Java record İle Yapılamayacak Şeyler

1. Records Cannot Extend Another Class

2. Records Cannot Be Extended

Örnek

Şu kod derlenmez

public class PremiumRecord extends InsuranceRecord {…}

3. Records Cannot Have Additional Instance Fields

Örnek

Şu kod derlenmez

public record InsuranceRecord(String type, float premium) {
  private String policyNumber;  // This won't compile
}

4. Private Canonical Constructors Are Not Allowed

Örnek

Şu kod derlenmez

public record InsuranceRecord(String type, float premium) {
  private InsuranceRecord(String type, float premium) {
    this.type = type;
    this.premium = premium;
  }
  public static InsuranceRecord newInstance(String type, float premium) {
    return new InsuranceRecord(type, premium);
  }
}

5.  Records Cannot Have Setters

Örnek

Şu kod derlenmez

public record InsuranceRecord(String type, float premium) {
  public void setType(String type) {
    this.type = type;  // Won't compile
  }
}

@Serial Anotasyonu

Giriş

Bu anotasyon sadece kodda var yani byte code'a girmiyor. Açıklaması şöyleşöyle

This annotation exists purely to engage better compile-time type checking. It is analogous in this way to the @Override annotation, which exists purely to capture design intent, so that humans and tools have more information to work with. 

Virtual Threads - Thread Pinning

Thread Pinning 

Virtual Threads için JDK'daki bir çok kod baştan yazılmış. Böylece thread unloading işlemi yapılabiliyor.  Ancak bir kaç işlemde istisna var. Buna Thread Pinning deniliyor

1. Object.wait()

2. synchronized blok içinde

3. native metod çalıştırırken

4. UDP Sockets

5. Files & DNS

Açıklaması şöyle

Pinning describes the condition where a virtual thread, which maps the platform thread, is stuck to the carrier thread. It means that the virtual thread can’t be unmounted from the carrier threads because the state of it can’t be stored in the heap memory. The pinned thread prevents others from utilizing the same platform thread.

1. synchronized Thread Pinning

Açıklaması şöyle

Only one thread can enter it at a time. The other threads attempting to enter will be blocked until the current (running) thread exits. They would need an uninterrupted access to shared resources to prevent race conditions as well as an accurate state of the data.

Örnek

Şu kod carrier thread'i bloke eder. 

var e = Executors.newVirtualThreadPerTaskExecutor();
for (int i = 0; i < 1000; i++) {
    e.submit(() -> { new Test().test(); });
}
e.shutdown();
e.awaitTermination(1, TimeUnit.DAYS);

class Test {
  synchronized void test() {
    sleep(4000);
  }
}

synchronized yerine  ReentrantLock kullanılır. Şöyle yaparız

var e = Executors.newVirtualThreadPerTaskExecutor();
for (int i = 0; i < 1000; i++) {
    e.submit(() -> { new Test().test(); });
}
e.shutdown();
e.awaitTermination(1, TimeUnit.DAYS);

class Test {
  private ReentrantLock lock = new ReentrantLock();
  void test() {
    lock.tryLock();
    try {
      sleep(4000);
    } finally {
      lock.unlock();
    }
  }
}

MySQL-J JDBC sürücüsündeki bir açıklama şöyle

Synchronized blocks in the Connector/J code were replaced with ReentrantLocks. This allows carrier threads to unmount virtual threads when they are waiting on IO operations, making Connector/J virtual-thread friendly. Thanks to Bart De Neuter for contributing to this patch. ”

2. native method Thread Pinning

Açıklaması şöyle

This method lets you use code from other languages into your JAVA project, like C or C++. Native methods are invoked within the JAVA virtual machine but executed outside its control.

3. Sockets Thread Pinning

TCP socketlerini okurken Virtual Threads bloke olmuyor, ama UDP socketlerinde oluyor. Açıklaması şöyle

However, not all Java constructs have been retrofitted that way. Such operations include synchronized methods and code blocks. Using them causes the virtual thread to become pinned to the carrier thread. When a thread is pinned, blocking operations will block the underlying carrier thread-precisely as it would happen in pre-Loom times.

