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AndroidVolley完全解析(三)，定制自己的Request

2015-05-15 17:56 381 查看
经过前面两篇文章的学习，我们已经掌握了Volley各种Request的使用方法，包括StringRequest、JsonRequest、ImageRequest等。其中StringRequest用于请求一条普通的文本数据，JsonRequest(JsonObjectRequest、JsonArrayRequest)用于请求一条JSON格式的数据，ImageRequest则是用于请求网络上的一张图片。

可是Volley提供给我们的Request类型就只有这么多，而我们都知道，在网络上传输的数据通常有两种格式，JSON和XML，那么如果想要请求一条XML格式的数据该怎么办呢？其实很简单，Volley提供了非常强的扩展机制，使得我们可以很轻松地定制出任意类型的Request，这也就是本篇文章的主题了。

在开始之前还是友情提醒一下，如果你还没有阅读过我前面两篇关于Volley的文章，建议先去阅读一下Android Volley完全解析(一)，初识Volley的基本用法和Android Volley完全解析(二)，使用Volley加载网络图片。


1. 自定义XMLRequest

下面我们准备自定义一个XMLRequest，用于请求一条XML格式的数据。那么该从哪里开始入手呢？额，好像是有些无从下手。遇到这种情况，我们应该去参考一下Volley的源码，看一看StringRequest是怎么实现的，然后就可以模仿着写出XMLRequest了。首先看下StringRequest的源码，如下所示：

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sourceprint?

01.
/**


02.
*
A canned request for retrieving the response body at a given URL as a String.


03.
*/


04.
public
class
StringRequest
extends
Request<String>
{


05.
private
final
Listener<String>
mListener;


06.


07.
/**


08.
*
Creates a new request with the given method.


09.
*


10.
*
@param method the request {@link Method}to use


11.
*
@param url URL to fetch the string at


12.
*
@param listener Listener to receive the String response


13.
*
@param errorListener Error listener,or null to ignore errors


14.
*/


15.
public
StringRequest(
int
method,
String url,Listener<String> listener,


16.
ErrorListener
errorListener) {


17.
super
(method,
url,errorListener);


18.
mListener
= listener;


19.
}


20.


21.
/**


22.
*
Creates a new GET request.


23.
*


24.
*
@param url URL to fetch the string at


25.
*
@param listener Listener to receive the String response


26.
*
@param errorListener Error listener,or null to ignore errors


27.
*/


28.
public
StringRequest(String
url,Listener<String> listener,ErrorListener errorListener) {


29.
this
(Method.GET,
url,listener,errorListener);


30.
}


31.


32.
@Override


33.
protected
void
deliverResponse(String
response) {


34.
mListener.onResponse(response);


35.
}


36.


37.
@Override


38.
protected
Response<String>
parseNetworkResponse(NetworkResponse response) {


39.
String
parsed;


40.
try
{


41.
parsed
=
new
String(response.data,
HttpHeaderParser.parseCharset(response.headers));


42.
}
catch
(UnsupportedEncodingException
e) {


43.
parsed
=
new
String(response.data);


44.
}


45.
return
Response.success(parsed,
HttpHeaderParser.parseCacheHeaders(response));


46.
}


47.
}


可以看到，StringRequest的源码很简练，根本就没几行代码，我们一起来分析下。首先StringRequest是继承自Request类的，Request可以指定一个泛型类，这里指定的当然就是String了，接下来StringRequest中提供了两个有参的构造函数，参数包括请求类型，请求地址，以及响应回调等，由于我们已经很熟悉StringRequest的用法了，相信这几个参数的作用都不用再解释了吧。但需要注意的是，在构造函数中一定要调用super()方法将这几个参数传给父类，因为HTTP的请求和响应都是在父类中自动处理的。

另外，由于Request类中的deliverResponse()和parseNetworkResponse()是两个抽象方法，因此StringRequest中需要对这两个方法进行实现。deliverResponse()方法中的实现很简单，仅仅是调用了mListener中的onResponse()方法，并将response内容传入即可，这样就可以将服务器响应的数据进行回调了。parseNetworkResponse()方法中则应该对服务器响应的数据进行解析，其中数据是以字节的形式存放在NetworkResponse的data变量中的，这里将数据取出然后组装成一个String，并传入Response的success()方法中即可。

了解了StringRequest的实现原理，下面我们就可以动手来尝试实现一下XMLRequest了，代码如下所示：

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sourceprint?

