The difference between , requestDispatcher and sendRedirect()_html/css_WEB-ITnose

1. Session information is stored in the server memory and can be accessed intermittently. Compared with cookies, it is stored on the server.
2. A man is like Bluetooth: he will only find you when you are close. After you left, he went to find other "devices". A woman is like Wi-Fi: she sees all the "devices" around her, but only chooses the stronger ones to "connect" to.
3. Session closure: browser close, active shutdown, session timeout
4. Session underlying implementation: cookie and url rewriting (the session ID is saved, which is to call response.encodeURL, then the id is automatically added)
5.session has the creation time and last access time, which is different from cookie (you have to write it yourself), but it returns the number of milliseconds, then new Date (method)
6.javabean class must be public, Otherwise it will not be accessible! ! ! Be sure to use public declaration
7.BeanUtils mainly provides various operations for JavaBean.
8.forward is server forwarding, inside the servlet, and sendRedirect is redirection (through the browser).

Forward forwarding is the forwarding between the same web application implemented inside the container, so the forward method can only redirect to a resource in the same web application. After redirection, the browser address bar URL remains unchanged. , and the sendRedirect method can redirect to any URL, because this method is implemented by modifying the http header, there are no restrictions on the URL, and the browser address bar URL changes after redirection. forward redirection passes the original HTTP request object (request) from one servlet instance to another instance, and the two are not the same application using sendRedirect. Based on the second point, the parameters are passed in different ways. The forward form parameter is passed along, so the parameters of the HTTP request can be obtained in the second instance. sendRedirect can only pass parameters through the link, response.sendRedirect("login.jsp?param1=a"). The process of using forward redirection is that the browser first sends a Request request to the destination Servlet, and then the Servlet on the server side sends the request to the destination URL, and then the server-side Servlet returns the Response to the browser side. The browser and server request and respond once (3 operations). In the process of forwarding using sendRedirect, the browser first sends a request to the destination Servlet. The Servlet sees sendRedirect and returns the destination URL to the browser. The browser then requests the destination URL, and the destination URL returns the response to the browser. The browser and server request and respond twice (four operations). You can see which way is slightly faster. Request and Response are shared between the caller and the callee of the forward method. The sendRedirect method has two Request and Response due to two browser server requests. If you use request.setAttribute to pass some attributes, you need to use forward. If you want to jump to the resources of another application, you need to use sendRedirect. Neither the forward method nor the sendRedirect method is called before a PrintWriter can be output to the client.
The forward method reports an error: java.lang.IllegalStateException: Cannot forward after response has been committed
sendRedirect reports an error: java.lang.IllegalStateException
at org.apache.catalina.connector.ResponseFacade.sendRedirect(ResponseFacade.java :435)

Let’s look at a specific example! ! ! Reference: http://zhaoyuqiang.blog.51cto.com/6328846/1132795