Volley（五）—— 自定义Request

详细解读Volley（四）—— 自定义Request

Volley中提供了几个Request，如果我们有特殊的需求，完全可以自定义Request的，自定义Request自然要继承Request，那么本篇就教大家来一步一步地定义一个自己的Request类。

一、继承Request

如果我们的request的对象不是string，也不是JsonObject，而是一个奇怪的对象呢？我这里建立了一个类，叫做：Kale，然后定义了一个CustomReqeust去继承Reqeust，得到如下的代码。

package com.kale.volleytest;

import com.android.volley.NetworkResponse;
import com.android.volley.Request;
import com.android.volley.Response;
import com.android.volley.Response.ErrorListener;
import com.android.volley.Response.Listener;

public class CustomReqeust extends Request<Kale>{

    public CustomReqeust(int method, String url, ErrorListener listener) {
        super(method, url, listener);
    }

    @Override
    protected Response<Kale> parseNetworkResponse(NetworkResponse response) {
        // TODO 自动生成的方法存根
        return null;
    }

    @Override
    protected void deliverResponse(Kale response) {
        // TODO 自动生成的方法存根

    }

}

分析：

public CustomReqeust(int method, String url, ErrorListener listener)

构造函数中调用了父类的方法，初始化了当前对象。传入三个参数：①请求方式，即POST/GET，②请求的URL，③出错时的回调监听器

protected Response<Kale> parseNetworkResponse(NetworkResponse response)

解析网络响应的结果，从NetworkResponse的代码中我们就可以知道它里面有什么东西了。

/**
 * Data and headers returned from {@link Network#performRequest(Request)}.
 */
public class NetworkResponse {
    /**
     * Creates a new network response.
     * @param statusCode the HTTP status code
     * @param data Response body
     * @param headers Headers returned with this response, or null for none
     * @param notModified True if the server returned a 304 and the data was already in cache
     * @param networkTimeMs Round-trip network time to receive network response
     */
    public NetworkResponse(int statusCode, byte[] data, Map<String, String> headers,
            boolean notModified, long networkTimeMs)

响应码啊，请求头什么的，最最主要的就是这个比特数组的data，响应的结果就在里面。我们可以*的进行处理了~

protected void deliverResponse(Kale response)

分发响应的结果，我们可以通过将这个response放到监听器里来获取响应结果。

二、分析StringRequest

我们现在已经对request的子类有了基本的认识，现在就来看看StringRequest的源码吧，别担心，很短！

package com.android.volley.toolbox;public class StringRequest extends Request<String> {
    // 建立监听器来获得响应成功时返回的结果
    private final Listener<String> mListener; 

    // 传入请求方法，url，成功时的监听器，失败时的监听器
    public StringRequest(int method, String url, Listener<String> listener,
            ErrorListener errorListener) {
        super(method, url, errorListener);
        // 初始化成功时的监听器
        mListener = listener;
    }

    /**
     * Creates a new GET request.
     * 建立一个默认的GET请求，调用了上面的构造函数
     */
    public StringRequest(String url, Listener<String> listener, ErrorListener errorListener) {
        this(Method.GET, url, listener, errorListener);
    }

    @Override
    protected void deliverResponse(String response) {
        // 用监听器的方法来传递下响应的结果
        mListener.onResponse(response);
    }

    @Override
    protected Response<String> parseNetworkResponse(NetworkResponse response) {
        String parsed;
        try {
            // 调用了new String(byte[] data, String charsetName) 这个构造函数来构建String对象，
            // 将byte数组按照特定的编码方式转换为String对象
            // 主要部分是data
            parsed = new String(response.data, HttpHeaderParser.parseCharset(response.headers));
        } catch (UnsupportedEncodingException e) {
            parsed = new String(response.data);
        }
        return Response.success(parsed, HttpHeaderParser.parseCacheHeaders(response));
    }
}

分析完代码我们应该就能知道改如何自定义Request了，其实没啥高深的东西。

三、自定义XMLRequest

代码来自：http://blog.****.net/guolin_blog/article/details/17612763

public class XMLRequest extends Request<XmlPullParser> {  

    private final Listener<XmlPullParser> mListener;  

    public XMLRequest(int method, String url, Listener<XmlPullParser> listener,
            ErrorListener errorListener) {
        super(method, url, errorListener);
        mListener = listener;
    }  

    public XMLRequest(String url, Listener<XmlPullParser> listener, ErrorListener errorListener) {
        this(Method.GET, url, listener, errorListener);
    }  

