404异常有关问题，最终要的是思路- httpURLconnection模拟get方法

public static Map<String, Object> get(URL url, String token) throws IOException {        HttpURLConnection conn = getURLConnection(url);//        conn.setRequestProperty("Content-Type", APPLICATION_JSON);        conn.setRequestMethod(HTTP_GET);        conn.setDoInput(true);//        conn.setDoOutput(true);        if (token != null) {            System.out.println(token);            conn.setRequestProperty("X-Auth-Token", token);        }        System.out.println(conn.toString());        if (conn.getResponseCode() == 401) {            throw new IOException("Authorize Error occurs and the response code is :" + conn.getResponseCode() + ",and the message is:" + conn.getResponseMessage());        }                System.out.println(conn.getResponseCode());                ObjectMapper mapper = new ObjectMapper();        mapper.configure(DeserializationConfig.Feature.FAIL_ON_UNKNOWN_PROPERTIES, false);        //        System.out.println(mapper.readValue(conn.getInputStream(), new TypeReference<Map<String, Object>>() {}));                return mapper.readValue(conn.getInputStream(), new TypeReference<Map<String, Object>>() {        });            }    /**     * Creates the HTTP URL connection     *      * @param url     *            the URL to be used to establish HTTP connection     * @return A HttpURLConnection     */    private static HttpURLConnection getURLConnection(URL url) throws IOException {        HttpURLConnection conn = (HttpURLConnection) url.openConnection();        // disable cache        conn.setUseCaches(false);        // turn off HTTP keep-alive        conn.setRequestProperty("Connection", "close");        return conn;    }

Exception in thread "main" java.io.FileNotFoundException: http://127.0.0.1:5000/v2/2835ba0b17384840941b5c5d653fb81a/servers/detail    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)    at java.lang.reflect.Constructor.newInstance(Constructor.java:525)    at sun.net.www.protocol.http.HttpURLConnection$6.run(HttpURLConnection.java:1664)    at sun.net.www.protocol.http.HttpURLConnection$6.run(HttpURLConnection.java:1662)    at java.security.AccessController.doPrivileged(Native Method)    at sun.net.www.protocol.http.HttpURLConnection.getChainedException(HttpURLConnection.java:1660)    at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1243)    at com.intel.cpa.openstack.HttpUtil.get(HttpUtil.java:148)    at com.intel.cpa.openstack.NovaAPI.listServers(NovaAPI.java:46)    at com.intel.cpa.openstack.NovaAPI.main(NovaAPI.java:37)Caused by: java.io.FileNotFoundException: http://127.0.0.1:5000/v2/2835ba0b17384840941b5c5d653fb81a/servers/detail    at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1613)    at java.net.HttpURLConnection.getResponseCode(HttpURLConnection.java:468)    at com.intel.cpa.openstack.HttpUtil.get(HttpUtil.java:137)    ... 2 more