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JSP built-in object (implicit object) -- input / output object

2022-07-26 07:58:00 【Super Qi】

jsp Implicit objects —— Input / Output object

1. effect

It mainly controls page output and input , Access information related to all requests and responses

2. request object

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a. effect

Saved the information submitted by the user , The information submitted by the user can be obtained by calling the corresponding method of the object

b. Common methods

1.String     getParameter(String name);
2.String     getParameterValues(String name);
3.Enumeration  getParameterNames();
4.setAttribute(String name,Object o);
5.Object getAttribute(String name);
6.Session  getSession(String name);
7.removeAttribute(String name);
8.setCharacterEncoding // Set the encoding of the request data , Only applicable to post Method 
9.getRequestDispatcher(String path);

c. Access request parameters

Get information submitted by the client ,request Object represents the request from the client

1. String getParameter("XX");  // obtain name Parameter values for 
2. String[] getParameterValues("XX");  // obtain name All parameter values 
3. String[] getParameterNames();   // Get all parameter names

example ：getParameter(“XX”) The return type is String

/***requestInfo.jsp***/
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title> Input data interface </title>
</head>
<body>
<form action="requestInfo_deal.jsp">
     user name ：<input type="text" name="username"><br>
     The secret &nbsp;&nbsp;&nbsp; code ：<input type="password" name="password"><br>
    <input type="submit" value=" Submit ">
    <input type="submit" value=" Cancel ">
</form>
</body>
</html>
/***requestInfo_deal.jsp***/
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title> Processing data pages </title>
</head>
<body>
<h1> What you just entered is ：</h1>
<%
    String name = request.getParameter("username");
    String password = request.getParameter("password");
    out.println(" full name ： Parameter name ："+name);
    out.println(" password ： Parameter name ："+password);
%>
</body>
</html>

example ：getParameterValues(“XX”) The return type is String[]

/***requestProduct.jsp***/
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>

<h1> Your hobby is ：</h1>
<form action="requestDeal.jsp" method="post">
    <input type="checkbox" name="chekBox" value="Basketball"> To play basketball 
    <input type="checkbox" name="chekBox" value="Football"> play football 
    <input type="checkbox" name="chekBox" value="Code"> Write code 
    <input type="checkbox" name="chekBox" value="Games"> Play the game 
    <br>
    <input type="submit" value=" Submit ">
    <input type="reset" value=" eliminate ">
</form>
</body>
</html>
/***requestDeal.jsp***/
<%@ page contentType="text/html;charset=UTF-8" language="java" pageEncoding="UTF-8" %>
<html>
<head>
    <title> Data processing </title>
</head>
<body>
<%
    request.setCharacterEncoding("UTF-8");
    String[] chekBoxes = request.getParameterValues("chekBox");
    out.print(" What are your hobbies ：");
    if (chekBoxes!=null){
        for (int i = 0;i<chekBoxes.length;i++){
            if (chekBoxes[i].equals("Basketball")){
                out.print(" To play basketball ");
            }
            if (chekBoxes[i].equals("Football")){
                out.print(" play football ");
            }
            if (chekBoxes[i].equals("Code")){
                out.print(" Write code ");
            }
            if (chekBoxes[i].equals("Games")){
                out.print(" Play the game ");
            }
        }
    }
%>
</body>
</html>

example ：getParameterNames() The return type is enumeration type Enumeration

/***requestInfo.jsp***/
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title> Input data interface </title>
</head>
<body>
<form action="requestDemo2.jsp">
     user name ：<input type="text" name="username"><br>
     The secret &nbsp;&nbsp;&nbsp; code ：<input type="password" name="password"><br>
    <input type="submit" value=" Submit ">
    <input type="submit" value=" Cancel ">
</form>
</body>
</html>
/***requestDemo2.jsp***/
<%
    Enumeration enumeration = request.getParameterNames();// Get yes name Parametric value
    while (enumeration.hasMoreElements()){   //enumeration.hasMoreElements() obtain Enumeration Number of parameters in 
        String pName = (String)enumeration.nextElement();
        String pValue = request.getParameter(pName);
        out.print(" Parameter name "+ pName+"<br>");
        out.print(" Parameter contents "+ pValue+"<br>");
    }
%>
</body>
</html>

