关于泛型的一点应用（数值类型间的转换）

╰+攻爆jí腚メ 2022-08-22 16:13 112阅读 0赞

private static Map<Class<? extends Number>, Constructor> constructorMap = Maps.newHashMap();
        static {
            // Integer Long Short Byte Double Float BigDecimal cache constructor method
            try {
                constructorMap.put(Integer.class, Integer.class.getConstructor(String.class));
                constructorMap.put(Long.class, Long.class.getConstructor(String.class));
                constructorMap.put(Short.class, Short.class.getConstructor(String.class));
                constructorMap.put(Byte.class, Byte.class.getConstructor(String.class));
                constructorMap.put(Double.class, Double.class.getConstructor(String.class));
                constructorMap.put(Float.class, Float.class.getConstructor(String.class));
                constructorMap.put(BigDecimal.class, BigDecimal.class.getConstructor(String.class));
            } catch (NoSuchMethodException e) {
                e.printStackTrace();
            }
        }

缓存常用数值类型 的反射方法  （频繁利用反射查找类内容 会影响性能）

/**
         * 将未知number对象转换到具体类
         * @param source 源对象
         * @param targetClass 目标类
         * @param <T>
         * @param <E>
         * @return
         */
        public static <T, E extends Number> E number2Target(T source, Class<E> targetClass) {
            if (targetClass.isPrimitive()) {
                throw new RuntimeException("targetClass should not be a basic type!");
            }
            try {
                Constructor<E> constructor = constructorMap.get(targetClass);
                if (source == null) return constructor.newInstance("0");
                if (!(source instanceof Number)) {
                    throw new RuntimeException("source should be a number!");
                }
                String number = source.toString();
                if (number.contains(".") && (targetClass.equals(Integer.class)
                        || targetClass.equals(Short.class) || targetClass.equals(Long.class)
                        || targetClass.equals(Byte.class))) {
                    return constructor.newInstance(number.substring(0, number.indexOf(".")));
                }
                return constructor.newInstance(number);
            } catch (InstantiationException e) {
                throw new ApolloRuntimeException("targetClass is no such constructor: TargetClass(String s)");
            } catch (IllegalAccessException e) {
                throw new ApolloRuntimeException("The constructor of targetClass is private, no permissions to access");
            } catch (InvocationTargetException e) {
                throw new ApolloRuntimeException("The constructor is error in processing");
            }
        }

利用泛型 跟反射 转换未知的number对象 为目标number对象 由于利用到了构造方法 so 基础类型无法使用

（欢迎大家指正 改造。。）