I. Data transfer between JS and JSP

.jsp gets the js value

Because JSPS are essentially servlets, they run in a server. So you can’t get the js value directly. The client variable needs to be submitted to the server, which then receives it.

In a JSP page: (1) Set the form, or node, in a JSP (hide/not hide)

   <form id="jsp_form" action="#" method="post">
             <input id="jspEle" type="hidden name="jspEle">
    </form>
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(2) In js code, submit the form

<script> function setElevalue(){ var tmp = "jsEle"; document.getElementById("jspEle").value = tmp; } function submit(){var jsp_form = document.getelementById ("jsp_form"); // Get the form jsp_form.submit(); // Submit the form} </script>Copy the code

(3) After the form is submitted, set the value in JSP. At this point you get the value of the variable in JS

The < %String jsP_js = request.getParameter("jspEle"); // jspEle is the hidden control name% >Copy the code

(2).js gets the value of JSP

You can use variables in the server, such as Request.

<%
	 int num = 5;
	 request.setAttribute("num", num); % >var num =  <% = request.getAttribute("num") % >; //5 num = ${requestScope.num}; / / 5Copy the code

Two. Data transfer between JSP and servlet

(1) JSP data into the servlet

1. Method 1: Asynchronous request Using Ajax, send asynchronous requests and send data to servlets. (For asynchronous requests, you can also write parameters in the URL.)

$.post("ajaxServlet", {username:"jack"},function(data){
	 alert(data);
 },"text"); // If type is not set, it is intelligent by default
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When submitting a form, you can serialize the form. Example: Submit a login form

$("#login_form").submit(function () {
	// Send an asynchronous request
	$.post("userServlet", $(this).serialize(), function (data){})})Copy the code

2. Method 2: Directly submit the form and set the action for the form

<form id="regist_form" method="post" action="userServlet" >
	<input id="rname"  type="text" name="uname" placeholder="Username" ">
    <input id="rpassword"  type="password" name="password" placeholder="Password" />
    <input id="rsubmit" type="submit" value="Registered"/>                                
</form>
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(2) Servlet data into JSP

1. Method 1: Store variables in a domain, such as session and cookie.

	request.getSession.setAttribute("user",user);
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You can also save a request and then forward it to access a JSP

request.getServletContext().getRequestDispatcher("/index.jsp").forward(request, response);
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Method 2: Return data in an asynchronous request Note: The returned data type must be the same as that preset for an asynchronous request. Return JSON data:

	ObjectMapper mapper = new ObjectMapper();
    String json = mapper.writeValueAsString(user);
    response.setContentType("application/json; charset=utf-8");
    response.getWriter().write(json);
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(three) JSP processing servlet incoming data

1. You can directly obtain the values stored in the Request session

	User user = (User)request.getAttribute("user");
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2. The data returned in the asynchronous request can be obtained directly from the returned data data. For jSON-type data, use the method of getting JSON data.

(4) Servlet processing JSP incoming data

1. Parameters passed in the asynchronous request

	String id = request.getParameter("id");
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For an asynchronous request to submit a form: Use the BeanUtils utility class to encapsulate it in an object (note: the name of the form must be the same as the variable name in the object)

    // Get parameters
    Map<String, String[]> map = request.getParameterMap();
    // Encapsulate parameters
    User registUser = new User();
    try {
    	BeanUtils.populate(registUser, map);
    } catch (IllegalAccessException e) {
        e.printStackTrace();
    } catch (InvocationTargetException e) {
         e.printStackTrace();
   }
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2. Parameters set in the URL

	String params = request.getQueryString();
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Add: The problem of garbled Chinese characters when receiving data can be solved by using this statement: (usually the user input data in the page)

String title = request.getParameter("title");
title = new String(title.getBytes("iso-8859-1"),"utf-8");// Of course utF-8 can be changed to GBK, Unicode
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Data transfer between JSP and JSP

You can use location.href to jump from JSP to JSP. Pass parameters in the URL. Ex. :

	location.href = "index.jsp? id="+ 1 +"";
	/ / in the index. The JSP
	var id = ${param.id};
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Data transfer between HTML and servlet

(1) HTML data is passed into the servlet

1. Approach 1: Use the href format of the A tag: through the hyperlink? + The name of the attribute to be passed = the value of the attribute. Multiple attributes need to be concatenated with &

	<a href="userServlet? username=jack&password=123"></a>
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2. Method 2: Use Ajax (JSP and Servlet data interaction section explained)