Google的GSON框架解析JSON数据

什么是JSON:
JSON即JavaScript Object Natation, 它是一种轻量级的数据交换格式, 与XML一样, 是广泛被采用的客户端和服务端交互的解决方案.
JSON对象:
JSON中对象(Object)以"{"开始, 以"}"结束. 对象中的每一个item都是一个key-value对, 表现为"key:value"的形式, key-value对之间使用逗号分隔. 如:{"name":"coolxing", "age"=24, "male":true, "address":{"street":"huiLongGuan", "city":"beijing", "country":"china"}}. JSON对象的key只能是string类型的, 而value可以是string, number, false, true, null, Object对象甚至是array数组, 也就是说可以存在嵌套的情况.
JSON数组:
JSON数组(array)以"["开始, 以"]"结束, 数组中的每一个元素可以是string, number, false, true, null, Object对象甚至是array数组, 数组间的元素使用逗号分隔. 如["coolxing", 24, {"street":"huiLongGuan", "city":"beijing", "country":"china"}].
JSON数据的解析:
解析JSON数据, 首先需要明确待解析的是JSON Object还是JSON array, 然后需要确定采用哪种解析技术. android平台上一般有2种解析技术可供选择:android内置的org.json包和google的开源gson库. 以下将分别采用这两种技术解析JSON对象和JSON数组.

1.  采用android内置的org.json包解析JSON对象. 假设待解析的JSON数据为json = "{\"name\":\"coolxing\", \"age\"=24, \"male\":true, \"address\":{\"street\":\"huiLongGuan\", \"city\":\"beijing\", \"country\":\"china\"}}", 其中\用于转义表达式中的双引号. 首先定义2个JavaBean:
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package text.com.bean; 
 
public class Address { 
    private String street; 
    private String city; 
    private String country; 
 
    public Address() { 
        super(); 
    } 
 
    public Address(String street, String city, String country) { 
        super(); 
        this.street = street; 
        this.city = city; 
        this.country = country; 
    } 
 
    public String getStreet() { 
        return street; 
    } 
 
    public void setStreet(String street) { 
        this.street = street; 
    } 
 
    public String getCity() { 
        return city; 
    } 
 
    public void setCity(String city) { 
        this.city = city; 
    } 
 
    public String getCountry() { 
        return country; 
    } 
 
    public void setCountry(String country) { 
        this.country = country; 
    } 
 
    @Override 
    public String toString() { 
        return "Address [street=" + street + ", city=" + city + ", country=" 
                + country + "]"; 
    } 
 
} 

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package text.com.bean; 
 
public class Person { 
    private String name; 
    private int age; 
    private boolean male; 
    private Address address; 
 
    public Person() { 
        super(); 
    } 
 
    public Person(String name, int age, boolean male, Address address) { 
        super(); 
        this.name = name; 
        this.age = age; 
        this.male = male; 
        this.address = address; 
    } 
 
    public String getName() { 
        return name; 
    } 
 
    public void setName(String name) { 
        this.name = name; 
    } 
 
    public int getAge() { 
        return age; 
    } 
 
    public void setAge(int age) { 
        this.age = age; 
    } 
 
    public boolean isMale() { 
        return male; 
    } 
 
    public void setMale(boolean male) { 
        this.male = male; 
    } 
 
    public Address getAddress() { 
        return address; 
    } 
 
    public void setAddress(Address address) { 
        this.address = address; 
    } 
 
    @Override 
    public String toString() { 
        return "Person [name=" + name + ", age=" + age + ", male=" + male 
                + ", address=" + address + "]"; 
    } 
 
} 

首先使用方法一解析代码如下：
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JSONObject jsonObject = new JSONObject(json); 
String name = jsonObject.getString("name"); 
int age = jsonObject.getInt("age"); 
boolean male = jsonObject.getBoolean("male"); 
JSONObject addressJSON = jsonObject.getJSONObject("address"); 
String street = addressJSON.getString("street"); 
String city = addressJSON.getString("city"); 
String country = addressJSON.getString("country"); 
Address address = new Address(street, city, country); 
Person person = new Person(name, age, male, address); 
System.out.println(person); 
LogCat的输出为Person [name=coolxing, age=24, male=true, address=Address [street=huiLongGuan, city=beijing, country=china]], 说明已经正确解析了JSON对象.

2. 采用gson库解析JSON对象. 假设带解析的JSON数据是json = "{\"name\":\"coolxing\", \"age\"=24, \"male\":true, \"address\":{\"street\":\"huiLongGuan\", \"city\":\"beijing\", \"country\":\"china\"}}", 首先需要到http://code.google.com/p/google-gson/下载jar包, 并将其添加到项目中. 具体的解析代码如下:
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Gson gson = new Gson(); 
Person person = gson.fromJson(json, Person.class); 
System.out.println(person); 
LogCat的输出为Person [name=coolxing, age=24, male=true, address=Address [street=huiLongGuan, city=beijing, country=china]], 说明已经正确解析了JSON对象, 是不是很简单?