01.
public
class
XMLRequest
extends
Request<XmlPullParser>
{


02.


03.
private
final
Listener<XmlPullParser>
mListener;


04.


05.
public
XMLRequest(
int
method,
String url,Listener<XmlPullParser> listener,


06.
ErrorListener
errorListener) {


07.
super
(method,
url,errorListener);


08.
mListener
= listener;


09.
}


10.


11.
public
XMLRequest(String
url,Listener<XmlPullParser> listener,ErrorListener errorListener) {


12.
this
(Method.GET,
url,listener,errorListener);


13.
}


14.


15.
@Override


16.
protected
Response<XmlPullParser>
parseNetworkResponse(NetworkResponse response) {


17.
try
{


18.
String
xmlString =
new
String(response.data,


19.
HttpHeaderParser.parseCharset(response.headers));


20.
XmlPullParserFactory
factory = XmlPullParserFactory.newInstance();


21.
XmlPullParser
xmlPullParser = factory.newPullParser();


22.
xmlPullParser.setInput(
new
StringReader(xmlString));


23.
return
Response.success(xmlPullParser,
HttpHeaderParser.parseCacheHeaders(response));


24.
}
catch
(UnsupportedEncodingException
e) {


25.
return
Response.error(
new
ParseError(e));


26.
}
catch
(XmlPullParserException
e) {


27.
return
Response.error(
new
ParseError(e));


28.
}


29.
}


30.


31.
@Override


32.
protected
void
deliverResponse(XmlPullParser
response) {


33.
mListener.onResponse(response);


34.
}


35.


36.
}


可以看到，其实并没有什么太多的逻辑，基本都是仿照StringRequest写下来的，XMLRequest也是继承自Request类的，只不过这里指定的泛型类是XmlPullParser，说明我们准备使用Pull解析的方式来解析XML。在parseNetworkResponse()方法中，先是将服务器响应的数据解析成一个字符串，然后设置到XmlPullParser对象中，在deliverResponse()方法中则是将XmlPullParser对象进行回调。

好了，就是这么简单，下面我们尝试使用这个XMLRequest来请求一段XML格式的数据。http://flash.weather.com.cn/wmaps/xml/china.xml这个接口会将中国所有的省份数据以XML格式进行返回，如下所示：

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sourceprint?

01.
<china
dn=
"day"
slick-uniqueid=
"3"
>


02.
<city
quName=
"黑龙江"
pyName=
"heilongjiang"
cityname=
"哈尔滨"
state1=
"0"
state2=
"0"
stateDetailed=
"晴"
tem1=
"18"
tem2=
"6"
windState=
"西北风3-4级转西风小于3级"
/>


03.
<city
quName=
"吉林"
pyName=
"jilin"
cityname=
"长春"
state1=
"0"
state2=
"0"
stateDetailed=
"晴"
tem1=
"19"
tem2=
"6"
windState=
"西北风3-4级转小于3级"
/>


04.
<city
quName=
"辽宁"
pyName=
"liaoning"
cityname=
"沈阳"
state1=
"0"
state2=
"0"
stateDetailed=
"晴"
tem1=
"21"
tem2=
"7"
windState=
"东北风3-4级"
/>


05.
<city
quName=
"海南"
pyName=
"hainan"
cityname=
"海口"
state1=
"1"
state2=
"1"
stateDetailed=
"多云"
tem1=
"30"
tem2=
"24"
windState=
"微风"
/>


06.
<city
quName=
"内蒙古"
pyName=
"neimenggu"
cityname=
"呼和浩特"
state1=
"0"
state2=
"0"
stateDetailed=
"晴"
tem1=
"19"
tem2=
"5"
windState=
"东风3-4级"
/>


