Java8集合filter过滤Integer数值为空问题解决方案

问题描述

项目使用mysql，主键使用int自增，实体映射为Integer，而自增主键势必会大于127，那么问题来了 ，使用java8循环做parentId（类似菜单，多层级）判断时候怎么办呢？

示例

  //id 是传递的父id  用来过滤用 ，可以为空        List<Channel> channels = allchannel.stream()                .filter(channel -> {                    if (id==null) {                        return channel.getParentId()==null;                    }else {                        return channel.getParentId()!=null&&channel.getParentId().equals(id);                    }                })                .collect(Collectors.toList());

解析

为什么大于127就不行了呢？ 因为java8内部的变量一般修饰符是final，而Integer可缓存的值是-128–127(详情查询源码729行)。为了解决此种问题可以使用equal取代==判断

附integer缓存源码

    /**     * Cache to support the object identity semantics of autoboxing for values between     * -128 and 127 (inclusive) as required by JLS.     *     * The cache is initialized on first usage.  The size of the cache     * may be controlled by the {@code -XX:AutoBoxCacheMax=<size>} option.     * During VM initialization, java.lang.Integer.IntegerCache.high property     * may be set and saved in the private system properties in the     * sun.misc.VM class.     */    private static class IntegerCache {        static final int low = -128;        static final int high;        static final Integer cache[];        static {            // high value may be configured by property            int h = 127;            String integerCacheHighPropValue =                sun.misc.VM.getSavedProperty("java.lang.Integer.IntegerCache.high");            if (integerCacheHighPropValue != null) {                try {                    int i = parseInt(integerCacheHighPropValue);                    i = Math.max(i, 127);                    // Maximum array size is Integer.MAX_VALUE                    h = Math.min(i, Integer.MAX_VALUE - (-low) -1);                } catch( NumberFormatException nfe) {                    // If the property cannot be parsed into an int, ignore it.                }            }            high = h;            cache = new Integer[(high - low) + 1];            int j = low;            for(int k = 0; k < cache.length; k++)                cache[k] = new Integer(j++);            // range [-128, 127] must be interned (JLS7 5.1.7)            assert IntegerCache.high >= 127;        }        private IntegerCache() {}    }