应项目要求修改网络问题，为了让项目更加健壮，使用Volley框架，这个android 推荐使用的网络框架，整体来说请求的方式网上都可以查的到，这里就不说，现在就说说添加头部验证，因为我们的项目在请求每一个链接的时候都会验证，所以添加头部是一个十分必要的情况。网上说让在请求里边添加getHeaders（）方法，方法是确实能用，但是是有前提的。

主要是使用不同的队列的问题：

    (1)Volley.newRequestQueue(this）

        如果是调用这个方法的话，那么在执行StringRequest方法的时候调用的HttpClientStack  这个类中的访问网络的方法：

/*
 * Copyright (C) 2011 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */


package com.android.volley.toolbox;


import com.android.volley.AuthFailureError;
import com.android.volley.Request;
import com.android.volley.Request.Method;


import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.NameValuePair;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpDelete;
import org.apache.http.client.methods.HttpEntityEnclosingRequestBase;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.client.methods.HttpPut;
import org.apache.http.client.methods.HttpUriRequest;
import org.apache.http.entity.ByteArrayEntity;
import org.apache.http.message.BasicNameValuePair;
import org.apache.http.params.HttpConnectionParams;
import org.apache.http.params.HttpParams;


import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;


/**
 * An HttpStack that performs request over an {@link HttpClient}.
 */
public class HttpClientStack implements HttpStack {
    protected final HttpClient mClient;


    private final static String HEADER_CONTENT_TYPE = "Content-Type";


    public HttpClientStack(HttpClient client) {
        mClient = client;
    }


    private static void addHeaders(HttpUriRequest httpRequest, Map<String, String> headers) {
        for (String key : headers.keySet()) {
            httpRequest.setHeader(key, headers.get(key));
        }
    }


    @SuppressWarnings("unused")
    private static List<NameValuePair> getPostParameterPairs(Map<String, String> postParams) {
        List<NameValuePair> result = new ArrayList<NameValuePair>(postParams.size());
        for (String key : postParams.keySet()) {
            result.add(new BasicNameValuePair(key, postParams.get(key)));
        }
        return result;
    }


    @Override
    public HttpResponse performRequest(Request<?> request, Map<String, String> additionalHeaders)
            throws IOException, AuthFailureError {
        HttpUriRequest httpRequest = createHttpRequest(request, additionalHeaders);
        addHeaders(httpRequest, additionalHeaders);
        addHeaders(httpRequest, request.getHeaders());
        onPrepareRequest(httpRequest);
        HttpParams httpParams = httpRequest.getParams();
        int timeoutMs = request.getTimeoutMs();
        // TODO: Reevaluate this connection timeout based on more wide-scale
        // data collection and possibly different for wifi vs. 3G.
        HttpConnectionParams.setConnectionTimeout(httpParams, 5000);
        HttpConnectionParams.setSoTimeout(httpParams, timeoutMs);
        return mClient.execute(httpRequest);
    }


    /**
     * Creates the appropriate subclass of HttpUriRequest for passed in request.
     */
    @SuppressWarnings("deprecation")
    /* protected */ static HttpUriRequest createHttpRequest(Request<?> request,
            Map<String, String> additionalHeaders) throws AuthFailureError {
        switch (request.getMethod()) {
            case Method.DEPRECATED_GET_OR_POST: {
                // This is the deprecated way that needs to be handled for backwards compatibility.
                // If the request‘s post body is null, then the assumption is that the request is
                // GET.  Otherwise, it is assumed that the request is a POST.
                byte[] postBody = request.getPostBody();
                if (postBody != null) {
                    HttpPost postRequest = new HttpPost(request.getUrl());
                    postRequest.addHeader(HEADER_CONTENT_TYPE, request.getPostBodyContentType());
                    postRequest.setHeader("Authorization","Basic YW5vbnltb3VzOjEyMzQ1Ng==");
                    HttpEntity entity;
                    entity = new ByteArrayEntity(postBody);
                    postRequest.setEntity(entity);
                    return postRequest;
                } else {
                    return new HttpGet(request.getUrl());
                }
            }
            case Method.GET:
            HttpGet  httpGet  =new HttpGet(request.getUrl());
//             httpGet.setHeader("Authorization","Basic YW5vbnltb3VzOjEyMzQ1Ng==");
                return httpGet;
            case Method.DELETE:
            HttpDelete  httpDelete =new HttpDelete(request.getUrl());
                return new HttpDelete(request.getUrl());
            case Method.POST: {
                HttpPost postRequest = new HttpPost(request.getUrl());
                postRequest.addHeader(HEADER_CONTENT_TYPE, request.getBodyContentType());
                setEntityIfNonEmptyBody(postRequest, request);
                return postRequest;
            }
            case Method.PUT: {
                HttpPut putRequest = new HttpPut(request.getUrl());
                putRequest.addHeader(HEADER_CONTENT_TYPE, request.getBodyContentType());
                setEntityIfNonEmptyBody(putRequest, request);
                return putRequest;
            }
            default:
                throw new IllegalStateException("Unknown request method.");
        }
    }


    private static void setEntityIfNonEmptyBody(HttpEntityEnclosingRequestBase httpRequest,
            Request<?> request) throws AuthFailureError {
        byte[] body = request.getBody();
        if (body != null) {
            HttpEntity entity = new ByteArrayEntity(body);
            httpRequest.setEntity(entity);
        }
    }


    /**
     * Called before the request is executed using the underlying HttpClient.
     *
     * <p>Overwrite in subclasses to augment the request.</p>
     */
    protected void onPrepareRequest(HttpUriRequest request) throws IOException {
        // Nothing.
    }
}

可以看到，这个里边是使用了HttpClient    来进行访问网络，但是再他设置访问方式的时候没有调用getHeaders这个方法

@Override
public Map<String, String> getHeaders() throws AuthFailureError {
Map<String, String> headers = new HashMap<String, String>();
// headers.put("Charset", "UTF-8");
// headers.put("Content-Type", "application/x-javascript");
// headers.put("Accept-Encoding", "gzip,deflate");
headers.put("Authorization", "Basic YW5vbnltb3VzOjEyMzQ1Ng==");
return headers;
}

//设置超时
public RetryPolicy getRetryPolicy() {
RetryPolicy retryPolicy = new DefaultRetryPolicy(1000,
DefaultRetryPolicy.DEFAULT_MAX_RETRIES,
DefaultRetryPolicy.DEFAULT_BACKOFF_MULT);
return retryPolicy;
}

     也就不会添加你设置的头部，那么访问肯定通不过。

所以你可以再里边给添加你的头部，或是，在里边调用getHeaders方法，把头部添加到相应的请求里。

（2） Volley.newRequestQueue(this,new HurlStack())

       这个创建的队列他在执行的时候调用的是HttpUrlConnition   这种访问网络的方式，

从这个代码中可以看到，

         可以看到这里边他调用了getHeaders这个方法，会给你添加相应的头部，所以，也可以使用这个。

Volley框架源码修改，添加头部验证Hreaders问题