你不知道的常用工具类

1. 空值判断

1. 空字符串判断

java复制代码boolean isEmpty =  StringUtils.isEmpty(str);

2. 空集合判断

java复制代码boolean isEmpty  = CollectionUtils.isNotEmpty(list);

3. 对象判空,在某些其它的工具类中 StringUtils既可以对字符串判空,也可以对对象进行判空

• org.apache.commons.lang3包

java复制代码StringUtils.isEmpty(CharSequence cs);

public static boolean isEmpty(CharSequence cs){
    return cs == null || cs.length() ==0
}

• 在org.springframework.util参数类型是Object的

java复制代码public static boolean isEmpty(Object obj){
    return obj == null || "".equals(obj);
}

4. 字符串转集合

java复制代码   // str = "2,5,8,7";
   String str = "2,5,8,7";
   List<Integer> idList = StringUtil.stringToList(str,",");

2.stream流操作相关的工具

1. 集合去重过滤

java复制代码List<User> userList = userService.getList();
//去掉某个字段为空的数据 
userList = userList.stream().filter(s =>StringUtils.isEmpty(s.getPhone()).collect(Collectors.toList());

2. 遍历操作

java复制代码
userList = userList.stream().map(user -> user.getName());
userList = userList.stream().map(user -> user.getName()).forEach(str -> {System.out.println(str)})
//提取所有的id
List<Integer> ids = userList.stream().map(User::getId()).collect(Collectors.toList());

3. 排序操作

java复制代码//根据id进行排序
userList = userList.stream().sorted(User::getId()).collect(Collectors.toList());
//倒序  不加reversed 顺序
userList = list.stream()
    .sorted(Comparator.comparing(User::getAge).reversed())
    .collect(Collectors.toList());
//根据其它排序 
userList = userList.stream().sorted((In1,In2) -> In1- In2).collect(Collectors.toList());

4. 判断操作

java复制代码//判断是否有名字为jack的 
boolean isExsit = userList.stream().anyMacth(s ->"jack".equals(s.getName()));
//判断某个字段是否全为空 
boolean isEmpty = userList.stream().nonoMatch(s -> s.getEmail().isEmpty());

5. 对象集合分组去重

java复制代码Map<Integer, List<PurchaseUpdate>> maps = updates.stream().collect(Collectors.groupingBy(PurchaseUpdate::getWriteId, Collectors.toList()));
maps.forEach((k,v) ->{
	v.forEach(update ->{
		vo.setId(update.getId());
		vo.setNumber(update.getCount());
		purchaseService.update(vo);
		
		build.append("xxxxx---------xxxxxx");
	})
	
});

6. 对象集合抽取某个元素组成新的数据或者按照符号拼接

java复制代码 String currentIds = list.stream().map(p ->p.getCurrentUser() == null ? null : p.getCurrentUser().toString()).collect(Collectors.joining(","));
 List<Integer> ids = list.stream().map(User::getId).collect(Collectors.toList());

7. 集合某个字段求和

java复制代码IntSummaryStatistics st = list.stream().mapToInt(Info::getAge).summaryStatistics();
System.out.println("求和:" + st.getSum());
System.out.println("平均数" + st.getAverage());
System.out.println("最大值:" + st.getMax());
System.out.println("总数:" +st.getCount());

8. 集合转Map

java复制代码Map<Integer,String> map = list.stream().collect(Collectors.toMap(Info::getAge ,Info::getName));
System.out.println(map.toString());

9. list转set

java复制代码Set<Info> collect = list.stream().collect(Collectors.toSet());
collect.forEach(e -> {
    System.out.println(e.toString());
});

10. list中对对个字段计算并求和

计算所有订单总共销售额

java复制代码double  total = details.stream()
    .filter(e -> e.getPrice() != null && e.getAmountActual() != null)
    .reduce(0.0 ,
    ( x, y)-> x + (y.getPrice().doubleValue() * y.getAmountActual().doubleValue()) ,Double::sum)

//如果本身字段是 BigDecimal类型
 BigDecimal ss = details.stream().reduce(BigDecimal.ZERO, (x, y) ->
                 x.add(y.getAmountActual().multiply(y.getPrice())), BigDecimal::add);

3.OkHttp3 请求, http请求

一个新的http客户端,使用简单,性能极好,可以完美代替HttpClient

java复制代码//get 请求 

OkHttpClient client = new OkHttpClient();

String run (String url) {
    Request request = new Request.Builder()
        .url(url)
        .build();

    try {
        Response res = client.newCall(request).execute();
        return res.body().string();
    } catch (Exception e){
        return e;
    }
}

//Post请求 
public static final MediaType JSON  = MediaType.get("application/json;charset=utf-8");
String run (String url ,String json) {
    RequestBody body = RequestBody.create(json,JSON);
    Request request = new Request.Builder()
        .url(url)
        .body(body)
        .build();
    try {
        Response res = client.newCall(request).execute();
        return res.body().string();
    }
}

4. 集合转符号分割的字符串

java复制代码List<String> list = new ArrayList<String>();
list.add("1");
list.add("2");
list.add("3");
String result = Joiner.on("-").join(list);

> 1-2-3

代码示例

java复制代码public List<WaterQualityDTO> getWaterQuality(String date, List<Integer> processIds) {
        List<WaterQualityDTO> list = new ArrayList<>();
        List<TaskOrderContent> taskList = contentRepository.findByTime(date,processIds);
        //查询所有的化验指标数据
        List<Indicators> indicators = indicatorsRepository.findAll();
        Map<Long,Indicators> indicatMap = new HashMap<>();
        if(!CollectionUtils.isEmpty(indicators)){
     //list  转成Map  以id 和对象为 key和value       indicatMap.putAll(indicators.stream().collect(Collectors.toMap(Indicators::getId, Function.identity())));
        }
        if(!CollectionUtils.isEmpty(taskList)){
        //去重 合并
            String ids = taskList.stream().map(TaskOrderContent::getProcessId)
                    .distinct()
                    .map(String::valueOf)
                    .collect(Collectors.joining(","));

            Map<Integer, List<ProcessChainDTO>> processNames = processService.getProcessChainsByProcessIds(ids);

            Map<Integer,List<TaskOrderContent>> group = taskList.stream().collect(
                    Collectors.groupingBy(TaskOrderContent ::getProcessId,Collectors.toList())
            );
            List<WaterQualityDTO.WaterRes> resList = new ArrayList<>();
            group.forEach((k,v) ->{
                resList.clear();
                WaterQualityDTO waterAssay = new WaterQualityDTO();
                String processName = processNames.get(k).stream().map(ProcessChainDTO::getName).collect(Collectors.joining("-"));
                waterAssay.setPointName(processName);
                waterAssay.setProcessId(k);
                waterAssay.setTestDate(date);

                v.stream().forEach(e ->{
                    WaterQualityDTO.WaterRes res = new WaterQualityDTO.WaterRes();
                    res.setCityName(processName);

                    res.setValue(e.getValue());

                });

            });
        }


        return null;
    }

本文转载自: 掘金

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