I want to read parameter passed by one JSP to another using HTTP POST method.
Following are my two JSP files.
One.jsp
<body>
<form action="Two.jsp" method="post">
<input type="text" value="test value" name="txtOne">
<input type="submit" value="Submit">
</form>
</body>
Two.jsp
<body>
<% response.getWriter().println(request.getParameter("txtOne")); %>
</body>
I can access the parameter in Two.jsp file using scriplet.
I want to avoid scriplet, so I am looking for JavaScript or jQuery solution.
So far I have searched and found JavaScript solution which only reads parameters sent using GET method(query string only).
Any suggestion will be appreciated.
Thanks in advance.
Solution:
I was able to get the value using JSTL:
${param.txtOne}
Try expression language - ${txtOne}, of if the method in one.jsp is GET instead of POST, you would be able to read URL in javascript and extract parameter value from there.
Yes you can get the value by use of JSTL
${param.txtOne}
Update
From EL info page
In EL there are several implicit objects available.
EL Scriptlet (out.print and null checks omitted!)
---------------------------------- ---------------------------------------------
${param.foo} request.getParameter("foo");
${paramValues.foo} request.getParameterValues("foo");
${header['user-agent']} request.getHeader("user-agent");
${pageContext.request.contextPath} request.getContextPath();
${cookie.somename} Too verbose (start with request.getCookies())
Implicit Objects
The JSP expression language defines a set of implicit objects:
pageContext: The context for the JSP page. Provides access to various objects including:
servletContext: The context for the JSP page’s servlet and any web components contained in the same application. See Accessing the Web Context.
session: The session object for the client. See Maintaining Client State.
request: The request triggering the execution of the JSP page. See Getting Information from Requests.
response: The response returned by the JSP page. See Constructing Responses.
In addition, several implicit objects are available that allow easy access to the following objects:
param: Maps a request parameter name to a single value
paramValues: Maps a request parameter name to an array of values
header: Maps a request header name to a single value
headerValues: Maps a request header name to an array of values
cookie: Maps a cookie name to a single cookie
initParam: Maps a context initialization parameter name to a single value
Finally, there are objects that allow access to the various scoped variables described in Using Scope Objects.
pageScope: Maps page-scoped variable names to their values
requestScope: Maps request-scoped variable names to their values
sessionScope: Maps session-scoped variable names to their values
applicationScope: Maps application-scoped variable names to their values
I want to avoid scriplet, so I am looking for JavaScript or jquery solution.
Simply you cannot.
request object can only accessible on server side, i.e in your JSP. You cannot access request or response object in client side that i.e javascript/jquery/whatever.
If you want access jsp value in javascript, try something like
var news=<%= request.getParameter("txtOne")) %>;
As a side note: Avoid scriplets and go for Expression language.
It is time for you to move to some MVC framework like struts than plain JSP. Then you can fill an ActionForm from parameters and use them on Two.jsp.
Related
I have an ArrayList of a class Room. I need to send it from a jsp to a servlet.
It seems the only way an html or a jsp can send values to a servlet is via a form, the method I tried was to pass it as a hidden parameter as follows:
<input type="hidden" name="allRooms" value="<%=request.getAttribute("allRooms") %>" />
But in the servlet to which i submit this form I get a compile error "String cannot be converted to List" for the following:
List<Room> allRooms=(List<Room>)request.getParameter("allRooms");
Just converting the parameter to an Object type first and then converting it to a List as shown below gives the same exception but this time as a Runtime Exception:
Object a=(Object)request.getParameter("allRooms");
List<Room> allRooms=(List<Room>)a;
Is there any method to pass the List to the servlet or I will have to set it as a session variable in the JSP ?
Thanks in advance.
Is there any method to pass the List to the servlet or I will have to set it as a session variable in the JSP ?
Use session.That is one best solution.
There is no way to represent an ArrayList in HTML to send via html form. Use session instead.
I think if you pass the following params, and array is formed in servlet side
param[0]=ss , param[1]=ssw
You could do this.
List<String> roomParams =(List<String>)request.getParameter("param");
But to make this.
List<Room> allRooms=(List<Room>)request.getParameter("allRooms");
That I think is not possible, so you should use Session attributes
session.setAttribute("allRooms", new ArrayList<Room>());
I believe you should not be sending the List to Servlet directly and should look out for other options.
How are you generating the ArrayList on the browser page? If it is generated from a multi-select element from UI, then you can access the request parameter values as Array in Servlet.
Shishir
I'm trying to retrieve attribute values set by a servlet in a JSP page, but I've only luck with parameters by ${param}. I'm not sure about what can I do different. Maybe its simple, but I couldn't manage it yet.
public void execute(HttpServletRequest request, HttpServletResponse response) {
//there's no "setParameter" method for the "request" object
request.setAttribute("attrib", "attribValue");
RequestDispatcher rd = request.getRequestDispatcher("/Test.jsp");
rd.forward(request,response);
}
In the JSP I have been trying to retrieve the "attribValue", but without success:
<body>
<!-- Is there another tag instead of "param"??? -->
<p>Test attribute value: ${param.attrib}
</body>
If I pass a parameter through all the process (invoking page, servlets and destination page), it works quite good.