* If there is Chinese garbled code on the page , stay request.getParameter() prefix request.setCharacterEncoding(“UTF-8”);

d. Manage properties in scope

When forwarding , The data that needs to be forwarded will be brought to the forwarding page for processing , use

request.setAttribute("key",Object);//key Key for value transmission , Used to get parameter values , by String type .Object It needs to be saved to  request Inside

Get this data on the forwarding page with

request.getAttribute("key");

example ：

<body>
    <%
    	request.setAttribute("username"," Zhang San ");
    	request.setAttribute("hobby"," To play basketball ");
    %>
    <%
    	 user name ：<%=request.getAttribute("username"); %>
         hobby ：<%=request.getAttribute("hobby"); %>
    %>
</body>

e. getParameter() And getAttribute() The difference between

getParameter The return value is String, Get the value in the form submitted by the client
getAttribute The return value is of any data type , Get the data set by the server

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f. obtain Cookie

1. cookie The definition of

Cookie It's a small piece of text message , With user requests and pages Web Transmission between server and browser . You can save the user's login information

2. cookie obtain

Cookie[] cookie = request.getCookies();

g. Methods of obtaining customer information

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3. response object

a. Definition ：

response Object processing jsp Generate a response and send it to the client . After the transaction is processed response The object will be destroyed

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b. Common methods

1. flushBuffer();  // Force all contents of the current buffer to be sent to the client 
2. getBufferSize(); // Get the actual buffer size 
3. getCharacterEncoding(); // Gets the character encoding format of the response 
4. setCharacterEncoding(); // Set the character encoding format of the response 
5. getContentType();  // Get the content of the response MIME type 
6. setContentType();  // Set the content of the response MIME type 
7. getOutputStream();  // Get the client's input stream 
8. sendError();  // Send error message to client 
9. setContentLength(); // Set the length of the response content （ Number of bytes ）

c. response Redirect pages

1. effect

Redirect client requests to a different page

response.sendRedirect(login.jsp?param=aaa&...);

2.response.sendRedirect() And jsp:forward The difference between

a. response.sendRedirect()： Jump on the client , The browser will redirect according to url Initiate request .request and response Will regenerate

b. jsp:forward： Jump on the server , browser url unchanged ,request Cannot regenerate , So it can be used request To pass parameters

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c. example

/***sendRedirect.jsp***/
<body>
    <form mothod="post">
         enter one user name ：
        <input type="text" name="name"/>
        <input type="submit" value="login"/>
    </form>
    <%
    	String name = request.getParameter("name");
    	if(name!=null){
            request.sendRedirect("redirect.jsp?sendname="+name);
            //?sendname= It is to pass values to the page after resetting 
            out.print(" Reset backward statement ！");// Used to distinguish jsp:forward
        }
    %>
</body>
/***redirect.jsp***/
<body>
    <%
    	String sendname = request.getParameter("sendname"); // Receive the value transmitted by redirection 
    %>
     user name ：<%=sendname %>
</body>

d. Set up HTTP Respond to the headlines

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example ：

<%@ page contentType="text/html;charset=gb2312"%> 
<body>
    <%@include file="work.html"%>
    <%	
    	String str1 = request.getParameter("word");
     	String str2 = request.getParameter("excel");
    	if(str1!=null && str1.equals("word")){
            response.setContentType("application/msword;charset=gb2312");
        }
    
    	if(str2!=null && str2.equals("excel")){
            response.setContentType("application/x-msexcel;charset=gb2312");
        }
    %>
</body>

<html>
    <head>
        <title>response.setContentType Example </title>
    </head>
    <body>
        <p>
             What kind of document is the current page saved as 
        </p>
        <form method="get" name="form">
            <input type="submit" value="word" name="word"/>
            <input type="submit" value="excel" name="excel"/>
        </form>
    </body>
</html>

response.setHeader("refresh","time","url");//refresh For refresh ,time Time for refresh .url Jump to the page after refreshing

e. Set the status display code

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f. Save client information

1.  Method ： addCookie(Cookie cookie);

2.  obtain ：request.getCookie() obtain 
3.  effect ： Save user's personalized information , Provide convenience for the next visit