07.
<city
quName=
"新疆"
pyName=
"xinjiang"
cityname=
"乌鲁木齐"
state1=
"0"
state2=
"0"
stateDetailed=
"晴"
tem1=
"22"
tem2=
"10"
windState=
"微风转东南风小于3级"
/>


08.
<city
quName=
"西藏"
pyName=
"xizang"
cityname=
"拉萨"
state1=
"1"
state2=
"7"
stateDetailed=
"多云转小雨"
tem1=
"18"
tem2=
"4"
windState=
"微风"
/>


09.
<city
quName=
"青海"
pyName=
"qinghai"
cityname=
"西宁"
state1=
"0"
state2=
"1"
stateDetailed=
"晴转多云"
tem1=
"18"
tem2=
"2"
windState=
"微风"
/>


10.
<city
quName=
"宁夏"
pyName=
"ningxia"
cityname=
"银川"
state1=
"0"
state2=
"0"
stateDetailed=
"晴"
tem1=
"19"
tem2=
"8"
windState=
"微风"
/>


11.
<city
quName=
"甘肃"
pyName=
"gansu"
cityname=
"兰州"
state1=
"0"
state2=
"0"
stateDetailed=
"晴"
tem1=
"21"
tem2=
"6"
windState=
"微风"
/>


12.
<city
quName=
"河北"
pyName=
"hebei"
cityname=
"石家庄"
state1=
"0"
state2=
"0"
stateDetailed=
"晴"
tem1=
"25"
tem2=
"12"
windState=
"北风小于3级"
/>


13.
<city
quName=
"河南"
pyName=
"henan"
cityname=
"郑州"
state1=
"0"
state2=
"0"
stateDetailed=
"晴"
tem1=
"24"
tem2=
"13"
windState=
"微风"
/>


14.
<city
quName=
"湖北"
pyName=
"hubei"
cityname=
"武汉"
state1=
"0"
state2=
"0"
stateDetailed=
"晴"
tem1=
"24"
tem2=
"12"
windState=
"微风"
/>


15.
<city
quName=
"湖南"
pyName=
"hunan"
cityname=
"长沙"
state1=
"2"
state2=
"1"
stateDetailed=
"阴转多云"
tem1=
"20"
tem2=
"15"
windState=
"北风小于3级"
/>


16.
<city
quName=
"山东"
pyName=
"shandong"
cityname=
"济南"
state1=
"1"
state2=
"1"
stateDetailed=
"多云"
tem1=
"20"
tem2=
"10"
windState=
"北风3-4级转小于3级"
/>


17.
<city
quName=
"江苏"
pyName=
"jiangsu"
cityname=
"南京"
state1=
"2"
state2=
"2"
stateDetailed=
"阴"
tem1=
"19"
tem2=
"13"
windState=
"西北风4-5级转3-4级"
/>


18.
<city
quName=
"安徽"
pyName=
"anhui"
cityname=
"合肥"
state1=
"2"
state2=
"1"
stateDetailed=
"阴转多云"
tem1=
"20"
tem2=
"12"
windState=
"西北风转北风3-4级"
/>


19.
<city
quName=
"山西"
pyName=
"shanxi"
cityname=
"太原"
state1=
"0"
state2=
"0"
stateDetailed=
"晴"
tem1=
"22"
tem2=
"8"
windState=
"微风"
/>


20.
<city
quName=
"陕西"
pyName=
"sanxi"
cityname=
"西安"
state1=
"1"
state2=
"0"
stateDetailed=
"多云转晴"
tem1=
"21"
tem2=
"9"
windState=
"东北风小于3级"
/>


21.
<city
quName=
"四川"
pyName=
"sichuan"
cityname=
"成都"
state1=
"1"
state2=
"1"
stateDetailed=
"多云"
tem1=
"26"
tem2=
"15"
windState=
"南风小于3级"
/>


22.
<city
quName=
"云南"
pyName=
"yunnan"
cityname=
"昆明"
state1=
"7"
state2=
"7"
stateDetailed=
"小雨"
tem1=
"21"
tem2=
"13"
windState=
"微风"
/>


