I'm really new to JSTL and having trouble grasping exactly how for each loops work. But say in my java bean I have a very simple while loop, that goes through and grabs properties of an object. I get the expected output from the loop when I log it. Which is simply a string that looks something like headerTest, headerMetaTest. Here is the code from my java bean:
Iterator<Resource> serviceList = null;
serviceList = resource.getChild("header").listChildren();
while(serviceList.hasNext()){
Resource child = serviceList.next();
headerTitle = child.adaptTo(ValueMap.class).get("headerTitle", "");
headerMeta = child.adaptTo(ValueMap.class).get("headerMeta, "");
}
However when I try to access it in the JSTL I'm getting nothing:
<c:forEach var="child" items="${serviceList}">
<p>${child.headerTitle}</p>
<p>${child.headerMeta}</p>
</c:forEach>
The puzzling part is I get no errors, nothing simply returns. Any ideas? Really, really lost on this one and any help is greatly appreciated. I'm a newb to this so code samples are a good way for me to learn and would be great if possible.
There are four scopes to be aware of in JSP pages.
page, request, session and application.
JSTL tags will usually look for attributes in that order.
page maps to attributes assigned during the processing of the page, these are usually quite
rare.
request is for attributes assigned to the ServletRequest, they are the most common
attributes to use as they last for the page request duration, and are then discarded.
eg
public void processMyServlet(ServletRequest request, ServletResponse){
...
request.setAttribute("myAttribute",attributeValue);
...
}
session is for attributes assigned to the HttpSession. This is useful for
user values that are used often during the user session.
eg
public void processMyServlet(HttpServletRequest request, HttpServletResponse){
...
request.getSession().setAttribute("myAttribute",attributeValue);
...
}
application is for attributes assigned to the ServletContext, this is useful for
values that are consistent across the application and do not change.
eg
public void processMyServlet(HttpServletRequest request, HttpServletResponse){
...
request.getServletContext().setAttribute("myAttribute",attributeValue);
...
}
If you are calling a servlet that dispatches your jsp then at the very least you will need.
request.setAttribute("serviceList",myResourceCollection);
somewhere during the servlet processing.
if you are doing everything in jsp then you will need something like
<% java code to create collection
request.setAttribute("serviceList",myResourceCollection);
%>
Related
i got a simple programm that begins on an input form where the user fills in 3 numbers. The form action refers to a controller servlet where i store the data in the Bean class with the setter methods I have defined.
number.setNumber1(Double.parseDouble(request.getParameter("number1")));
Till now I stored the Number object in the request with
request.setAttribute("numbers", number);
and forwarded it to the output page where i could get it with ${numbers.biggestNumber ( getter-Method that simply determines the biggest Number) }. A tutorial i am using says I could also get the data directly from the Bean by using this piece of code:
<jsp:useBean id="num" scope="session" class="model.Numbers"/>
<c:out value="${num.biggestNumber}/>
but somehow the Bean uses another object of the Numbers-class. I see the advantage of this technique, because I dont have to put the Numbers object into the request. Can someone tell me how I can use the same Numbers object I stored the data before?
I already read that I shouldnt use "jsp:setProperty..." to store the data on the input page, but if i cant get the information i wrote manually to the Bean, I have to ask myself why I should use the JSP JavaBeans annotation at all.
I used the search function but could not find an answer suitable to my question, or maybe I am just not experienced enough to get them in a more advanced context... Any help would be welcome
if you are using this one,
request.setAttribute("numbers", number);
And using requestDispacher redirecting then at target page you can do likewise,
into JSP file :
<jsp:useBean id="numbers" scope="request" class="model.Numbers"/>
<c:out value="${numbers.biggestNumber}/>
Here,
you did with wrong scope=session, means you are putting value into 'request' scope and try to pull it from session is wrong.
also maintain name of attribute 'same' while putting/getting from scope. here, name="numbers" maintain while putting/getting
Okay my mistake was that I thought JavaBeans-Jsp-Tags would save time and code. Indeed I had to create a HttpSession-Object that stores the ID of the used JavaBean
HttpSession sess = request.getSession(true);
sess.setAttribute("number", number);
Now the JavaBean-Tag in my Output.jsp knows which object to use (the one created in the Input.jsp). As far as I do understand now, the only advantage of the JavaBean-Jsp-Tag above normal Parameters added to the Request is that I can use the Bean-Class in the whole Session and am not dependend on the Request-Object.
I am creating a wizard-like interface consisting of 3 jsp pages and 3 Struts actions using Struts 1.3. The flow is like below:
page1>action1 ->page2>action2 -> page3>action3
I use a session form bean (an action form with session scope) to share data between requests. The problem I am having is that the data I submitted in page2 is available in action 2, but not in action 3. I am in doubt it might be I don't have a form on page3 to hold those data, or because I call action3 via jQuery post method instead of a regular form submit, but I am really not sure.
I have been digging all the internet for almost a day and still no luck. Could anyone offer some help. Thanks a lot.
