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>>(){});