I have a question.
I'm planing to serve two version of web service. And I want to make process below
There is two version of web service, like A and B.
If a user first access to A, I serve the service A whenever the user request.
To do above I'll store a version, that user can access, in user database.
The issue I have to solve is that if the server response with a certain version, like A, the client request with the version after received the version from server. For example,
user send first request
server set the version for the user and store it in data base
server response with the version in response header
user send another request with the version that server send in header
the user always send a request with the version after once the server response with the version
It looks like confusing, but the process is like cookie (if the server set the cookie in response once, the client always send the cookie to server for every request).
Is there any way to do it using HTTP header ?
It is possible to do the versioning using custom accept headers like the following:
Accept-version: v1
Accept-version: v2
It is also possible to use custom vendor type responses if required according to RFC6838
We know the difference between POST and GET, but why should a client state the method type when issuing http requests? Why should it make a difference for the server? in the end, it is the server job to deal with those requests according to their URL and Content. either by redirecting, blocking or accepting and using data (existing in the URL or request body).
An endpoint can accept both GET and POST requests (along with PUT, PATCH and DELETE). If the client does not explicitly state what type of request they are sending, the server will interpret it as a GET request (the default).
Consider the following PHP example, sitting on https://api.example.com/resources/:
<?php
if ($_POST["request"]) {
// Create new resource
}
else if ($_GET["request"]) {
// List existing resources
}
In both instances, the request parameter is sent to the same page, and different logic is run based on what the method is. But considering the same data is sent to the same page in both instances, the server wouldn't know which one of the two conditions to step into if the client doesn't explicitly specify the method.
In RESTful programming, both the client and server have been programmed to understand the request, but the client has no knowledge of the server itself. It is up to the server to process the request, based off of what the client asks it to do. And the client asks it to do different things by specifying the method.
I am current Apache Tomcat user designing an Akka HTTP based replacement for a HTTPS web service that uses client certificates for authentication and authorization. Using Tomcat I am accustomed to retrieving the client X509Certificate with a servlet request attribute
request.getAttribute("javax.servlet.request.X509Certificate")
I need the certificate for some additional authorization checks inside the handler for select routes. How would retrieve the client certificate in this way with Akka HTTP 10.0.x?
You need to enable decorating requests with TLS session info through the config settings for the server:
akka.http.server.parsing.tls-session-info-header = on
And then extract the info for a specific request using the synthetic header akka.http.scaladsl.model.headers.Tls-Session-Info like so:
headerValueByType[`Tls-Session-Info`]() { sessionInfo =>
val sslSession = sessionInfo.getSession()
sslSession.getPeerCertificates
... etc ...
What is the conceptual difference between forward() and sendRedirect()?
In the web development world, the term "redirect" is the act of sending the client an empty HTTP response with just a Location header containing the new URL to which the client has to send a brand new GET request. So basically:
Client sends a HTTP request to some.jsp.
Server sends a HTTP response back with Location: other.jsp header
Client sends a HTTP request to other.jsp (this get reflected in browser address bar!)
Server sends a HTTP response back with content of other.jsp.
You can track it with the web browser's builtin/addon developer toolset. Press F12 in Chrome/IE9/Firebug and check the "Network" section to see it.
Exactly the above is achieved by sendRedirect("other.jsp"). The RequestDispatcher#forward() doesn't send a redirect. Instead, it uses the content of the target page as HTTP response.
Client sends a HTTP request to some.jsp.
Server sends a HTTP response back with content of other.jsp.
However, as the original HTTP request was to some.jsp, the URL in browser address bar remains unchanged. Also, any request attributes set in the controller behind some.jsp will be available in other.jsp. This does not happen during a redirect because you're basically forcing the client to create a new HTTP request on other.jsp, hereby throwing away the original request on some.jsp including all of its attribtues.
The RequestDispatcher is extremely useful in the MVC paradigm and/or when you want to hide JSP's from direct access. You can put JSP's in the /WEB-INF folder and use a Servlet which controls, preprocesses and postprocesses the requests. The JSPs in the /WEB-INF folder are not directly accessible by URL, but the Servlet can access them using RequestDispatcher#forward().
