Volley

JSON，图像等的异步下载
网络请求的排序（scheduling）
网络请求的优先级处理
缓存
多级别取消请求
和Activity和生命周期的联动（Activity结束时同时取消所有网络请求）

HttpURLConnection urlConnection = null;
try {
   URL url = new URL("http://www.android.com/");
   urlConnection = (HttpURLConnection) url.openConnection();
   InputStream in = new BufferedInputStream(urlConnection.getInputStream());
   ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
   byte[] buffer = new byte[1024]; // Adjust if you want
   int bytesRead;
   while ((bytesRead = in.read(buffer)) != -1) {
     outputStream.write(buffer, 0, bytesRead);
   }
   JSONObject resultJSON = new JSONObject(outputStream.toString());

}catch (Exception e) {
       e.printStackTrace();
} finally {
     urlConnection.disconnect();
}

JsonObjectRequest

String url = "<SERVER_API>";

JsonObjectRequest jsonObjRequest = new JsonObjectRequest(Request.Method.GET,
                            url, null, 
                            new Response.Listener<JSONObject>() {
    @Override
    public void onResponse(JSONObject response) {
    }
}, new Response.ErrorListener() {

    @Override
    public void onErrorResponse(VolleyError error) {
    }
});

mVolleyQueue.add(jsonObjRequest);

StringRequest

String url = "<SERVER-API>";

StringRequest stringRequest = new StringRequest(Request.Method.GET, url, new Response.Listener<String>() {
    @Override
    public void onResponse(String response) {
    }
}, new Response.ErrorListener() {
    @Override
    public void onErrorResponse(VolleyError error) {
    }
});

mVolleyQueue.add(stringRequest);

GsonRequest

public class GsonRequest<T> extends Request<T>{
    private Gson mGson;

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

    @Override
    protected Response<T> parseNetworkResponse(NetworkResponse response) {
        try {
            String jsonString = new String(response.data, HttpHeaderParser.parseCharset(response.headers));
                T parsedGSON = mGson.fromJson(jsonString, mJavaClass);
            return Response.success(parsedGSON,
                    HttpHeaderParser.parseCacheHeaders(response));

        } catch (UnsupportedEncodingException e) {
            return Response.error(new ParseError(e));
        } catch (JsonSyntaxException je) {
            return Response.error(new ParseError(je));
        }
    }
}        

图片的下载

SSL connections

 SslHttpStack implements HtpStack

    @Override
    public HttpResponse performRequest(Request<?> request, Map<String, String> additionalHeaders)
            throws IOException, AuthFailureError {
        HttpUriRequest httpRequest = createHttpRequest(request, additionalHeaders);
    -----------------------
    -----------------------

    /* Register schemes, HTTP and HTTPS */
        SchemeRegistry registry = new SchemeRegistry();
        registry.register(new Scheme("http", new PlainSocketFactory(), 80));
        registry.register(new Scheme("https", new EasySSLSocketFactory(mIsConnectingToYourServer), 443));

        /* Make a thread safe connection manager for the client */
        ThreadSafeClientConnManager manager = new ThreadSafeClientConnManager(httpParams, registry);
        HttpClient httpClient = new DefaultHttpClient(manager, httpParams); 
    }

多部分 发送请求

public class MultiPartRequest extends JsonRequest<JSONObject> {

    /* To hold the parameter name and the File to upload */
    private Map<String,File> fileUploads = new HashMap<String,File>();

    /* To hold the parameter name and the string content to upload */
    private Map<String,String> stringUploads = new HashMap<String,String>();

    public void addFileUpload(String param,File file) {
        fileUploads.put(param,file);
    }

    public void addStringUpload(String param,String content) {
        stringUploads.put(param,content);
    }

    public Map<String,File> getFileUploads() {
        return fileUploads;
    }

    public Map<String,String> getStringUploads() {
        return stringUploads;
    }

}

 private static void setMultiPartBody(HttpEntityEnclosingRequestBase httpRequest,
            Request<?> request) throws AuthFailureError {

        // Return if Request is not MultiPartRequest
        if(request instanceof MultiPartRequest == false) {
            return;
        }

        MultipartEntity multipartEntity = new MultipartEntity(HttpMultipartMode.BROWSER_COMPATIBLE);  
        //Iterate the fileUploads
        Map<String,File> fileUpload = ((MultiPartRequest)request).getFileUploads();
        for (Map.Entry<String, File> entry : fileUpload.entrySet()) {
            multipartEntity.addPart(((String)entry.getKey()), new FileBody((File)entry.getValue()));
        }

        //Iterate the stringUploads
        Map<String,String> stringUpload = ((MultiPartRequest)request).getStringUploads();
        for (Map.Entry<String, String> entry : stringUpload.entrySet()) {
            try {
                multipartEntity.addPart(((String)entry.getKey()), new StringBody((String)entry.getValue()));
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        httpRequest.setEntity(multipartEntity);
    }

增加

public String getBodyContentType() {
    return "application/x-www-form-urlencoded; charset=UTF-8";
}

public class MyStringRequest extends StringRequest{
    private Map<String, String> headers = new HashMap<String, String>();
    @Override
    public Map<String, String> getHeaders() throws AuthFailureError {
        return headers;
    }

    public void setHeader(String title, String content) {
        headers.put(title, content);
    }
}

处理错误的编码

@Override
public void onErrorResponse(VolleyError error) {
    // Handle your error types accordingly.For Timeout & No connection error, you can show 'retry' button.
    // For AuthFailure, you can re login with user credentials.
    // For ClientError, 400 & 401, Errors happening on client side when sending api request.
    // In this case you can check how client is forming the api and debug accordingly.
    // For ServerError 5xx, you can do retry or handle accordingly.
    if( error instanceof NetworkError) {
    } else if( error instanceof ClientError) { 
    } else if( error instanceof ServerError) {
    } else if( error instanceof AuthFailureError) {
    } else if( error instanceof ParseError) {
    } else if( error instanceof NoConnectionError) {
    } else if( error instanceof TimeoutError) {
    }

}

@Override
public void onErrorResponse(VolleyError error) {
    hideProgressDialog();
    if(error instanceof AuthFailureError) {
        showAlertError(ResourcesUtil.getString(R.string.login_error_invalid_credentials));
    }else if(error instanceof ClientError) {
        // Convert byte to String.
        String str = null;
        try {
            str = new String(error.networkResponse.data, "UTF8");
            JSONObject errorJson = new JSONObject(str);
            if( errorJson.has(Constants.ERROR)) {
                JSONObject err = errorJson.getJSONObject(Constants.ERROR);
                if(err.has(Constants.ERROR_MESSAGE)) {
                        String errorMsg = errorJson.has(Constants.ERROR_MESSAGE);
                        showAlertError(errorMsg);
                }
                return;
            }
        } catch (Exception e) {
            e.printStackTrace();
        }

    } else {
        MessageUtil.showMessage(ResourcesUtil.getString(R.string.error_service), true);
    }
}

取消请求

request.cancel();

( or )

for( Request<T> req : mRequestList) {
    req.cancel();
}

( or )

volleyQueue.cancelAll(Object);

优先请求集合

Priority priority;
public void setPriority(Priority priority) {
    this.priority = priority;
}

/*
 * If prioirty set use it,else returned NORMAL
 * @see com.android.volley.Request#getPriority()
 */
public Priority getPriority() {
    if( this.priority != null) {
        return priority;
    } else {
        return Priority.NORMAL; 
    }
}