问题
i'm currently working with JSF, but since i'm a old and grouchy php-dev i always mess up with the GET-Parameters of an request. (In PHP you can access the request Paramerts whenever you want, using the $_GET["paramname"] Array.
Now, i'm working on an User Managment System. (CRUD) Usually i go with a list of all available users, having options like edit / delete. The edit link is then pointing to http:\\localhost\editUser.xhtml?userId=5 for example.
I have also an Controller called UserEditController which basically holds the user entity and invokes the update.
So, inside this Controller I'm using the @PostConstruct Annotation to load the user with the id 5 from the DataService and store it inside a property.
Problem here is: Wenn entering PostConstruct-Method in the APPLY_REQUEST_VALUES-Phase im not able to access the request Parameter Map of Faces Context (Will return null for userId)
Controller (simplified):
@Named
@RequestScoped
UserEditController{
@Inject
private UserDataService userDataService;
private User currentUser;
@PostConstruct
public void initValues(){
String id = FacesContext.getCurrentInstance().getExternalContext().getRequestParameterMap().get("userId");
this.currentUser = userDataService.getUserById(id);
}
public String saveCurrentUser(){
userDataService.updateUser(this.currentUser);
return "userManagement"; //return to overview after saving
}
//getter and setter
}
This works as intened. All the Form-Fields now are bound to user's properties like #{userEditController.currentUser.forename} etc.
I now added a save button with action attribute {userEditController.saveCurrentUser()}
However the script then enters the APPLY_REQUEST_VALUES-Phase And the UserEditController's initValues is called again.
- this results in a nullpointer Exception, when trying to access the RequestParameterMap
- and obviously i dont want to reload the user BEFORE saving it :-)
This sounds like a stupid question but i think i'm messing up between the PHP-Style and the JSF-Style to handle things.
Any Help would be appreciated.
回答1:
The common way to pass the user (or userID) to your BackingBean, is using one of the following options:
http://www.mkyong.com/jsf2/4-ways-to-pass-parameter-from-jsf-page-to-backing-bean/
I think the main problem is that your bean is @RequestScoped. If you push the save button on your edit-page you are sending a new request, so a new instance of a request scoped bean will be created. Just change your bean to @ViewScoped.
More info:
- Communication in JSF 2
回答2:
I tried to change it to ViewScoped but then its ending up with "calling the constructor" for the bean everytime i access a property...
Meanwhile i tried a lot of things, nothing worked as expected:
The ONLY case where i can get it to work is setting the Controllers to "SessionScoped". But i don't think this is a good approach since i would need to take care of "cleaning" values and cause a lot of unneded (initialized) beans...
I've created a simple Project to play arround. Heres the Session Scoped Version that is working. But if i change the scope, i would need to "reload" the current user when hitting the save button. And without access to request parameters i have no clue, how to achieve that.
(i tried passing the users id again with the "form", but then i have problems to pass the id "for the first time")
Heres my sample. (Getter and Setter are available and not mentioned to keep it short)
User-Class:
public class User {
private String firstname;
private String lastname;
public User (String f, String l){
this.firstname = f;
this.lastname = l;
}
}
DBSimulator:
@Named("dbSimulator")
@SessionScoped
public class DBSimulator implements Serializable {
/**
*
*/
private static final long serialVersionUID = 659826879566280911L;
private Map<String, User> data;
public DBSimulator() {
//Load data
User u1 = new User("Mickey", "Maus");
User u2 = new User("Peter", "Pan");
this.data = new HashMap<String, User>();
this.data.put("Mickey", u2);
this.data.put("Max", u1);
}
public List<User> getUserList(){
List<User> l = new LinkedList<User>();
for (Map.Entry<String, User> user : data.entrySet()) {
l.add(user.getValue());
}
return l;
}
public void saveUser(User user){
this.data.put(user.getFirstname(), user);
