code cheat sheet

content/posts/_index.md

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-path = "posts" 
 template = "posts.html" 
 transparent = true 
 sort_by = "date" 

content/posts/code-cheat-sheet.md

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+title = "code cheat sheet"
+date = "2024-10-12"
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+
+## Java
+### 去除空格
+```java
+public String trim(String str) {
+    // "\u0020" 半角空格, office空格, 全角空格
+    return str.trim().replace("\u00a0", "").replace("\u3000", "");
+} 
+```
+
+## Spring
+### 获取Servlet相关参数
+```java
+ServletRequestAttributes servletRequestAttributes = (ServletRequestAttributes) RequestContextHolder.getRequestAttributes();
+HttpServletResponse response = servletRequestAttributes.getResponse();
+HttpServletRequest request = servletRequestAttributes.getRequest();
+```
+## Library
+### Hutool
+#### ExcelUtil
+```java
+ExcelReader reader = ExcelUtil.getReader(FileUtil.file("公务用车车辆管理员信息.xlsx"), 0);
+List<Map<String, Object>> carManagerMaps = reader.readAll();
+//  所有用车管理员userCode
+List<String> carManagersUserCode = carManagerMaps.stream()
+        .map(map -> map.get("账号").toString())
+        .collect(Collectors.toList());
+
+final List<LinkedHashMap<String, String>> rows = carManagersUserCode.stream().map(userCode -> {
+    LinkedHashMap<String, String> row = new LinkedHashMap<>();
+    row.put("账号", userCode);
+    return row;
+}).collect(Collectors.toList());
+
+ExcelWriter excelWriter = ExcelUtil.getWriter();
+
+excelWriter.renameSheet("所有车辆管理员账号");
+excelWriter.write(rows, true);
+
+response.setContentType("application/vnd.ms-excel;charset=utf-8");
+response.setHeader("Content-Disposition", "attachment;filename=test_1.xls");
+ServletOutputStream out = response.getOutputStream();
+excelWriter.flush(out, true);
+
+excelWriter.close();
+IoUtil.close(out);
+```
+
+```java
+ExcelReader reader = ExcelUtil.getReader(FileUtil.file("path"), 0);
+```
+```
+ExcelWriter excelWriter = ExcelUtil.getWriter();
+```
+## DB
+### 时间段重叠问题
+```sql
+DELIMITER $$
+CREATE TRIGGER check_time_overlap
+    BEFORE INSERT
+    ON t_meeting_pre_form
+    FOR EACH ROW
+BEGIN
+    IF EXISTS (SELECT 1
+               FROM t_meeting_pre_form
+               WHERE (not (NEW.meeting_time_top >= meeting_time_bottom
+                   or NEW.meeting_time_bottom <= meeting_time_top))
+                 AND NEW.meeting_room_id = meeting_room_id
+                 AND NEW.meeting_date = meeting_date
+                 AND delete_mark = 0) THEN
+        SIGNAL SQLSTATE '45000'
+            SET MESSAGE_TEXT = '会议室预定时间重叠';
+    END IF;
+    END$$
+DELIMITER ;
+```