Java小tips

Java小工具

1. J8 stream

Map转List>

List<Map<String,String>> B
= A.entrySet().stream().map(m->{
                    Map<String,String> u = new Map<String,String>();
                    u.setKey(m.getKey());
                    u.setTitle(m.getValue());
                    return u;
                }).collect(Collectors.toList());

Map>转Map

Map<String, List<String>> parameters;
Map<String, String[]> collect = parameters.entrySet().stream()
                .collect(Collectors.toMap(entry-> entry.getKey(),entry -> entry.getValue().toArray()));

null/nutNull

String

空

str.isEmpty()

不为空

StringUtils.isNotBlank(str)

List

• 空

if(list == null || list.size() ==0 ){
　　//为空的情况
}else{
　　//不为空的情况
}

• 不为空

if(list!=null && !list.isEmpty()){
　　　//不为空的情况
}else{
　　　//为空的情况
}

• list.isEmpty() 和 list.size()==0 没有区别 。isEmpty()判断有没有元素，而size()返回有几个元素， 如果判断一个集合有无元素 建议用isEmpty()方法.比较符合逻辑用法。

容器操作

1.List去重

• 利用set集合特性保持顺序一致去重
  // Set去重并保持原先顺序的两种方法
  public static void delRepeat(List list) {
  //方法一（注：会改变顺序）
  List listNew = new ArrayList(new TreeSet(list));
  //方法二
  List listNew2 = new ArrayList(new LinkedHashSet(list));
  }

数据类型

1. 判断是否为正数

public static boolean isIntegerForDouble(double obj) {
        double eps = 1e-10;  // 精度范围
        return obj-Math.floor(obj) < eps;
    }

2. 判断精度

private static boolean doubleAccuracy(String str, int doubleSize) {
        try {
            double num = Double.valueOf(str);//把字符串强制转换为数字
            if (str.trim().contains(".")) {
                int currentPlace = str.trim().length() - str.trim().indexOf(".") - 1;
                return currentPlace < doubleSize;
            }
            return true;
        } catch (Exception e) {
            return false;//如果抛出异常，返回False
        }
    }

参考

时间

获取最近30分钟

 // 获取前30分钟日期
                        Calendar calendar = Calendar.getInstance();
                        Date late = calendar.getTime();
                        calendar.add(Calendar.MINUTE, -30);
                        Date early = calendar.getTime();
                        query.setStartTime(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(early));
                        query.setEndTime(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(late));

String转Date

        String end = "2020-06-27";
     // SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd");
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat( "yyyy-MM-dd HH:mm:ss " ); 
        Date endTime = simpleDateFormat.parse(end);

注：例如MM是月份，mm是分；HH是24小时制，而hh是12小时制。

Date转String

   SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"); 
   String str = format.format(date); 

Date比较

    Date endDate = DateUtil.parseDate(endStr);
    Date startDate = DateUtil.parseDate(startStr);
    if (DateUtil.compare(endDate, startDate) < 0) {
        return stringBuilder.append("结束时间不能早于开始时间").toString();
    }

改变Date时分秒

        Date now = new Date();
        Calendar calendar = Calendar.getInstance();
        calendar.setTime(now);
        calendar.set(Calendar.HOUR_OF_DAY, 23);
        calendar.set(Calendar.MINUTE, 59);
        calendar.set(Calendar.SECOND, 59);
        Date now2= calendar.getTime();
        System.out.println(now2);

文件

Hutool

https://www.hutool.cn/

File->MultipartFile

File file = new File("F:/hejing/InstrumentJsonData.txt");
if(file.isFile() && file.exists()) {
  ...
}
 public static void main(String[] args) throws Exception {
        // File file = new File("F:/hejing/InstrumentJsonData.txt");
        String strUrl = "F:/hejing/InstrumentJsonData.txt";
        File file = new File(strUrl);
        InputStream inputStream = new FileInputStream(file);
        MultipartFile multipartFile = new MockMultipartFile(file.getName(), inputStream);
        log.info("file转multipartFile成功. {}",multipartFile);
    }

    XSSFWorkbook xssfWorkbook = new XSSFWorkbook(inputStream);
    XSSFSheet xssfSheet = xssfWorkbook.getSheetAt(0);
    int rowSize = xssfSheet.getLastRowNum();

MultipartFile->File

        CommonsMultipartFile cmf = (CommonsMultipartFile)file;
        DiskFileItem dfi = (DiskFileItem)cmf.getFileItem();
        File f = dfi.getStoreLocation();

MultipartFile->inputStream

        CommonsMultipartFile commonsMultipartFile = (CommonsMultipartFile)file;
        DiskFileItem fileItem = (DiskFileItem)commonsMultipartFile.getFileItem();
        InputStream fileInputStream = fileItem.getInputStream();

Excel

流程

1. 配置路径 yml

   dataplatform:
     filePath: D:\file\

2. 创建config类

   @Configuration(value = "filePathConfig")
   @ConfigurationProperties(prefix = "dataplatform")
   @Data
   public class FilePathConfig {
       public static final String SEPARATOR;
       static {
           SEPARATOR = FileUtil.isWindows() ? "\\" : "/";
       }
       String filePath;
   }

3. 读

4. 写
5. 设置标记
   设置颜色：https://blog.csdn.net/yuefenghui/article/details/67673994
   颜色： https://vimsky.com/zh-tw/examples/detail/java-method-org.apache.poi.ss.usermodel.Font.setColor.html

前后端

前端：array->后端接收

["1","2","3"]
public String save(@Param("switch")boolean switch1,String slider,String input,String redio,String checkbox){
    JSONArray obj = JSON.parseArray(checkbox);
    sout(JSON.parseArray(checkbox).size());
    fori(){
       obj.get(i);
    }
}

curl请求form、json

1. application/x-www-form-urlencoded

curl -X POST 'http://localhost:8080/formPost' -d 'id=1&name=foo&mobile=13612345678'

1. application/json

curl -X POST -H "Content-Type: application/json" 'http://localhost:8080/jsonPost' -d '{"id":2,"name":"foo","mobile":"13656635451"}'

https://blog.csdn.net/weixin_34400525/article/details/86254617