You can for example have a JSP file in /WEB-INF/login.jsp and a LoginServlet which is mapped on an url-pattern of /login. When you invoke http://example.com/context/login, then the servlet's doGet() will be invoked. You can do any preprocessing stuff in there and finally forward the request like:
request.getRequestDispatcher("/WEB-INF/login.jsp").forward(request, response);
When you submit a form, you normally want to use POST:
<form action="login" method="post">
This way the servlet's doPost() will be invoked and you can do any postprocessing stuff in there (e.g. validation, business logic, login the user, etc).
If there are any errors, then you normally want to forward the request back to the same page and display the errors there next to the input fields and so on. You can use the RequestDispatcher for this.
If a POST is successful, you normally want to redirect the request, so that the request won't be resubmitted when the user refreshes the request (e.g. pressing F5 or navigating back in history).
User user = userDAO.find(username, password);
if (user != null) {
request.getSession().setAttribute("user", user); // Login user.
response.sendRedirect("home"); // Redirects to http://example.com/context/home after succesful login.
} else {
request.setAttribute("error", "Unknown login, please try again."); // Set error.
request.getRequestDispatcher("/WEB-INF/login.jsp").forward(request, response); // Forward to same page so that you can display error.
}
A redirect thus instructs the client to fire a new GET request on the given URL. Refreshing the request would then only refresh the redirected request and not the initial request. This will avoid "double submits" and confusion and bad user experiences. This is also called the POST-Redirect-GET pattern.
See also:
How do servlets work? Instantiation, sessions, shared variables and multithreading
doGet and doPost in Servlets
How perform validation and display error message in same form in JSP?
HttpServletResponse sendRedirect permanent
requestDispatcher - forward() method
When we use the forward method, the request is transferred to another resource within the same server for further processing.
In the case of forward, the web container handles all processing internally and the client or browser is not involved.
When forward is called on the requestDispatcherobject, we pass the request and response objects, so our old request object is present on the new resource which is going to process our request.
Visually, we are not able to see the forwarded address, it is transparent.
Using the forward() method is faster than sendRedirect.
When we redirect using forward, and we want to use the same data in a new resource, we can use request.setAttribute() as we have a request object available.
SendRedirect
In case of sendRedirect, the request is transferred to another resource, to a different domain, or to a
different server for further processing.
When you use sendRedirect, the container transfers the request to the client or browser, so the URL given inside the sendRedirect method is visible as a new request to the client.
In case of sendRedirect call, the old request and response objects are lost because it’s treated as new request by the browser.
In the address bar, we are able to see the new redirected address. It’s not transparent.
sendRedirect is slower because one extra round trip is required, because a completely new request is created and the old request object is lost. Two browser request are required.
But in sendRedirect, if we want to use the same data for a new resource we have to store the data in session or pass along with the URL.
Which one is good?
Its depends upon the scenario for which method is more useful.
If you want control is transfer to new server or context, and it is treated as completely new task, then we go for sendRedirect.
Generally, a forward should be used if the operation can be safely repeated upon a browser reload of the web page and will not affect the result.
Source
The RequestDispatcher interface allows you to do a server side forward/include whereas sendRedirect() does a client side redirect. In a client side redirect, the server will send back an HTTP status code of 302 (temporary redirect) which causes the web browser to issue a brand new HTTP GET request for the content at the redirected location. In contrast, when using the RequestDispatcher interface, the include/forward to the new resource is handled entirely on the server side.
The main important difference between the forward() and sendRedirect() method is that in case of forward(), redirect happens
at server end and not visible to client, but in case of
sendRedirect(), redirection happens at client end and it's visible to
client.
Either of these methods may be "better", i.e. more suitable, depending on what you want to do.
A server-side redirect is faster insofar as you get the data from a different page without making a round trip to the browser. But the URL seen in the browser is still the original address, so you're creating a little inconsistency there.
A client-side redirect is more versatile insofar as it can send you to a completely different server, or change the protocol (e.g. from HTTP to HTTPS), or both. And the browser is aware of the new URL. But it takes an extra back-and-forth between server and client.
