HttpClient设置请求头

public static String USER_AGENT[] = {
"Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Firefox/45.0",
"Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/43.0.2357.130 Safari/537.36",
"Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/46.0.2486.0 Safari/537.36 Edge/13.10586"
};
public static final String ACCEPT = "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8";
public static final String ACCEPT_LANGUAGE = "zh-CN,zh;q=0.8,en-US;q=0.5,en;q=0.3";
public static final String ACCEPT_ENCODING = "gzip, deflate";
public static final String CONNECTION = "keep-alive";
public static final String PRAGRAM = "no-cache";
public static final String CACHE_CONTROL = "no-cache";
public String host = "";

private Random random = new Random(System.currentTimeMillis());

void setHeader(HttpRequest request) {
// request.setHeader("Host", "log.aixifan.com");
request.setHeader("User-Agent", USER_AGENT[random.nextInt(USER_AGENT.length)]);
request.setHeader("Accept", ACCEPT);
request.setHeader("Accept-Language", ACCEPT_LANGUAGE);
request.setHeader("Accept-Encoding", ACCEPT_ENCODING);
request.setHeader("Connection", CONNECTION);
request.setHeader("Pragram", PRAGRAM);
request.setHeader("Cache-Control", CACHE_CONTROL);
}

有一个问题：

如果设置了请求头Host，则返回400.