This is a sample to set HTTP Keep Alive Timeout in HTTP Client introduced from Open JDK 11.
It is a good rule to make the Keep Alive Timeout value on the client side shorter than that on the server side in order to prevent communication errors when the connection is closed from the server side and the request from the client is processed at the same time.
Therefore, it is important to know the setting method on the client side.
Use the latest Open JDK 13 at the time of writing. It also uses jshell to execute the code. As an aside, jshell is really useful.
~ $ java --version
openjdk 13.0.1 2019-10-15
OpenJDK Runtime Environment (build 13.0.1+9)
OpenJDK 64-Bit Server VM (build 13.0.1+9, mixed mode, sharing)
The HTTP Client Keep Alive Timeout can be set with the java property jdk.httpclient.keepalive.timeout.
-Djdk.httpclient.keepalive.timeout=60
Or
System.setProperty("jdk.httpclient.keepalive.timeout", "99999");
It can be set by such a method.
This setting is read by the jdk.internal.net.http.ConnectionPool class.
Since the variable that holds the timeout value is static, it must be set before loading the above class, and it seems that it cannot be changed after loading (unverified).
As far as the source code is concerned, the default value in Open JDK 13 is 1200 seconds.
The source of ConnectionPool (JDK 13) is [here](https://github.com/openjdk/jdk13/blob/master/src/java.net.http/share/classes/jdk/internal/net/http/ConnectionPool You can refer to it from .java).
This is a sample in jshell. HTTP GET to qiita.com. Set Keep Alive Timeout to 10 seconds.
jshell execution sample
jshell> import java.net.http.*
jshell> System.setProperty("jdk.httpclient.keepalive.timeout", "10")
$1 ==> null
jshell> HttpClient client = HttpClient.newBuilder().version(HttpClient.Version.HTTP_1_1).build()
client ==> jdk.internal.net.http.HttpClientImpl@57baeedf(1)
jshell> HttpRequest request = HttpRequest.newBuilder().uri(URI.create("https://qiita.com")).build()
request ==> https://qiita.com GET
jshell> HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString())
response ==> (GET https://qiita.com) 200
Since it is not possible to check whether the Timeout value has changed with the above sample alone, try monitoring the TCP status with the netstat command of the OS. In the example below, the netstat command is executed every second and the command result is narrowed down by the Public IP address of qiita.com.
netstat
while true; do date; netstat -n -p TCP | egrep "13.114.xxx.xxx|176.34.xxx.xxx|13.113.xxx.xxx"; sleep 1; done
Thursday, November 21, 2019 18:31:34 JST
Thursday, November 21, 2019 18:31:35 JST
tcp4 0 0 xxx.xxx.xxx.xxx.62156 13.114.xxx.xxx.443 ESTABLISHED
Thursday, November 21, 2019 18:31:36 JST
tcp4 0 0 xxx.xxx.xxx.xxx.62156 13.114.xxx.xxx.443 ESTABLISHED
Thursday, November 21, 2019 18:31:37 JST
tcp4 0 0 xxx.xxx.xxx.xxx.62156 13.114.xxx.xxx.443 ESTABLISHED
Thursday, November 21, 2019 18:31:38 JST
tcp4 0 0 xxx.xxx.xxx.xxx.62156 13.114.xxx.xxx.443 ESTABLISHED
Thursday, November 21, 2019 18:31:39 JST
tcp4 0 0 xxx.xxx.xxx.xxx.62156 13.114.xxx.xxx.443 ESTABLISHED
Thursday, November 21, 2019 18:31:40 JST
tcp4 0 0 xxx.xxx.xxx.xxx.62156 13.114.xxx.xxx.443 ESTABLISHED
Thursday, November 21, 2019 18:31:41 JST
tcp4 0 0 xxx.xxx.xxx.xxx.62156 13.114.xxx.xxx.443 ESTABLISHED
Thursday, November 21, 2019 18:31:42 JST
tcp4 0 0 xxx.xxx.xxx.xxx.62156 13.114.xxx.xxx.443 ESTABLISHED
Thursday, November 21, 2019 18:31:43 JST
tcp4 0 0 xxx.xxx.xxx.xxx.62156 13.114.xxx.xxx.443 ESTABLISHED
Thursday, November 21, 2019 18:31:44 JST
tcp4 0 0 xxx.xxx.xxx.xxx.62156 13.114.xxx.xxx.443 ESTABLISHED
Thursday, November 21, 2019 18:31:45 JST
tcp4 0 0 xxx.xxx.xxx.xxx.62156 13.114.xxx.xxx.443 ESTABLISHED
Thursday, November 21, 2019 18:31:46 JST
tcp4 0 0 xxx.xxx.xxx.xxx.62156 13.114.xxx.xxx.443 TIME_WAIT
After the TCP connection is established, it becomes ʻESTABLISHEDfor 10 seconds, and since it is actively closed 1 second later, it can be seen that it has moved toTIME_WAIT`.
I was able to confirm that the settings are valid.
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