}
}
UserManagement-Controller:
@Named
@SessionScoped
public class UserManagementController implements Serializable {
/**
*
*/
private static final long serialVersionUID = -4300851229329827994L;
@Inject
private DBSimulator dbSimulator;
private List<User> users;
public UserManagementController() {
System.out.println("UserManagementController:construct()");
}
@PostConstruct
public void LoadUsers(){
this.setUsers(this.dbSimulator.getUserList());
}
}
UserEdit Controller
@Named
@SessionScoped
public class UserEditController implements Serializable{
/**
*
*/
private static final long serialVersionUID = 1867483972880755108L;
@Inject
private DBSimulator dbSimulator;
private User user;
public UserEditController() {
System.out.println("UserEditController:construct()");
}
public String activateUser(User user){
this.setUser(user);
System.out.println("setting User");
return "userEdit";
}
public String save(){
//Save user
this.dbSimulator.saveUser(user);
return "userManagement";
}
}
and finaly both XHTML files: UserManagement.xhtml
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
xmlns:h="http://java.sun.com/jsf/html"
xmlns:ui="http://java.sun.com/jsf/facelets"
xmlns:f="http://java.sun.com/jsf/core">
<h:head>
<title>Test</title>
</h:head>
<h:body>
<h:outputText value="Select user to edit." />
<h:dataTable value="#{userManagementController.users}" var="user">
<h:column>
<f:facet name="header">Firstname</f:facet>
<h:outputText value="#{user.firstname}" />
</h:column>
<h:column>
<f:facet name="header">Lastname</f:facet>
<h:outputText value="#{user.lastname}" />
</h:column>
<h:column>
<f:facet name="header">Options</f:facet>
<h:form>
<h:commandLink action="userEdit" actionListener="#{userEditController.activateUser(user)}" value="edit user" />
</h:form>
</h:column>
</h:dataTable>
</h:body>
</html>
UserEdit.xhtml
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"
xmlns:h="http://java.sun.com/jsf/html"
xmlns:ui="http://java.sun.com/jsf/facelets"
xmlns:f="http://java.sun.com/jsf/core">
<h:head>
<title>Test</title>
</h:head>
<h:body>
<h:form>
<h:inputText value="#{userEditController.user.firstname}"></h:inputText>
<br /><br />
<h:inputText value="#{userEditController.user.lastname}"></h:inputText>
<br /><br />
<h:commandButton value="save" action="#{userEditController.save}"></h:commandButton>
</h:form>
</h:body>
</html>
ps.: I don't want anyone to "correct" my code - but maybe with the complete example somebody is able to see, where my headeck comes from :)
Working with ViewScoped Beans generates the following console Output:
[pageload]
12:07:49,126 INFO [stdout] (http--0.0.0.0-8090-3) UserManagementController:construct()
12:07:49,334 INFO [stdout] (http--0.0.0.0-8090-3) UserManagementController:construct()
12:07:49,341 INFO [stdout] (http--0.0.0.0-8090-3) UserManagementController:construct()
[edit click]
12:08:35,410 INFO [stdout] (http--0.0.0.0-8090-3) UserManagementController:construct()
12:08:35,411 INFO [stdout] (http--0.0.0.0-8090-3) UserManagementController:construct()
12:08:35,412 INFO [stdout] (http--0.0.0.0-8090-3) UserManagementController:construct()
12:08:35,413 INFO [stdout] (http--0.0.0.0-8090-3) UserManagementController:construct()
12:08:35,414 INFO [stdout] (http--0.0.0.0-8090-3) UserManagementController:construct()
12:08:35,414 INFO [stdout] (http--0.0.0.0-8090-3) UserManagementController:construct()
12:08:35,415 INFO [stdout] (http--0.0.0.0-8090-3) UserManagementController:construct()
12:08:35,416 INFO [stdout] (http--0.0.0.0-8090-3) UserManagementController:construct()
12:08:35,416 INFO [stdout] (http--0.0.0.0-8090-3) UserManagementController:construct()
12:08:35,417 INFO [stdout] (http--0.0.0.0-8090-3) UserManagementController:construct()
12:08:35,476 INFO [stdout] (http--0.0.0.0-8090-3) UserEditController:construct()
12:08:35,478 INFO [stdout] (http--0.0.0.0-8090-3) setting User
12:08:35,494 INFO [stdout] (http--0.0.0.0-8090-3) UserEditController:construct()
12:08:35,497 INFO [stdout] (http--0.0.0.0-8090-3) UserEditController:construct()
And obviously the user is not set anymore, because the (ViewScoped) UserEditController has been reconstructed twice after setting the user...
来源：https://stackoverflow.com/questions/13362897/jsf-best-way-to-pass-parameters