Gson fromJson() 用法

Posted 2020-12-31 Reboost

1.纯数组JSON 字符串转换	[ {"name": "zhangsan","age": "10","phone": "11111","email": "[email protected]"},  {"name": "lisi","age": "20","phone": "22222","email": "[email protected]"},   ...] 解析代码如下： public class UserBean {     //变量名跟JSON数据字段名必须一致     private String name ;     private String age;     private String phone;     private String email;     ... }    //拿到本地JSON 并转成String  String strByJson = ConstructTestJsonStr();//此处函数内容省略    //Json的解析类对象  JsonParser parser = new JsonParser();  //将JSON的String 转成一个JsonArray对象  JsonArray jsonArray = parser.parse(strByJson).getAsJsonArray();    Gson gson = new Gson();  ArrayList<UserBean> userBeanList = new ArrayList<>();    //加强for循环遍历JsonArray  for (JsonElement user : jsonArray) {         //使用GSON，直接转成Bean对象         UserBean userBean = gson.fromJson(user, UserBean.class);         userBeanList.add(userBean);  }
2.有数据头的纯数组 数据转换	{"muser": [{"name": "zhangsan","age": "10","phone": "11111","email": "[email protected]"}, {"name": "lisi","age": "20","phone": "22222","email": "[email protected]"}, ...] } //解析有数据头的纯数组 //拿到本地JSON 并转成String String strByJson = ConstructTestJsonStr();//此处函数内容省略；   //先转JsonObject JsonObject jsonObject = new JsonParser().parse(strByJson).getAsJsonObject(); //再转JsonArray 加上数据头 JsonArray jsonArray = jsonObject.getAsJsonArray("muser");   Gson gson = new Gson(); ArrayList<UserBean> userBeanList = new ArrayList<>();   //循环遍历 for (JsonElement user : jsonArray) {         //通过反射 得到UserBean.class         UserBean userBean = gson.fromJson(user, new TypeToken<UserBean>() {}.getType());         userBeanList.add(userBean); }
3.有数据头的复杂 数据转换	{ "code": 200,"msg": "OK", "muser": [{"name": "zhangsan","age": "10","phone": "11111","email":"[email protected]"},       {"name": "lisi","age": "20","phone": "22222","email": "[email protected]"},     ...] }  被解析对象不是纯数组数据，还有其它字段+数组（含头），方法如下：  根据 JSON 建立Bean，注意这里的 Bean 是返回所有字段，因为 GSON 能直接解析成 List ，所以 Bean 是下面这样的，同样把占地方的get/set省略： public class ResultBean {     //注意变量名与字段名必须一致     private int code;     private String msg;     private List<UserBean> muser;     public class UserBean{         private String name ;         private String age;         private String phone;         private String email;         ...     }     ... } //有消息头 复杂数据 常规方式 方法如下 //拿到Json字符串 String strByJson =  ConstructTestJsonStr();//此处函数内容省略； //GSON直接解析成对象 ResultBean resultBean = new Gson().fromJson(strByJson,ResultBean.class); //对象中拿到集合 List<ResultBean.UserBean> userBeanList = resultBean.getMuser(); 三句话搞定，由此看出GSON的强大
4.只解析复杂JSON中的 数组或数组中的某部分内容	有数据头 复杂数据 截取方式，如对第3例中JSON数据内容只想取“muser”数组中年龄（age）大于30岁的怎么办？ 方法1：全部解析，再从 List 中取。（但假如有1万条数据？全部解析太麻烦），方法2：条件遍历！（以下代码示例）： //解析代码：   //拿到JSON字符串 String strByJson =  ConstructTestJsonStr();//此处函数内容省略； List<UserBean> userBeanList = new ArrayList<>();   //拿到数组 JsonObject jsonObject = new JsonParser().parse(strByJson).getAsJsonObject(); JsonArray jsonArray = jsonObject.getAsJsonArray("muser");   //循环遍历数组  for (JsonElement user : jsonArray) {         UserBean userBean = new Gson().fromJson(user, new TypeToken<UserBean>() {         }.getType());         //根据条件过滤         if (Integer.parseInt(userBean.getAge()) > 30) {             userBeanList.add(userBean);         }   }
5.嵌套超复杂JSON 数据转换	三种方式：1，全部解析出来；2，要什么解析什么；3，JsonReader，第1/2招前述已解释，下面示例JsonReader（类似逐节点解释XML） //通过JsonReader的方式去解析 private void parseComplexJArrayByReader() throws IOException {     String strByJson = JsonToStringUtil.getStringByJson(this, R.raw.juser_4);     JsonReader reader = new JsonReader(new StringReader(strByJson));     try {         reader.beginObject();         String tagName = reader.nextName();         if (tagName.equals("group")) {             //读group这个节点             readGroup(reader);         }         reader.endObject();     } finally {         reader.close();     } }   //读group这个节点 private void