It's available in the default EL scope already, so just
${attrib}
should do.
If you like to explicitly specify the scope (EL will namely search the page, request, session and application scopes in sequence for the first non-null attribute value matching the attribute name), then you need to refer it by the scope map instead, which is ${requestScope} for the request scope
${requestScope.attrib}
This is only useful if you have possibly an attribute with exactly the same name in the page scope which would otherwise get precedence (but such case usually indicate poor design after all).
See also:
Our EL wiki page
Java EE 6 tutorial - Expression Language
Maybe a comparison between EL syntax and scriptlet syntax will help you understand the concept.
param is like request.getParameter()
requestScope is like request.getAttribute()
You need to tell request attribute from request parameter.
have you tried using an expression tag?
<%= request.getAttribute("attrib") %>
If the scope is of request type, we set the attribute using request.setAttribute(key,value) in request and retrieve using ${requestScope.key} in jsp .
This is probably due to my misunderstanding and incomplete information of JSP and JSTL. I have a web page where I have input elements such as
<input name="elementID" value="${param.elementID}"/>
When I am trying to save the form, I check for that elementID and other elements to conform to certain constraints "numeric, less than XXX". I show an error message if they don't. All the parameters are saved and user does not need to type it again after fixing the error.
After saved, when I am redirecting to the same page for the object to be edited, I am looking a way to set the parameter like request.setParameter("elementID",..) Is there a way to do this ? However the only thing I can find is request.setAttribute.
HTTP responses does not support passing parameters.
JSP/Servelets allows you to either use request.setAttribute or session.setAttribute for that purpose. Both methods are available when processing the page you're redirecting to, So basically, you got it right...
Also, from what you describe, you may want to check client-side validation: don't submit the form until you're validating it using client-side scripting (javascript)
After the servlet processes the form, (ie. saves the user input in the database), have the servlet forward (not redirect, because that would lose the request params) the request to the same jsp which contains the form. So there is no need to set the params since the servlet is just passing back the same request object.
The jsp which contains the form should have inputs similar to this:
<form>
...
<input type="text" value="${elementid}"/>
...
</form>
The syntax ${varname} is EL. So if the elementid already has a value, it that textfield will contain that value. Alternatively if you have not used EL and/or JSTL, you use scriptlets (but that is highly unadvisable, EL and/or JSTL should be the way):
<form>
...
<input type="text" value="<%= request.getParameter("elementid") %>"/>
...
</form>
I had to include <%# page isELIgnored="false"%> to my jsp to allow code like ${elementid} to work
I have an attribute which I have forwarded from a servelet to a jsp file and while I can use this object with EL I'd like to know how to access it inside the java tags. An example is something like the following:
Searching for "${search_phrase}" returned
<c:forEach var="video" items="${results}">
${video.getVideoName()}
${video.getVideoID()}
</c:forEach>
So results here is an ArrayList of type Video which is forwarded from a servlet to a jsp
I would like to access this ArrayList inside <% %> tags in order to perform some more involved tasks that I cant do with EL.
Anybody know how to do this?
On a side note, this ArrayList I'm creating could potentially get large. Where is this stored? On the server or in some users temp files? If it's stored in server memory does it get cleaned after some period of time / an event such as the user that requested the ArrayList closes connection to server?
It all depends where you stored the list. If you stored it in a request attribute (and not anywhere else), then it will be eligible to garbage-collection when the request has been handled.
If you stored it in a session attribute, then it will be stored in the server memory (and/or the file system or the database depending on the container configuration) until the session times out or is invalidated, or until you remove it. HTTP is a stateless protocol. The user doesn't have a connection to the server.
Java code between <% %> is not a java tag. It's scriptlet, and should not be used in a JSP. If you need to do something that EL or JSP tags can't do easily, then either
write a custom JSP tag yourself, put the Java code in this JSP tag, and invoke the tag from the JSP, or
or write a custom EL function, and invoke this function from the JSP
or prepare the work in a controller (servlet, MVC framework action) before dispatching to the JSP, so that the JSP can generate the markup easily.
The list is accessible using the getAttribute method corresponding to the setAttribute method you used to store the list:
HttpServletRequest.setAttribute() --> HttpServletRequest.getAttribute()
HttpSession.setAttribute() --> HttpSession.getAttribute()
ServletContext.setAttribute() --> ServletContext.getAttribute()
I think you should use something like
<c:forEach var="video" items="${results}">
<c:forEach var="videoType" items="${video.types}"> //suppose videoType is an object
<c:out value="${videoTypeDetails}" />
</c:forEach>
</c:forEach>
What is the difference between getAttribute() and getParameter() methods within HttpServletRequest class?
getParameter() returns http request parameters. Those passed from the client to the server. For example http://example.com/servlet?parameter=1. Can only return String
getAttribute() is for server-side usage only - you fill the request with attributes that you can use within the same request. For example - you set an attribute in a servlet, and read it from a JSP. Can be used for any object, not just string.
