java小知识点

目录

统计条目

LambdaQueryWrapper 

遍历并按某种条件统计

返回找到的第一个值（找主键）

map放入不同的List--Collections.singletonList

JSON.toJSONString

JSON.parseObject

统计条目

Long modelCounts = modelMapper.selectCount(modelQueryWrapper);

LambdaQueryWrapper 

LambdaQueryWrapper<AppRelease> arLqr =new LambdaQueryWrapper<AppRelease>().eq(AppRelease::isDeleted, false).eq(AppRelease::getAppId, appId).orderByDesc(AppRelease::getCreateTime).last("limit 1");return appReleaseMapper.selectOne(arLqr);

遍历并按某种条件统计

long keyCount =table.getFields().stream().filter(t -> Objects.equals(t.getIsKey(), true)).count();

返回找到的第一个值（找主键）

TableFieldDto tableKey =table.getFields().stream().filter(t -> Objects.equals(t.getIsKey(), true)).findFirst().get();

map放入不同的List--Collections.singletonList

List<Datasource> datasourceList = datasourceMapper.selectList(datasourceQueryWrapper);
List<AppInterface> appInterfaceList = appInterfaceMapper.selectList(null);Map<String, List<Object>> map = new TreeMap<>();
map.put("datasource", Collections.singletonList(datasourceList));
map.put("interface", Collections.singletonList(appInterfaceList));

equalsIgnoreCase() 方法用于将字符串与指定的对象比较，不考虑大小写。而equals()会判断大小写区别。

JSON.toJSONString

将对象转化为Json字符串

JSON.parseObject

将json字符串转化为相应的对象

result格式1

{"studentName":"true","studentAge":"123" 
}

JSONObject jsonObject=JSON.parseObject(result);      //转换成object
jsonObject.getString("studentAge")    //获取object中studentAge字段;  
System.out.println(jsonObject.getString("studentName")+":"+jsonObject.getInteger("studentAge"));                                                     

result格式2

[{"studentName":"lily","studentAge":12},{"studentName":"lucy","studentAge":15}
]

JSONArray jsonArray = JSON.parseArray(result);
//JSONArray jsonArray1 = JSONArray.parseArray(result);//因为JSONArray继承了JSON，所以这样也是可以的//遍历方式1int size = jsonArray.size();for (int i = 0; i < size; i++){JSONObject jsonObject2 = jsonArray.getJSONObject(i);  System.out.println(jsonObject2.getString("studentName")+":"+jsonObject2.getInteger("studentAge"));}//遍历方式2for (Object obj : jsonArray) {JSONObject jsonObject2 = (JSONObject) obj;   
System.out.println(jsonObject2.getString("studentName")+":"+jsonObject2.getInteger("studentAge"));}

result格式3

{"success":"true","data":{"shop_uid":"123"}
}

JSONObject shop_user =JSON.parseObject(result);  
System.out.println(JSON.parseObject(shop_user.getString("data")).getString("shop_uid"));

result格式4

{"success": "true","data": {"shop_uid": "123","dataChild": {"uidChild": "456"      //多层json嵌套}}
}

JSONObject shop_user =JSON.parseObject(result);//注意:多层嵌套这里data不能先用getString("data"), 再parseObject来获取dataChild对象
JSONObject dataObject = shop_user.getJSONObject("data");dataObject.getJSONObject("dataChild").getString("uidChild");

result格式5

{"teacherName":"crystall","teacherAge":27,"course":{"courseName":"english","code":1270},"students":[{"studentName":"lily","studentAge":12},{"studentName":"lucy","studentAge":15}]
}

JSONObject jsonObject = JSON.parseObject(COMPLEX_JSON_STR);//JSONObject jsonObject1 = JSONObject.parseObject(COMPLEX_JSON_STR);//因为JSONObject继承了JSON，所以这样也是可以的
String teacherName = jsonObject.getString("teacherName");
Integer teacherAge = jsonObject.getInteger("teacherAge");
JSONObject course = jsonObject.getJSONObject("course");
JSONArray students = jsonObject.getJSONArray("students");
System.out.println(teacherName+","+teacherAge+","+course+","+students);