java - 如何使用 for 循环使用键集迭代 HashMap

Question

我正在尝试使用键集检索 Employee 和 Department 表。我的 HashMap 中有 jsonObject。如何使用 for 循环迭代 Employee.employeeId。任何人都可以帮我吗...

我的 simple.json:

{
    "routings": {
        "routing1": {
            "targetCollection-name": "EmployeeData",
            "sourcetables-data": {
                "Employee": [{
                    "name": "employeeId",
                    "sourceDataType": "number",
                    "targetField": "employeeId",
                    "targetDataType": "double"
                }, {
                    "name": "firstName",
                    "sourceDataType": "varchar2",
                    "targetField": "firstName",
                    "targetDataType": "string"
                }, {
                    "name": "lastName",
                    " sourceDataType": "varchar2",
                    "targetField": "lastName",
                    "targetDataType": "string"
                }, {
                    "name": "contactNumber1",
                    "sourceDataType": "number",
                    "targetField": "contactNumbers",
                    "targetDataType": "array"
                }],
                "department": [{
                    "name": "departmentNumber",
                    "sourceDataType": "number",
                    "targetField": "departmentNumber",
                    "targetDataType": "double"
                }, {
                    "name": "departmentType",
                    "sourceDataType": "number",
                    "targetField": "departmentType",
                    "targetDataType": "double"
                }, {
                    "name": "startDate",
                    "sourceDataType": "timestamp",
                    "targetField": "startDate",
                    "targetDataType": "date"
                }],
                "foriegnkey": [{
                    "parentTable": "Employee",
                    "parentkey": "employeeId",
                    "childTable": "department",
                    "childKey": "empId"
                }]
            }
        }
    }

}

我的代码:

public class DataParse {

    public static void main(String a[]){

        String FILEPATH = "C:\\Users\\BNSK\\Downloads\\simple.json"; 

        Map<String,Object> resultMap = new HashMap<String,Object>();
        ObjectMapper mapperObj = new ObjectMapper();

        System.out.println("Input Json: "+FILEPATH);
        try {
            resultMap = mapperObj.readValue(new File(FILEPATH),
                            new TypeReference<HashMap<String,Object>>(){});
            System.out.println("Output Map: "+resultMap);


for (String key : resultMap.keySet()) {
             Object routings= resultMap.get(key);
           System.out.println(routings);

        }



        } catch (IOException e) {

            e.printStackTrace();
        }
    }

Answer 1

Elliot 是对的，我还想补充一点，在 Java 8 中，您可以使用流(和 lambda 表达式)轻松迭代 Map 键

resultMap.keySet().stream().forEach(key -> {
    // do your thing here 
});