首先StringRequest是繼承自Request類的，Request可以指定一個泛型類，這裡指定的當然就是String了，接下來StringRequest中提供了兩個有參的構造函數，參數包括請求類型，請求地址，以及響應回調等，由於我們已經很熟悉StringRequest的用法了，相信這幾個參數的作用都不用再解釋了吧。但需要注意的是，在構造函數中一定要調用super()方法將這幾個參數傳給父類，因為HTTP的請求和響應都是在父類中自動處理的。另外，由於Request類中的deliverResponse()和parseNetworkResponse()是兩個抽象方法，因此StringRequest中需要對這兩個方法進行實現。deliverResponse()方法中的實現很簡單，僅僅是調用了mListener中的onResponse()方法，並將response內容傳入即可，這樣就可以將服務器響應的數據進行回調了。parseNetworkResponse()方法中則應該對服務器響應的數據進行解析，其中數據是以字節的形式存放在NetworkResponse的data變量中的，這裡將數據取出然後組裝成一個String，並傳入Response的success()方法中即可。

自定義xmlRequest

public class XmlRequest  extends Request {
    private final Response.Listener mListener;

    public XmlRequest(int method, String url, Response.Listener listener, Response.ErrorListener errorListener) {
        super(method, url, errorListener);
        mListener = listener;
    }

    public XmlRequest(String url, Response.Listener listener, Response.ErrorListener errorListener) {
        this(Method.GET, url, listener, errorListener);
    }
// parseNetworkResponse()方法中則應該對服務器響應的數據進行解析，
// 其中數據是以字節的形式存放在NetworkResponse的data變量中的，
// 這裡將數據取出然後組裝成一個String，並傳入Response的success()方法中即可
    @Override
    protected Response parseNetworkResponse(NetworkResponse response) {
        try {
            String xmlString = new String(response.data, HttpHeaderParser.parseCharset(response.headers));
            XmlPullParserFactory factory = XmlPullParserFactory.newInstance();
            XmlPullParser xmlPullParser = factory.newPullParser();
            /**
             * Set the input source for parser to the given reader and
             * resets the parser. The event type is set to the initial value
             * START_DOCUMENT.
             * Setting the reader to null will just stop parsing and
             * reset parser state,
             * allowing the parser to free internal resources
             * such as parsing buffers.
             */
//        為了給予閱讀器，設置輸入源給分析器。 和 重新設置 分析器 。事件類型會給一個初始值 START_DOCUMENT 開始文檔
//        設置的閱讀器如果為空會停止分析並且重新設置 分析器的狀態      允許分析器來解析釋放的內部資源 例如解析緩沖區
            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);
    }

    @Override
    public Map getHeaders() throws AuthFailureError {
        // self-defined user agent
        Map headerMap = new HashMap();
        headerMap.put("User-Agent", "android-open-project-analysis/1.0");
        return headerMap;
    }
}

    // 發起請求
    XmlRequest request = new XmlRequest(StringUtil.preUrl(Constants.DEFAULT_XML_REQUEST_URL),
            new Response.Listener() {
                @Override
                public void onResponse(XmlPullParser parser) {
                    try {
                        weatherDataList.clear();
                        int eventType = parser.getEventType();
                        while (eventType != XmlPullParser.END_DOCUMENT) {
                            switch (eventType) {
                                case XmlPullParser.START_TAG:
                                    String nodeName = parser.getName();
                                    if ("city".equals(nodeName)) {
                                        Map weatherMap = new HashMap();
                                        weatherMap.put("city", parser.getAttributeValue(2));
                                        weatherMap.put("detail", parser.getAttributeValue(5));
                                        weatherMap.put("temp", parser.getAttributeValue(7)+"℃ 到 "+parser.getAttributeValue(6)+"℃");
                                        weatherMap.put("wind", parser.getAttributeValue(8));
                                        weatherDataList.add(weatherMap);
                                    }
                                    break;
                            }
                            eventType = parser.next();
                        }


                        adapter.notifyDataSetChanged();
                    } catch (XmlPullParserException e) {
                        e.printStackTrace();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }

                }
            }, new Response.ErrorListener() {

        @Override
        public void onErrorResponse(VolleyError arg0) {
            ToastUtil.showToast(getActivity(), getResources().getString(R.string.request_fail_text));
        }
    });

public class GsonRequest extends Request {

    private final Response.Listener mlisten;

    private Gson gson;
    private Class mClass;

    public GsonRequest(int method, String url,Class clazz, Response.Listener listener, Response.ErrorListener errorListener) {
        super(method, url, errorListener);
        mClass = clazz;
        gson = new Gson();
        mlisten = listener;
    }

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



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

    @Override
    protected void deliverResponse(T t) {
        mlisten.onResponse(t);
    }
}

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;
    }
}

public class Weather {
    private WeatherInfo weatherinfo;

    public WeatherInfo getWeatherinfo() {
        return weatherinfo;
    }

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

    RequestQueue quene = VolleyUtil.getQueue(this);
    GsonRequest gsonRequest = new GsonRequest(
            "http://www.weather.com.cn/adat/sk/101010100.html", Weather.class,
            new Response.Listener() {
                @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);
        }
    });
    quene.add(gsonRequest);