jsf - How to populate options of h:selectOneMenu from database? -

i creating web application, have read list of objects / entities db , populate in jsf <h:selectonemenu>. unable code this. can show me how it?

i know how list<user> db. need know is, how populate list in <h:selectonemenu>.

<h:selectonemenu value="#{bean.name}">     ...? </h:selectonemenu>

based on question history, you're using jsf 2.x. so, here's jsf 2.x targeted answer. in jsf 1.x forced wrap item values/labels in ugly selectitem instances. fortunately not needed anymore in jsf 2.x.

basic example

to answer question directly, use <f:selectitems> value points list<t> property preserve db during bean's (post)construction. here's basic kickoff example assuming t represents string.

<h:selectonemenu value="#{bean.name}">     <f:selectitems value="#{bean.names}" /> </h:selectonemenu>

with

@managedbean @requestscoped public class bean {      private string name;     private list<string> names;       @ejb     private nameservice nameservice;      @postconstruct     public void init() {         names = nameservice.list();     }      // ... (getters, setters, etc) }

simple that. actually, t's tostring() used represent both dropdown item label , value. so, when you're instead of list<string> using list of complex objects list<someentity> , haven't overridden class' tostring() method, see com.example.someentity@hashcode item values. see next section how solve properly.

also note bean <f:selectitems> value not need same bean bean <h:selectonemenu> value. useful whenever values applicationwide constants have load once during application's startup. make property of application scoped bean.

<h:selectonemenu value="#{bean.name}">     <f:selectitems value="#{data.names}" /> </h:selectonemenu>

complex objects available items

whenever t concerns complex object (a javabean), such user has string property of name, use var attribute hold of iteration variable in turn can use in itemvalue and/or itemlabel attribtues (if omit itemlabel, label becomes same value).

example #1:

<h:selectonemenu value="#{bean.username}">     <f:selectitems value="#{bean.users}" var="user" itemvalue="#{user.name}" /> </h:selectonemenu>

with

private string username; private list<user> users;  @ejb private userservice userservice;  @postconstruct public void init() {     users = userservice.list(); }  // ... (getters, setters, etc)

or when has long property id rather set item value:

example #2:

<h:selectonemenu value="#{bean.userid}">     <f:selectitems value="#{bean.users}" var="user" itemvalue="#{user.id}" itemlabel="#{user.name}" /> </h:selectonemenu>

with

private long userid; private list<user> users;  // ... (the same in previous bean example)

complex object selected item

whenever set t property in bean , t represents user, need bake custom converter converts between user , unique string representation (which can id property). note itemvalue must represent complex object itself, type needs set selection component's value.

<h:selectonemenu value="#{bean.user}" converter="#{userconverter}">     <f:selectitems value="#{bean.users}" var="user" itemvalue="#{user}" itemlabel="#{user.name}" /> </h:selectonemenu>

with

private user user; private list<user> users;  // ... (the same in previous bean example)

and

@managedbean @requestscoped public class userconverter implements converter {      @ejb     private userservice userservice;      @override     public object getasobject(facescontext context, uicomponent component, string submittedvalue) {         if (submittedvalue == null || submittedvalue.isempty()) {             return null;         }          try {             return userservice.find(long.valueof(submittedvalue));         } catch (numberformatexception e) {             throw new converterexception(new facesmessage(string.format("%s not valid user id", submittedvalue)), e);         }     }      @override     public string getasstring(facescontext context, uicomponent component, object modelvalue) {         if (modelvalue == null) {             return "";         }          if (modelvalue instanceof user) {             return string.valueof(((user) modelvalue).getid());         } else {             throw new converterexception(new facesmessage(string.format("%s not valid user", modelvalue)), e);         }     }  }

(please note converter bit hacky in order able inject @ejb in jsf converter; 1 have annotated @facesconverter(forclass=user.class), but unfortunately doesn't allow @ejb injections)

don't forget make sure complex object class has equals() , hashcode() implemented, otherwise jsf during render fail show preselected item(s), , you'll on submit face validation error: value not valid.

public class user {      private long id;      @override     public boolean equals(object other) {         return (other != null && getclass() == other.getclass() && id != null)             ? id.equals(((user) other).id)             : (other == this);     }      @override     public int hashcode() {         return (id != null)              ? (getclass().hashcode() + id.hashcode())             : super.hashcode();     }  }

complex objects generic converter

head answer: implement converters entities java generics.

complex objects without custom converter

the jsf utility library omnifaces offers special converter out box allows use complex objects in <h:selectonemenu> without need create custom converter. selectitemsconverter conversion based on readily available items in <f:selectitem(s)>.

<h:selectonemenu value="#{bean.user}" converter="omnifaces.selectitemsconverter">     <f:selectitems value="#{bean.users}" var="user" itemvalue="#{user}" itemlabel="#{user.name}" /> </h:selectonemenu>

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