在Java開發中，有時需要儲存一個資料結構成字串，可能你會考慮用Json，但是當Json字串轉換成Java物件時，轉換成的是JsonObject，並不是你想要的Class型別的物件，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包匯入到專案中，這個匯入包的簡單步驟就不展示了，Gson的下載連結：http://download.csdn.NET/detail/qxs965266509/8367275

現在，我先自定義一個Class類

1. publicclass Student {  
2.     public
   int id;  
3.     public String nickName;  
4.     publicint age;  
5.     public ArrayList<String> books;  
6.     public HashMap<String, String> booksMap;  
7. }  

    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物件使用Gson轉換成Json的字串

案例一：僅包含基本資料型別的資料結構

1. Gson gson = new Gson();  
2.     Student student = new Student();  
3.     student.id = 1;  
4.     student.nickName = ”喬曉鬆”;  
5.     student.age = 22;  
6.     student.email = ”[email protected]”;  
7.     Log.e(”MainActivity”, gson.toJson(student));  

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 ：

1. {“email”:“[email protected]”,“nickName”:“喬曉鬆”,“id”:1,“age”:22}  

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

案例二：除了基本資料型別還包含了List集合

1. Gson gson = new Gson();  
2.         Student student = new Student();  
3.         student.id = 1;  
4.         student.nickName = ”喬曉鬆”;  
5.         student.age = 22;  
6.         student.email = ”[email protected]”;  
7.         ArrayList<String> books = new ArrayList<String>();  
8.         books.add(”數學”);  
9.         books.add(”語文”);  
10.         books.add(”英語”);  
11.         books.add(”物理”);  
12.         books.add(”化學”);  
13.         books.add(”生物”);  
14.         student.books = books;  
15.         Log.e(”MainActivity”, gson.toJson(student));  

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));

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

{"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：除了基本資料型別還包含了List和Map集合

1. Gson gson = new Gson();  
2.         Student student = new Student();  
3.         student.id = 1;  
4.         student.nickName = ”喬曉鬆”;  
5.         student.age = 22;  
6.         student.email = ”[email protected]”;  
7.         ArrayList<String> books = new ArrayList<String>();  
8.         books.add(”數學”);  
9.         books.add(”語文”);  
10.         books.add(”英語”);  
11.         books.add(”物理”);  
12.         books.add(”化學”);  
13.         books.add(”生物”);  
14.         student.books = books;  
15.         HashMap<String, String> booksMap = new HashMap<String, String>();  
16.         booksMap.put(”1”, “數學”);  
17.         booksMap.put(”2”, “語文”);  
18.         booksMap.put(”3”, “英語”);  
19.         booksMap.put(”4”, “物理”);  
20.         booksMap.put(”5”, “化學”);  
21.         booksMap.put(”6”, “生物”);  
22.         student.booksMap = booksMap;  
23.         Log.e(”MainActivity”, gson.toJson(student));  

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 ：

1. {“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}  

{"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：把案例三輸出的字串使用Gson轉換成Student物件

1. Gson gson = new Gson();  
2.         Student student = new Student();  
3.         student.id = 1;  
4.         student.nickName = ”喬曉鬆”;  
5.         student.age = 22;  
6.         student.email = ”[email protected]”;  
7.         ArrayList<String> books = new ArrayList<String>();  
8.         books.add(”數學”);  
9.         books.add(”語文”);  
10.         books.add(”英語”);  
11.         books.add(”物理”);  
12.         books.add(”化學”);  
13.         books.add(”生物”);  
14.         student.books = books;  
15.         HashMap<String, String> booksMap = new HashMap<String, String>();  
16.         booksMap.put(”1”, “數學”);  
17.         booksMap.put(”2”, “語文”);  
18.         booksMap.put(”3”, “英語”);  
19.         booksMap.put(”4”, “物理”);  
20.         booksMap.put(”5”, “化學”);  
21.         booksMap.put(”6”, “生物”);  
22.         student.booksMap = booksMap;  
23.         String result = gson.toJson(student);  
24.         Student studentG = gson.fromJson(result, Student.class);  
25.         Log.e(”MainActivity”, “id:” + studentG.id);  
26.         Log.e(”MainActivity”, “nickName:” + studentG.nickName);  
27.         Log.e(”MainActivity”, “age:” + studentG.age);  
28.         Log.e(”MainActivity”, “email:” + studentG.email);  
29.         Log.e(”MainActivity”, “books size:” + studentG.books.size());  
30.         Log.e(”MainActivity”, “booksMap size:” + studentG.booksMap.size());  

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());

1. id:1  
2. nickName:喬曉鬆  
3. age:22  
4. email:[email protected]  
5. books size:6  
6. booksMap size:6  

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

1. public HashMap<String,Book> booksMap;  
2. public class Book{  
3.     public int id;  
4.     public String name;  
5. }  

  public HashMap<String,Book> booksMap;

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

把booksMap轉換成字串和上面的案例是一樣的，但是booksMap的Json字串換成booksMap的例項物件就有點不同了，因為booksMap有自定義的泛型

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