Gson常用方法

一.Gson中的fromJson()实现反序列化

相当强大,不仅可以转基本类型,还可以把相应格式的字符串转为list或map

    public static void main(String[] args) {
        Gson gson = new Gson();
        //1.将字符串转为int(在去掉双引号上感觉很强大)
        int i = gson.fromJson("\"250\"", int.class);
        System.out.println(i);
        //2.将字符串转为double(在去掉双引号上感觉很强大)
        double d = gson.fromJson("\"99.99\"", double.class);
        System.out.println(d);
        //3.将字符串转为boolean类型
        boolean b = gson.fromJson("true", boolean.class);
        System.out.println(b);
        //4.将字符串转为字符串类型(在去掉双引号上感觉很强大,但也存在限制,
        //   比如多个双引号时会报错)
        System.out.println("\"String\"");
        String str = gson.fromJson("\"String\"", String.class);
        System.out.println(str);
           System.out.println("\"I feel very \"good \"\"");
           //输出 ; "I feel very "good ""
           String str2 = gson.fromJson("\"I feel very \"good \"", String.class);
           //报错 : com.google.gson.JsonSyntaxException: com.google.gson.stream.MalformedJsonException
        // 5.将json格式的字符串转为map,但map中的value值如果还包含map格式或List型格式的值,则会被转换为
        //    class com.google.gson.internal.LinkedTreeMap或java.util.ArrayList,且之后下一级仍会被转换,而不
        //      是简单地用字符串代替(很强大)
        Map map = gson.fromJson("{\n" +
                "    \"date\":\"2019-02-25\",\n" +
                "    \"data\":[\n" +
                "        [\n" +
                "            {\n" +
                "                \"name\":\"why\",\n" +
                "                \"age\":18\n" +
                "            },\n" +
                "            {\n" +
                "                \"name\":\"xm\",\n" +
                "                \"age\":19\n" +
                "            }\n" +
                "        ],\n" +
                "        [\n" +
                "            {\n" +
                "                \"name\":\"xiaohong\",\n" +
                "                \"age\":20\n" +
                "            },\n" +
                "            {\n" +
                "                \"name\":\"xiaogou\",\n" +
                "                \"age\":21\n" +
                "            }\n" +
                "        ]\n" +
                "    ],\n" +
                "    \"school\":{\n" +
                "        \"address\":\"北京\",\n" +
                "        \"district\":\"昌平\"\n" +
                "    }\n" +
                "}", Map.class);
        System.out.println(map.get("school"));
        //输出 : {address=北京, district=昌平}
        System.out.println(map.get("school").getClass());
        //输出 : class com.google.gson.internal.LinkedTreeMap
        System.out.println(((Map) map.get("school")).get("address"));
        //输出 : 北京
        System.out.println(map.get("data"));
        //输出 : [[{name=why, age=18.0}, {name=xm, age=19.0}], [{name=xiaohong, age=20.0}, {name=xiaogou, age=21.0}]]
        System.out.println(map.get("data").getClass());
        //输出 : class java.util.ArrayList
        System.out.println(((List)map.get("data")).get(0));
        //输出 : [{name=why, age=18.0}, {name=xm, age=19.0}]
        System.out.println((((List)map.get("data")).get(0)).getClass());
        //输出 : class java.util.ArrayList
        System.out.println(((List)(((List)map.get("data")).get(0))).get(0).getClass());
        //输出 : class com.google.gson.internal.LinkedTreeMap
        //6.实体类字符串转实体类
        String usrStr = "{\"hisName\":\"why\",\"hisAge\":18,\"hisWeight\":100.0}";
        User usr = gson.fromJson(usrStr, User.class);
        System.out.println(usr.getHisName());
        //输出 : why
    }

2.Gson中的toJson()实现序列化

1.将Object转为字符串,如果obj为json格式,某个key值为null,则不包含

    public static String objectToString(Object obj) {
        Gson gson = new Gson();
        String jsonObject = gson.toJson(obj);
        return jsonObject;
    }

2.将Object转为字符串,如果obj为json格式,某个key值为null也包含

    public static String objToStringIncludeNull(Object obj) {
        GsonBuilder gsonBuilder = new GsonBuilder();
        String jsonString = gsonBuilder.serializeNulls().create().toJson(obj);
        return jsonString;
    }

    public static void main(String[] args) {
        Map map = new HashMap();
        map.put("name","why");
        map.put("age","27");
        map.put("sex",null);
        map.put("address","");
        System.out.println(map);
        //输出 : {address=, sex=null, name=why, age=27}
        System.out.println(map.toString());
        //输出 : {address=, sex=null, name=why, age=27}
        System.out.println(objectToString(map));
        //输出 : {"address":"","name":"why","age":"27"}
        System.out.println(objToStringIncludeNull(map));
        //输出 : {"address":"","sex":null,"name":"why","age":"27"}

        User user = new User();
        user.setHisAge(18);
        // 字符串没设置值的话会默认为null,数字没设置值得话默认为0
        System.out.println(objectToString(user));
        //输出 :{"hisAge":18,"hisWeight":0.0}
        System.out.println(objToStringIncludeNull(user));
        //输出 :{"hisName":null,"hisAge":18,"hisWeight":0.0}
    }