DefaultHttpClient进行BasicAuth重复请求的问题【转】

其实一般的只要设置一个 BasicScheme 加在 DefaultHttpClient 上面即可进行 BasicAuth 认证, 但是这个简单的方法会出现一些问题, 就是需要进行认证的请求, httpClient都不会在第一次请求服务器的时候携带认证信息, 而是在请求一次被服务器拒绝后再重新发一次请求重新进行认证. 从而导致了重复请求的问题.

通过抓包显示, DefaultHttpClient 里面的是储存了 auth 信息(用户名/密码)的, 但是所有HTTP请求都几乎会做了两遍, 第一次返回 401 unauthorized , 然后 defaultHttpClient 马上进行第二次重复请求, 添加了 auth 信息, 才返回200, 而使用 curl 进行对同样网址进行认证请求时抓包, 结果都是只进行一个请求, 直接返回200, 由此得到了 DefaultHttpClient 在进行 BasicAuth 的这个问题.

唯一的原因只有是 HttpClient 的配置问题, 在查找了大量的关于 org.apache.http.impl.client.DefaultHttpClient 相关资料后才发现正确的配置方法, 可以说是较为复杂的.

先贴代码片段, 注意这里的代码未经过删减, 是我参与的 安能饭否 项目中的实际代码:

   /**
     * Setup DefaultHttpClient
     *
     * <p>
     * Use ThreadSafeClientConnManager.
     * </p>
     *
     */
    private void prepareHttpClient() {

        // Create and initialize HTTP parameters
        HttpParams params = new BasicHttpParams();
        ConnManagerParams.setMaxTotalConnections(params, 10);
        HttpProtocolParams.setVersion(params, HttpVersion.HTTP_1_1);

        // Create and initialize scheme registry
        SchemeRegistry schemeRegistry = new SchemeRegistry();
        schemeRegistry.register(new Scheme("http", PlainSocketFactory
                .getSocketFactory(), 80));
        schemeRegistry.register(new Scheme("https", SSLSocketFactory
                .getSocketFactory(), 443));

        // Create an HttpClient with the ThreadSafeClientConnManager.
        ClientConnectionManager cm = new ThreadSafeClientConnManager(params,
                schemeRegistry);
        mClient = new DefaultHttpClient(cm, params);

        // TODO: need to release this connection in httpRequest()
        // cm.releaseConnection(conn, validDuration, timeUnit);

        // Setup BasicAuth
        BasicScheme basicScheme = new BasicScheme();
        mAuthScope = new AuthScope(SERVER_HOST, AuthScope.ANY_PORT);

        // mClient.setAuthSchemes(authRegistry);
        mClient.setCredentialsProvider(new BasicCredentialsProvider());

        // Generate BASIC scheme object and stick it to the local
        // execution context
        localcontext = new BasicHttpContext();
        localcontext.setAttribute("preemptive-auth", basicScheme);

        // first request interceptor
        mClient.addRequestInterceptor(preemptiveAuth, 0);
    }

    /**
     * HttpRequestInterceptor for DefaultHttpClient
     */
    private HttpRequestInterceptor preemptiveAuth = new HttpRequestInterceptor() {
        @Override
        public void process(final HttpRequest request, final HttpContext context) {
            AuthState authState = (AuthState) context
                    .getAttribute(ClientContext.TARGET_AUTH_STATE);
            CredentialsProvider credsProvider = (CredentialsProvider) context
                    .getAttribute(ClientContext.CREDS_PROVIDER);
            HttpHost targetHost = (HttpHost) context
                    .getAttribute(ExecutionContext.HTTP_TARGET_HOST);

            if (authState.getAuthScheme() == null) {
                AuthScope authScope = new AuthScope(targetHost.getHostName(),
                        targetHost.getPort());
                Credentials creds = credsProvider.getCredentials(authScope);
                if (creds != null) {
                    authState.setAuthScheme(new BasicScheme());
                    authState.setCredentials(creds);
                }
            }
        }
    };


    /**
     * Setup Credentials for HTTP Basic Auth
     *
     * @param username
     * @param password
     */
    public void setCredentials(String username, String password) {
        mUserId = username;
        mPassword = password;
        mClient.getCredentialsProvider().setCredentials(mAuthScope,
                new UsernamePasswordCredentials(username, password));
        isAuthenticationEnabled = true;
    }

这里并没有太多可以解释的, 目前看来是进行 BasicAuth 的基本配置, 直接搬去用就可以了. 如果说流量和请求对你的项目来说是一种负担的话.

其实关键的地方在于:

// first request interceptor
mClient.addRequestInterceptor(preemptiveAuth, 0);

这里会在 httpClient 发出第一次请求前把anth信息强行添加到请求中去, 从而避免了重复请求.