JSON数据处理之jackson

相关Jar包：

1. jackson-annotations-2.9.8.jar
2. jackson-core-2.9.8.jar
3. jackson-databind-2.9.8.jar

核心内容

jackson核心对象
ObjectMapper mapper = new ObjectMapper();

常用方法：
1.对象转JSON

• writeValue(参数1， obj)
  参数1：
  File：将obj对象转换为json字符串，并保存到指定的文件中
  Writer：将obj对象转换为json字符串，并将json数据填充到字符输出流中
  OutputStream：将obj对象转换为json字符串，并将json数据填充到字节输出流中
• writeValueAsString(obj)：将对象转换为json字符串

2.JSON转对象

• readValue(String content, Class valueType)
  content：json字符串
  valueType：要转换的Java对象类型（如：Person.class)

对象转JSON

1. Java基本对象转JSON

public void test1() throws Exception {
        // 1.创建person对象
        Person p1 = new Person();
        p1.setName("Lisa");
        p1.setAge(15);
        p1.setGender(0);
        // 2.创建Jackson核心对象ObjectMapper
        ObjectMapper mapper = new ObjectMapper();
        // 3.调用方法进行转换
        String json = mapper.writeValueAsString(p1);
        System.out.println(json); // {"name":"Lisa","age":15,"gender":0}
    }

2. list转JSON

public void test2() throws Exception {
        // 1.创建person对象
        Person p1 = new Person();
        p1.setName("Lisa");
        p1.setAge(20);
        p1.setGender(0);
        Person p2 = new Person();
        p2.setName("Lily");
        p2.setAge(18);
        p2.setGender(0);
        Person p3 = new Person();
        p3.setName("Harry");
        p3.setAge(22);
        p3.setGender(1);
        ArrayList list = new ArrayList();
        list.add(p1);
        list.add(p2);
        list.add(p3);
        // 2.创建Jackson核心对象ObjectMapper
        ObjectMapper mapper = new ObjectMapper();
        // 3.调用方法进行转换
        String json = mapper.writeValueAsString(list);
        System.out.println(json);   
        // [{"name":"Lisa","age":20,"gender":0},{"name":"Lily","age":18,"gender":0},{"name":"Harry","age":22,"gender":1}]
    }

4. map转JSON

public void test3() throws Exception {
        // 1.创建map并保存数据
        Map<String, Object> map = new HashMap<String, Object>();
        map.put("name", "Lisa");
        map.put("age", 18);
        map.put("gender", 0);
        // 2.创建Jackson核心对象ObjectMapper
        ObjectMapper mapper = new ObjectMapper();
        // 3.调用方法进行转换
        String json = mapper.writeValueAsString(map);
        System.out.println(json);   // {"gender":0,"name":"Lisa","age":18}
    }

JSON转对象

1. JSON转Java基本对象

public void test4() throws Exception {
        // 1.创建json字符串
        String json = "{\"name\":\"Lisa\",\"age\":18,\"gender\":0}";
        // 2.创建Jackson核心对象ObjectMapper
        ObjectMapper mapper = new ObjectMapper();
        // 3.调用方法进行转换
        Person person = mapper.readValue(json, Person.class);
        System.out.println(person); // Person{name='Lisa', age=18, gender=0}

    }

2. JSON转list

public void test5() throws Exception {
        // 1.创建json字符串
        String json = "[{\"name\":\"Lisa\",\"age\":20,\"gender\":0},{\"name\":\"Lily\",\"age\":18,\"gender\":0}]";
        // 2.创建Jackson核心对象ObjectMapper
        ObjectMapper mapper = new ObjectMapper();
        // 3.调用方法进行转换
        List list = mapper.readValue(json, List.class);
        System.out.println(list);
        //[{name=Lisa, age=20, gender=0}, {name=Lily, age=18, gender=0}]
    }

3. JSON转map

public void test6() throws Exception {
        // 1.创建json字符串
        String json = "{\"name\":\"Lisa\",\"age\":20,\"gender\":0}";
        // 2.创建Jackson核心对象ObjectMapper
        ObjectMapper mapper = new ObjectMapper();
        // 3.调用方法进行转换
        Map map = mapper.readValue(json, Map.class);
        System.out.println(map);
        // {name=Lisa, age=20, gender=0}
    }