Google Gson的使用方法,實現Json結構的相互轉換

原文鏈接

在Java開發中，有時需要保存一個數據結構成字符串，可能你會考慮用Json，但是當Json字符串轉換成Java對象時，轉換成的是JsonObject，並不是你想要的Class類型的對象，操作起來就很不是愉悅，下面說的就可以解決了這種問題。

首先，需要把Google的Gson的Jar包導入到項目中，這個導入包的簡單步驟就不展示了，Gson的下載鏈接：http://download.csdn.NET/detail/qxs965266509/8367275

現在，我先自定義一個Class類

public class Student {
    public int id;
    public String nickName;
    public int age;
    public ArrayList<String> books;
    public HashMap<String, String> booksMap;
}

案例一，案例二，案例三都是把Java的Class對象使用Gson轉換成Json的字符串

案例一：

僅包含基本數據類型的數據結構

Gson gson = new Gson();
    Student student = new Student();
    student.id = 1;
    student.nickName = "喬曉鬆";
    student.age = 22;
    student.email = "[email protected]";
    Log.e("MainActivity", gson.toJson(student));

輸出結果是 ：

{"email":"[email protected]","nickName":"喬曉鬆","id":1,"age":22}

案例二：

除了基本數據類型還包含了List集合

Gson gson = new Gson();
        Student student = new Student();
        student.id = 1;
        student.nickName = "喬曉鬆";
        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;
        Log.e("MainActivity", gson.toJson(student));

輸出結果是 ：

{"books":["數學","語文","英語","物理","化學","生物"],"email":"[email protected]","nickName":"喬曉鬆","id":1,"age":22}

案例三：

除了基本數據類型還包含了List和Map集合

Gson gson = new Gson();
        Student student = new Student();
        student.id = 1;
        student.nickName = "喬曉鬆";
        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;
        Log.e("MainActivity", gson.toJson(student));

輸出結果是 ：

{"books":["數學","語文","英語","物理","化學","生物"],"booksMap":{"3":"英語","2":"語文","1":"數學","6":"生物","5":"化學","4":"物理"},"email":"[email protected]","nickName":"喬曉鬆","id":1,"age":22}

案例四：
把案例三輸出的字符串使用Gson轉換成Student對象

Gson gson = new Gson();
        Student student = new Student();
        student.id = 1;
        student.nickName = "喬曉鬆";
        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;
        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());

輸出結果是 ：

id:1
nickName:喬曉鬆
age:22
email:[email protected]
books size:6
booksMap size:6

通過這4個案例我解決你一定就把Gson的基本用法學會了，當然我們的需求可能需要把List或者Map等集合的泛型換成我們自定義個class，這也是可以解決的，請看案例

案例五：

泛型的使用

public HashMap<String,Book> booksMap;

public class Book{
    public int id;
    public String name;
}

把booksMap轉換成字符串和上面的案例是一樣的，但是booksMap的Json字符串換成booksMap的實例對象就有點不同了，因爲booksMap有自定義的泛型

HashMap<String, Book> booksMap = gson.fromJson(result, new TypeToken<HashMap<String, Book>>() { }.getType());

如果什麼疑問，請到我的博客列表頁面，QQ或者郵件聯繫我！如有轉載請著名來自http://blog.csdn.net/qxs965266509

源代碼下載鏈接：http://download.csdn.net/detail/qxs965266509/8367689