List双重for根据字段去重 修改需要迭代器 要不会抛异常 public class Test { public static void main(String[] args) { List<User3> list = new ArrayList<User3>(); list.add(new User3("1", "张三1")); list.add(new User3("1", "张三2")); list.add(new User3("2", "张三3")); list.add(new User3("2", "张三4")); list.add(new User3("3", "张三5")); System.out.println("去重前："); for (User3 user : list) { System.out.println(user); } System.out.println("去重后："); List<User3> repeatList = new ArrayList<User3>();// 用于存放重复的元素的list for (int i = 0; i < list.size() - 1; i++) { for (int j = list.size() - 1; j > i; j--) { if (list.get(j).getId().equals(list.get(i).getId())) { repeatList.add(list.get(j));// 把相同元素加入list(找出相同的) list.remove(j);// 删除重复元素 } } } for (User3 user : list) { System.out.println(user); } System.out.println("相同的元素："); for (User3 user : repeatList) { System.out.println(user); } } } class User3 { private String id; private String name; public User3(String id, String name) { super(); this.id = id; this.name = name; } public String getId() { return id; } public void setId(String id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } @Override public String toString() { return "User3 [id=" + id + ", name=" + name + "]"; } }

mybatis-plus实体类中出现非数据库映射字段解决办法 如果需要在mybatis映射实体类中加入非数据库映射字段。那么可以使用@TableField(exist = false)进行标识对应字段不属于数据库的映射字段即可。

获取几位随机数 　 /** * 随机数 * @param len 几位随机数 * @return */ public static String getRandom4(int len) { String source = "0123456789"; Random r = new Random(); StringBuilder rs = new StringBuilder(); for (int j = 0; j < len; j++) { rs.append(source.charAt(r.nextInt(10))); } return rs.toString(); }

spring事务控制@Transactional(readOnly = false, propagation = Propagation.REQUIRED, rollbackFor = Exception.class) @Transactional(readOnly = false, propagation = Propagation.REQUIRED, rollbackFor = Exception.class)propagation用法讲解：1、PROPAGATION_REQUIRED:如果存在一个事务，则支持当前事务。如果没有事务则开启。2、PROPAGATION_SUPPORTS:如果存在一个事务，支持当前事务。如果没有事务，则非事务的执行。3、PROPAGATION_MANDATORY:如果已经存在一个事务，支持当前事务。如果没有一个活动的事务，则抛出异常。4、PROPAGATION_REQUIRES_NEW:总是开启一个新的事务。如果一个事务存在，则将这个存在的事务挂起。5、PROPAGATION_NOT_SUPPORTED:总是非事务地执行，并挂起任何存在的事务。6、PROPAGATION_NEVER:总是非事务地执行，如果存在一个活动事务，则抛出异常。7、 PROPAGATION_NESTED:如果一个活动的事务存在，则运行在一个嵌套的事务中，如果没有活动事务，则按TransactionDefinition.PROPAGATION_REQUIRED属性执行

Java接收 上传文件 返回路径 postman测试提交controller层 @PostMapping(value = "/file/upload") @ApiOperation(value = "上传家长单图片", httpMethod = "POST") @ResponseBody public BaseResponse fileUpload(@RequestPart(value = "file") MultipartFile file) { if (file.isEmpty()){ // TODO return BaseResponse.fail(); } return BaseResponse.success(studentPickInfoService.uploadFile(file)); } service @Value("${upload.root-dir}") private String uploadRootDir;//文件路径 @Value("${upload.root-url}") private String uploadRootUrl;//访问文件域名 private final DateFormat df = new SimpleDateFormat("yyyy-MM-dd"); @Override public String uploadFile(MultipartFile file) { try { String dir = "/ask_leave/student/" + df.format(new Date()) + "/"; String uploadRootDirPath = uploadRootDir + dir; File imgPath = new File(uploadRootDirPath); if (!imgPath.exists()) { imgPath.mkdirs(); } if (!file.isEmpty()) { String originalFileName = file.getOriginalFilename(); String suffix = getFileSuffix(originalFileName); String fileName = UUIDGenerator.generate() + "." + suffix; String filePath = uploadRootDirPath + fileName; System.out.println(filePath); System.out.println(uploadRootUrl + dir + fileName); file.transferTo(new File(filePath)); return uploadRootUrl + dir + fileName; } else { throw new BusinessException(5001, "文件上传失败"); } } catch (IOException e) { throw new BusinessException(5001, "文件上传失败"); } } private String getFileSuffix(String fileName) { String suffix = "jpg"; if (org.apache.commons.lang3.StringUtils.isNotBlank(fileName) && fileName.lastIndexOf(".") > 0) { String[] arrStr = fileName.split("\\."); suffix = arrStr[arrStr.length - 1]; } return suffix; }