The reset() method on the form is being called with each request and thus you are losing state. You can programmatically control this.
public class MyForm extends ActionForm {
boolean reset = true;
private String[] checkboxes = {};
#Override
public void reset(ActionMapping mapping, HttpServletRequest request) {
if (reset) {
this.checkboxes = new String[];
// etc
}
reset = true;
}
public void doNotReset() {
reset = false;
}
}
Have action2 call doNotReset() on the form.
I suppose that you might have assigned a same form to both the action in StrutsConfig.xml and hence it is not giving the ClassCastException. By the way, if you want to access the same form bean which was filled on action 2 stuff, do the following
Look at the strutsConfig file for actionMapping of both the actions (2 and 3). keep the name of form different for separate action (e.g. form2 for action2 and form3 for action3).
In Action3, instead of casting the form, use this form2 = (FormBean2) session.getAttribute("form2");
The reason for above is since both the actions are using the same form, struts might have overwriting it. Hopefully above will solve your problem.
Thank you for all your inputs. Here is how I solved my problem. I don't really like this solution, but it possibly the neatest one I can find.
In page 3 I added hidden fields for what ever property I want to be available in action 3. Struts will store the values in those hidden field and when the form is submitted again, the data will then re-populated to the action form.
It seems to me that Struts works like this: when it loads page 3, it try to populate the form in page 3 with values of myForm. When the form is submitted, the process is reversed, it populate myForm with values from the user's form. The problem is that, before populating myForm with values submitted by user, it resets myForm's properties. And because after reseting, it doesn't find the value for those fields, it leaves it empty.
I don't think it makes sense for Struts to work that way, but... so be it.
How are you accessing the form bean of page2 in action2 as well as in action3.
I suppose you are accessing the wrong way. Are you getting an exception regarding invalidCast or something.
I'm attempting to create a custom jsp tag. Everything is working fine, except for the fact that I the request seems to be out-of-scope for my custom function.
Here is the relevant bit from the .tag file:
<%!
private String process(String age, BigDecimal amount)
{
//Attempting to access request here results in an compile time error trying to:
String url=request.getURL;
}
%>
I'm very new to JSP so I'm sure I'm missing something obvious..but I can't seem to figure out what. Any help is appreciated.
I suspect that's because the custom function itself is not defined within the main execution of the JSP's service call, but is defined as a separate method within the generated JSP class. As such, the request variable is not visible tot it implicitly.
To clarify, if you had a look at the java source that the JSP compiler generates (which is appserver specific), you'll see how it hangs together.
I think you'll have to declare the request object as a parameter to your function, and pass it in when you invoke it.
<%!
private String process(String age, BigDecimal amount, ServletRequest request) {
String url=request.getURL;
....
}
%>
I have to warn you: the question may be rather silly, but I can't seem to wrap my head around it right now.
I have two managed beans, let's say A and B:
class A
{
private Date d8; // ...getters & setters
public String search()
{
// search by d8
}
}
class B
{
private Date d9; //...getters & setters
public String insert()
{
// insert a new item for date d9
}
}
and then I have two JSP pages, pageA.jsp (the search page) and pageB.jsp (the input page).
What I would like to do is placing a commandbutton in pageB so to open the search page pageA passing the parameter d9 somehow, or navigating to pageA directly after b.insert(). What I would like to do is showing the search result after the insertion.
Maybe it's just that I can't see the clear, simple solution, but I'd like to know what the best practice might be here, also...
I though of these possible solutions:
including **A** in **B** and linking the command button with **b.a.search**
passing **d9** as a **hiddenInput** and adding a new method **searchFromB** in **A** (ugly!)
collapsing the two beans into one
JSF 1.1/1.2 raw doesn't provide an easy way to do this. Seam/Spring both have ways around this and there are a couple of things you can do. JSF 2 should also have solutions to this once it is released.
Probably the easiest and most expedient would be to collapse the two beans into one and make it session scoped. The worry, of course, is that this bean will not get removed and stay in session until the session times out. Yay Memory leaks!
The other solution would be to pass the date on as a GET parameter. For instance, you action method could call the
FacesContext.getCurrentInstance().getExternalContext().redirect("pageB?d9=" + convertDateToLong(d9));
and then get the parameter on the other side.
You should configure the navigation flow in faces-config.xml. In ideal scenario you would return a "status" message which would decide the flow. Read more at following link:
http://www.horstmann.com/corejsf/faces-config.html
http://publib.boulder.ibm.com/infocenter/rtnlhelp/v6r0m0/index.jsp?topic=/com.businessobjects.integration.eclipse.doc.devtools/developer/JSF_Walkthrough8.html
As far as passing the values from one page to another is concerned you can use backing beans. More about backing beans here:
http://www.netbeans.org/kb/articles/jAstrologer-intro.html
http://www.coderanch.com/t/214065/JSF/java/backing-beans-vs-managed-beans
Hope i have understood and answered correctly to your question
Way to share values between beans
FacesContext facesContext = FacesContext.getCurrentInstance();
Application app = facesContext.getApplication();
ExpressionFactory elFactory = app.getExpressionFactory();
ELContext elContext = facesContext.getELContext();
ValueExpression valueExp = elFactory.createValueExpression(elContext, expression, Object.class);
return valueExp.getValue(elContext);
In above code "expression" would be something like #{xyzBean.beanProperty}
Since JSF uses singleton instances, you should be able to access the values from other beans. If you find more details on this technique, I am sure you'll get what you are looking for.
