JDK 23 Early-Access Release Notes

javax.lang.model.type.TypeMirror::toString for an inner class always returns a qualified class name.

The undocumented DontYieldALot product flag was introduced to mitigate a scheduling anomaly that could arise on the Solaris operating system. It has not been needed for many years nor has it operated as described for many years. The flag has now been marked as deprecated and will be obsoleted and then removed in future releases.

The locale data based on the Unicode Consortium's CLDR has been upgraded to version 45. Besides the usual addition of new locale data and translation changes, there is one notable number format change from the upstream CLDR, affecting the java.text.CompactNumberFormat class:

• Compact form for Italian "million" switched back to "Mln" (CLDR-17482)

Note that locale data is subject to change in a future release of the CLDR. Although not all locale data changes affect the JDK, users should not assume stability across releases. For more details, please refer to the Unicode Consortium's CLDR release notes and their locale data deltas.

Fixed an issue on Debian Linux distros where jpackage could not always build an accurate list of required packages from shared libraries with symbolic links in their paths, causing installations to fail due to missing shared libraries.

The size of CipherInputStream's internal buffer has been increased from 512 bytes to 8192 bytes.

The JMX Subject Delegation feature has been removed. The method javax.management.remote.JMXConnector.getMBeanServerConnection(Subject delegationSubject) will throw an UnsupportedOperationException if a non-null delegation subject is provided. If a client application needs to perform operations as or on behalf of multiple identities, it will need to make multiple calls to JMXConnectorFactory.connect() and to the getMBeanServerConnection() method on the returned JMXConnector.

See Security in Java Management Extensions Guide for more information.

The java.security.debug system property now accepts arguments which add thread ID, thread name, caller information and timestamp information to debug statements for all components or a specific component.

+timestamp can be appended to debug options to print a timestamp for that debug option. +thread can be appended to debug options to print thread and caller information for that debug option.

Examples: -Djava.security.debug=all+timestamp+thread adds timestamp and thread information to every debug statement generated.

-Djava.security.debug=properties+timestamp adds timestamp information to every debug statement generated for the properties component.

You can also specify -Djava.security.debug=help which will display a complete list of supported components and arguments.

See Enabling Debugging in JGSS and Kerberos for more information.

JDK 17 introduced the performance improvement that made OCSP client unconditionally use GET requests for small requests, while doing POST requests for everything else. This is explicitly allowed and recommended by RFC 5019 and RFC 6960. However, we have seen OCSP responders that, despite RFC requirements, are not working well with GET requests.

This release introduces a new JDK system property to allow fallback to POST-only behavior to unblock interaction with those OCSP responders: -Dcom.sun.security.ocsp.useget={false,true}. This amends the original change that introduced GET OCSP requests (JDK-8179503). The default behavior is not changed; the option defaults to true. Set the option to false to disable GET OCSP requests. Any value other than false (case-insensitive) defaults to true.

This option is non-standard, and might go away once problematic OCSP responders get upgraded.

The current javax.security.auth.Subject::doAs and Subject::getSubject APIs are deprecated for removal as they have dependencies on Security Manager APIs that are also deprecated for removal. These APIs will not work as expected when the Security Manager support is removed in a future release. Applications should be transitioning to the replacement APIs (Subject::callAs and Subject::current) that were introduced in JDK 18.

To further prepare applications for the eventual removal of the Security Manager, we have implemented a new mechanism for subject authorization and have modified the behavior of the APIs above to behave differently depending on whether a Security Manager is allowed or disallowed:

• If a Security Manager is allowed, which means it is either already set or allowed to be set dynamically, there is no behavior change.

• If a Security Manager is disallowed, which means it is not set and not allowed to be set dynamically, a doAs or callAs call binds a Subject object to the period of execution of an action. This subject can be inherited by child threads if they are started and terminate within the execution of its parent thread using structured concurrency. The subject can only be retrieved using the current method inside the action. The getSubject method will always throw an UnsupportedOperationException.

