Gson fromJson() 用法
|
1.純數組JSON 字符串轉換 |
[ {"name": "zhangsan","age": "10","phone": "11111","email": "[email protected]"}, {"name": "lisi","age": "20","phone": "22222","email": "[email protected]"}, ...] 解析代碼如下： public class UserBean { //變量名跟JSON數據字段名必須一致 private String name ; private String age; private String phone; private String email; ... }
//拿到本地JSON 並轉成String String strByJson = ConstructTestJsonStr();//此處函數內容省略
//Json的解析類對象 JsonParser parser = new JsonParser(); //將JSON的String 轉成一個JsonArray對象 JsonArray jsonArray = parser.parse(strByJson).getAsJsonArray();
Gson gson = new Gson(); ArrayList<UserBean> userBeanList = new ArrayList<>();
//加強for循環遍歷JsonArray for (JsonElement user : jsonArray) { //使用GSON，直接轉成Bean對象 UserBean userBean = gson.fromJson(user, UserBean.class); userBeanList.add(userBean); } |
|
2.有數據頭的純數組 數據轉換 |
{"name": "lisi","age": "20","phone": "22222","email": "[email protected]"}, //解析有數據頭的純數組 //拿到本地JSON 並轉成String String strByJson = ConstructTestJsonStr();//此處函數內容省略；
//先轉JsonObject JsonObject jsonObject = new JsonParser().parse(strByJson).getAsJsonObject(); //再轉JsonArray 加上數據頭 JsonArray jsonArray = jsonObject.getAsJsonArray("muser");
Gson gson = new Gson(); ArrayList<UserBean> userBeanList = new ArrayList<>();
//循環遍歷 for (JsonElement user : jsonArray) { //通過反射 得到UserBean.class UserBean userBean = gson.fromJson(user, new TypeToken<UserBean>() {}.getType()); userBeanList.add(userBean); } |
|
3.有數據頭的復雜 數據轉換 |
"muser": [{"name": "zhangsan","age": "10","phone": "11111","email":"[email protected]"},
{"name": "lisi","age": "20","phone": "22222","email": "[email protected]"},
...]
}
被解析對象不是純數組數據，還有其它字段+數組（含頭），方法如下： 根據 JSON 建立Bean，註意這裏的 Bean 是返回所有字段，因為 GSON 能直接解析成 List ，所以 Bean 是下面這樣的，同樣把占地方的get/set省略： public class ResultBean {
//註意變量名與字段名必須一致
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; ... } ... } //有消息頭 復雜數據 常規方式 方法如下 //拿到Json字符串 String strByJson = ConstructTestJsonStr();//此處函數內容省略； //GSON直接解析成對象 ResultBean resultBean = new Gson().fromJson(strByJson,ResultBean.class); //對象中拿到集合 List<ResultBean.UserBean> userBeanList = resultBean.getMuser(); 三句話搞定，由此看出GSON的強大 |
|
4.只解析復雜JSON中的 數組或數組中的某部分內容 |
有數據頭 復雜數據 截取方式，如對第3例中JSON數據內容只想取“muser”數組中年齡（age）大於30歲的怎麽辦？ 方法1：全部解析，再從 List 中取。（但假如有1萬條數據？全部解析太麻煩），方法2：條件遍歷！（以下代碼示例）： //解析代碼：
//拿到JSON字符串 String strByJson = ConstructTestJsonStr();//此處函數內容省略； List<UserBean> userBeanList = new ArrayList<>();
//拿到數組 JsonObject jsonObject = new JsonParser().parse(strByJson).getAsJsonObject(); JsonArray jsonArray = jsonObject.getAsJsonArray("muser");
//循環遍歷數組 for (JsonElement user : jsonArray) { UserBean userBean = new Gson().fromJson(user, new TypeToken<UserBean>() { }.getType()); //根據條件過濾 if (Integer.parseInt(userBean.getAge()) > 30) { userBeanList.add(userBean); } } |
|
5.嵌套超復雜JSON 數據轉換 |
三種方式：1，全部解析出來；2，要什麽解析什麽；3，JsonReader，第1/2招前述已解釋，下面示例JsonReader（類似逐節點解釋XML） //通過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")) { //讀group這個節點 readGroup(reader); } reader.endObject(); } finally { reader.close(); } }
//讀group這個節點 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(); }
//讀用戶基本消息 user節點 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(); }
//讀用戶其他消息 info節點 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.簡單數據+LIST+MAP 轉換 |
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("數學"); books.add("語文"); books.add("英語"); books.add("物理"); books.add("化學"); books.add("生物"); student.books = books; HashMap<String, String> booksMap = new HashMap<String, String>(); booksMap.put("1", "數學"); booksMap.put("2", "語文"); booksMap.put("3", "英語"); booksMap.put("4", "物理"); booksMap.put("5", "化學"); 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());
打印輸出 id:1 nickName: Jack age:22 email:[email protected] books size:6 booksMap size:6 |
|
7.把List或者Map等集合 的泛型換成自定義個class |
泛型定義 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基礎開發")); booksMap.put("book2", new Book(2, "Java設計模式")); 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()); } 輸出結果 dataStr:{"book2":{"id":2,"name":"Java設計模式"},"book1":{"id":1,"name":"Java基礎開發"},"book3":{"id":3,"name":"Java算法"}} key:book2 value:Book{id=2, name=‘Java設計模式‘} key:book1 value:Book{id=1, name=‘Java基礎開發‘} key:book3 value:Book{id=3, name=‘Java算法‘} |
Gson fromJson() 用法