java getMethod() on generic type

Question

i want use reflection on generic type

i have this class

package it.ciro.service;

import it.ciro.dao.SysMyAbDao;
import org.apache.log4j.Logger;

import java.io.Serializable;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;

/**
 * Created by ciro on 09/12/2016.
 */
public class SelectOption<E extends Serializable> {

    private SysMyAbDao dao;
    private Class<E> entity;
    private ArrayList<Class<E>> entityAll;
    private Map<String,String> optionList = new HashMap<String,String>();
    protected Logger logger;

    public SelectOption(SysMyAbDao dao,Class<E> entity,String idName, String labelName ){
        logger  = Logger.getLogger(this.getClass());

        this.dao = dao;
        this.entity = entity;
        entityAll = dao.findAll();
        try{
            Method idMethod = this.entity.getMethod(idName);
            Method labelMethod = this.entity.getClass().getMethod(labelName);
            for (Class<E> single : entityAll) {
                optionList.put((String)idMethod.invoke(single),(String)labelMethod.invoke(single));
            }
        }catch (NoSuchMethodException ex){
            ex.printStackTrace();
            logger.error(ex.getMessage());
        } catch (InvocationTargetException e) {
            logger.error(e.getMessage());
        } catch (IllegalAccessException e) {
            logger.error(e.getMessage());
        }
    }

    public Map<String, String> getOptionList() {
        return optionList;
    }
}

and in my controller

SelectOption<GeoProvince> selectOption = new SelectOption(geoRegionDao,GeoRegion.class,"idGeoRegion","name");

but i get

java.lang.NoSuchMethodException: java.lang.Class.idGeoRegion()

java search on generic type e not on type that I use in constructor

I expect the search to be made about the type I spend in controller. In GeoRegion class the method exists.

this is SysMyAbDao

public abstract class SysMyAbDao<T, E, Id extends Serializable> {
    protected String message;
    protected Boolean status;
    protected T t ;
    protected Logger logger;
    protected Long totalRow;
    private Class<T> type;

    public SysMyAbDao(Class<T> type){
        this.type = type;
    }
    .....

GeoRegion class

public class GeoRegion  implements java.io.Serializable {

     private int idRegion;
     private String name;
     private String code;
     private Set<GeoProvince> geoProvinces = new HashSet<GeoProvince>(0);
     private Set<GeoCity> geoCities = new HashSet<GeoCity>(0);

    public GeoRegion() {
    }


    public GeoRegion(int idRegion) {
        this.idRegion = idRegion;
    }
    public GeoRegion(int idRegion, String name, String code, Set<GeoProvince> geoProvinces, Set<GeoCity> geoCities) {
       this.idRegion = idRegion;
       this.name = name;
       this.code = code;
       this.geoProvinces = geoProvinces;
       this.geoCities = geoCities;
    }

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name="id_region", unique=true, nullable=false)
    public int getIdRegion() {
        return this.idRegion;
    }

    public void setIdRegion(int idRegion) {
        this.idRegion = idRegion;
    }


    @Column(name="name")
    public String getName() {
        return this.name;
    }

    public void setName(String name) {
        this.name = name;
    }


    @Column(name="code", unique=true)
    public String getCode() {
        return this.code;
    }

    public void setCode(String code) {
        this.code = code;
    }

    @OneToMany(fetch=FetchType.LAZY, mappedBy="geoRegion")
    public Set<GeoProvince> getGeoProvinces() {
        return this.geoProvinces;
    }

    public void setGeoProvinces(Set<GeoProvince> geoProvinces) {
        this.geoProvinces = geoProvinces;
    }

    @OneToMany(fetch=FetchType.LAZY, mappedBy="geoRegion")
    public Set<GeoCity> getGeoCities() {
        return this.geoCities;
    }

    public void setGeoCities(Set<GeoCity> geoCities) {
        this.geoCities = geoCities;
    }
}

Can you post the code for GeoRegion class ?

Vasu
– Vasu

2016-12-09 22:16:50 +00:00
Commented Dec 9, 2016 at 22:16 — Vasu
– Vasu, Commented Dec 9, 2016 at 22:16
@javaguy posted

ciro
– ciro

2016-12-11 20:24:20 +00:00
Commented Dec 11, 2016 at 20:24 — ciro
– ciro, Commented Dec 11, 2016 at 20:24

D. Schmidt · Accepted Answer · 2016-12-10 14:23:25Z

2

You have an extra getClass() in this line:

Method labelMethod = this.entity.getClass().getMethod(labelName);

In fact, you are calling getClass() on the Class<E> object. And as the class of Class<E> is not E but java.lang.Class you get the NoSuchMethodException you posted.

Also the instance which you are invoking your method on (single in your case), should be of type E and not of type Class<E>.

Overall you would end up with something like:

public SelectOption(SysMyAbDao<E, ?, ? extends Serializable> dao,
                    Class<E> entityClass, 
                    String idName, 
                    String labelName) { 
    this.dao = dao;
    this.entityClass = entityClass;
    this.entityAll = dao.findAll(); // make sure your SysMyAbDao<E, ?, ?>#findAll() returns a Collection<E>
    try{
        Method idMethod = this.entityClass.getMethod(idName);
        Method labelMethod = this.entityClass.getMethod(labelName);
        for (E instance : entityAll) {
            optionList.put((String)idMethod.invoke(instance),(String)labelMethod.invoke(instance));
        }
    } catch (NoSuchMethodException ex){
        ...
    }
}

edited Dec 10, 2016 at 14:23

answered Dec 9, 2016 at 21:56

D. Schmidt

1671 silver badge7 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

ciro Over a year ago

not work beacuse SysMyAbDao is abstract and generic class. edit question with code

D. Schmidt Over a year ago

@ciro: Then you should fix the type of your dao-parameter accordingly. I assumed that the first generic type is the one that is returned by the findAll()-method in the changed code above.

ciro Over a year ago

in which way please?

Joe C · Accepted Answer · 2016-12-09 22:06:30Z

0

You are trying to invoke your method on single, which is a Class object.

I don't see any instances of GeoRegion in this code. But in order for this to work, you need to use this method on one of them:

E instance = getSomeObjectFromSomewhere();
optionList.put((String)idMethod.invoke(instance),(String)labelMethod.invoke(instance));

edited Dec 9, 2016 at 22:06

answered Dec 9, 2016 at 21:55

Joe C

15.8k8 gold badges42 silver badges52 bronze badges

1 Comment

ciro Over a year ago

i don't know At prior if Class i GeoRegion or other clasd

Collectives™ on Stack Overflow

java getMethod() on generic type

2 Answers 2

3 Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

3 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related