SendRedirect() will search the content between the servers. it is slow because it has to intimate the browser by sending the URL of the content. then browser will create a new request for the content within the same server or in another one.
RquestDispatcher is for searching the content within the server i think. its the server side process and it is faster compare to the SendRedirect() method. but the thing is that it will not intimate the browser in which server it is searching the required date or content, neither it will not ask the browser to change the URL in URL tab. so it causes little inconvenience to the user.
Technically redirect should be used either if we need to transfer control to different domain or to achieve separation of task.
For example in the payment application
we do the PaymentProcess first and then redirect to displayPaymentInfo. If the client refreshes the browser only the displayPaymentInfo will be done again and PaymentProcess will not be repeated. But if we use forward in this scenario, both PaymentProcess and displayPaymentInfo will be re-executed sequentially, which may result in incosistent data.
For other scenarios, forward is efficient to use since as it is faster than sendRedirect
Request Dispatcher is an Interface which is used to dispatch the request or response from web resource to the another web resource. It contains mainly two methods.
request.forward(req,res): This method is used forward the request from one web resource to another resource. i.e from one servlet to another servlet or from one web application to another web appliacation.
response.include(req,res): This method is used include the response of one servlet to another servlet
NOTE: BY using Request Dispatcher we can forward or include the request or responses with in the same server.
request.sendRedirect(): BY using this we can forward or include the request or responses across the different servers. In this the client gets a intimation while redirecting the page but in the above process the client will not get intimation
Simply difference between Forward(ServletRequest request, ServletResponse response) and sendRedirect(String url) is
forward():
The forward() method is executed in the server side.
The request is transfer to other resource within same server.
It does not depend on the client’s request protocol since the forward () method is provided by the servlet container.
The request is shared by the target resource.
Only one call is consumed in this method.
It can be used within server.
We cannot see forwarded message, it is transparent.
The forward() method is faster than sendRedirect() method.
It is declared in RequestDispatcher interface.
sendRedirect():
The sendRedirect() method is executed in the client side.
The request is transfer to other resource to different server.
The sendRedirect() method is provided under HTTP so it can be used only with HTTP clients.
New request is created for the destination resource.
Two request and response calls are consumed.
It can be used within and outside the server.
We can see redirected address, it is not transparent.
The sendRedirect() method is slower because when new request is created old request object is lost.
It is declared in HttpServletResponse.
I am new to servelts programming. and Just today, I started learning it. and I am a little bit confused concerning
HttpServletRequest. it is written in a tutorial that, the class doGET() has some methods such as form "query" data, HTTP request headers, and the client’s hostname.
As far as I understood, the HttpServletRequest is something like a protocol allows the SERVER to
receive a request from the CLIENT side. My question is, Why the CLIENT side is interesting in
knowing something like the client’s host-name or HTTP request headers.
If you found the question is silly please do not vote my question down, because I do not want to lose this account with stack overflow.
First of all HttpServletRequest is an interface implemented by your Servlet Container.
HttpServlet is a convenience class which your Servlet can extend from and get hold of all the HTTP specific methods. doGet() is one such method to process the GET requests.
HttpServletRequest is something like a protocol allows the SERVER to receive a request from the CLIENT side
HTTP is a request-response protocol. Your container forms a HttpServletRequest object from the actual request received by the Web Server and forwards it to your Servlet's service() method.
Why the CLIENT side is interesting in
knowing something like the client’s host-name or HTTP request headers.
If you are talking about Servlets, it is always executed in server side . Hence, methods like request.getHeader() is used by the Servlet to read headers from the request sent by the client. These headers provide some extra information about the request (or response).Many of the headers associated with a request are handled by the server itself. Take, for example, how a server restricts access to its documents. The server uses HTTP headers, and servlets need not know the details. When a server receives a request for a restricted page, it checks that the request includes an appropriate Authorization header that contains a valid username and a password. If it doesn't, the server itself issues a response containing a WWW-Authenticate header, to tell the browser its access to a resource was denied. When the client sends a request that includes the proper Authorization header, the server grants the access and gives any servlet invoked access to the user's name via the getRemoteUser() call.
Read HTTP Made Really Easy, An Overview of Request Headers.