How to enabled http1.1 and http2.0 both together in a spring boot REST application in tomcat 9.0.14 - spring-boot

Question

I have enabled http 2.0 with SSL in a spring boot 2.1.2 REST application with embedded tomcat using configuration "server.http2.enabled=true" and other SSL configurations in application.properties file. It is working fine. When a http2 client post https request, my server is processing and responding properly (java 9 http client is being used). But when the http client version chanced to 1.1, below exception is seen -
WARNING: Using incubator modules: jdk.incubator.httpclient
java.util.concurrent.ExecutionException: java.io.IOException: Engine is closed
at java.base/java.util.concurrent.CompletableFuture.reportGet(CompletableFuture.java:395)
at java.base/java.util.concurrent.CompletableFuture.get(CompletableFuture.java:2022)
at KnHttp2Client.sendGet(KnHttp2Client.java:81)
at KnHttp2Client.main(KnHttp2Client.java:113)
Caused by: java.io.IOException: Engine is closed
I have tried to post https request using apache-http-client4.5.7 also still I am getting below Exception
Jan 30, 2019 4:45:12 PM org.apache.http.impl.execchain.RetryExec execute
INFO: I/O exception (org.apache.http.NoHttpResponseException) caught when processing request to {s}->https://localhost:8443: The target server failed to respond
Jan 30, 2019 4:45:12 PM org.apache.http.impl.execchain.RetryExec execute
INFO: Retrying request to {s}->https://localhost:8443
org.apache.http.NoHttpResponseException: localhost:8443 failed to respond
at org.apache.http.impl.conn.DefaultHttpResponseParser.parseHead(DefaultHttpResponseParser.java:141)
at org.apache.http.impl.conn.DefaultHttpResponseParser.parseHead(DefaultHttpResponseParser.java:56)
at org.apache.http.impl.io.AbstractMessageParser.parse(AbstractMessageParser.java:259)
at org.apache.http.impl.DefaultBHttpClientConnection.receiveResponseHeader(DefaultBHttpClientConnection.java:163)
at org.apache.http.impl.conn.CPoolProxy.receiveResponseHeader(CPoolProxy.java:157)
at org.apache.http.protocol.HttpRequestExecutor.doReceiveResponse(HttpRequestExecutor.java:273)
at org.apache.http.protocol.HttpRequestExecutor.execute(HttpRequestExecutor.java:125)
at org.apache.http.impl.execchain.MainClientExec.execute(MainClientExec.java:272)
at org.apache.http.impl.execchain.ProtocolExec.execute(ProtocolExec.java:185)
at org.apache.http.impl.execchain.RetryExec.execute(RetryExec.java:89)
at org.apache.http.impl.execchain.RedirectExec.execute(RedirectExec.java:110)
at org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:185)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:83)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:108)
at apacheclient.KnConnPoolClient$1.run(KnConnPoolClient.java:48)
at java.base/java.lang.Thread.run(Thread.java:844)
After setting setRetryHandler(new DefaultHttpRequestRetryHandler(0, true)) got below exception <br>
org.apache.http.NoHttpResponseException: localhost:8443 failed to respond
at org.apache.http.impl.conn.DefaultHttpResponseParser.parseHead(DefaultHttpResponseParser.java:141)
at org.apache.http.impl.conn.DefaultHttpResponseParser.parseHead(DefaultHttpResponseParser.java:56)
at org.apache.http.impl.io.AbstractMessageParser.parse(AbstractMessageParser.java:259)
at org.apache.http.impl.DefaultBHttpClientConnection.receiveResponseHeader(DefaultBHttpClientConnection.java:163)
at org.apache.http.impl.conn.CPoolProxy.receiveResponseHeader(CPoolProxy.java:157)
at org.apache.http.protocol.HttpRequestExecutor.doReceiveResponse(HttpRequestExecutor.java:273)
at org.apache.http.protocol.HttpRequestExecutor.execute(HttpRequestExecutor.java:125)
at org.apache.http.impl.execchain.MainClientExec.execute(MainClientExec.java:272)
at org.apache.http.impl.execchain.ProtocolExec.execute(ProtocolExec.java:185)
at org.apache.http.impl.execchain.RetryExec.execute(RetryExec.java:89)
at org.apache.http.impl.execchain.RedirectExec.execute(RedirectExec.java:110)
at org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:185)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:83)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:108)
at apacheclient.KnConnPoolClient$1.run(KnConnPoolClient.java:48)
at java.base/java.lang.Thread.run(Thread.java:844)
Working client for with http 2.0
{HttpClient httpClient = HttpClient.newBuilder()
.version(HttpClient.Version.HTTP_2)
.build();
HttpRequest request = HttpRequest.newBuilder()
.uri(URI.create("https://localhost:8443/....."))
.GET()
.build();
CompletableFuture<HttpResponse<String>> resp = httpClient.sendAsync(request, HttpResponse.BodyHandler.asString()); }
When the http client version is changed to 1.1 as below it is not working
{HttpClient httpClient = HttpClient.newBuilder()
.version(HttpClient.Version.HTTP_1_1)
.build();}
Below client code with Apache client is also not working
{
final CloseableHttpClient httpclient =
HttpClients.custom().setConnectionManager(pool).build();
final String url = "https://localhost:8443/....";
for (int i = 0; i < 1; i++) {
new Thread(new Runnable() {
public void run() {
try {
HttpGet httpGet = new HttpGet(url);
CloseableHttpResponse response =httpclient.execute(httpGet);
HttpEntity entity = response.getEntity();
System.out.println(EntityUtils.toString(entity));
EntityUtils.consume(entity);
response.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}).start();
}
I expect that the server which supports http 2.0 should support http 1.1 also.

Answer 1

This is a known issue in Spring Boot, see issue #15764.
Currently, only http/2 is supported when Tomcat is configured, but Jetty and Undertow are supporting both. Until this issue is addressed, you can switch to Jetty or Undertow as a workaround.