JSON數據處理之jackson

相關Jar包：

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

核心內容

jackson核心對象
ObjectMapper mapper = new ObjectMapper();

常用方法：
1.對象轉JSON

• writeValue(參數1， obj)
  參數1：
  File：將obj對象轉換爲json字符串，並保存到指定的文件中
  Writer：將obj對象轉換爲json字符串，並將json數據填充到字符輸出流中
  OutputStream：將obj對象轉換爲json字符串，並將json數據填充到字節輸出流中
• writeValueAsString(obj)：將對象轉換爲json字符串

2.JSON轉對象

• readValue(String content, Class valueType)
  content：json字符串
  valueType：要轉換的Java對象類型（如：Person.class)

對象轉JSON

1. Java基本對象轉JSON

public void test1() throws Exception {
        // 1.創建person對象
        Person p1 = new Person();
        p1.setName("Lisa");
        p1.setAge(15);
        p1.setGender(0);
        // 2.創建Jackson核心對象ObjectMapper
        ObjectMapper mapper = new ObjectMapper();
        // 3.調用方法進行轉換
        String json = mapper.writeValueAsString(p1);
        System.out.println(json); // {"name":"Lisa","age":15,"gender":0}
    }

2. list轉JSON

public void test2() throws Exception {
        // 1.創建person對象
        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.創建Jackson核心對象ObjectMapper
        ObjectMapper mapper = new ObjectMapper();
        // 3.調用方法進行轉換
        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轉JSON

public void test3() throws Exception {
        // 1.創建map並保存數據
        Map<String, Object> map = new HashMap<String, Object>();
        map.put("name", "Lisa");
        map.put("age", 18);
        map.put("gender", 0);
        // 2.創建Jackson核心對象ObjectMapper
        ObjectMapper mapper = new ObjectMapper();
        // 3.調用方法進行轉換
        String json = mapper.writeValueAsString(map);
        System.out.println(json);   // {"gender":0,"name":"Lisa","age":18}
    }

JSON轉對象

1. JSON轉Java基本對象

public void test4() throws Exception {
        // 1.創建json字符串
        String json = "{\"name\":\"Lisa\",\"age\":18,\"gender\":0}";
        // 2.創建Jackson核心對象ObjectMapper
        ObjectMapper mapper = new ObjectMapper();
        // 3.調用方法進行轉換
        Person person = mapper.readValue(json, Person.class);
        System.out.println(person); // Person{name='Lisa', age=18, gender=0}

    }

2. JSON轉list

public void test5() throws Exception {
        // 1.創建json字符串
        String json = "[{\"name\":\"Lisa\",\"age\":20,\"gender\":0},{\"name\":\"Lily\",\"age\":18,\"gender\":0}]";
        // 2.創建Jackson核心對象ObjectMapper
        ObjectMapper mapper = new ObjectMapper();
        // 3.調用方法進行轉換
        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轉map

public void test6() throws Exception {
        // 1.創建json字符串
        String json = "{\"name\":\"Lisa\",\"age\":20,\"gender\":0}";
        // 2.創建Jackson核心對象ObjectMapper
        ObjectMapper mapper = new ObjectMapper();
        // 3.調用方法進行轉換
        Map map = mapper.readValue(json, Map.class);
        System.out.println(map);
        // {name=Lisa, age=20, gender=0}
    }