Devops Monk

# Audit your application JAR and all its dependencies
jdeps \
  --multi-release 11 \
  --class-path 'target/dependency/*' \
  --ignore-missing-deps \
  myapp.jar

# Check for internal JDK dependencies
jdeps \
  --multi-release 11 \
  --class-path 'target/dependency/*' \
  --jdk-internals \
  myapp.jar

mvn dependency:copy-dependencies -DoutputDirectory=target/dependency
jdeps --multi-release 11 \
      --class-path 'target/dependency/*' \
      --jdk-internals \
      target/myapp.jar

# Check current version
mvn -version

# Upgrade via SDKMAN
sdk install maven 3.9.6
sdk use maven 3.9.6

<properties>
  <maven.compiler.release>11</maven.compiler.release>
</properties>

<build>
  <plugins>
    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-compiler-plugin</artifactId>
      <version>3.12.1</version>
    </plugin>
    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-surefire-plugin</artifactId>
      <version>3.2.5</version>
    </plugin>
  </plugins>
</build>

# Update the Gradle wrapper
./gradlew wrapper --gradle-version=8.7

# build.gradle.kts
java {
    toolchain {
        languageVersion.set(JavaLanguageVersion.of(11))
    }
}

<!-- pom.xml -->
<dependencies>
  <!-- JAXB API -->
  <dependency>
    <groupId>jakarta.xml.bind</groupId>
    <artifactId>jakarta.xml.bind-api</artifactId>
    <version>2.3.3</version>
  </dependency>
  <!-- JAXB Runtime -->
  <dependency>
    <groupId>com.sun.xml.bind</groupId>
    <artifactId>jaxb-impl</artifactId>
    <version>2.3.3</version>
    <scope>runtime</scope>
  </dependency>
</dependencies>

<dependency>
  <groupId>jakarta.annotation</groupId>
  <artifactId>jakarta.annotation-api</artifactId>
  <version>1.3.5</version>
</dependency>

// Old — breaks on Java 11
import sun.misc.BASE64Encoder;
String encoded = new BASE64Encoder().encode(bytes);

// New — available since Java 8
import java.util.Base64;
String encoded = Base64.getEncoder().encodeToString(bytes);
String decoded = Base64.getDecoder().decode(encodedString);

// Old
Class<?> caller = sun.reflect.Reflection.getCallerClass();

// New (Java 9+)
Class<?> caller = StackWalker
    .getInstance(StackWalker.Option.RETAIN_CLASS_REFERENCE)
    .getCallerClass();

// Old — using internal SAX parser
import com.sun.org.apache.xerces.internal.impl.xs.XSDeclarationPool;

// New — use the public javax.xml.parsers API
DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();

java \
  --add-opens java.base/java.lang=ALL-UNNAMED \
  --add-opens java.base/java.util=ALL-UNNAMED \
  --add-opens java.base/java.lang.reflect=ALL-UNNAMED \
  --add-opens java.base/java.io=ALL-UNNAMED \
  --add-opens java.rmi/sun.rmi.transport=ALL-UNNAMED \
  -jar myapp.jar

<plugin>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-maven-plugin</artifactId>
  <configuration>
    <jvmArguments>
      --add-opens java.base/java.lang=ALL-UNNAMED
      --add-opens java.base/java.util=ALL-UNNAMED
    </jvmArguments>
  </configuration>
</plugin>

# Old Java 8 flags → Java 11 equivalents

# Verbose GC logging
-verbose:gc
→ -Xlog:gc

# Detailed GC with heap info
-XX:+PrintGCDetails
→ -Xlog:gc*

# With timestamps and file output
-XX:+PrintGCDateStamps -XX:+PrintGCDetails -Xloggc:/var/log/gc.log
→ -Xlog:gc*:file=/var/log/gc.log:time,uptime,pid:filecount=5,filesize=20m

# GC pauses only
-XX:+PrintGCApplicationStoppedTime
→ -Xlog:safepoint

# Object ages
-XX:+PrintTenuringDistribution
→ -Xlog:gc+age*=debug

# Do NOT use in Java 11 — these flags are removed:
-XX:+CMSClassUnloadingEnabled
-XX:CMSInitiatingOccupancyFraction=70
-XX:+UseCMSInitiatingOccupancyOnly
-XX:MaxPermSize=256m        # PermGen is gone; use -XX:MaxMetaspaceSize=
-XX:PermSize=128m           # Gone

<!-- Maven -->
<properties>
  <maven.compiler.release>11</maven.compiler.release>
</properties>

// Gradle Kotlin DSL
tasks.withType<JavaCompile>().configureEach {
    options.release.set(11)
}

mvn clean test

# Or with --add-opens for test-time reflection
mvn clean test \
  -DargLine="--add-opens java.base/java.lang=ALL-UNNAMED \
             --add-opens java.base/java.util=ALL-UNNAMED"