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JSP built-in object (implicit object)

2022-07-26 07:58:00 【Super Qi】

jsp Implicit objects

1. Definition ：

It refers to that it can be used in... Without declaration and creation jsp The object used directly by the page script

2. characteristic ：

a. jsp Implicit objects cannot pass new Go to get the instance , It's directly in the java Objects used in scripts

b. jsp Use java Define an implicit object to access the dynamic content of the web page

c. The name of the implicit object is jsp Reserved words

3. effect ：

These objects make it easier for users to send requested information to mobile clients , And respond to client requests and store customer information , Greatly simplified jsp The complexity of development

4. classification

page 、 request、 response、 session、 application、out、config、pageContext、exception

5. By function

a. Input / Output object

request
response
out

b. Scope object

session
application
page
request

c. Servlet object

pageContent
config

d. Error object

exception

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6. Important method ( When forwarding web pages )

a. Set properties ：

public void setAttribute(String name, Object o){
    }

b. Get attributes ：

public java.lang.Object getAttribute(String name)

example ：

<body>
    <%
    	request.setAttribute("username"," Zhang San ");
    	request.setAttribute("password","123456")
    %>
     user name ：<%=request.getAttribute("username")%><br>
     password ：<%=request.getAttribute("password")%>
</body>

7. Save scope of implicit object

a. page Range ： Only related to the current page

b. request Range ： Only related to pages between the same request , This object will be deleted automatically after the request

c. session Range ： Session scope allows objects to be created and bound to a session , Objects bound to the session scope are deleted when they are not needed

d. application Range ： If the object is non session related , Then define it in the scope of application .* It is mainly used for different sessions to share data

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