readGroup(JsonReader reader) throws IOException {     reader.beginObject();     while (reader.hasNext()) {         String tagName = reader.nextName();         if (tagName.equals("user")) {             readUser(reader);         } else if (tagName.equals("info")) {             readInfo(reader);         }     }     reader.endObject(); }   //读用户基本消息 user节点 private void readUser(JsonReader reader) throws IOException {     reader.beginObject();     while (reader.hasNext()) {         String tag = reader.nextName();         if (tag.equals("name")) {             String name = reader.nextString();             nameText.setText(name);         } else if (tag.equals("age")) {             String age = reader.nextString();             ageText.setText(age);         }         ...         else {             reader.skipValue();//忽略         }     }     reader.endObject(); }   //读用户其他消息 info节点 private void readInfo(JsonReader reader) throws IOException {     reader.beginObject();     while (reader.hasNext()) {         String tag = reader.nextName();         if (tag.equals("address")) {             String address = reader.nextString();             addressText.setText(address);         } else if (tag.equals("work")) {             String work = reader.nextString();             workText.setText(work);         }         ...         else {             reader.skipValue();//忽略         }     }     reader.endObject(); }
6.简单数据+LIST+MAP 转换	public class Student {                    public int id;                    public String nickName;                    public int age;                    public ArrayList<String> books;                    public HashMap<String, String> booksMap; } Student student = new Student(); student.id = 1; student.nickName = "Jack"; student.age = 22; student.email = "[email protected]"; ArrayList<String> books = new ArrayList<String>(); books.add("数学"); books.add("语文"); books.add("英语"); books.add("物理"); books.add("化学"); books.add("生物"); student.books = books; HashMap<String, String> booksMap = new HashMap<String, String>(); booksMap.put("1", "数学"); booksMap.put("2", "语文"); booksMap.put("3", "英语"); booksMap.put("4", "物理"); booksMap.put("5", "化学"); booksMap.put("6", "生物"); student.booksMap = booksMap;   Gson gson = new Gson(); String result = gson.toJson(student); Student studentG = gson.fromJson(result, Student.class);   Log.e("MainActivity", "id:" + studentG.id); Log.e("MainActivity", "nickName:" + studentG.nickName); Log.e("MainActivity", "age:" + studentG.age); Log.e("MainActivity", "email:" + studentG.email); Log.e("MainActivity", "books size:" + studentG.books.size()); Log.e("MainActivity", "booksMap size:" + studentG.booksMap.size());   打印输出 id:1 nickName: Jack age:22 email:[email protected] books size:6 booksMap size:6
7.把List或者Map等集合 的泛型换成自定义个class	泛型定义 public HashMap<String,Book> booksMap; public class Book{               public int id;               public String name; } HashMap<String, Book> booksMap = gson.fromJson(result, new TypeToken<HashMap<String, Book>>() { }.getType());   Gson gson = new Gson(); HashMap<String, Book> booksMap = new HashMap<>(); booksMap.put("book1", new Book(1, "Java基础开发")); booksMap.put("book2", new Book(2, "Java设计模式")); booksMap.put("book3", new Book(3, "Java算法")); String dataStr = gson.toJson(booksMap); System.out.println("dataStr:" + dataStr); HashMap<String, Book> booksMap2 = gson.fromJson(dataStr, new TypeToken<HashMap<String, Book>>() {         }.getType());         for (Map.Entry<String, Book> entry : booksMap2.entrySet()) { System.out.println("key:"+entry.getKey() + "    value:" + entry.getValue().toString()); } 输出结果 dataStr:{"book2":{"id":2,"name":"Java设计模式"},"book1":{"id":1,"name":"Java基础开发"},"book3":{"id":3,"name":"Java算法"}} key:book2    value:Book{id=2, name=‘Java设计模式‘} key:book1    value:Book{id=1, name=‘Java基础开发‘} key:book3    value:Book{id=3, name=‘Java算法‘}