For applications or libraries that do not use the Security Manager, developers should switch to the new current method to retrieve the current subject. Actions should always be executed using the doAs or callAs APIs. If in a rare case you are storing a subject in an AccessControlContext and then calling AccessController.doPrivileged with that context, the code will not work correctly in this mode. Instead, you should replace that code with callAs or doAs on the subject itself, preferably callAs since it is not deprecated. If your code depends on the automatic inheritance of subject in a newly created platform thread, it should either be modified to use structured concurrency or the current subject should be explicitly passed into the new thread.

If you are not using a Security Manager and cannot transition to the replacement APIs, you can continue using the current APIs by adding -Djava.security.manager=allow on the command line as a workaround. This allows the old implementation to be used even if a Security Manager is never set. Please note that in a future version the Security Manager will be removed and this workaround will no longer work.

The GZipInputStream read methods have been modified to remove the usage of InputStream::available() when determining if the stream contains a concatenated GZIP stream. These methods will now read any additional data in the underlying InputStream and check for the presence of a GZIP stream header.

Debug output related to JGSS/Kerberos, including those for the JAAS Krb5LoginModule, the JGSS framework, and the Kerberos 5 and SPNEGO mechanisms (whether implemented in pure Java or through a native bridge), is now directed to the standard error output stream (System.err) instead of the standard output stream (System.out). Additionally, debug output is now prefixed with a category tag, such as krb5loginmodule, jgss, krb5, etc.

A new lightweight locking mechanism for uncontended object monitor locking was introduced in JDK 21 under JDK-8291555. The LockingMode flag was introduced to allow selection of this new mechanism (LM_LIGHTWEIGHT, value 2) in place of the default mechanism (LM_LEGACY, value 1). In this release the LockingMode default has been changed to LM_LIGHTWEIGHT.

This is not expected to change any semantic behavior of Java monitor locking and it is expected to be performance neutral for almost all applications.

If you need to revert to the legacy mechanism you can set the command-line flag -XX:LockingMode=1, but note that it is expected the legacy mode will be removed in a future release.

For a java.text.DecimalFormat created with an empty String pattern, the value returned by DecimalFormat.getMaximumFractionDigits() will now be 340, instead of the previous value, Integer.MAX_VALUE. This prevents an OutOfMemoryError from occurring when DecimalFormat.toPattern() is called. If the desired maximum fractional digits should exceed 340, it is recommended to achieve this behavior using the method DecimalFormat.setMaximumFractionDigits().

The JVMTI GetCurrentContendedMonitor implementation has been aligned with the spec, so the monitor is returned only when the specified thread is waiting to enter or re-enter the monitor and the monitor is not returned when the specified thread is waiting in the java.lang.Object.wait to be notified.

The JDWP ThreadReference.CurrentContendedMonitor command spec was updated to match the JVMTI GetCurrentContendedMonitor spec. It states now: "The thread may be waiting to enter the object's monitor, or in java.lang.Object.wait waiting to re-enter the monitor after being notified, interrupted, or timed-out."

This part has been removed from the command description: "... it may be waiting, via the java.lang.Object.wait method, for another thread to invoke the notify method."

The JDI ThreadReference.currentContendedMonitor method spec was updated to match the JVMTI GetCurrentContendedMonitor spec. It states now: "The thread can be waiting for a monitor through entry into a synchronized method, the synchronized statement, or Object.wait() waiting to re-enter the monitor after being notified, interrupted, or timed-out."

This part has been added to the method description: "... or Object.wait() waiting to re-enter the monitor after being notified, interrupted, or timed-out."

And this part has been removed from the method description: "The status() method can be used to differentiate between the first two cases and the third."

The JVMTI GetObjectMonitorUsage function returns the following data structure:

    typedef struct {
        jthread owner;
        jint entry_count;
        jint waiter_count;
        jthread* waiters;
        jint notify_waiter_count;
        jthread* notify_waiters;
    } jvmtiMonitorUsage;

Two fields in this structure are specified as:

• waiter_count [jint]: The number of threads waiting to own this monitor
• waiters [jthread*]: The waiter_count waiting threads

In previous releases, the waiters field included the threads waiting to enter or re-enter the monitor as specified, but also (incorrectly) the threads waiting to be notified in java.lang.Object.wait(). That has been fixed in the current release. The waiter_count always matches the returned number of threads in the waiters field.

