Json、FastJson、Gson

JSON
JSON(JavaScript Object Notation) 是一种轻量级的数据交换格式。
JSON数据作为目前网络中主流的数据传输格式之一，应用十分广泛。

对象：JSONObject对象表示为“{}”扩起来的内容，数据结构为 {key：value,key：value,…}的键值对的结构。
例如：{name:zhangsan,age:20}

数组：JSONArray数组表示为中括号“[]”扩起来的内容，数
据结构为 [value,value,value,…]的单值的结构。
例如：[“北京”，”上海”，”广州”]

创建json字符串
需要json-lib.jar包
1、{“id”:12,”address”:”广州”,”age”:20,”name”:”张三”}

public class CreateJsonDemo1 {    public static void main(String[] args) {        Student student = new Student("张三",20,12,"广州");        //创建JSONObject对象        JSONObject obj = new JSONObject(student);        String str = obj.toString();        System.out.println(str);    }}

2、{“student”:{“id”:12,”address”:”广州”,”age”:20,”name”:”张三”}}

public static String createJSON2(){        Student student = new Student("张三",20,12,"广州");        JSONObject obj1 = new JSONObject(student);        JSONObject obj2 = new JSONObject();        try {            obj2.put("student", obj1);        } catch (JSONException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }        return obj2.toString();    }

3、[{“id”:12,”address”:”广州”,”age”:20,”name”:”张三”},{“id”:12,”address”:”广州”,”age”:20,”name”:”张三”},{“id”:12,”address”:”广州”,”age”:20,”name”:”张三”}]

public static String createJSON3(){        Student student1 = new Student("张三",20,12,"广州");        Student student2= new Student("张三",20,12,"广州");        Student student3= new Student("张三",20,12,"广州");        List<Student> list = new ArrayList<Student>();        list.add(student1);        list.add(student2);        list.add(student3);        JSONArray array = new JSONArray(list);        return array.toString();    }

解析json字符串
1、{“id”:12,”address”:”广州”,”age”:20,”name”:”张三”}

public class JSONDemo1 {    public static void main(String[] args) throws JSONException {        String str = CreateJSONUtils.createJSON1();        System.out.println(str);        JSONObject obj = new JSONObject(str);        Student student = new Student();        String name = obj.getString("name");        student.setName(name);        int id = obj.getInt("id");        student.setId(id);        String address = obj.getString("address");        student.setAddress(address);        int age = obj.getInt("age");        student.setAge(age);        System.out.println(student);    }}

2{“student”:{“id”:12,”address”:”广州”,”age”:20,”name”:”张三”}}

public class JSONDemo2 {    public static void main(String[] args) throws JSONException {        String str = CreateJSONUtils.createJSON2();        System.out.println(str);        JSONObject obj1 = new JSONObject(str);        JSONObject obj2 = obj1.getJSONObject("student");        Student student = new Student();        student.setAddress(obj2.getString("address"));        student.setAge(obj2.getInt("age"));        student.setId(obj2.getInt("id"));        student.setName(obj2.getString("name"));        System.out.println(student);    }}

3、[{“id”:12,”address”:”广州”,”age”:20,”name”:”张三”},
{“id”:12,”address”:”广州”,”age”:20,”name”:”张三”},
{“id”:12,”address”:”广州”,”age”:20,”name”:”张三”}]

public class JSONDemo3 {    public static void main(String[] args) throws JSONException {        String str = CreateJSONUtils.createJSON3();        System.out.println(str);        List<Student> list = new ArrayList<Student>();        JSONArray array  =new JSONArray(str);        for(int i=0;i<array.length();i++){            JSONObject obj = array.getJSONObject(i);            Student student = new Student();            student.setAddress(obj.getString("address"));            student.setAge(obj.getInt("age"));            student.setId(obj.getInt("id"));            student.setName(obj.getString("name"));            list.add(student);        }        for(Student s:list){            System.out.println(s);        }    }}

FastJson
FastJson是一个Json处理工具包，包括“序列化”和“反序列化”两部分。
特点：
速度最快：测试表明，fastjson具有极快的性能，超越任其他的Java Json parser。包括自称最快的JackJson。
功能强大：完全支持Java Bean、集合、Map、日期、Enum，支持范型，支持自定义类型。
无依赖：能够直接运行在Java SE 5.0以上版本
支持Android
开源 (Apache 2.0)
使用：（需要fastjson.jar）

//一个对象。{"address":"广州","age":20,"id":1503,"name":"张三"}public class FastJsonDemo1 {    public static void main(String[] args) {        Student student = new Student("张三", 20, 1503, "广州");        // 1:生成json字符串        String json = JSON.toJSON(student).toString();        System.out.println(json);        // 2;解析成对象。        Student stu = JSON.parseObject(json, Student.class);// 反射        System.out.println(stu);    }}

//[{"address":"广州","age":20,"id":1503,"name":"张三"},{"address":"广州","age":20,"id":1503,"name":"张三"},{"address":"广州","age":20,"id":1503,"name":"张三"}]public class FastJsonDemo2 {    public static void main(String[] args) {        List<Student> list = new ArrayList<Student>();        list.add(new Student("张三", 20, 1503, "广州"));        list.add(new Student("张三", 20, 1503, "广州"));        list.add(new Student("张三", 20, 1503, "广州"));        String json = JSON.toJSON(list).toString();        System.out.println(json);        //解析        List<Student> array = JSON.parseArray(json, Student.class);        for(Student s:array){            System.out.println(s);        }    }}

通常和Json结合使用

//json跟fastjson结合使用。public class FastjsonDemo3 {    public static void main(String[] args) throws Exception {        String path = "http://litchiapi.jstv.com/api/GetFeeds?column=7&PageSize=20&pageIndex=1&val=100511D3BE5301280E0992C73A9DEC41";        byte[] b = HttpUtils.loadData(path);        List<News> list = new ArrayList<News>();        String json = new String(b,0,b.length,"utf-8");        System.out.println(json);        JSONObject obj1 = new JSONObject(json);        JSONArray array = obj1.getJSONObject("paramz").getJSONArray("feeds");        for(int i=0;i<array.length();i++){            JSONObject obj2 = array.getJSONObject(i).getJSONObject("data");            News news = JSON.parseObject(obj2.toString(), News.class);            list.add(news);        }        for(News n:list){            System.out.println(n);        }    }}

Gson（需要gson.jar）
Gson这个Java类库可以把Java对象转换成JSON，也可以把JSON字符串转换成一个相等的Java对象。
Gson支持任意复杂Java对象包括没有源代码的对象。

public class GSONDemo1 {    public static void main(String[] args) {        Student student = new Student("张三", 20, 1503, "广州");        // 创建GSON对象        Gson gson = new Gson();        String str = gson.toJson(student);        System.out.println(str);        //解析成对象        Student stu = gson.fromJson(str, Student.class);        System.out.println(stu);    }}