Gson的使用方法

Gson是一个可用于将Java对象转换为JSON表示形式的Java库。也可用于将JSON字符串转换为等效的Java对象。

Gson目标

1. 提供简单的toJson()和fromJson()方法将Java对象转换为JSON，反之亦然.
2. 允许将先前存在的不可修改对象转换为JSON或从JSON转换。
3. 支持Java泛型
4. 允许对象的自定义表示
5. 支持任意复杂的对象

以上内容来自官网

现在，我们自定义一个class类

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

接下来的三个例子都是把Java的Class对象使用Gson转换成Json的字符串

1. 包含基本数据类型的数据结构

Gson gson = new Gson();  
    Student student = new Student();  
    student.id = 1;  
    student.nickName = "乔晓松";  
    student.age = 22;    
    Log.e("MainActivity", gson.toJson(student)); 

输出结果：

{"nickName":"乔晓松","id":1,"age":22} 

2. 包含List集合

Gson gson = new Gson();  
        Student student = new Student();  
        student.id = 1;  
        student.nickName = "乔晓松";  
        student.age = 22;   
        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;  
        Log.e("MainActivity", gson.toJson(student)); 

输出结果：

{"books":["数学","语文","英语","物理","化学","生物"],"nickName":"乔晓松","id":1,"age":22}  

3. List和Map集合同时存在

Gson gson = new Gson();  
        Student student = new Student();  
        student.id = 1;  
        student.nickName = "乔晓松";  
        student.age = 22;  
        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;  
        Log.e("MainActivity", gson.toJson(student));  

输出结果：

{"books":["数学","语文","英语","物理","化学","生物"],"booksMap":{"3":"英语","2":"语文","1":"数学","6":"生物","5":"化学","4":"物理"},"nickName":"乔晓松","id":1,"age":22}  

4. 使用Gson，将字符串转换为Student对象

Gson gson = new Gson();  
        Student student = new Student();  
        student.id = 1;  
        student.nickName = "乔晓松";  
        student.age = 22;  
        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;  
        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", "books size:" + studentG.books.size());  
        Log.e("MainActivity", "booksMap size:" + studentG.booksMap.size());  

输出结果：

id:1  
nickName:乔晓松  
age:22  
books size:6  
booksMap size:6  

5. 泛型的使用

public HashMap<String,Book> booksMap;  
  
public class Book{  
    public int id;  
    public String name;  
}  

把booksMap转换成字符串和上面的举例一样，但是booksMap的Json字符串转换成booksMap的实例对象就有点不同，因为booksMap有自定义的房型

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

参考：http://blog.csdn.net/qxs965266509/article/details/42774691