基本设计

• 设计思想：以空间换时间
• 实现原理：将版本号转为int数组，使用Guava Cache 对处理过的版本数据做缓存（采用lru的淘汰策略），通过int数组的比较达到比较版本的效果

依赖

    <dependency>
        <groupId>com.google.guava</groupId>
        <artifactId>guava</artifactId>
        <version>18.0</version>
    </dependency>
    <dependency>
        <groupId>org.apache.commons</groupId>
        <artifactId>commons-lang3</artifactId>
        <version>3.4</version>
    </dependency>

源码

    public class CachedVersionCompareUtil {
    private static Cache<String, int[]> cache = CacheBuilder.newBuilder().expireAfterWrite(1,
        TimeUnit.HOURS).maximumSize(1000).build();

    private static final int[] EMPTY_INT_ARRAY = new int[0];

    /**
     * version1 > version2  return 1
     * version1 < version2  return -1
     * version1 == version2 return 0
     * @param version1
     * @param version2
     * @return
     */
    public static int compare(String version1, String version2) {
        int[] left = calculate(version1);
        int[] right = calculate(version2);
        if (left.length == 0 && right.length == 0) {
            return 0;
        } else if (left.length != 0 && right.length != 0) {
            int index = 0;
            while (index < left.length && index < right.length) {
                if (left[index] == right[index]) {
                    index += 1;
                } else {
                    return (left[index] < right[index]) ? -1 : 1;
                }
            }
            if (index == left.length && index == right.length) {
                return 0;
            }
            return index == left.length ? -1 : 1;
        } else {
            return left.length == 0 ? -1 : 1;
        }
    }

    private static int[] calculate(final String version) {
        if (StringUtils.isEmpty(version)) {
            return EMPTY_INT_ARRAY;
        }
        try {
            return cache.get(version, new Callable<int[]>() {
                @Override
                public int[] call() throws Exception {
                    return doCalculate(version);
                }
            });
        } catch (Exception e) {
            return doCalculate(version);
        }
    }

    private static int[] doCalculate(String version) {
        String[] array = version.split("\\.");
        int[] intArray = new int[array.length];
        for (int index = 0; index < array.length; index++) {
            intArray[index] = NumberUtils.toInt(array[index].trim());
        }
        return intArray;
    }
}