摘抄的ObjectMapper用法

ObjectMapper使用小例子：

首先有个实体对象：

public class User implements Serializable {
/** * */ private static final long serialVersionUID = 1L; private String username; private int age; private String[] list; private Date datetime; <.....省略set get.....> }

先创建个对象

static ObjectMapper omapper = new ObjectMapper();

一、对象转换为json数据

1.  User u = new User();
     u.setAge(24);
     u.setUsername("dobble");
     omapper.writeValue(new File("D:/aa.txt"), u);//写到文件中
     omapper.writeValue(System.out, u);//输出到控制台

输出:{"username":"dobble","age":24,"list":null,"datetime":null}

2.  List<Integer> list=new ArrayList<Integer>();
     list.add(1);
     list.add(2);
     list.add(3);
     String result = omapper.writeValueAsString(list);//序列化
     System.out.println(result);

输出:[1,2,3]

3.  omapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);<1>

DateFormat df = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");<2>
omapper.setDateFormat(df);

User uu = new User();
     uu.setAge(24);
     uu.setDatetime(new Date());
     String[] sts = {"a1","a2","a3"};
     uu.setList(sts);
     uu.setUsername("json");
String r1 = omapper.writeValueAsString(uu);
    System.out.println(r1);

输出1：不加时间格式为-------{"username":"json","age":24,"list":["a1","a2","a3"],"datetime":1463552017876}
加了设置<1>为--------{"username":"json","age":24,"list":["a1","a2","a3"],"datetime":"2016-05-18T06:26:13.414+0000"}
加了自定义<<2>格式为-{"username":"json","age":24,"list":["a1","a2","a3"],"datetime":"2016-05-18 02:30:51"}

4.  JsonGenerator jg = omapper.getFactory().createGenerator(System.out, JsonEncoding.UTF8);
    jg.writeObject(uu); //用的是例3的uu对象
     System.out.println();

输出：加了时间格式---{"username":"json","age":24,"list":["a1","a2","a3"],"datetime":"2016-05-18 02:36:46"}

 

2.json数据转换为对象

File ff = new File("D:/aa.txt");
String str = FileUtils.readFileToString(ff);//可以直接读文件 文件中为json数据
//        String jsonStr = "{\"username\":\"misty\",\"age\":\"24\"}";//也可以自己写json数据
User user = omapper.readValue(str, User.class);
System.out.println(user.getAge()+"--"+user.getUsername());

输出为：24--dobble

获取复杂json数据的特定数据：
String test="{"results":[
{"objectID":357,"geoPoints":[{"x":504604.59802246094,"y":305569.9150390625}]},
{"objectID":358,"geoPoints":[{"x":504602.2680053711,"y":305554.43603515625}]}
]}";//双引号要加转义字符，为了方便可以放到文件中读取

String test = FileUtils.readFileToString(new File("D:/aa.txt")); //将上面字符串放到aa.txt中
JsonNode jnode = omapper.readTree(test);
     JsonNode node = jnode.get("results");
     for(int i=0;i<node.size();i++){
       System.out.println(node.get(i).get("objectID"));
JsonNode no= node.get(i).get("geoPoints");
       for(int j=0;j<no.size();j++){
         double n1 = no.get(j).get("x").doubleValue();
         double n2 = no.get(j).get("y").doubleValue();
         System.out.println(n1 + "--" + n2);
       }
     }
输出为：357
504604.59802246094--305569.9150390625
358
504602.2680053711--305554.43603515625