fastJson (ObjectMapper) 和 Gson 对象的初步使用呢（一）

首先，两者都是json字符串的转换工具，只不过是性能上、使用上不同

首先使用fastJson

        //定义一个对象        Student student = new Student("张三","123456","男",20);        //创建一个objectMapper 对象，需要导入依赖包  就是这个包 codehaus.jackson        ObjectMapper objectMapper = new ObjectMapper();        //将对象转换成json字符串形式        String s = objectMapper.writeValueAsString(student);        //输出结果：{"username":"张三","password":"123456","gender":"男","age":20}        System.out.println(s);        //将json字符串转换到map集合中        Map<String,Object> map = objectMapper.readValue(s, Map.class);        //输出的是一个个键值对形式        for (Map.Entry<String, Object> entry : map.entrySet()) {            System.out.println(entry.getKey());            System.out.println(entry.getValue());            System.out.println("---------------------分割线-----------------------");        }        //将json字符串再转换成student对象        Student stu = objectMapper.readValue(s, Student.class);        //Student{username='张三', password='123456', gender='男', age=20}        System.out.println(stu);

Gson的使用（建议使用）

            Student student = new Student("李四","123456","女",18);        //使用gson对象将student对象转换成json字符串        String gson_stu = new Gson().toJson(student);        //{"username":"李四","password":"123456","gender":"女","age":18}        System.out.println(gson_stu);        //将json字符串转换成对象的形式        Student stu = new Gson().fromJson(gson_stu, Student.class);        //Student{username='李四', password='123456', gender='女', age=18}        System.out.println(stu);        //将json转换成map形式        Map<String,Object> map = new Gson().fromJson(gson_stu, Map.class);        for (Map.Entry<String, Object> entry : map.entrySet()) {            System.out.println(entry.getKey() + "==========>" + entry.getValue());        }        //这种尝试是不可以的       /* List list = new Gson().fromJson(gson_stu, List.class);        for (Object o : list) {            o.toString();        }       */       //定义一个集合，集合中添加多个引用类型的成员       List<Student> list = new ArrayList<Student>();       list.add(student);       list.add(new Student("王五","123344","男",20));       list.add(new Student("赵柳","22344545","男",223));        //将对象转换成json字符串格式        String gson_list = new Gson().toJson(list);        //[{"username":"李四","password":"123456","gender":"女","age":18},{"username":"王五","password":"123344","gender":"男","age":20},{"username":"赵柳","password":"22344545","gender":"男","age":223}]        System.out.println(gson_list);        //将该对象转换成list集合中 =====>这样做是不行的//        List<Student> list_gson = new Gson().fromJson(gson_list, List.class);//        for (Student student1 : list_gson) {//            System.out.println(student1);//        }        //这样也是不行的//        Student student1 = new Gson().fromJson(gson_list, Student.class);//        System.out.println(student1);//        Map<String,List<Student>> fromJson = new Gson().fromJson(gson_list, Map.class);//        for (Map.Entry<String, List<Student>> entry : fromJson.entrySet()) {//            System.out.println(entry.getKey() + "===========>" + entry.getValue());//        }        //将json转换成list集合  ========》成功        List<Student> list1 = new Gson().fromJson(gson_list, new TypeToken<List<Student>>() {}.getType());        for (Student student1 : list1) {            System.out.println(student1);        }        //定义一个Map集合，将map集合转换成json字符串        Map<String,String> map1 = new HashMap<String, String>();        map1.put("111","zhangsan");        map1.put("222","lisi");        String s = new Gson().toJson(map1);        //{"111":"zhangsan","222":"lisi"}        System.out.println(s);        //再将json字符串转换成map对象        Map<String,String> map2 = new Gson().fromJson(s, Map.class);        //{111=zhangsan, 222=lisi}        System.out.println(map2);                        //如果map中存放着student对象        Map<String,Student> map3 = new HashMap<String, Student>();        map3.put("狗子",new Student("zhangsna","111","男",20));        map3.put("二蛋",new Student("lisi","222","女",22));        map3.put("瓜皮",new Student("wangwu","333","男",23));        String s1 = new Gson().toJson(map3);        //{"二蛋":{"username":"lisi","password":"222","gender":"女","age":22},"狗子":{"username":"zhangsna","password":"111","gender":"男","age":20},"瓜皮":{"username":"wangwu","password":"333","gender":"男","age":23}}        System.out.println(s1);        //成功        Map<String,Student> map4 = new Gson().fromJson(s1, Map.class);        for (Map.Entry<String, Student> entry : map4.entrySet()) {            System.out.println(entry.getKey() + "============>" + entry.getValue());        }