    @Override
    protected Response<XmlPullParser> parseNetworkResponse(NetworkResponse response) {
        try {
            String xmlString = new String(response.data,
                    HttpHeaderParser.parseCharset(response.headers));
            XmlPullParserFactory factory = XmlPullParserFactory.newInstance();
            XmlPullParser xmlPullParser = factory.newPullParser();
            xmlPullParser.setInput(new StringReader(xmlString));
            return Response.success(xmlPullParser, HttpHeaderParser.parseCacheHeaders(response));
        } catch (UnsupportedEncodingException e) {
            return Response.error(new ParseError(e));
        } catch (XmlPullParserException e) {
            return Response.error(new ParseError(e));
        }
    }  

    @Override
    protected void deliverResponse(XmlPullParser response) {
        mListener.onResponse(response);
    }  

} 

这里用到了XmlPull的知识，如果不是很了解，可以去这篇文章看看：http://www.cnblogs.com/tianzhijiexian/p/4020250.html

测试代码：

XMLRequest xmlRequest = new XMLRequest(
                "http://flash.weather.com.cn/wmaps/xml/china.xml",
                new Response.Listener<XmlPullParser>() {
                    @Override
                    public void onResponse(XmlPullParser response) {
                        try {
                            int eventType = response.getEventType();
                            while (eventType != XmlPullParser.END_DOCUMENT) {
                                switch (eventType) {
                                case XmlPullParser.START_TAG:
                                    String nodeName = response.getName();
                                    if ("city".equals(nodeName)) {
                                        String pName = response.getAttributeValue(0);
                                        Log.d("TAG", "pName is " + pName);
                                    }
                                    break;
                                }
                                eventType = response.next();
                            }
                        } catch (XmlPullParserException e) {
                            e.printStackTrace();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }
                }, new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {
                        Log.e("TAG", error.getMessage(), error);
                    }
                });
        mQueue.add(xmlRequest);

结果：

四、自定义GsonRequest

代码来自：http://blog.****.net/guolin_blog/article/details/17612763

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

    private final Listener<T> mListener;

    private Gson mGson;

    private Class<T> mClass;

    public GsonRequest(int method, String url, Class<T> clazz, Listener<T> listener,
            ErrorListener errorListener) {
        super(method, url, errorListener);
        mGson = new Gson();
        mClass = clazz;
        mListener = listener;
    }

    public GsonRequest(String url, Class<T> clazz, Listener<T> listener,
            ErrorListener errorListener) {
        this(Method.GET, url, clazz, listener, errorListener);
    }

    @Override
    protected Response<T> parseNetworkResponse(NetworkResponse response) {
        try {
            String jsonString = new String(response.data,
                    HttpHeaderParser.parseCharset(response.headers));
            return Response.success(mGson.fromJson(jsonString, mClass),
                    HttpHeaderParser.parseCacheHeaders(response));
        } catch (UnsupportedEncodingException e) {
            return Response.error(new ParseError(e));
        }
    }

    @Override
    protected void deliverResponse(T response) {
        mListener.onResponse(response);
    }

}

代码十分简单，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。

用法：

建立一个对象类，比如这里的weather、WeatherInfo类，然后初始化GsonRequest对象，最后把GsonRequest对象添加到队列中。

Weather：

public class Weather {

    private WeatherInfo weatherinfo;

    public WeatherInfo getWeatherinfo() {
        return weatherinfo;
    }

    public void setWeatherinfo(WeatherInfo weatherinfo) {
        this.weatherinfo = weatherinfo;
    }

