用Jackson解析JSON。爲什麼使用HashMap而不是我的類型？

我使用的是傑克遜庫來解析JSON：用Jackson解析JSON。爲什麼使用HashMap而不是我的類型？

{ 
"employees": [ 
{ "firstName":"John" , "lastName":"Doe" }, 
{ "firstName":"Anna" , "lastName":"Smith" }, 
{ "firstName":"Peter" , "lastName":"Jones" } 
] 
}

下面是我在做什麼：

public void testJackson() throws IOException { 
    JsonFactory factory = new JsonFactory(); 
    ObjectMapper mapper = new ObjectMapper(factory); 
    File from = new File("emp.txt"); // JSON object comes from 
    TypeReference<HashMap<String, Object>> typeRef = new TypeReference<HashMap<String, Object>>() {}; 
    HashMap<String, Object> o = mapper.readValue(from, typeRef); 
    Employees employees = new Employees(); 
    employees.employees = (List<Employer>)o.get("employees"); // retrieving list of Employer(s) 
    employees.showEmployer(1); // choose second to print out to console 

    System.out.println("Got " + o); // just result of file reading 
} 

public static class Employees { 
    public List<Employer> employees; 

    public void showEmployer(int i) { 
     System.out.println(employees.get(i)); 
    } 
} 

public static class Employer { 
    public String firstName; 
    public String lastName; 
}

輸出我得到：

{的firstName = Anna，lastName = Smith}

Got {employees = [{firstName = John， lastName = Doe}，{firstNam E =安娜，姓氏=史密斯}，{=的firstName彼得，的lastName =瓊斯}]}

但我不期待在我的List元素是HashMap實例，但Employer對象。這是什麼Jackson圖書館應該是，不是嗎？你們能糾正我的錯誤嗎？

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2012-11-27 Eugene

我還沒有使用過傑克遜，但看起來你得到了你所要求的 - 一個String，Object對的HashMap。也許你需要在地圖的「價值」部分更加明確？由於該值是Employee對象的數組，因此您可以嘗試：

TypeReference<HashMap<String, List<Employee>>> typeRef = new TypeReference<HashMap<String, List<Employee>>>() {}; 
HashMap<String, List<Employee>> o = mapper.readValue(from, typeRef);

來源

2012-11-27 22:49:26

用Jackson解析JSON。爲什麼使用HashMap而不是我的類型？

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