Eğer carrier therad'in bloke olma durumu varsa, virtual thread sayısı artırılır. En fazla kaç thread olabileceği  jdk.virtualThreadScheduler.maxPoolSize ile atanabilir

pinned thread Tracing

Açıklaması şöyle

Use the following JVM parameters as options to trace the pinned thread

-Djdk.tracePinnedThreads=full Prints a complete stack trace when a thread jams while pinned, highlighting native frames and frames holding monitors.

-Djdk.tracePinnedThreads=short Limits the output to just the problematic frames.

OpenRewrite

Giriş

OpenRewrite bir static kod analiz aracı. Diğer araçlardan farklı olarak sadece rapor üretmiyor aynı zamanda kodu da değiştirebiliyor.

1. dryRun Goal

target/rewrite dizini altında bir patch dosyası oluşturur

2. run Goal

Kodları direkt değiştirir

3. Recipe Listesi

3.1 CommonStaticAnalysis Recipe

Sanırım en işe yarayan recipe'lerden bir tanesi. Bur recipe ile yapılabilecek işlerin listesi burada

https://docs.openrewrite.org/recipes/staticanalysis/commonstaticanalysis

Benim hazelcast kodunda çalıştırdıklarım şöyle

1. org.openrewrite.staticanalysis.UseDiamondOperator
2. org.openrewrite.staticanalysis.UnncessaryThrows
3. org.openrewrite.staticanalysis.NoRedundantJumpStatements
4. org.openrewrite.staticanalysis.NestedEnumsAreNotStatic
5. org.openrewrite.staticanalysis.RemoveRedundantTypeCast
6. org.openrewrite.staticanalysis.LambdaBlockToExpression. EE için koşmadım
7. org.openrewrite.staticanalysis.UnnecessaryExplicitTypeArguments
8. org.openrewrite.staticanalysis.SimplifyTernaryRecipes
9. org.openrewrite.staticanalysis.ReplaceRedundantFormatWithPrintf
10. org.openrewrite.staticanalysis.InstanceOfPatternMatch.  EE için koşmadım. OS için yarım koştum
11. org.openrewrite.staticanalysis.JavaApiBestPractices
12. org.openrewrite.staticanalysis.PrimitiveWrapperClassConstructorToValueOf
13. org.openrewrite.staticanalysis.NoPrimitiveWrappersForToStringOrCompareTo
14. org.openrewrite.staticanalysis.UseMapContainsKey

AddSerialAnnotationToserialVersionUID 

Örnek

Şöyle yaparız

./mvnw 
-Dskip-modulepath-tests 
-Dcheckstyle.skip 
 clean 
 org.openrewrite.maven:rewrite-maven-plugin:run 
-Drewrite.recipeArtifactCoordinates=org.openrewrite.recipe:rewrite-static-analysis:RELEASE 
-Drewrite.activeRecipes=org.openrewrite.staticanalysis.AddSerialAnnotationToserialVersionUID 
-Drewrite.exportDatatables=true

MissingOverrideAnnotation

Örnek

Şöyle yaparız

./mvnw 
-Dskip-modulepath-tests 
-Dcheckstyle.skip 
 clean 
 org.openrewrite.maven:rewrite-maven-plugin:run 
-Drewrite.recipeArtifactCoordinates=org.openrewrite.recipe:rewrite-static-analysis:RELEASE 
-Drewrite.activeRecipes=org.openrewrite.staticanalysis.MissingOverrideAnnotation
-Drewrite.exportDatatables=true -Drewrite.options=ignoreAnonymousClassMethods=true

Örnek

Şöyle yaparız

<plugin>
  <groupId>org.openrewrite.maven</groupId>
  <artifactId>rewrite-maven-plugin</artifactId>
  <version>5.23.1</version>
  <configuration>
    <activeRecipes>
      <recipe>org.openrewrite.staticanalysis.CommonStaticAnalysis</recipe>
    </activeRecipes>
  </configuration>
  <dependencies>
    <dependency>
      <groupId>org.openrewrite.recipe</groupId>
      <artifactId>rewrite-static-analysis</artifactId>
      <version>1.3.1</version>
    </dependency>
  </dependencies>
</plugin>  

Eğer proje çok büyükse sadece bazı şeyleri çalıştırmak için proje kök dizininde bir tane rewrite.yml dosyası oluştururuz.  Şöyle yaparız. Eğer proje multi-module ise yine en tepedeki dizine koymak lazım

---
type: specs.openrewrite.org/v1beta/recipe
name: orcun.CommonStaticAnalysis
displayName: Common static analysis issues
description: Resolve common static analysis issues discovered through 3rd party tools.
recipeList:
  - org.openrewrite.staticanalysis.UseDiamondOperator

pom.xml şöyle olur.