}

WeatherInfo：

public class WeatherInfo {

    private String city;

    private String temp;

    private String time;

    public String getCity() {
        return city;
    }

    public void setCity(String city) {
        this.city = city;
    }

    public String getTemp() {
        return temp;
    }

    public void setTemp(String temp) {
        this.temp = temp;
    }

    public String getTime() {
        return time;
    }

    public void setTime(String time) {
        this.time = time;
    }

}

Java测试代码：

GsonRequest<Weather> gsonRequest = new GsonRequest<Weather>(
        "http://www.weather.com.cn/data/sk/101010100.html", Weather.class,
        new Response.Listener<Weather>() {
            @Override
            public void onResponse(Weather weather) {
                WeatherInfo weatherInfo = weather.getWeatherinfo();
                Log.d("TAG", "city is " + weatherInfo.getCity());
                Log.d("TAG", "temp is " + weatherInfo.getTemp());
                Log.d("TAG", "time is " + weatherInfo.getTime());
            }
        }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                Log.e("TAG", error.getMessage(), error);
            }
        });
mQueue.add(gsonRequest); 

五、重写getBody()方法来添加post参数

我们可以在JsonRequest类中发现如下代码：

/**
  * Returns the raw POST or PUT body to be sent.
  *
  * @throws AuthFailureError in the event of auth failure
  */
 @Override
 public byte[] getBody() {
     try {
return mRequestBody == null ? null : mRequestBody.getBytes(PROTOCOL_CHARSET);  
     } catch (UnsupportedEncodingException uee) {
         VolleyLog.wtf("Unsupported Encoding while trying to get the bytes of %s using %s",
                 mRequestBody, PROTOCOL_CHARSET);
         return null;
     }
 }  

不用看代码，直接看注释，说明这里执行post请求，所以我们可以在这里设置post参数。这里

return mRequestBody == null ? null : mRequestBody.getBytes(PROTOCOL_CHARSET); 

返回的就是post参数了。

如果我们想要传递POST数据，可以参考上面的代码，重写Request的getBody()方法，放入自己的参数，举例如下：

　　 /** http请求编码方式 */
    private static final String PROTOCOL_CHARSET = "utf-8";  

    private String mUserName; 

@Override
    public byte[] getBody() {
        try {
            return mUserName == null ? null : mUserName.getBytes(PROTOCOL_CHARSET);
        } catch (UnsupportedEncodingException uee) {
            VolleyLog.wtf("Unsupported Encoding while trying to get the bytes of %s using %s", mUserName, PROTOCOL_CHARSET);
            return null;
        }
    }  

完整代码（来自：http://blog.****.net/ttdevs/article/details/17586205）：

public class CustomReqeust extends Request<String> {
    /** http请求编码方式 */
    private static final String PROTOCOL_CHARSET = "utf-8";  

    private Listener<String> mListener;
    private String mUserName;  

    public CustomReqeust(String url, String userName, Listener<String> listener, ErrorListener errorListener) {
        super(Method.POST, url, errorListener);
        mUserName = userName;
        mListener = listener;
    }  

    @Override
    protected Response<String> parseNetworkResponse(NetworkResponse response) {
        String parsed;
        try {
            parsed = new String(response.data, HttpHeaderParser.parseCharset(response.headers));
        } catch (UnsupportedEncodingException e) {
            parsed = new String(response.data);
        }
        return Response.success(parsed, HttpHeaderParser.parseCacheHeaders(response));
    }  

    @Override
    protected void deliverResponse(String response) {
        mListener.onResponse(response);
    }  

    @Override
    public byte[] getBody() {
        try {
            return mUserName == null ? null : mUserName.getBytes(PROTOCOL_CHARSET);
        } catch (UnsupportedEncodingException uee) {
            VolleyLog.wtf("Unsupported Encoding while trying to get the bytes of %s using %s", mUserName, PROTOCOL_CHARSET);
            return null;
        }
    }
}

测试代码：

private void customRequest() {
    CustomReqeust request = new CustomReqeust(URL, "CustomVolley", new Listener<String>() {  

        @Override
        public void onResponse(String arg0) {
            Toast.makeText(getApplicationContext(), arg0, Toast.LENGTH_LONG).show();
            Log.d("onResponse", arg0);
        }
    }, new ErrorListener() {  

        @Override
        public void onErrorResponse(VolleyError arg0) {
            Toast.makeText(getApplicationContext(), arg0.toString(), Toast.LENGTH_LONG).show();
            Log.d("onErrorResponse", arg0.toString());
        }
    });
    mQueue.add(request);
}  

抓包结果：

得到了传递的username = CustomVolley