使用Gson解析json数据

谁借莪１个温暖的怀抱￠ 2022-06-13 13:13 410阅读 0赞

`Gson`是谷歌提供的用来解析`json`的开源库，使用简单方便，`Android`项目中使用，直接将`jar`包放在`libs`文件夹下导入。或者直接在`Dependencies`里添加依赖`Library dependency`里搜索`gson`，后直接添加`google`的gson依赖即可。

# 1.解析单个数据 #

已给`json`数据`"{'name':'jack','age':'18','home_address':'beijing'}"`

先创建Student类。

代码：

public class Student { 
    
        private String name;//不加注解，则默认与json数据的键值对里键名相同
        private int age;
        @SerializedName("home_address")//加注解，则按照注解的字符串来解析json数据中的键名
        private String address;
    
        //setter and getter
        ...
    
        @Override
        public String toString() {
            return "[name=" + name + " age=" + age + " address=" + address + "]";
        }
    }

创建Gson对象

代码：

//json字符串
    String jsonStu = "{'name':'jack','age':18,'home_address':'beijing'}";
    
    Gson gson = new Gson();
    Student student = gson.fromJson(jsonStu, Student.class);
    System.out.println(student);

结果：

[name=jack age=18 address=beijing]

## 1.1.改为泛型兼容 ##

创建`GsonUtil`工具类

代码：

public static <T> T gsonFromJson(String jsonStr, Class<T> tClass) {
        Gson gson = new Gson();
        T t = gson.fromJson(jsonStr, tClass);
        return t;

创建Teacher类：

public class Teacher { 
    
        private String name;
        private String course;
        @SerializedName("headteacher")
        private boolean isHeadTeacher;
    
        //setter and getter
        ...
    
        @Override
        public String toString() {
            return "[name=" + name + " course=" + course + " isHeadTeacher=" + isHeadTeacher + "]";
        }
    }

测试：

String jsonStu = "{'name':'jack','age':18,'home_address':'beijing'}";
    String jsonTea = "{'name':'tom','course':'math','headteacher':false}";
    Student student = GsonUtil.gsonFromJson(jsonStu, Student.class);
    Teacher teacher = GsonUtil.gsonFromJson(jsonTea, Teacher.class);
    System.out.println(student);
    System.out.println(teacher);

结果：

[name=jack age=18 address=beijing]
    [name=tom course=math isHeadTeacher=false]

## 1.2.含有嵌套的数据 ##

例如json字符串`"{'name':'jack','age':18,'grade':{'math':99,'chinese':88}}"`

单独创建或者内部类创建Grade类即可，仍旧用`gson.fromJson()`解析或者`GsonUtil`工具类解析。

# 2.解析json数组 #

比如给定的json数据：

String jsonArray = "[{'course':'math','score':88}," +//注意json数组是有[]括起来的
            "{'course':'chinese','score':99}," +
            "{'course':'english','score':77}]";

创建类Grade：

代码：

public class Grade { 
        private String course;
        private double score;
    
        //setter and getter
        ...
    
        @Override
        public String toString() {
            return "[course=" + course + " score=" + score + "]";
        }
    }

解析json数组：

代码：

ArrayList<Grade> grades = new ArrayList<>();
    grades = new Gson().fromJson(jsonArray, new TypeToken<ArrayList<Grade>>() {
    }.getType());
    for (Grade grade : grades) {
        System.out.println(grade);
    }

结果：

[course=math score=88.0]
    [course=chinese score=99.0]
    [course=english score=77.0]

## 2.1.改为泛型兼容 ##

代码 ：

public static <T> ArrayList<T> gsonFromJsonArray(String jsonArray, Class<T> tClass) {
        ArrayList<T> list = new ArrayList<>();//保存结果的list
        Gson gson = new Gson();
        //先解析为JsonObject类型
        ArrayList<JsonObject> jsonObjects = gson.fromJson(jsonArray, new TypeToken<ArrayList<JsonObject>>() {
        }.getType());
        for (JsonObject jsonObject : jsonObjects) {
            //将JsonObject类型换成需要的类型
            list.add(gson.fromJson(jsonObject, tClass));
        }
        return list;
    }

# 3.JavaBean转json数据 #

使用`new Gson().toJson()`，参数传入类或列表。

代码：

Student student = new Student();
    student.setAddress("china");
    student.setAge(12);
    student.setName("jack");
    
    ArrayList<Grade> grades = new ArrayList<>();
    grades.add(new Grade("math", 66));
    grades.add(new Grade("chinese", 88));
    
    student.setGrade(grades);
    
    String jsonStr = new Gson().toJson(student);
    System.out.println(jsonStr);

结果：

{"name":"jack","age":12,"home_address":"china","grade":[{"name":"math","score":66.0},{"name":"chinese","score":88.0}]}