23.
<city
quName=
"贵州"
pyName=
"guizhou"
cityname=
"贵阳"
state1=
"1"
state2=
"3"
stateDetailed=
"多云转阵雨"
tem1=
"21"
tem2=
"11"
windState=
"东风小于3级"
/>


24.
<city
quName=
"浙江"
pyName=
"zhejiang"
cityname=
"杭州"
state1=
"3"
state2=
"1"
stateDetailed=
"阵雨转多云"
tem1=
"22"
tem2=
"14"
windState=
"微风"
/>


25.
<city
quName=
"福建"
pyName=
"fujian"
cityname=
"福州"
state1=
"1"
state2=
"2"
stateDetailed=
"多云转阴"
tem1=
"28"
tem2=
"18"
windState=
"微风"
/>


26.
<city
quName=
"江西"
pyName=
"jiangxi"
cityname=
"南昌"
state1=
"2"
state2=
"1"
stateDetailed=
"阴转多云"
tem1=
"23"
tem2=
"15"
windState=
"北风3-4级转微风"
/>


27.
<city
quName=
"广东"
pyName=
"guangdong"
cityname=
"广州"
state1=
"3"
state2=
"2"
stateDetailed=
"阵雨转阴"
tem1=
"26"
tem2=
"20"
windState=
"微风"
/>


28.
<city
quName=
"广西"
pyName=
"guangxi"
cityname=
"南宁"
state1=
"3"
state2=
"3"
stateDetailed=
"阵雨"
tem1=
"23"
tem2=
"19"
windState=
"东北风小于3级"
/>


29.
<city
quName=
"北京"
pyName=
"beijing"
cityname=
"北京"
state1=
"0"
state2=
"0"
stateDetailed=
"晴"
tem1=
"26"
tem2=
"10"
windState=
"微风"
/>


30.
<city
quName=
"天津"
pyName=
"tianjin"
cityname=
"天津"
state1=
"1"
state2=
"0"
stateDetailed=
"多云转晴"
tem1=
"22"
tem2=
"13"
windState=
"东北风3-4级转小于3级"
/>


31.
<city
quName=
"上海"
pyName=
"shanghai"
cityname=
"上海"
state1=
"7"
state2=
"1"
stateDetailed=
"小雨转多云"
tem1=
"20"
tem2=
"16"
windState=
"西北风3-4级"
/>


32.
<city
quName=
"重庆"
pyName=
"chongqing"
cityname=
"重庆"
state1=
"1"
state2=
"3"
stateDetailed=
"多云转阵雨"
tem1=
"21"
tem2=
"14"
windState=
"微风"
/>


33.
<city
quName=
"香港"
pyName=
"xianggang"
cityname=
"香港"
state1=
"3"
state2=
"1"
stateDetailed=
"阵雨转多云"
tem1=
"26"
tem2=
"22"
windState=
"微风"
/>


34.
<city
quName=
"澳门"
pyName=
"aomen"
cityname=
"澳门"
state1=
"3"
state2=
"1"
stateDetailed=
"阵雨转多云"
tem1=
"27"
tem2=
"22"
windState=
"东北风3-4级转微风"
/>


35.
<city
quName=
"台湾"
pyName=
"taiwan"
cityname=
"台北"
state1=
"9"
state2=
"7"
stateDetailed=
"大雨转小雨"
tem1=
"28"
tem2=
"21"
windState=
"微风"
/>


36.
<city
quName=
"西沙"
pyName=
"xisha"
cityname=
"西沙"
state1=
"3"
state2=
"3"
stateDetailed=
"阵雨"
tem1=
"30"
tem2=
"26"
windState=
"东北风4-5级"
/>


37.
<city
quName=
"南沙"
pyName=
"nanshadao"
cityname=
"南沙"
state1=
"1"
state2=
"1"
stateDetailed=
"多云"
tem1=
"32"
tem2=
"27"
windState=
"东风4-5级"
/>


38.
<city
quName=
"钓鱼岛"
pyName=
"diaoyudao"
cityname=
"钓鱼岛"
state1=
"7"
state2=
"1"
stateDetailed=
"小雨转多云"
tem1=
"23"
tem2=
"19"
windState=
"西南风3-4级转北风5-6级"
/>


39.
</china>


确定了访问接口后，我们只需要在代码中按照以下的方式来使用XMLRequest即可：

view
sourceprint?

