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

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<Interceptor> 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<Cookie> 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<String, List<Cookie>> cookieStore = new HashMap<>();

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

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

  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。