3. 采用android内置的org.json包解析JSON数组. 假设待解析的JSON数据为json = "[{\"name\":\"coolxing\", \"age\"=24, \"male\":true, \"address\":{\"street\":\"huiLongGuan\", \"city\":\"beijing\", \"country\":\"china\"}}, {\"name\":\"min\", \"age\"=20, \"male\":false, \"address\":{\"street\":\"heiShiJiao\", \"city\":\"daLian\", \"country\":\"china\"}}]", 解析代码如下:
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List<Person> persons = new ArrayList<Person>(); 
JSONArray jsonArray = new JSONArray(json); 
for(int i = 0; i < jsonArray.length(); i++) { 
    JSONObject jsonObject = jsonArray.getJSONObject(i); 
    String name = jsonObject.getString("name"); 
    int age = jsonObject.getInt("age"); 
    boolean male = jsonObject.getBoolean("male"); 
    JSONObject addressJSON = jsonObject.getJSONObject("address"); 
    String street = addressJSON.getString("street"); 
    String city = addressJSON.getString("city"); 
    String country = addressJSON.getString("country"); 
    Address address = new Address(street, city, country); 
    Person person = new Person(name, age, male, address); 
    persons.add(person); 
} 
System.out.println(persons); 
LogCat的输出为[Person [name=coolxing, age=24, male=true, address=Address [street=huiLongGuan, city=beijing, country=china]], Person [name=min, age=20, male=false, address=Address [street=heiShiJiao, city=daLian, country=china]]], 说明已经正确解析了JSON数组.

4. 采用gson库解析JSON数组. 待解析的JSON数据同上, 具体代码为:
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Gson gson = new Gson(); 
Type listType = new TypeToken<List<Person>>(){}.getType(); 
List<Person> persons = gson.fromJson(json, listType); 
LogCat的输出为[Person [name=coolxing, age=24, male=true, address=Address [street=huiLongGuan, city=beijing, country=china]], Person [name=min, age=20, male=false, address=Address [street=heiShiJiao, city=daLian, country=china]]], 说明已经正确解析了JSON数组.
new TypeToken<List<Person>>(){}.getType(); 这句代码表示创建一个TypeToken的匿名子类对象, 并调用对象的getType()方法.

org.json包和gson库还有很多其他有用的API, 需要的时候可查看文档. 比如有的时候需要通过java对象或java集合和数组生成json数据上传给服务器, 当然你可以自我构造json字符串, 但会很麻烦. 这个时候就可以使用其中的有关API, 方便的完成这项工作.


测试用例：

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package text.com; 
 
import java.io.BufferedReader; 
import java.io.File; 
import java.io.FileInputStream; 
import java.io.InputStreamReader; 
import java.lang.reflect.Type; 
import java.util.List; 
 
import text.com.bean.Address; 
import text.com.bean.Person; 
 
import com.google.gson.Gson; 
import com.google.gson.reflect.TypeToken; 
 
public class JsonTest { 
    String jsonString = ""; 
 
    public static void main(String[] args) { 
        // Person p1 = new Person("zhangsan", 12, true, new Address("北京", "海淀区", 
        // "30号")); 
        // Person p2 = new Person("zhangsan", 12, true, new Address("北京", "海淀区", 
        // "30号")); 
        // Person p3 = new Person("zhangsan", 12, true, new Address("北京", "海淀区", 
        // "30号")); 
        // List<Person> list = new ArrayList<Person>(); 
        // list.add(p1); 
        // list.add(p2); 
        // list.add(p3); 
        // Gson gson = new Gson(); 
        // Type typeOfT = new TypeToken<List<Person>>(){}.getType(); 
        // String json = gson.toJson(list, typeOfT); 
        // System.out.println("json:"+json); 
 
        // String str = readTxtFile("D:\\cjjworkspace\\Test\\json.txt"); 
        // System.out.println("文件内容：" + str); 
         Gson gson = new Gson(); 
        // Type typeOfT = new TypeToken<List<Person>>(){}.getType(); 
        // List<Person> personList = gson.fromJson(str, typeOfT); 
 
        Person p1 = new Person("zhangsan", 12, true, new Address("北京", "海淀区", "30号")); 
        Type typeOfT = new TypeToken<Person>(){}.getType(); 
        String str = gson.toJson(p1, typeOfT); 
        System.out.println(str); 
    } 
 
    public static String readTxtFile(String filePath) { 
        String encoding = "utf-8"; 
        StringBuilder sb = new StringBuilder(); 
        try { 
            File file = new File(filePath); 
            if (file.isFile() && file.exists()) { // 判断文件是否存在 
                InputStreamReader read = new InputStreamReader(new FileInputStream(file), encoding);// 考虑到编码格式 
                BufferedReader bufferedReader = new BufferedReader(read); 
                String str = ""; 
                while ((str = bufferedReader.readLine()) != null) { 
                    sb.append(str); 
                } 
                read.close(); 
                return sb.toString(); 
            } else { 
                System.out.println("找不到指定的文件"); 
                return null; 
            } 
        } catch (Exception e) { 
            System.out.println("读取文件内容出错"); 
            e.printStackTrace(); 
        } 
        return sb.toString(); 
    }