java - 内部 map 具有多个键值对的 map 内部的 map

Question

我获取CSV文件的值，但在内部映射中映射值时遇到困难。

CSV文件如下所示：



对于每个EmpID，都有一个FirstName，一个LastName以及Groupmbr的多个条目。

对于特定的EmpId（201），我试图获得如下输出：

{
   201= {
      EmpID= 201, 
      FirstName= Sravan, 
      LastName= Jabbala, 
      Groupmbr= [
          PayrollAccess,
          AcctspayableAccess,
          AcctsReceivableAccess2
      ]
   }
}

外部 Map应该包含每个 EmpId（键）和一个内部地图，其中包含有关雇员的详细信息：例如 key=FirstName和 value=Sravan。

这就是我读取CSV文件的方式。

[代码段]

如何填写地图，以便获得理想的结果？

Answer 1

如果我对所需输出的假设是正确的，那么这可以帮助您：

结构如下：

{                                 // ---. the outer map with all EmpIds as keys
   201= {                         //    |---.  for each EmpId, an inner map with the employee's data
      EmpID= 201,                 //    |   | -- an Integer
      FirstName= Sravan,          //    |   | -- some String
      LastName= Jabbala,          //    |   | -- some String
      Groupmbr= [                 //    |   |--.  a List of Strings
          PayrollAccess,          //    |   |  |
          AcctspayableAccess,     //    |   |  |
          AcctsReceivableAccess2  //    |   |  |
      ]                           //    |   |--´
   }                              //    |---´
}                                 // ---´

因此，您的 map2（我建议您给它一个更有意义的名称）具有以下签名：

Map<String, Map<String, Object>>  // this is when you want to cast the EmpID to a String 
Map<Integer, Map<String, Object>> // here you could keep the id as number might be easier to work with?)

让我们在本示例中使用第二个版本。第一个整数是 EmpID，而 Map<String, Object>将是员工的数据。如您所知，数据可以是 Integer, String甚至是 List，因此在此“内部映射”中，我们将仅保留“对象”并稍后处理它们的类型。

现在，我们将阅读CSV：

Scanner s = new Scanner(new File("c:\path\to\your\file.csv");  // this is easier than the buffered reader and almost works the same
s.nextLine();                   // we read the header (first line) of the csv - and forget it right away

while (s.hasNextLine()) {       // as long as we didn't reach the end of the file, we continue reading line by line
    String line = s.nextLine(); // we read the next line
    String[] employeeData = line.split(';'); 

    Integer empId = Integer.valueOf(employeeData[0]); // this will read the EmpId as Integer
    if(empId != empIdSearchedByUser){    // if I assume correctly, you want only the employee that corresponds to the user's input
       continue;                         // that's a fail first anchor :)
    }  

    Map<String, Object> employee;        // we just tell java that we'll work with another map... but we don't know yet if it already exists or not
    if(map2.containsKey(empId){          // in this case the empId is already present (when the same employee in in multiple groups)
       employee = map2.get(empId);       // so we get the existing employee
    } else {
       employee = new HashMap<>();       // otherwise we create a new inner map (for each EmpID/line read we will create a new inner map 
       map2.put(empId, employee);        // and add the inner map to our main map
    }

    // the following three lines are redundant and don't need to be 
    // executed every time for each employee - if the map "employee" already has the entry "FirstName" - then we'll just write it again.. 
    // you can also add some ifs around it.
    employee.put("EmpID", empId);        // Integer is an Object so we can add the number directly to our map without casting it any more 
    employee.put("FirstName", employeeData[1].trim());  //FirstName is a String, we just read it and trim it (to remove all possible whitespaces)
    employee.put("LastName", employeeData[2].trim());   // the same

    List<String> groups;                 // the groups - again we don't know if the list is already present or not..
    if(employee.containsKey("Groupmbr")){
        groups = (ArrayList<String>) employee.get("Groupmbr");  // in case we already have a list, we get it and we cast it (!) from Object to ArrayList
    } else {
        groups = new ArrayList<String>();
        employee.put("Groupmbr", groups);
    }
    groups.add(employeeData[3].trim());  // finally we add the groupe to the list
}  // and this is it.. 

现在，您有了一个具有单个条目（用户正在寻找的雇员）的Map（map2），并且该地图中的所有雇员数据。现在，您可以遍历员工数据图并进行打印。

如果您想读取整个CSV并将所有员工加载到地图中，也可以删除 if(empId==...)。

顺便说一句，我将重命名 map2变量。使用易于识别的变量。为了进一步清理代码，您可能需要将映射键放在静态变量中（或从CSV标头动态读取它们）。但是，在代码中包含修复字符串会很快变得很丑陋-这也浪费了内存。

我希望这会有所帮助（即使时间很长）