问题
How can I write a custom converter when working with PrimeFaces components that use a list of POJO? My particular problem is with <p:pickList>
<p:pickList converter="????" value="#{bean.projects}" var="project"
itemLabel="#{project.name}" itemValue="#{project}">
Without a converter I get java.lang.ClassCastException because JSF sets the submitted values with unconverted java.lang.String submitted values.
回答1:
It's possible, whithout other database access, but i don't know the best way. I use a very specific converter, works only for picklist. Try this:
@FacesConverter(value = "primeFacesPickListConverter")public class PrimeFacesPickListConverter implements Converter {
@Override
public Object getAsObject(FacesContext arg0, UIComponent arg1, String arg2) {
Object ret = null;
if (arg1 instanceof PickList) {
Object dualList = ((PickList) arg1).getValue();
DualListModel dl = (DualListModel) dualList;
for (Object o : dl.getSource()) {
String id = "" + ((Project) o).getId();
if (arg2.equals(id)) {
ret = o;
break;
}
}
if (ret == null)
for (Object o : dl.getTarget()) {
String id = "" + ((Project) o).getId();
if (arg2.equals(id)) {
ret = o;
break;
}
}
}
return ret;
}
@Override
public String getAsString(FacesContext arg0, UIComponent arg1, Object arg2) {
String str = "";
if (arg2 instanceof Project) {
str = "" + ((Project) arg2).getId();
}
return str;
}
and Picklist:
<p:pickList converter="primeFacesPickListConverter" value="#{bean.projects}" var="project"
itemLabel="#{project.name}" itemValue="#{project}">
Work's for me, improvements is necessary.
回答2:
After research on how to write custom converter, here is the solution.
1. create a Java Class that implement javax.faces.convert.Converter;
public class ProjectConverter implements Converter{
@EJB
DocumentSBean sBean;
public ProjectConverter(){
}
public Object getAsObject(FacesContext context, UIComponent component, String value){
return sBean.getProjectById(value);
//If u look below, I convert the object into a unique string, which is its id.
//Therefore, I just need to write a method that query the object back from the
//database if given a id. getProjectById, is a method inside my Session Bean that
//does what I just described
}
public String getAsString(FacesContext context, UIComponent component, Object value)
{
return ((Project) value).getId().toString(); //--> convert to a unique string.
}
}
2. Register your custom converter in faces-config.xml
<converter>
<converter-id>projectConverter</converter-id>
<converter-class>org.xdrawing.converter.ProjectConverter</converter-class>
</converter>
3. So now inside Primefaces component, u just do converter="projectConverter". Note that projectConverter is the <convert-id> I just created. So to solve my problem above, I do this:
<p:pickList converter="projectConverter" value="#{bean.projects}" var="project"
itemLabel="#{project.name}" itemValue="#{project}">
回答3:
Yes, you can write a converter that serializes/deserializes the objects in the picklist like this:
@FacesConverter(value="PositionMetricConverter")
public class PositionMetricConverter implements Converter {
private static final Logger log = Logger.getLogger(PositionMetricConverter.class.getName());
@Override
public Object getAsObject(FacesContext facesContext, UIComponent uiComponent, String value) {
try {
byte[] data = Base64.decodeBase64(value);
ObjectInputStream ois = new ObjectInputStream(new ByteArrayInputStream(data));
Object o = ois.readObject();
ois.close();
return o;
} catch (Exception e) {
log.log(Level.SEVERE, "Unable to decode PositionMetric!", e);
return null;
}
}
@Override
public String getAsString(FacesContext facesContext, UIComponent uiComponent, Object value) {
try {
ByteArrayOutputStream baos = new ByteArrayOutputStream();
ObjectOutputStream oos = new ObjectOutputStream(baos);
oos.writeObject(value);
oos.close();
return Base64.encodeBase64String(baos.toByteArray());
} catch (IOException e) {
log.log(Level.SEVERE, "Unable to encode PositionMetric!", e);
return "";
}
}
}
Then apply this converter on your picklist like this:
<p:pickList converter="PositionMetricConverter" value="#{bean.positionMetrics}"
var="positionMetric" itemLabel="#{positionMetric.name}" itemValue="#{positionMetric}"/>
and make sure your objects are serializable.
回答4:
This problem is not primefaces related, just general JSF related.
Why should you hit the database again? Your bean already contains the list of Objects you want to display in a component, or is it request scoped?
- Create a Superclass for your Hibernate Pojo's containing an id field. If you don't want to create a super class just use the pojo class, but you need more converter classes.
- With that Superclass you can create a generic converter for all Pojo Classes containing a list of Pojo's passed in the constructor.
- Add the converter as a property in your session bean and use that converter in your JSF component.
If you access the final list via a get property in your bean or the nested one in the converter is of your choice.
public class SuperPojo
{
protected Integer id;
//constructor & getter
}
public class PojoTest extends SuperPojo
{
private String label = null;
//constructor & getter
}
public class SuperPojoConverter<T extends SuperPojo> implements Converter
{
private Collection<T> superPojos;
public IdEntityConverter(Collection<T> superPojos)
{
this.superPojos = superPojos;
}
@Override
public Object getAsObject(FacesContext context, UIComponent component, String value)
{
//catch exceptions and empty or null value!
final int intValue = Integer.parseInt(value);
for(SuperPojo superPojo : this.superPojos)
if(superPojo.getId().intValue() == intValue)
return superPojo;
return null;
}
@Override
public String getAsString(FacesContext context, UIComponent component, Object value)
{
//catch null and instanceof
return String.valueOf(((SuperPojo)value).getId().intValue());
}
public Collection<T> getSuperPojos()
{
return this.superPojos;
}
}
public class Bean
{
private SuperPojoConverter<PojoTest> pojoTestConverter = null;
public Bean()
{
final List<PojoTest> pojoTests = //get list from hibernate
this.pojoTestConverter = new SuperPojoConverter<PojoTest>(pojoTests);
}
public SuperPojoConverter<PojoTest> getPojoTestConverter()
{
return this.pojoTestConverter;
}
}
<h:selectOneMenu value="#{selPojoTest}" converter="#{bean.getPojoTestConverter}">
<f:selectItems value="#{bean.getPojoTestConverter.getSuperPojos}" var="varPojoTest" itemLabel="#{varPojoTest.label}" itemValue="#{varPojoTest}"/>
</h:selectOneMenu>
回答5:
is there any way to implement that without 2 database hits?
I mean, when you have
#{bean.projects}
this is a database hit.
and when the converter puts
sBean.getProjectById(value);
is a unnecessary database hit, since bean.projects already have id and value of the objects
回答6:
Yes, it's possible:
public class DocumentSBean sBean implements Serializable{
private List<Document> projects;
// projects methods...
// ...
public Converter getDocumentConverter(){
return docConverter;
}
private Converter docConverter = new Converter() {
@Override
public Object getAsObject(FacesContext context, UIComponent component, String value) {
return projects.stream().filter(p -> p.getName().equals(value)).findFirst().orElse(null);
}
@Override
public String getAsString(FacesContext context, UIComponent component, Object value) {
return (value != null)
? ((Document) value).toString()
: null;
}
};
}
<p:pickList converter="#{sBean.documentConverter}" value="#...
来源：https://stackoverflow.com/questions/3621251/how-to-write-a-custom-converter-for-ppicklist