java实用小技巧

1、任何类型对象判空：

        if (ObjectUtils.isEmpty(任意对象)) {
            
        }

2、 redisTemplate缓存

package org.springframework.data.redis.core;

redisTemplate.opsForValue().get(key);
redisTemplate.opsForValue().set(key, value, redisTime, TimeUnit.SECONDS);

3、字符串解析为list

public void test() {
    List<Student> stuList = JSON.parseObject(JSON.toJSONString("字符串"), 
            new TypeReference<List<Student>>(){});
}

4、对象内容拷贝

5、可变参，取最大值

@Slf4j
public class GetMaxAmount {

    public static void main(String[] args) {
        Map<String, Object> slmItem = Maps.newHashMap();
        slmItem.put("balance6", new BigDecimal("20.0"));
        slmItem.put("balance12", new BigDecimal("23.0"));
        slmItem.put("balance36", new BigDecimal("22.0"));
        BigDecimal bigDecimal = getMaxAmount(slmItem, "balance12", "balance36");
        System.out.println("max value:" + bigDecimal);
    }

    private static BigDecimal getMaxAmount(Map<String, Object> item, String... args) {
        BigDecimal retAmountj;
        try {
            List<BigDecimal> balances = new ArrayList<>();
            for (String arg : args) {
                BigDecimal balance = (BigDecimal) item.get(arg);
                balances.add(balance==null?BigDecimal.ZERO:balance);
            }
            retAmountj = Collections.max(balances);
        } catch (Exception e) {
//            log.error("getMaxAmount BigDecimal转换异常，Exception：", e);
            retAmountj = null;
        }
        return retAmountj;
    }
}

6、ObjectMapper反序列化

    public static void main(String[] args) throws Exception {
        String str = "{\"DS\":{\"o2o\":\"文案1\"}}";
        ObjectMapper objectMapper=new ObjectMapper().configure(
                DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
        Map<String, Map<String, String>> map = objectMapper.readValue(str,
                new TypeReference<Map<String, Map<String, String>>>(){});
        System.out.println("解析结果：" + map);
        System.out.println("done");
    }

输出结果：

解析结果：{DS={o2o=文案1}}
done

参考：
Jackson之ObjectMapper对象的使用
https://blog.youkuaiyun.com/qq_41834086/article/details/111152470
链接: link

7、单元测试 报对象空指针

7.1

    @Before
    public void init() {
        MockitoAnnotations.initMocks(this);
    }

7.2
@RunWith(MockitoJUnitRunner.class)
@PrepareForTest(A.class, B.class)

8、校验必填字段

    public static boolean commonFieldsCheck(Map<String, Object> requestMap, String[] commmon) {
        if (requestMap == null) {
            return false;
        }
        for (String field : commmon) {
            if (!requestMap.containsKey(field) || StringUtils.isEmpty(String.valueOf(requestMap.get(field)))) {
                return false;
            } else {
                continue;
            }
        }
        return true;
    }

9、private boolean checkBlankOrNull(Object var)

private boolean checkBlankOrNull(Object var) {
    if (var == null) {
        return false;
    }
    if (var instanceof String && StringUtils.isNotBlank((String) var)) {
        return true;
    }
    if (var instanceof Map && !((Map) var).isEmpty()) {
        return true;
    }
    if (var instanceof List && !((List) var).isEmpty()) {
        return true;
    }
    return false;
}

10、日志打印耗时时间

    public static void main(String[] args) throws InterruptedException {
        DateTime dateTimeStart = new DateTime();
        Thread.sleep(10*1000);

        boolean showTime = true;
        if (showTime) {
            DateTime dateTimeEnd = new DateTime();
            Interval interval = new Interval(dateTimeStart.getMillis(), dateTimeEnd.getMillis());
            Period period = interval.toPeriod();
            String periodStr = period.getMillis() + "min" + period.getSeconds() + "s"
                    + period.getMillis() + "ms";
            log.info("耗时时间：" + periodStr);
            System.out.println("done");
        }
    }

11、判断语句内 赋值

12、 lambda表达式用法

13、求集合中对象数量Collections.frequency

    public void frequency() {
        List<String> list = Lists.newArrayList("aaa", "bbb","aaa");
        System.out.println("num;" + Collections.frequency(list, "aaa"));
    }

14、spring注入：两个实现类注入到一个map

15、阿波罗字段映射（张坤大佬）

16、JSONObject getDate(“currentDate”);

17、