Analysis of session objects and method instances in java

The session object is used to record the access status of each client within the session scope, so as to track the operation status of each client. The information stored in the session can obtain the valid data of these sessions when the browser makes subsequent requests. .

You can use the session object (the built-in object of jsp) directly in the jsp page, or you can get back the session object through pageContext.getSession() or request.getSession.

session can save user information and implement functions such as shopping carts.

HTTP protocol is a stateless protocol. The client sends a request to the server, and then the server returns a response. The connection is closed. The server does not save the relevant information about the connection, so during the next connection, The server no longer has previous connection information and cannot determine that this connection has the same client information as the previous connection. Therefore, a session must be used to record information about the connection.

From the moment the client opens the browser to connect to the server to the moment the client closes the browser and leaves the server, it is called a session. When a client accesses the server, he or she may repeatedly connect to several pages on the server, repeatedly refresh a page, or continuously submit information to a page, etc. The server should know that this is the same client through some method, and then a session is needed. object.

The working principle of session is as follows:

1. When a customer accesses a page on the server for the first time, the server will allocate a session object to the user and specify a unique ID for the session, and Send the ID to the client and write it into the cookie, so that the client and the server's session establish a one-to-one correspondence;

2. When the client continues to access other resources on the server, the server no longer A new session object is allocated to the client until the client browser is closed, times out, or the invalidate() method of the session is called to invalidate it, and the session between the client and the server ends.

3. When the customer reopens the browser to access the website, the server will reassign a session object to the customer and reassign the sessionID.

session object is mainly used for attribute operations and session management. Commonly used methods are as follows:

1, public void setAttribute(String name,String value)Set the specified name The value of the attribute and adds it to the session scope. If this attribute exists within the session scope, changes the value of the attribute.

2, public Object getAttribute(String name)Get the value of the attribute with the specified name in the session scope. The return value type is object. If the attribute does not exist, null is returned.

3. public void removeAttribute(String name), delete the session attribute with the specified name. If the attribute does not exist, an exception will occur.

4, public void invalidate(), invalidate the session. The current session can be invalidated immediately, and all objects stored in the original session can no longer be accessed.

5, public String getId( ), get the current session ID. Each session has a unique identifier sessionID on the server side. The only data sent by the session object to the browser is the sessionID, which is generally stored in a cookie.

6, public void setMaxInactiveInterval(int interval) Set the maximum duration of the session in seconds. A negative number indicates that the session will never expire.

7, public int getMaxInActiveInterval(), Get the maximum duration of the session.

8. Use the getCreationTime() and getLastAccessedTime() methods of the session object to obtain the session creation time and last access time, but the return value is milliseconds. Generally, you need to use the following conversion to obtain the specific date and time. time.

Date creationTime = new Date(session.getCreationTime());
Date accessedTime = new Date(session.getLastAccessedTime());

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    会话ID： <br>
    是否新会话：<br>
    设置和获取属性对象：用户名 =
    
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     会话创建时间：<br>
     上次访问时间：<br>
     会话持续时间（s）：<br>
     
     修改后的会话持续时间（s）：<br>
     
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Several commonly used methods to obtain session

1.spring mvc

HttpServletRequest request = ((ServletRequestAttributes) RequestContextHolder.getRequestAttributes()).getRequest();

2.struts2

(1)

ActionContext context = ActionContext.getContext(); 
Map request = (Map) context.get("request"); 
Map session = context.getSession(); 
Map application = context.getApplication();

(2)

ActionContext actionContext = ActionContext.getContext(); 
HttpServletRequest request = (HttpServletRequest) actionContext
.get(ServletActionContext.HTTP_REQUEST); 
HttpSession session = request.getSession(); 
ServletContext context = (ServletContext) actionContext 
 .get(ServletActionContext.SERVLET_CONTEXT);

3. Obtain

HttpServletRequest request = ServletActionContext.getRequest(); 
HttpSession session = request.getSession();

through ServletActionContext

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