快速创建Map的工具类

主要是简化代码。

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * @author lyu
 * @description:
 * @create 2024-09-14 16:31
 */
public class MapUtils {

    private  MapUtils() {
        throw new UnsupportedOperationException("Disable creation of instance objects through reflection");
    }

    public static <K, V> Map<K, V> of(K k1, V v1) {
        Map<K, V> map = new HashMap<>();
        map.put(k1, v1);
        return map;
    }

    public static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2) {
        Map<K, V> map = of(k1, v1);
        map.put(k2, v2);
        return map;
    }

    public static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3) {
        Map<K, V> map = of(k1, v1, k2, v2);
        map.put(k3, v3);
        return map;
    }

    public static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4) {
        Map<K, V> map = of(k1, v1, k2, v2, k3, v3);
        map.put(k4, v4);
        return map;
    }

    public static <K, V> Map<K, V> of(K k1, V v1, K k2, V v2, K k3, V v3, K k4, V v4, K k5, V v5) {
        Map<K, V> map = of(k1, v1, k2, v2, k3, v3, k4, v4);
        map.put(k5, v5);
        return map;
    }

    /**
     * 建造者
     * @param <K> key class
     * @param <V> value class
     */
    public static class Builder<K, V> {
        
        public static class KeyValue<K, V> {
            private final K key;
            private final V value;

            public KeyValue(K key, V value) {
                this.key = key;
                this.value = value;
            }

            public K getKey() {
                return key;
            }

            public V getValue() {
                return value;
            }
        }

        private final List<KeyValue<K, V>> element = new ArrayList<>();

        public Builder<K, V> keyValue(K k, V v) {
            element.add(new KeyValue<>(k, v));
            // 链式调用
            return this;
        }

        public Map<K, V> build() {
            Map<K, V> map = new HashMap<>();
            element.forEach(elm -> map.put(elm.getKey(), elm.getValue()));
            element.clear();
            return map;
        }
    }
}

使用方式

import org.junit.Test;

import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.util.Date;
import java.util.Map;

/**
 * @author lyu
 * @description:
 * @create 2024-09-14 16:52
 */
public class Main {
    @Test
    public void test1(){
        System.out.println(MapUtils.of("k", "v", "k2", "c","k3", "c","k4", "c"));
    }

    @Test
    public void test2(){
        Map<String, Integer> map = new MapUtils.Builder<String, Integer>()
                .keyValue("one", 1)
                .keyValue("two", 2)
                .keyValue("three", 3)
                .keyValue("12",2)
                .keyValue("qwe",23)
                .build();
        System.out.println(map);
    }

    @Test
    public void test3(){
        Map<String, Date> map = new MapUtils.Builder<String, Date>()
                .keyValue("one", new Date())
                .keyValue("two", new Date())
                .build();
        System.out.println(map);
    }

    @Test
    public void refection() throws NoSuchMethodException, InvocationTargetException, InstantiationException, IllegalAccessException {
        Class<MapUtils> clazz = MapUtils.class;
        // 获取无参构造函数
        Constructor<?> constructor = clazz.getDeclaredConstructor();
        //禁用安全检查
        constructor.setAccessible(true);
        // 创建对象
        Object person = constructor.newInstance();
        System.out.println(person);
    }

其中注意的一点是 MapUtils 构造方法是私有的，但是可通过反射去创建对象了，违反了工具类的设计初衷，那么可以在私有构造方法中抛出异常，那么通过反射也是不能创建对象的！