import java.lang.reflect.Field;

import java.util.ArrayList;

import java.util.HashMap;

import java.util.List;

import java.util.Map;

public class ListToMap {

    //list转化为map

    public static <K, V> Map<K, V> listToMap(List<V> vList, String kName) {

        Map<K, V> map = new HashMap<K, V>();

        if (vList == null || kName == null || vList.size() == 0) {

            return map;

        }

        Field kField = getField(vList.get(0).getClass(), kName);

        for (V v : vList) {

            try {

                map.put((K) kField.get(v), v);

            } catch (IllegalArgumentException e) {

                e.printStackTrace();

            } catch (IllegalAccessException e) {

                e.printStackTrace();

            }

        }

        return map;

    }

    //获取key对应的类型字段

    private static <V> Field getField(Class<V> clazz, String kName) {

        if (clazz == null || kName == null) {

            return null;

        }

        for (Field fieldElem : clazz.getDeclaredFields()) {

            fieldElem.setAccessible(true);

            if (fieldElem.getName().equals(kName)) {

                return fieldElem;

            }

        }

        return null;

    }

    //调用示例

    public static void main(String[] args) throws IllegalArgumentException, IllegalAccessException {

        List<Person> pList = new ArrayList<Person>();

        Person p1 = new Person(2, "taxuexing");

        pList.add(p1);

        Person p2 = new Person(3, "jikewang");

        pList.add(p2);

        Map<Integer, Person> map = ListToMap.listToMap(pList, "age");

        System.out.println(map.get(2).getUserName());

        System.out.println(map.get(3).getUserName());

    }

}

public class Person {

    private String userName;

    private int age;

    Person(){

    }

    Person(int age, String userName){

        this.age = age;

        this.userName = userName;

    }

    public String getUserName() {

        return userName;

    }

    public void setUserName(String userName) {

        this.userName = userName;

    }

    public int getAge() {

        return age;

    }

    public void setAge(int age) {

        this.age = age;

    }

}