Add commandButton action attribute referencing to B'insert method
<h:commandLink action="#{b.insert}" value="insert"/>
In B'insert method,add d9 parameter as request parameter. Then return an arbitrary string from insert method.
FacesContext fc = FacesContext.getCurrentInstance();
fc.getExternalContext().getRequestMap().put("d9", d9);
Then go to faces context and add navigation from B to A with "from-outcome" as the arbitrary String you returned from insert method. But don't add redirect tag to navigation tags as it will destroy the request coming from B and the parameter you added (d9) will be cleared.
<from-outcome>return string of insert method</from-outcome>
<to-view-id>address of A</to-view-id>
Then you might get the "d9" in A class by fetching it from request map at its constructor or in a place where its more appropriate (getters). You might add it into a session scope or place it to a hidden variable if you want to keep track of it later.
in class A, when page is navigated, A should be initialized as it will be referenced.
FacesContext fc = FacesContext.getCurrentInstance();
fc.getExternalContext().getRequestMap().get("d9", d9);
Sorry i cant give full code, as i have no ide at here, its internet machine at work. I could not give details therefore.
In my opinion, the simplest way is 3-rd option - have both query and insert methods in same class. And you can do something like that:
public String query () {
//...
}
public String Insert() {
//insert
return Query(); }
If your classes are managed Beans you can load class A from class B and call A.query() in your insert method at the end. Also class A can have
<managed-bean-scope>session</managed-bean-scope>
parameter in faces-config.xml and it wouldn't be instantiated again when loaded.
I'm using Spring, but this question applies to all JSP-controller type designs.
The JSP page references data (using tags) which is populated by the corresponding controller. My question is, where is the appropriate place to perform formatting, in JSP or the controller?
So far I've been preparing the data by formatting it in my controller.
public class ViewPersonController extends org.springframework.web.servlet.mvc.AbstractController
{
private static final Format MY_DATE_FORMAT = new SimpleDateFormat(...);
protected ModelAndView handleRequestInternal(HttpServletRequest request, HttpServletResponse response)
{
Person person = get person from backing service layer or database
Map properties = new HashMap();
// No formatting required, name is a String
properties.put("name", person.getName());
// getBirthDate() returns Date and is formatted by a Format
properties.put("birthDate", MY_DATE_FORMAT.format(person.getBirthDate()));
// latitude and longitude are separate fields in Person, but in the UI it's one field
properties.put("location", person.getLatitude() + ", " + person.getLongitude());
return new ModelAndView("viewPerson", "person", properties);
}
}
The JSP file would look something like:
Name = <c:out value="${person. name}" /><br>
Birth Date = <c:out value="${person. birthDate}" /><br>
Location = <c:out value="${person. location}" /><br>
I know that JSP does have some provisions for formatting,
<%# taglib uri="http://java.sun.com/jstl/fmt" prefix="fmt" %>
<fmt:formatDate type="date" value="${person. birthDate}" />
But this only works with Java's java.util.Format. What if I need more complex or computed values. In such a case putting the code in the JSP would be cumbersome (and ugly).
I'm curious if this is following the spirit Spring/JSP/MVC. In other words, is the controller part of the view? Where is the preferred place to perform view related formatting? Should my controller just be returning the object (Person) instead of a Map of formatted values?
JSPs typically do not have a lot (or any?) code in them, so your options would be
controller
tag libraries
I would say that a tag library would probably be what you want for most cases, because typically the view is the code that cares about things like formatting.
If standard tag libraries don't get you there, they are not hard to create, so you can roll your own.
I typically do formatting, etc. in the bean or a view "helper". This has several advantages including the following:
Easier to test
Flexibility to change your view technologies without worrying about porting or rewriting what you've done in custom tablibs.
Cleaner and easier to maintain controller and view code.
I prefer to consider formatting part of the display layer, thus done in the JSP. I used Velocity most recently, but same idea with JSP: controller returns a data model, and the view is responsible for rendering that data into a visible representation. Plenty of JSP tag libraries out there for common needs.
You mention complex or computed values. Those sound like elements of the results data model to me, so should be done in the controller, even if they can in principle be determined by other data, such as sum, max and other aggregate values. By formatting in the view I mean basic things like date and number formats, line splitting, alignment. Of course the exact line between data and formatted representation depends on the application, but I think you get the idea.
The way I would do it is -
an instance of the Person class would be the only object in the Model of the ModelAndView
I would move the "presentation logic" into the Person class itself. For example,
public class Person {
public String getLocation() {
return this.latitude.concat(", ").concat(this.longitude);
}
}
I think overall this approach:
1 - strengthens your domain model.
2 - reduces code duplication (what if you wanted to show the location in another JSP? With your approach you'd have a lot of code duplicated)