<plugin>
  <groupId>org.openrewrite.maven</groupId>
  <artifactId>rewrite-maven-plugin</artifactId>
  <version>5.23.1</version>
  <configuration>
    <activeRecipes>
      <recipe>orcun.CommonStaticAnalysis</recipe>
    </activeRecipes>
  </configuration>
  <dependencies>
    <dependency>
      <groupId>org.openrewrite.recipe</groupId>
      <artifactId>rewrite-static-analysis</artifactId>
      <version>1.3.1</version>
    </dependency>
  </dependencies>
</plugin>  

3.2 Migration

CompareEnumsWithEqualityOperator 

Örnek

Şöyle yaparız

./mvnw 
-Dskip-modulepath-tests 
-Dcheckstyle.skip 
clean 
org.openrewrite.maven:rewrite-maven-plugin:run 
-Drewrite.recipeArtifactCoordinates=org.openrewrite.recipe:rewrite-migrate-java:RELEASE 
-Drewrite.activeRecipes=org.openrewrite.staticanalysis.CompareEnumsWithEqualityOperator 
-Drewrite.exportDatatables=true

StringRulesRecipes

Örnek

Şöyle yaparız

./mvnw 
-T1 
-Dskip-modulepath-tests 
-Dcheckstyle.skip 
clean 
org.openrewrite.maven:rewrite-maven-plugin:run 
-Drewrite.recipeArtifactCoordinates=org.openrewrite.recipe:rewrite-migrate-java:RELEASE 
-Drewrite.activeRecipes=org.openrewrite.java.migrate.lang.StringRulesRecipes$RedundantCallRecipe 
-Drewrite.exportDatatables=true

Project Panama - Bridge The Gap Between Java And Native Code

Giriş

Açıklaması şöyle

Project Panama represents a significant advancement in the Java ecosystem, primarily focusing on enhancing Java’s interaction with foreign APIs, particularly those written in languages like C and C++. Traditionally, Java used the Java Native Interface (JNI) to invoke foreign functions, but JNI had several limitations. Project Panama addresses these by removing the need to write native code wrappers in Java, replacing the ByteBuffer API with a more advanced Memory API, and introducing a secure, memory-efficient method to invoke native code from Java. The project comprises several key components, including the Foreign-Function and Memory API, the Vector API, and the JExtract tool​​.

JEP-401 - Project Valhalla - Improve Java’s Memory Efficiency

Giriş

Java'nın kullandığı Memory Model özellikle Integer[] gibi yapılarda işlemcinin israf edilmesine sebep oluyor. Bunu gösteren bir şekil burada

Sebebi ise şöyle. 

Accessing the value of an Integer (non-primitive) includes an extra memory access

Çünkü her bir Integer için kullanılan Metadata nesnesi bellekte rastgele bir yerde duruyor

Bu da günümüzdeki modern işlemcilerde CPU cache israfına sebep oluyor

Project Valhalla

İlk fikir 2014 yılında ortaya atıldı. Açıklaması şöyle

... give the user the ability to flatten his objects and enjoy the performance of primitives in exchange for some limitations ...

Kod olarak şöyle

// Before
public class Point {
  private final int x;
  private final int y;
}

// After
public primitive class Point {
  private final int x;
  private final int y;
}

GSON Kullanımı

Maven

Şu satırı dahil ederiz

<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
    <version>2.8.9</version>
</dependency>

Gson Sınıfı

Gson Sınıfı toJson() ile nesneyi JSON String'e çevirir. fromJson() ile JSON String'den nesneye çevirir

@SerializedName Anotasyonu

@SerializedName Anotasyonu yazısına taşıdım

@Expose Anotasyonu

@Expose Anotasyonu yazısına taşıdım

@Since Anotasyonu

@Since Anotasyonu yazısına taşıdım