Generally, a parameter is a string value that is most commonly known for being sent from the client to the server (e.g. a form post) and retrieved from the servlet request. The frustrating exception to this is ServletContext initial parameters which are string parameters that are configured in web.xml and exist on the server.
An attribute is a server variable that exists within a specified scope i.e.:
application, available for the life of the entire application
session, available for the life of the session
request, only available for the life of the request
page (JSP only), available for the current JSP page only
request.getParameter()
We use request.getParameter() to extract request parameters (i.e. data sent by posting a html form ). The request.getParameter() always returns String value and the data come from client.
request.getAttribute()
We use request.getAttribute() to get an object added to the request scope on the server side i.e. using request.setAttribute(). You can add any type of object you like here, Strings, Custom objects, in fact any object. You add the attribute to the request and forward the request to another resource, the client does not know about this. So all the code handling this would typically be in JSP/servlets. You can use request.setAttribute() to add extra-information and forward/redirect the current request to another resource.
For example,consider about first.jsp,
//First Page : first.jsp
<%# page import="java.util.*" import="java.io.*"%>
<% request.setAttribute("PAGE", "first.jsp");%>
<jsp:forward page="/second.jsp"/>
and second.jsp:
<%# page import="java.util.*" import="java.io.*"%>
From Which Page : <%=request.getAttribute("PAGE")%><br>
Data From Client : <%=request.getParameter("CLIENT")%>
From your browser, run first.jsp?CLIENT=you and the output on your browser is
From Which Page : *first.jsp*
Data From Client : you
The basic difference between getAttribute() and getParameter() is that the first method extracts a (serialized) Java object and the other provides a String value. For both cases a name is given so that its value (be it string or a java bean) can be looked up and extracted.
It is crucial to know that attributes are not parameters.
The return type for attributes is an Object, whereas the return type for a parameter is a String. When calling the getAttribute(String name) method, bear in mind that the attributes must be cast.
Additionally, there is no servlet specific attributes, and there are no session parameters.
This post is written with the purpose to connect on #Bozho's response, as additional information that can be useful for other people.
The difference between getAttribute and getParameter is that getParameter will return the value of a parameter that was submitted by an HTML form or that was included in a query string. getAttribute returns an object that you have set in the request, the only way you can use this is in conjunction with a RequestDispatcher. You use a RequestDispatcher to forward a request to another resource (JSP / Servlet). So before you forward the request you can set an attribute which will be available to the next resource.
-getParameter() :
<html>
<body>
<form name="testForm" method="post" action="testJSP.jsp">
<input type="text" name="testParam" value="ClientParam">
<input type="submit">
</form>
</body>
</html>
<html>
<body>
<%
String sValue = request.getParameter("testParam");
%>
<%= sValue %>
</body>
</html>
request.getParameter("testParam") will get the value from the posted form of the input box named "testParam" which is "Client param". It will then print it out, so you should see "Client Param" on the screen. So request.getParameter() will retrieve a value that the client has submitted. You will get the value on the server side.
-getAttribute() :
request.getAttribute(), this is all done server side. YOU add the attribute to the request and YOU submit the request to another resource, the client does not know about this. So all the code handling this would typically be in servlets.getAttribute always return object.
getParameter - Is used for getting the information you need from the Client's HTML page
getAttribute - This is used for getting the parameters set previously in another or the same JSP or Servlet page.
Basically, if you are forwarding or just going from one jsp/servlet to another one, there is no way to have the information you want unless you choose to put them in an Object and use the set-attribute to store in a Session variable.
Using getAttribute, you can retrieve the Session variable.
from http://www.coderanch.com/t/361868/Servlets/java/request-getParameter-request-getAttribute
A "parameter" is a name/value pair sent from the client to the server
- typically, from an HTML form. Parameters can only have String values. Sometimes (e.g. using a GET request) you will see these
encoded directly into the URL (after the ?, each in the form
name=value, and each pair separated by an &). Other times, they are
included in the body of the request, when using methods such as POST.
An "attribute" is a server-local storage mechanism - nothing stored in
scoped attribues is ever transmitted outside the server unless you
explicitly make that happen. Attributes have String names, but store
Object values. Note that attributes are specific to Java (they store
Java Objects), while parameters are platform-independent (they are
only formatted strings composed of generic bytes).
There are four scopes of attributes in total: "page" (for JSPs and tag
files only), "request" (limited to the current client's request,
destroyed after request is completed), "session" (stored in the
client's session, invalidated after the session is terminated),
"application" (exist for all components to access during the entire
deployed lifetime of your application).
The bottom line is: use parameters when obtaining data from the
client, use scoped attributes when storing objects on the server for
use internally by your application only.
Another case when you should use .getParameter() is when forwarding with parameters in jsp:
<jsp:forward page="destination.jsp">
<jsp:param name="userName" value="hamid"/>
</jsp:forward>
In destination.jsp, you can access userName like this:
request.getParameter("userName")
Basic difference between getAttribute() and getParameter() is the return type.
java.lang.Object getAttribute(java.lang.String name)
java.lang.String getParameter(java.lang.String name)