01.
XMLRequest
xmlRequest =
new
XMLRequest(


02.
"http://flash.weather.com.cn/wmaps/xml/china.xml"
,


03.
new
Response.Listener<XmlPullParser>()
{


04.
@Override


05.
public
void
onResponse(XmlPullParser
response) {


06.
try
{


07.
int
eventType
= response.getEventType();


08.
while
(eventType
!= XmlPullParser.END_DOCUMENT) {


09.
switch
(eventType)
{


10.
case
XmlPullParser.START_TAG:


11.
String
nodeName = response.getName();


12.
if
(
"city"
.equals(nodeName))
{


13.
String
pName = response.getAttributeValue(
0
);


14.
Log.d(
"TAG"
,
"pName
is "
+ pName);


15.
}


16.
break
;


17.
}


18.
eventType
= response.next();


19.
}


20.
}
catch
(XmlPullParserException
e) {


21.
e.printStackTrace();


22.
}
catch
(IOException
e) {


23.
e.printStackTrace();


24.
}


25.
}


26.
},
new
Response.ErrorListener()
{


27.
@Override


28.
public
void
onErrorResponse(VolleyError
error) {


29.
Log.e(
"TAG"
,
error.getMessage(),error);


30.
}


31.
});


32.
mQueue.add(xmlRequest);


可以看到，这里XMLRequest的用法和StringRequest几乎是一模一样的，我们先创建出一个XMLRequest的实例，并把服务器接口地址传入，然后在onResponse()方法中解析响应的XML数据，并把每个省的名字打印出来，最后将这个XMLRequest添加到RequestQueue当中。

现在运行一下代码，观察控制台日志，就可以看到每个省的名字都从XML中解析出来了，如下图所示。




2. 自定义GsonRequest

JsonRequest的数据解析是利用Android本身自带的JSONObject和JSONArray来实现的，配合使用JSONObject和JSONArray就可以解析出任意格式的JSON数据。不过也许你会觉得使用JSONObject还是太麻烦了，还有很多方法可以让JSON数据解析变得更加简单，比如说GSON。遗憾的是，Volley中默认并不支持使用自家的GSON来解析数据，不过没有关系，通过上面的学习，相信你已经知道了自定义一个Request是多么的简单，那么下面我们就来举一反三一下，自定义一个GsonRequest。

首先我们需要把gson的jar包添加到项目当中，jar包的下载地址是：https://code.google.com/p/google-gson/downloads/list 。

接着定义一个GsonRequest继承自Request，代码如下所示：

view
sourceprint?

01.
public
class
GsonRequest<T>
extends
Request<T>
{


02.


03.
private
final
Listener<T>
mListener;


04.


05.
private
Gson
mGson;


06.


07.
private
Class<T>
mClass;


08.


09.
public
GsonRequest(
int
method,
String url,Class<T> clazz,Listener<T> listener,


10.
ErrorListener
errorListener) {


11.
super
(method,
url,errorListener);


12.
mGson
=
new
Gson();


13.
mClass
= clazz;


14.
mListener
= listener;


15.
}


16.


17.
public
GsonRequest(String
url,Class<T> clazz,Listener<T> listener,


18.
ErrorListener
errorListener) {


19.
this
(Method.GET,
url,clazz,listener,errorListener);


20.
}


21.


22.
@Override


23.
protected
Response<T>
parseNetworkResponse(NetworkResponse response) {


24.
try
{


25.
String
jsonString =
new
String(response.data,


26.
HttpHeaderParser.parseCharset(response.headers));


27.
return
Response.success(mGson.fromJson(jsonString,
mClass),


28.
HttpHeaderParser.parseCacheHeaders(response));


29.
}
catch
(UnsupportedEncodingException
e) {


30.
return
Response.error(
new
ParseError(e));


31.
}


32.
}


33.


