jackson快速小结

1 对象转换为json

ObjectMapper mapper = new ObjectMapper();
Staff obj = new Staff();


mapper.writeValue(new File("c:\\file.json"), obj);


String jsonInString = mapper.writeValueAsString(obj);

2 json转换为object

ObjectMapper mapper = new ObjectMapper();
String jsonInString = "{'name' : 'mkyong'}";

//JSON from file to Object
Staff obj = mapper.readValue(new File("c:\\file.json"), Staff.class);

//JSON from URL to Object
Staff obj = mapper.readValue(new URL("http://mkyong.com/api/staff.json"), Staff.class);

//JSON from String to Object
Staff obj = mapper.readValue(jsonInString, Staff.class);

3 格式化输出

// Convert object to JSON string and pretty print
      jsonInString = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(staff);
      System.out.println(jsonInString);

{

"name" : "mkyong",

"age" : 33,

"position" : "Developer",

"salary" : 7500,

"skills" : [ "java", "python" ]

}

4 使用@JsonView, 控制哪些字段输出

先定义view

public class Views {

  public static class Normal{};

  public static class Manager extends Normal{};

}

对于normal的，是看不到薪酬，如果经理，则看到

public class Staff {

  @JsonView(Views.Normal.class)
  private String name;

  @JsonView(Views.Normal.class)
  private int age;

  @JsonView(Views.Normal.class)
  private String position;

  @JsonView(Views.Manager.class)
  private BigDecimal salary;

  @JsonView(Views.Normal.class)
  private List<String> skills;

则：

// Salary will be hidden
      System.out.println("Normal View");
      String normalView = mapper.writerWithView(Views.Normal.class).writeValueAsString(staff);
      System.out.println(normalView);

      String jsonInString = "{\"name\":\"mkyong\",\"age\":33,\"position\":\"Developer\",\"salary\":7500,\"skills\":[\"java\",\"python\"]}";
      Staff normalStaff = mapper.readerWithView(Views.Normal.class).forType(Staff.class).readValue(jsonInString);
      System.out.println(normalStaff);

      // Display everything
      System.out.println("\nManager View");
      String managerView = mapper.writerWithView(Views.Manager.class).writeValueAsString(staff);
      System.out.println(managerView);

      Staff managerStaff = mapper.readerWithView(Views.Manager.class).forType(Staff.class).readValue(jsonInString);
      System.out.println(managerStaff);

输出：

Normal View

{"name":"mkyong","age":33,"position":"Developer","skills":["java","python"]}

Staff [name=mkyong, age=33, position=Developer, salary=null, skills=[java, python]]

Manager View

{"name":"mkyong","age":33,"position":"Developer","salary":7500,"skills":["java","python"]}

Staff [name=mkyong, age=33, position=Developer, salary=7500, skills=[java, python]]

5 常见问题

json转变为数组

String json = "[{\"name\":\"mkyong\"}, {\"name\":\"laplap\"}]";

List<Staff> list = mapper.readValue(json, new TypeReference<List<Staff>>(){});

把json转变为map

String json = "{\"name\":\"mkyong\", \"age\":33}";

Map<String, Object> map = mapper.readValue(json, new TypeReference<Map<String,Object>>(){});