学习杂物（一）java学习笔记

来源：互联网发布：calendar java设置今天编辑：程序博客网时间：2024/04/29 13:38

1、Map的初始化：

Map<String,Object> map = new HashMap<>();

2、Sql的case when方法：

(case 字段  when '字段值' then '替换的值' when '字段值' then '替换的值' else '替换的值'end)

else如果有需求可以有时候不放

3、JSP里的c标签if用法

<c:if text="值的判断句">    ……if里要执行的内容……</c:if>例如：<c:if test="${tEFeedbackPage.feedStatus == 1}">    <input value="未回复" /></c:if>

4、JSP里的c标签forEach遍历List的用法

<c:forEach items="${传来的遍历的List名}" var="循环List的别名">    <input value='${listAns.nickname}' />    <input value='${listAns.time}' /></c:forEach >

var中可以用这些属性值：
index当前这次迭代从 0 开始的迭代索引
count当前这次迭代从 1 开始的迭代计数
first用来表明当前这轮迭代是否为第一次迭代的标志
last用来表明当前这轮迭代是否为最后一次迭代的标志
begin属性值开始的位置
end属性值结束的位置
step属性值迭代步长

5、MiniDao里的 <#if> 在模糊查询的用法(例如)

SELECT(select count(1) from t_e_answer t4 where t1.id=t4.question_id) as ansNum,t1.id,t2.typecode,t1.question_title AS questionTitle,t1.question_status AS questionStatus,t1.question_time AS questionTime,t3.nickname,t1.scan_num AS scanNumFROM t_e_question t1INNER JOIN t_s_type t2 ON t1.question_type = t2.typecodeINNER JOIN t_e_person t3 ON t1.person_id = t3.idWHERE t1.del_flag = 0<#if tEQuestionEntity.questionTitle ?exists && tEQuestionEntity.questionTitle ?length gt 0>    and t1.question_title like concat('%',:tEQuestionEntity.questionTitle, '%')</#if><#if tEQuestionEntity.questionStatus ?exists && tEQuestionEntity.questionStatus ?length gt 0>    and t1.question_status = :tEQuestionEntity.questionStatus</#if><#if timeGroupDto.questionTime_begin ?exists && timeGroupDto.questionTime_begin ?length gt 0 && timeGroupDto.questionTime_end ?exists && timeGroupDto.questionTime_end ?length gt 0>    and t1.question_time BETWEEN :timeGroupDto.questionTime_begin and :timeGroupDto.questionTime_end</#if><#if nickname ?exists && nickname ?length gt 0>    and t3.nickname like concat('%',:nickname, '%')</#if><#if tEQuestionEntity.scanNum ?exists && tEQuestionEntity.scanNum ?length gt 0>    and t1.scan_num = :tEQuestionEntity.scanNum</#if><#if typecode ?exists && typecode ?length gt 0>    and t2.typecode  like concat('%',:typecode, '%')</#if><#if index ?exists && index ?length gt 0 && columns ?exists && index ?length gt 0>    ORDER BY  ${columns}  ${index}</#if>LIMIT :pageIndex,:rows

1 0