34.
@Override


35.
protected
void
deliverResponse(T
response) {


36.
mListener.onResponse(response);


37.
}


38.


39.
}


可以看到，GsonRequest是继承自Request类的，并且同样提供了两个构造函数。在parseNetworkResponse()方法中，先是将服务器响应的数据解析出来，然后通过调用Gson的fromJson方法将数据组装成对象。在deliverResponse方法中仍然是将最终的数据进行回调。

那么下面我们就来测试一下这个GsonRequest能不能够正常工作吧，调用http://www.weather.com.cn/data/sk/101010100.html这个接口可以得到一段JSON格式的天气数据，如下所示：

view
sourceprint?

1.
{
"weatherinfo"
:{
"city"
:
"北京"
,
"cityid"
:
"101010100"
,
"temp"
:
"19"
,
"WD"
:
"南风"
,
"WS"
:
"2级"
,
"SD"
:
"43%"
,
"WSE"
:
"2"
,
"time"
:
"19:45"
,
"isRadar"
:
"1"
,
"Radar"
:
"JC_RADAR_AZ9010_JB"
}}


接下来我们使用对象的方式将这段JSON字符串表示出来。新建一个Weather类，代码如下所示：

view
sourceprint?

01.
public
class
Weather
{


02.


03.
private
WeatherInfo
weatherinfo;


04.


05.
public
WeatherInfo
getWeatherinfo() {


06.
return
weatherinfo;


07.
}


08.


09.
public
void
setWeatherinfo(WeatherInfo
weatherinfo) {


10.
this
.weatherinfo
= weatherinfo;


11.
}


12.


13.
}


Weather类中只是引用了WeatherInfo这个类。接着新建WeatherInfo类，代码如下所示：

view
sourceprint?

01.
public
class
WeatherInfo
{


02.


03.
private
String
city;


04.


05.
private
String
temp;


06.


07.
private
String
time;


08.


09.
public
String
getCity() {


10.
return
city;


11.
}


12.


13.
public
void
setCity(String
city) {


14.
this
.city
= city;


15.
}


16.


17.
public
String
getTemp() {


18.
return
temp;


19.
}


20.


21.
public
void
setTemp(String
temp) {


22.
this
.temp
= temp;


23.
}


24.


25.
public
String
getTime() {


26.
return
time;


27.
}


28.


29.
public
void
setTime(String
time) {


30.
this
.time
= time;


31.
}


32.


33.
}


WeatherInfo类中含有city、temp、time这几个字段。下面就是如何调用GsonRequest了，其实也很简单，代码如下所示：

view
sourceprint?

01.
GsonRequest<Weather>
gsonRequest =
new
GsonRequest<Weather>(


02.
"http://www.weather.com.cn/data/sk/101010100.html"
,
Weather.
class
,


03.
new
Response.Listener<Weather>()
{


04.
@Override


05.
public
void
onResponse(Weather
weather) {


06.
WeatherInfo
weatherInfo = weather.getWeatherinfo();


07.
Log.d(
"TAG"
,
"city
is "
+ weatherInfo.getCity());


08.
Log.d(
"TAG"
,
"temp
is "
+ weatherInfo.getTemp());


09.
Log.d(
"TAG"
,
"time
is "
+ weatherInfo.getTime());


10.
}


11.
},
new
Response.ErrorListener()
{


12.
@Override


13.
public
void
onErrorResponse(VolleyError
error) {


14.
Log.e(
"TAG"
,
error.getMessage(),error);


15.
}


16.
});


17.
mQueue.add(gsonRequest);


可以看到，这里onResponse()方法的回调中直接返回了一个Weather对象，我们通过它就可以得到WeatherInfo对象，接着就能从中取出JSON中的相关数据了。现在运行一下代码，观察控制台日志，打印数据如下图所示：



这样的话，XMLRequest和GsonRequest的功能就基本都实现了，我们也是借助这两个例子深刻地理解了自定义Request的方法，对Volley的认识也是更加深入了。好了，本篇文章就到此结束，下篇文章中我们将对Volley进行更深层次的研究
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