What changed in Java 11

A modern HTTP client in the JDK supporting HTTP/2, WebSocket, and both synchronous and asynchronous requests.

// Built once and shared — it owns a connection pool and an executor.
var client = java.net.http.HttpClient.newBuilder()
    .connectTimeout(Duration.ofSeconds(5))
    .build();

System.out.println("version    = " + client.version());
System.out.println("timeout    = " + client.connectTimeout().orElseThrow());
System.out.println("reusable, so create one per application, not per request");

version    = HTTP_2
timeout    = PT5S
reusable, so create one per application, not per request

Journey: Incubator in 9 and 10, standard in 11.

Asked as

• Why did the JDK need a new HTTP client?
• How do you make concurrent HTTP calls with the JDK client?
• Is the JDK HttpClient thread-safe and reusable?

Scenario question

• A service creates a new HttpClient per request and is running out of file descriptors under load.

  What is wrong and how do you fix it?

  What a good answer weighs

  HttpClient is designed to be created once and shared — it holds a connection pool and an executor. Creating one per request creates a pool per request and leaks the resources. Make it a singleton and configure its timeouts and executor deliberately.

isBlank, lines, strip, stripLeading, stripTrailing and repeat, filling gaps that every project had a StringUtils class for.

System.out.println("[" + "  hi  ".strip() + "]");
System.out.println("blank? " + "   ".isBlank());
System.out.println("ab".repeat(3));
"one\ntwo".lines().forEach(l -> System.out.println("line: " + l));

[hi]
blank? true
ababab
line: one
line: two

Asked as

• What is the difference between trim() and strip()?
• Why did trim() need replacing rather than fixing?

JAXB, JAX-WS, JAF, Common Annotations and CORBA were removed from the JDK entirely.

Asked as

• Why does upgrading from Java 8 to 11 break builds that never used modules?
• What do you do when javax.xml.bind is missing on 11?

Scenario question

• A Java 8 service fails to compile on 11 with "package javax.xml.bind does not exist". Nothing in the code changed.

  What happened and what is the fix?

  What a good answer weighs

  JAXB was removed from the JDK in 11, so a class that was previously free now needs an explicit dependency — jakarta.xml.bind plus an implementation. The instructive part is that the code was always depending on something it never declared; the removal only made the dependency visible.

java Hello.java compiles in memory and runs, with no separate javac step and no .class file.

Asked as

• How do you run a Java file without compiling it first?
• What are the limits of single-file source launch?