Essential Guide to Migrating Java 8 Projects to Java 17: Compilation, Logging, and GC Tips

Compilation Related

JEP 320 – Removal of Java EE and CORBA Modules

Java 11 removed the Java EE and CORBA modules, so code that imports javax.annotation.* will fail to compile. Add the dependency manually:

<dependency>
    <groupId>javax.annotation</groupId>
    <artifactId>javax.annotation-api</artifactId>
    <version>1.3.2</version>
</dependency>

Replacing sun.misc Packages

Classes such as sun.misc.BASE64Encoder are no longer available. Replace them with standard alternatives or update the library (e.g., Netty) that depends on them.

[ERROR]   symbol:   class BASE64Encoder
[ERROR]   location: package sun.misc

Lombok and com.sun.tools.javac Packages

Older Lombok versions use internal compiler APIs, causing errors like:

Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.2:compile … module jdk.compiler does not "opens com.sun.tools.javac.processing" to unnamed module

Upgrade Lombok to a recent version (e.g., 1.18.24) to resolve the issue.

<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <version>1.18.24</version>
</dependency>

Kotlin Version Constraints

Kotlin versions prior to 1.6.0 cannot target Java 17. Upgrade Kotlin to at least 1.6.0 to compile against the new bytecode.

Analyzing Deprecated Dependencies

Use

jdeps --jdk-internals --multi-release 17 --class-path . encloud-api.jar

to list modules that need updating.

Parameter Migration

Unified Logging Overview

Java 9 introduced Unified Logging, replacing the old -Xloggc style GC logging with the unified -Xlog syntax. Example:

java -Xlog:gc=debug -version

Selectors follow the pattern <tag-set>=<level>. The default tag is all and level info, equivalent to java -Xlog:all=info -version.

To enable all GC tags at debug level:

$ java -Xlog:gc=debug -version
[0.023s][debug][gc] …

Wildcard * can be used for prefix matching, e.g., java -Xlog:gc*=debug -version.

List all available tags with java -Xlog:help.

GC Parameter Migration

Old GC flags are replaced by Unified Logging selectors: -XX:+PrintGCDetails →

-Xlog:gc*

-XX:+PrintGC

→

-Xlog:gc

-Xloggc:<file>

→ -Xlog:gc:file=<file> Many deprecated flags (e.g., -XX:+PrintTenuringDistribution) are now covered by selectors such as -Xlog:gc+age=trace.

Recommended Unified Logging Configuration

-Xlog:
  // selections
    codecache+sweep*=trace,
    class+unload,
    class+load,
    os+thread,
    safepoint,
    gc*,
    gc+stringdedup=debug,
    gc+ergo*=trace,
    gc+age=trace,
    gc+phases=trace,
    gc+humongous=trace,
    jit+compilation=debug
  // output
  :file=/path_to_logs/app.log
  // decorators
  :level,tags,time,uptime,pid
  // output options
  :filesize=104857600,filecount=5

Runtime Related

Reflection and Private API Access

Since Java 9, accessing internal packages (e.g., sun.misc) requires --add-exports or --add-opens flags, such as:

--add-opens java.base/java.lang=ALL-UNNAMED
--add-opens java.base/java.io=ALL-UNNAMED
…

GC Algorithm Choices

CMS is deprecated; G1 is the default, while ZGC is experimental but may consume three times the RES memory due to its three‑view design.

G1 Tuning Tips

Avoid setting explicit young generation sizes ( -Xmn, -XX:NewSize, etc.) – let G1 manage them.

Adjust -XX:InitiatingHeapOccupancyPercent (default 45) to control when concurrent marking starts.

-XX:InitiatingHeapOccupancyPercent=55

}