httpclient post提交报java.net.UnknownHostException,该怎么解决

url="http://www.dianpin.com";        CityDetails citys = new CityDetails();        // String targetRequest=citys.getCityDetails();        String targetRequest = "aaa";        HttpClient httpClient = new HttpClient();        httpClient.getHostConfiguration().setHost(url);        // 创建POST方法的实例        PostMethod postMethod = new PostMethod();        // 使用系统提供的默认的恢复策略        postMethod.getParams().setParameter(HttpMethodParams.RETRY_HANDLER,                new DefaultHttpMethodRetryHandler());        postMethod.setRequestHeader( "User-Agent", "fake");         // 填入各个表单域的值        NameValuePair[] data = { new NameValuePair("request", targetRequest) };        // 将表单的值放入postMethod中        postMethod.setRequestBody(data);        try {            // 执行postMethod            int statusCode = httpClient.executeMethod(postMethod);            // HttpClient对于要求接受后继服务的请求，象POST和PUT等不能自动处理转发            // 301或者302            if (statusCode == HttpStatus.SC_MOVED_PERMANENTLY                    || statusCode == HttpStatus.SC_MOVED_TEMPORARILY) {                // 从头中取出转向的地址                Header locationHeader = postMethod                        .getResponseHeader("location");                String location = null;                if (locationHeader != null) {                    location = locationHeader.getValue();                    System.out                            .println("The page was redirected to:" + location);                } else {                    System.err.println("Location field value is null.");                }            }            if (statusCode != HttpStatus.SC_OK) {                System.err.println("Method failed: "                        + postMethod.getStatusLine());            }            // 读取内容            byte[] responseBody = postMethod.getResponseBody();            // 处理内容            String str = new String(responseBody);            //writeXML(str);            System.out.println(str);        } catch (HttpException e) {            // 发生致命的异常，可能是协议不对或者返回的内容有问题            System.out.println("Please check your provided http address!");            e.printStackTrace();        } catch (IOException e) {            // 发生网络异常            e.printStackTrace();        } finally {            // 释放连接            postMethod.releaseConnection();        }    }