map2 = new HashMap<>();
    Map map3 = new HashMap<>();
    map3.put(1,2);
    request.setAttribute("map1",map1);
    request.setAttribute("map2",map2);
    request.setAttribute("map3",map3);
%>
${empty map1}<br>
${empty map2}<br>
${empty map3}<br>

</body>
</html>

image-20220128015905919

4.JavaBean

null：true

An empty object ：false

image-20220128020204032

image-20220128020235373

image-20220128020305951

3.EL operation

image-20220128020447954

image-20220128020641249

JSTL Study

1. Use of labels

image-20220128021250000

image-20220128021452441

    JSTL Use 
    1. download JSTL The required jar package 
    （standard.jar and jstl.jar）
    2. In the project web In the catalog WEB-INF New China lib Catalog , take jar Copy it in 
    3. choice “ file ”————> Project structure ————> modular ————> rely on ————>“+”————> The corresponding lib Import the directory 

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<html>
<head>
    <title>11</title>
<%--    JSTL Use 
    1. download JSTL The required jar package 
    （standard.jar and jstl.jar）
    2. In the project web In the catalog WEB-INF New China lib Catalog , take jar Copy it in 
    3. choice “ file ”————> Project structure ————> modular ————> rely on ————>“+”————> The corresponding lib Import the directory 
--%>
</head>
<body>
<c:if test="${1==1}">
    Hello JSTL
</c:if>
</body>
</html>

image-20220128101843633

2.if label

image-20220128101913859

 Format :
    <c:if test="${num > 100}" var="String" scope="String">
    ...
    </c:if>

notes ：

  1. Label operations are generally domain objects
  2. if The label doesn't have else, If you want to else The effect of , You need to set two completely opposite conditions

3. Condition label

choose,when and otherwise label

image-20220128103737388

Grammar format

image-20220128103756950

attribute

  1. choose Tags have no properties
  2. when There is only one tag test attribute , Must attribute
  3. otherwise The label must be set in the last when After tag

Be careful ：

  1. choose Labels and otherwise Tags have no properties , and when The label must have a test attribute
  2. choose The tag must contain at least one when label , There can be no otherwise label
  3. otherwise The label must be set at the last when After tag

image-20220128103415652

4. Laminated label

Grammar format

image-20220128104941729

attribute

image-20220128104958665

image-20220128105016000

eg:

( Traverse the subject content multiple times )

image-20220128105053045

as follows

image-20220128105111238

（ loop ）

image-20220128105128665

as follows

image-20220128105428826

image-20220128105525405

版权声明
本文为[Love you, Bai~]所创，转载请带上原文链接，感谢
https://yzsam.com/2022/04/202204230137132882.html

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