Also, the JDWP ObjectReference.MonitorInfo command spec was updated to clarify what the waiters threads are:

waiters: "The total number of threads that are waiting to enter or re-enter the monitor, or waiting to be notified by the monitor."

The behavior of this JDWP command is kept the same, and is intentionally different to GetObjectMonitorUsage.

Native executables and libraries on Linux have switched to using RPATH instead of RUNPATH in this release.

JDK native executables and libraries use embedded runtime search paths to locate other internal JDK native libraries. On Linux these can be defined as either RPATH or RUNPATH. The main difference is that the dynamic linker considers RPATH before the LD_LIBRARY_PATH environment variable, while RUNPATH is only considered after LD_LIBRARY_PATH.

By making the change to using RPATH, it is no longer possible to replace JDK internal native libraries using LD_LIBRARY_PATH.

The legacy JRE locale data has been removed from the JDK. The legacy JRE locale data, (COMPAT is an alias for this locale data), remained after the CLDR locale data based on the Unicode Consortium's Common Locale Data Registry became the default since JDK 9. It served as an application's migration means for the time being. Since JDK 21, users have been notified of its future removal with the startup warning message as the use of JRE/COMPAT locale data was deprecated. It is now removed from JDK 23, so specifying JRE or COMPAT in java.locale.providers system property no longer has any effect. Applications using JRE/COMPAT locale data are encouraged to migrate to CLDR locale data or consider a workaround discussed in the CSR.

Array element bases are no longer unconditionally aligned to 8 bytes. Instead, they are now aligned to their element type size. This improves footprint in some JVM modes. As Java array element alignment is not exposed to users, there is no impact on regular Java code that accesses individual elements.

There are implications for bulk access methods. Unsafe accesses to arrays could now be unaligned. For example, Unsafe.getLong(byteArray, BYTE_ARRAY_BASE_OFFSET + 0) is not guaranteed to work on platforms that do not allow unaligned accesses, the workaround is Unsafe.{get, put}Unaligned* family of methods. The ByteBuffer and VarHandle APIs that allow views of byte[] are updated to reflect this change (JDK-8318966). Arrays that are acquired via GetPrimitiveArrayCritical should not be operated upon under the assumption of particular array base alignment as well.

The following root certificates have been added to the cacerts truststore:

+ Certainly
  + certainlyrootr1
    DN: CN=Certainly Root R1, O=Certainly, C=US

+ Certainly
  + certainlyroote1
    DN: CN=Certainly Root E1, O=Certainly, C=US

TrimNativeHeapInterval has been made an official product switch. It allows the JVM to trim the native heap at periodic intervals.

This option is only available on Linux with glibc.

The var handle returned by MethodHandles::byteArrayViewVarHandle no longer supports atomic access modes, and the var handle returned by MethodHandles::byteBufferViewVarHandle no longer supports atomic access modes when accessing heap buffers. Additionally, the ByteBuffer::alignedSlice and ByteBuffer::alignmentOffset methods are updated to reflect these changes. They no longer report aligned slices or offsets for heap byte buffers when the accessed 'unitSize' is greater than 1, and instead throw an UnsupportedOperationException in those cases.

The removed functionality was based on an implementation detail in the reference JVM implementation that is not mandated by the JVM specification, and is therefore not guaranteed to work on an arbitrary JVM implementation. This also allows the reference implementation to align array elements more loosely, if it is deemed beneficial 1.

