胡言乱语小笔记 --后端

利用 ObjectMapper 转对象 指定泛型类型

   new ObjectMapper().readValue(json, new TypeReference<HashMap<String, Bean>>(){});
    
    new ObjectMapper().readValue(json, new TypeReference<Map<String, List<Map<String, String>>>>() {})

对象集合根据某个值进行分组求和, 获取求和后的Map

List<Product> productList = new ArrayList<>();
//获取ProductType相同的重量合计Map<产品类型, 总重量>
Map<String, BigDecimal> productTypeWeight = productList.stream().collect(Collectors.groupingBy(
				Product::ProductType,
				Collectors.reducing(BigDecimal.ZERO, Product::getWeight, BigDecimal::add)));

Iterable类型使用Stream流式处理

StreamSupport.stream(Iterable.spliterator(), false).collect(Collectors.toList());

StringJoiner对象 指定分隔符

老项目中使用了JdbcTemplate 需手写sql字符串, 以前的写法是使用StringBuffer进行字符串拼接, 会导致大意忘记最后加空格

StringBuffer sqlBuf = new StringBuffer();
		sqlBuf.append("SELECT ");
		sqlBuf.append("(SELECT xx.org_desc FROM pub_organizations xx WHERE xx.org_code = mm.factory_code) AS factoryName ");
		sqlBuf.append("FROM mkt_bid_order mm ");
		sqlBuf.append("INNER JOIN pub_step ss ON mm.ID = ss.source_id ");

使用StringJoiner对象, 指定空格分隔, StringJoiner对象底层维护的是StringBuffer对象

//指定空格进行分隔
StringJoiner auditItem = new StringJoiner(" ");
		auditItem.add("(SELECT review_detail_desc FROM (");
		auditItem.add("SELECT ROW_NUMBER() OVER (ORDER BY id) AS rownum, zz.review_detail_desc");
		auditItem.add("FROM mkt_check_review xx");

String.join()方法就是使用StringJoiner对象来实现

StopWatch 统计接口耗时时间

    StopWatch stopWatch = new StopWatch("任务名称");
    stopWatch.start(); //开始记时;
    stopWatch.stop();  // 结束记时;
    stopWatch.getLastTaskTimeMillis(); //获取毫秒值