通用类型上的 java getMethod()

Question

我想在泛型上使用反射

我有这门课

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;
    }
}

在我的 Controller 中

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

但是我明白了

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

java 搜索泛型 e 而不是我在构造函数中使用的类型

我希望搜索是关于我在 Controller 中花费的类型。在 GeoRegion 类中存在该方法。

这是 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;
    }
    .....

地理区域类

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;
    }
}

Answer 1

你有一个额外的 getClass()在这一行中:

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

实际上，您正在调用 getClass()在 Class<E> 上目的。并且作为 Class<E> 的类不是 E但是java.lang.Class你得到 NoSuchMethodException你发布了。

此外，您调用方法的实例(在您的情况下为 single)的类型应为 E而不是 Class<E> 类型.

总的来说，你最终会得到这样的结果:

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){
        ...
    }
}