也许这是一个少见的情况，我使用HttpClient写了一个调用第三方服务的请求，在本机测试和腾讯云上测试都没有问题，但是放到阿里云之后，刚启动的时候是没有问题的，但是每次过零点之后，就会报异常：
java.net.UnknownHostException: www.xxxx.com: System error,异常栈如下：
java.net.UnknownHostException: wwww.xxx.com: System error
at java.base/java.net.Inet4AddressImpl.lookupAllHostAddr(Native Method)
at java.base/java.net.InetAddress$PlatformNameService.lookupAllHostAddr(InetAddress.java:925)
at java.base/java.net.InetAddress.getAddressesFromNameService(InetAddress.java:1505)
at java.base/java.net.InetAddress$NameServiceAddresses.get(InetAddress.java:844)
at java.base/java.net.InetAddress.getAllByName0(InetAddress.java:1495)
at java.base/java.net.InetAddress.getAllByName(InetAddress.java:1354)
at java.base/java.net.InetAddress.getAllByName(InetAddress.java:1288)
at org.apache.http.impl.conn.SystemDefaultDnsResolver.resolve(SystemDefaultDnsResolver.java:45)
at org.apache.http.impl.conn.DefaultHttpClientConnectionOperator.connect(DefaultHttpClientConnectionOperator.java:111)
at org.apache.http.impl.conn.PoolingHttpClientConnectionManager.connect(PoolingHttpClientConnectionManager.java:353)
at org.apache.http.impl.execchain.MainClientExec.establishRoute(MainClientExec.java:380)
at org.apache.http.impl.execchain.MainClientExec.execute(MainClientExec.java:236)
at org.apache.http.impl.execchain.ProtocolExec.execute(ProtocolExec.java:184)
at org.apache.http.impl.execchain.RetryExec.execute(RetryExec.java:88)
at org.apache.http.impl.execchain.RedirectExec.execute(RedirectExec.java:110)
at org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:184)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:82)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:107)
只要重启一下java进程就好了。
在网上查找，说是jvm dns缓存导致的，在启动参数中添加下面两个参数:
设置解析成功的域名记录JVM中缓存的有效时间，这里修改为1秒钟有效，0表示禁止缓存，-1表示永远有效
-Dsun.net.inetaddr.ttl=1
设置解析失败的域名记录JVM中缓存的有效时间，这里修改为1秒钟有效，0表示禁止缓存，-1表示永远有效
-Dsun.net.inetaddr.negative.ttl=1
但是我设置了，貌似没有什么效果，有条件的同学可以试试。
最终没办法 ，使用Java jdk 自带的http服务重新写了一个请求，观察一段时间不再报那个异常，具体原因还是清楚，如果有知道的，谢谢告知。
package global.util; import java.io.BufferedReader;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.URL;
import javax.net.ssl.HttpsURLConnection;
import org.apache.http.Header;
import global.common.log.DKLog; public class HttpUtil {
//发送https post请求
public static String sendHttpsPostRequest(String data, String requestUri, Header... headers) {
DataOutputStream wr = null;
BufferedReader in = null;
HttpsUrlConnection con = null;
try {
URL obj = new URL(requestUri);
//https请求
con = (HttpsURLConnection) obj.openConnection();
if(headers != null) {
for(Header header : headers) {
con.setRequestProperty(header.getName(), header.getValue());
}
}
con.setRequestProperty("Content-Type", " application/json");
con.setConnectTimeout(15000);
// 添加请求头
con.setRequestMethod("POST");
// 发送Post请求
con.setDoOutput(true);
wr = new DataOutputStream(con.getOutputStream());
wr.writeBytes(data);
wr.flush();
int responseCode = con.getResponseCode();
if (responseCode == 200) {
in = new BufferedReader(new InputStreamReader(con.getInputStream()));
String inputLine;
StringBuffer response = new StringBuffer();
while ((inputLine = in.readLine()) != null) {
response.append(inputLine);
}
return response.toString();
} else {
DKLog.system.error("请求服务器异常，返回异常码：{}", responseCode);
}
} catch (Exception e) {
DKLog.system.error("Http请求失败,{},data:{}", requestUri, data, e);
} finally {
if (wr != null) {
try {
wr.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if (in != null) {
try {
in.close();
} catch (IOException e) {
e.printStackTrace();
} }
if(con != null){
con.disconnect();
}
}
return null;
} }