OkHttp如何移除User-Agent，Accept-Encoding等框架自动添加的请求头参数

摘要：移除头部参数然后再将自定义的拦截器设置为网络拦截器信任所有证书设置应用拦截器无效，因为是在应用拦截器之后添加的这样就能达到移除自动添加的请求头参数的目的了。

使用OkHttp网络框架在进行网络请求时会发现，传到后台的请求头中会比我们自己添加的参数多出几个额外参数。查看源码会发现

 private Response getResponseWithInterceptorChain() throws IOException {
    // Build a full stack of interceptors.
    List interceptors = new ArrayList<>();
    interceptors.addAll(client.interceptors());
    interceptors.add(retryAndFollowUpInterceptor);
    interceptors.add(new BridgeInterceptor(client.cookieJar()));
    interceptors.add(new CacheInterceptor(client.internalCache()));
    interceptors.add(new ConnectInterceptor(client));
    if (!retryAndFollowUpInterceptor.isForWebSocket()) {
      interceptors.addAll(client.networkInterceptors());
    }
    interceptors.add(new CallServerInterceptor(
        retryAndFollowUpInterceptor.isForWebSocket()));

    Interceptor.Chain chain = new RealInterceptorChain(
        interceptors, null, null, null, 0, originalRequest);
    return chain.proceed(originalRequest);
  }

OkHttp会默认添加一个桥接拦截器BridgeInterceptor，查看BridgeInterceptor的源码

MediaType contentType = body.contentType();
      if (contentType != null) {
        requestBuilder.header("Content-Type", contentType.toString());
      }

      long contentLength = body.contentLength();
      if (contentLength != -1) {
        requestBuilder.header("Content-Length", Long.toString(contentLength));
        requestBuilder.removeHeader("Transfer-Encoding");
      } else {
        requestBuilder.header("Transfer-Encoding", "chunked");
        requestBuilder.removeHeader("Content-Length");
      }
    }

    if (userRequest.header("Host") == null) {
      requestBuilder.header("Host", hostHeader(userRequest.url(), false));
    }

    if (userRequest.header("Connection") == null) {
      requestBuilder.header("Connection", "Keep-Alive");
    }

    // If we add an "Accept-Encoding: gzip" header field we"re responsible for also decompressing
    // the transfer stream.
    boolean transparentGzip = false;
    if (userRequest.header("Accept-Encoding") == null) {
      transparentGzip = true;
      requestBuilder.header("Accept-Encoding", "gzip");
    }

    List cookies = cookieJar.loadForRequest(userRequest.url());
    if (!cookies.isEmpty()) {
      requestBuilder.header("Cookie", cookieHeader(cookies));
    }

    if (userRequest.header("User-Agent") == null) {
      requestBuilder.header("User-Agent", Version.userAgent());
    }

在BridgeInterceptor中会默认添加User-Agent，Accept-Encoding等请求头参数。有时候我们并不需要这些默认添加的参数，那么我们如何才能做到移除它们呢？

通过上面第一段的部分源码

interceptors.add(retryAndFollowUpInterceptor);
interceptors.add(new BridgeInterceptor(client.cookieJar()));
interceptors.add(new CacheInterceptor(client.internalCache()));
interceptors.add(new ConnectInterceptor(client));
if (!retryAndFollowUpInterceptor.isForWebSocket()) {
  interceptors.addAll(client.networkInterceptors());
}

可以看到OkHttp内部在添加完BridgeInterceptor后，才开始添加networkInterceptors，所以我们需要借助网络拦截器来重新拦截请求头，并操作头部参数。

首先我们要自定义一个拦截器，在拦截器中移除我们不需要的参数。

public class NetInterceptorimplements Interceptor {

    private HttpClient builder;

    public NetInterceptor() {
        super();
    }

    public NetInterceptor(HttpClient builder) {
        this.builder = builder;
    }

    @Override
    public Response intercept(Chain chain) throws IOException {
        Request request = chain.request();
        //移除头部参数
        request = request.newBuilder()
                    .removeHeader("User-Agent")
                    .removeHeader("Accept-Encoding")
                    .build();
        Response response = chain.proceed(request);
        if (response.body() != null && response.body().contentType() != null) {
            MediaType mediaType = response.body().contentType();
            String content = response.body().string();
            ResponseBody responseBody = ResponseBody.create(mediaType, content);
            return response.newBuilder().body(responseBody).build();
        } else {
            return response;
        }
    }

}

然后再将自定义的拦截器设置为网络拦截器

  mOkBuilder = new Builder()
                .connectTimeout(mbuilder.getConnectTimeout(), TimeUnit.SECONDS)
                .readTimeout(mbuilder.getReadTimeout(), TimeUnit.SECONDS)
                .writeTimeout(mbuilder.getWriteTimeout(), TimeUnit.SECONDS)
                .sslSocketFactory(createSSLSocketFactory(), new TrustAllCerts())// 信任所有证书
                .hostnameVerifier(new TrustAllHostnameVerifier())
                .cookieJar(new CookieJar() {
                    private final HashMap> cookieStore = new HashMap<>();

                    @Override
                    public void saveFromResponse(HttpUrl httpUrl, List list) {
                        cookieStore.put(httpUrl.host(), list);
                    }

                    @Override
                    public List loadForRequest(HttpUrl httpUrl) {
                        List cookies = cookieStore.get(httpUrl.host());
                        return cookies != null ? cookies : new ArrayList();
                    }
                });

  NetInterceptor netInterceptor = new NetInterceptor(mbuilder);
  //mOkBuilder.addNetworkInterceptor(netInterceptor);//设置应用拦截器无效，因为BridgeInterceptor是在应用拦截器之后添加的
  mOkBuilder.addNetworkInterceptor(netInterceptor);

这样就能达到移除BridgeInterceptor自动添加的请求头参数的目的了。