Httpclient 4，错误 302。如何重定向？

Question

我想访问一个首先需要（tomcat 服务器）身份验证的站点，然后使用 POST 请求登录并让该用户查看该站点的页面。我使用 Httpclient 4.0.1

第一次身份验证工作正常，但登录时总是抱怨此错误：“302 Moved Temporarily”

我保留 cookie 并保留上下文，但什么也没有。实际上，登录似乎有效，因为如果我输入了错误的参数或用户||密码，我会看到登录页面。所以我想不起作用的是自动重定向。

按照我的代码，它总是抛出 IOException，302：

    DefaultHttpClient httpclient = new DefaultHttpClient();
    CookieStore cookieStore = new BasicCookieStore();
    httpclient.getParams().setParameter(
      ClientPNames.COOKIE_POLICY, CookiePolicy.BROWSER_COMPATIBILITY); 
    HttpContext context = new BasicHttpContext();
    context.setAttribute(ClientContext.COOKIE_STORE, cookieStore);
    //ResponseHandler<String> responseHandler = new BasicResponseHandler();

    Credentials testsystemCreds = new UsernamePasswordCredentials(TESTSYSTEM_USER,  TESTSYSTEM_PASS);
    httpclient.getCredentialsProvider().setCredentials(
            new AuthScope(AuthScope.ANY_HOST, AuthScope.ANY_PORT),
            testsystemCreds);

    HttpPost postRequest = new HttpPost(cms + "/login");
    List<NameValuePair> formparams = new ArrayList<NameValuePair>();
    formparams.add(new BasicNameValuePair("pUserId", user));
    formparams.add(new BasicNameValuePair("pPassword", pass));
    postRequest.setEntity(new UrlEncodedFormEntity(formparams, "UTF-8"));
    HttpResponse response = httpclient.execute(postRequest, context);
    System.out.println(response);

    if (response.getStatusLine().getStatusCode() != HttpStatus.SC_OK)
        throw new IOException(response.getStatusLine().toString());

    HttpUriRequest currentReq = (HttpUriRequest) context.getAttribute( 
            ExecutionContext.HTTP_REQUEST);
    HttpHost currentHost = (HttpHost)  context.getAttribute( 
            ExecutionContext.HTTP_TARGET_HOST);
    String currentUrl = currentHost.toURI() + currentReq.getURI();        
    System.out.println(currentUrl);

    HttpEntity entity = response.getEntity();
    if (entity != null) {
        long len = entity.getContentLength();
        if (len != -1 && len < 2048) {
            System.out.println(EntityUtils.toString(entity));
        } else {
            // Stream content out
        }
    }

Answer 1

对于 4.1 版本：

DefaultHttpClient  httpclient = new DefaultHttpClient();
    httpclient.setRedirectStrategy(new DefaultRedirectStrategy() {                
        public boolean isRedirected(HttpRequest request, HttpResponse response, HttpContext context)  {
            boolean isRedirect=false;
            try {
                isRedirect = super.isRedirected(request, response, context);
            } catch (ProtocolException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            if (!isRedirect) {
                int responseCode = response.getStatusLine().getStatusCode();
                if (responseCode == 301 || responseCode == 302) {
                    return true;
                }
            }
            return isRedirect;
        }
    });

Answer 2

对于 HttpClient 4.3.x ：

HttpClient httpClient = HttpClientBuilder.create().setRedirectStrategy(new LaxRedirectStrategy()).build();

Answer 3

在更高版本的 HttpCLient (4.1+) 中，您可以这样做：

DefaultHttpClient client = new DefaultHttpClient()
client.setRedirectStrategy(new LaxRedirectStrategy())

LaxRedirectStrategy 将自动重定向 HEAD、GET 和 POST 请求。如需更严格的实现，请使用 DefaultRedirectStrategy。

Answer 4

您必须实现自定义重定向处理程序，该处理程序将指示对 POST 的响应是重定向。这可以通过重写 isRedirectRequested() 方法来完成，如下所示。

DefaultHttpClient client = new DefaultHttpClient();
client.setRedirectHandler(new DefaultRedirectHandler() {                
    @Override
    public boolean isRedirectRequested(HttpResponse response, HttpContext context) {
        boolean isRedirect = super.isRedirectRequested(response, context);
        if (!isRedirect) {
            int responseCode = response.getStatusLine().getStatusCode();
            if (responseCode == 301 || responseCode == 302) {
                return true;
            }
        }
        return isRedirect;
    }
});

在更高版本的 HttpClient 中，类名为 DefaultRedirectStrategy，但可以使用类似的解决方案。

Answer 5

httpclient.setRedirectHandler(new DefaultRedirectHandler());

见HttpClientJavadoc

Answer 6

对于 GET 和 PUT 之外的其他方法，HttpClient 4.1 不会自动处理重定向。

Answer 7

Extend the DefaultRedirectStrategy class and override the methods.
@Override
    protected URI createLocationURI(String arg0) throws ProtocolException {
        // TODO Auto-generated method stub
        return super.createLocationURI(arg0);
    }

    @Override
    protected boolean isRedirectable(String arg0) {
        // TODO Auto-generated method stub
        return true;
    }

    @Override
    public URI getLocationURI(HttpRequest arg0, HttpResponse arg1,
            HttpContext arg2) throws ProtocolException {
        // TODO Auto-generated method stub
        return super.getLocationURI(arg0, arg1, arg2);
    }

    @Override
    public HttpUriRequest getRedirect(HttpRequest request,
            HttpResponse response, HttpContext context)
            throws ProtocolException {
          URI uri = getLocationURI(request, response, context);
          String method = request.getRequestLine().getMethod();
          if (method.equalsIgnoreCase(HttpHead.METHOD_NAME)) {
              return new HttpHead(uri);
          } else {
              return new HttpPost(uri);
          }

    }

    @Override
    public boolean isRedirected(HttpRequest request, HttpResponse response,
            HttpContext context) throws ProtocolException {
        // TODO Auto-generated method stub
        return super.isRedirected(request, response, context);
    }

in this case isRedirectable method will always return true and getRedirect method will return post request in place of get request.