Java4Android之Gson

一般而言，我们通过http请求传送数据，采用json数据传输。如何解析json，一个我们用的库是Gson。我引用一个入门的例子在此，作为学习范本。在后续的相关代码中，其实是会使用到的。

参考及转载：

http://www.cnblogs.com/chenlhuaf/archive/2011/05/01/gson_test.html

http://blog.sina.com.cn/s/blog_64e467d60101ibpd.html

使用Gson进行解析：下载google-gson-2.2.2-release.zip包。

包含两种主要操作：一种是将对象或者不同的内容转化为JSON格式，一种是将JSON格式的内容还原到相应的对象属性或者其他属性。

1、首先使用：Gson gson = new Gson();<wbr></wbr>创建gson对象

2、要把数据转化为JSON格式时，可以在新建一个JavaBean类：

publicclassPerson {

<wbr><wbr><wbr></wbr></wbr></wbr>privateStringname;

<wbr><wbr><wbr></wbr></wbr></wbr>privateintage;

<wbr><wbr><wbr></wbr></wbr></wbr>publicString getName() {

<wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>returnname;

<wbr><wbr><wbr></wbr></wbr></wbr>}

<wbr><wbr><wbr></wbr></wbr></wbr>publicvoidsetName(String name) {

<wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>this.name= name;

<wbr><wbr><wbr></wbr></wbr></wbr>}

<wbr><wbr><wbr></wbr></wbr></wbr>publicintgetAge() {

<wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>returnage;

<wbr><wbr><wbr></wbr></wbr></wbr>}

<wbr><wbr><wbr></wbr></wbr></wbr>publicvoidsetAge(intage) {

<wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>this.age= age;

<wbr><wbr><wbr></wbr></wbr></wbr>}

<wbr><wbr><wbr></wbr></wbr></wbr>@Override

<wbr><wbr><wbr></wbr></wbr></wbr>publicString toString() {

<wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>returnname+":"+age;

<wbr><wbr><wbr></wbr></wbr></wbr>}

}

<wbr></wbr>

在主函数中使用如下语句：

Person p =newPerson();

p.setAge(22);

p.setName("Curry");

persons.add(p);//将Person对象加入到gson中

String str = gson.toJson(p);

<wbr></wbr>

直接输出，得到以下结果：{"name":"Curry","age":22}

<wbr></wbr>

而当在gson中加入list类型的对象时：

Listpersons=newArrayList();

for(inti = 0; i < 3; i++) {

<wbr><wbr><wbr></wbr></wbr></wbr><wbr><wbr><wbr></wbr></wbr></wbr>Person p =newPerson();

<wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>p.setName("name"+ i);

<wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>p.setAge(i * 5);

<wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>persons.add(p);

<wbr><wbr><wbr></wbr></wbr></wbr>}

String str = gson.toJson(persons);

将输出以下结果：（格式是数组类型的）[{"name":"name0","age":0},{"name":"name1","age":5},{"name":"name2","age":10}]

<wbr></wbr>

HashMap tool =newHashMap();

tool.put("ID","22");

String str = gson.toJson(tool);

以上表示加入的对象本身就是Map类型的，则输出以下结果：{"ID":"22"}

<wbr></wbr>

而如果加入的JavaBean中还包括其他的List类型的数据，例如：（代码片段）

publicclassPerson {

<wbr><wbr><wbr></wbr></wbr></wbr>privateStringname;

<wbr><wbr><wbr></wbr></wbr></wbr>privateintage;

<wbr><wbr><wbr></wbr></wbr></wbr>privateArrayListcar;

则输出结果变成这样：

[{"name":"name0","age":0,"car":["cc","ford"]},{"name":"name1","age":5,"car":["cc","ford"]},{"name":"name2","age":10,"car":["cc","ford"]}]

1、<wbr><wbr></wbr></wbr>解析JSON对象，将其还原为JavaBean，或者相应的数据类型

String json = "{\"name\":\"Duke\",\"address\":\"Menlo Park\",\"dateOfBirth\":\"Feb 1, 2000 12:00:00 AM\"}";//JSON格式的数据

Gson gson =newGson();

Student student = gson.fromJson(json, Student.class);//指定了要还原的class，保存在gson中。

System.out.println("student.getName()<wbr></wbr>= "+ student.getName());

System.out.println("student.getAddress() = "+ student.getAddress());

System.out.println("student.getDateOfBirth() = "

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>+ student.getDateOfBirth());//可以直接从student对象中获取到所有数据了。

<wbr></wbr>

4、如果Json对象本身是List形式的，或者其他的类型，则采用以下方法：

可以借助TypeToken获取泛型参数的类型。

String json ="[{\"name\":\"Duke\",\"address\":\"Menlo Park\",\"dateOfBirth\":\"Feb 1, 2000 12:00:00 AM\"}]";

Gson gson =newGson();

//使用Type类，取得相应类型对象的class属性。

Type listType=newTypeToken<ArrayList<Student>>(){}.getType();//TypeToken内的泛型就是Json数据中的类型

<wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>ArrayList list = gson.fromJson(json, listType);//使用该class属性，获取的对象均是list类型的

<wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>System.out.println("student.getName()<wbr></wbr>= "+ list.get(0).getName());//从list中取得内容即可

<wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>System.out.println("student.getAddress() = "+ list.get(0).getAddress());

<wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>System.out.println("student.getDateOfBirth() = "

<wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr><wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>+ list.get(0).getAddress());

<wbr></wbr>

<wbr></wbr>

因此，无论是把对象转化为Json格式，还是把Json格式还原为对象时，都需要确定好相应的数据类型或者JavaBean的格式。这样就可以很方便的使用Gson进行转化了。