Affected clients should consider using direct (off-heap) byte buffers, for which aligned access can reliably be guaranteed. Or they should use a long[] to store their data, which has stronger alignment guarantees than byte[]. A MemorySegment backed by a long[] array can be accessed through an atomic access mode and any primitive type, using the newly introduced Foreign Function and Memory API 3 as follows:

long[] arr = new long[10];
MemorySegment arrSeg = MemorySegment.ofArray(arr);
VarHandle vh = ValueLayout.JAVA_INT.varHandle(); // accessing aligned ints
vh.setVolatile(arrSeg, 0L, 42); // 0L is offset in bytes
long result = vh.getVolatile(arrSeg, 0L); // 42

Parsing of date/time strings now allows the "loose matching" of spaces. This enhancement is mainly to address the [incompatible changes](https://www.oracle.com/java/technologies/javase/20-relnote-issues.html#JDK-8284840) introduced in JDK 20 with CLDR version 42. That version replaced ASCII spaces (U+0020) between time and the am/pm marker with NNBSP (Narrow No-Break Space, U+202F) in some locales. The "loose matching" is performed in the "lenient" parsing style for both date/time parsers in java.time.format and java.text packages. In the "strict" parsing style, those spaces are considered distinct, as before.

To utilize the "loose matching" in the java.time.format package, applications will need to explicitly set the leniency by calling DateTimeFormatterBuilder.parseLenient() because the default parsing mode is strict:

    var dtf = new DateTimeFormatterBuilder()
        .parseLenient()
        .append(DateTimeFormatter.ofLocalizedTime(FormatStyle.SHORT))
        .toFormatter(Locale.ENGLISH);

In the java.text package, the default parsing mode is lenient. Applications will be able to parse all space separators automatically, which is the default behavior changes with this feature. In case they need to strictly parse the text, they can do:

    var df = DateFormat.getTimeInstance(DateFormat.SHORT, Locale.ENGLISH);
    df.setLenient(false);

A new jdk.SerializationMisdeclaration JFR event type is added to the platform. Such events are triggered at runtime when some aspects of serialization related fields and methods are improperly declared. By enabling jdk.SerializationMisdeclaration, JFR will trigger an event for each incorrectly declared aspect of a serializable class when it is loaded in the JVM.

For example, if method writeObject() on a Serializable class has the correct signature but is unintentionally declared public, it is not selected by the serialization machinery. This might come to a surprise to the developer of the class. To help diagnose such problems, jdk.SerializationMisdeclaration events should be enabled.

The standard default.jfc profile does not enable these events, while the standard profile.jfc profile does.

The m-let feature has been removed. This removal has no impact on the JMX agent used for local and remote monitoring, the built-in instrumentation of the Java virtual machine, or tooling that uses JMX. The API classes that have been removed are:

• javax.management.loading.MLet
• javax.management.loading.MLetContent
• javax.management.loading.PrivateMLet
• javax.management.loading.MLetMBean

The -Xnoagent option of the java launcher, which was deprecated for removal in a previous release, has now been removed. Before it was deprecated for removal, this option was treated as non-operational when specified. Launching java with this option will now result in an error and the process will fail to launch. Applications using this option when launching the java command are expected to remove it.

The method java.lang.ThreadGroup.stop() has been removed in this release. This inherently unsafe method was deprecated in JDK 1.2 (1998), deprecated for removal in Java 18, and re-specified/degraded in Java 20 to throw UnsupportedOperationException unconditionally. Code that uses this method will no longer compile. Code using this method that is compiled to older releases will throw NoSuchMethodError if executed on JDK 23. It previously threw UnsupportedOperationException`.

The methods java.lang.Thread.suspend(), java.lang.Thread.resume(), java.lang.ThreadGroup.suspend(), and java.lang.ThreadGroup.resume() have been removed in this release. These deadlock prone methods were deprecated in JDK 1.2 (1998), deprecated for removal in Java 14, and re-specified/degraded in Java 19/20 to throw UnsupportedOperationException unconditionally. Code that uses these methods will no longer compile. Code using these methods that is compiled to older releases will throw NoSuchMethodError if executed on JDK 23. It previously threw UnsupportedOperationException`.

The following root certificates have been added to the cacerts truststore:

+ GlobalSign
  + globalsignr46
    DN: CN=GlobalSign Root R46, O=GlobalSign nv-sa, C=BE

+ GlobalSign
  + globalsigne46
    DN: CN=GlobalSign Root E46, O=GlobalSign nv-sa, C=BE