ArchUnit Layered Architecture Enforcement Kullanımı

Giriş

Açıklaması şöyle

In layered architectures, we define different layers and how those interact with each other.

Örnek

Şöyle yaparız

@ArchTest
static final ArchRule persistence_should_not_access_services =
  noClasses()
  .that()
  .resideInAPackage("..persistence..")
  .should()
  .accessClassesThat()
  .resideInAPackage("..service..");

@ArchTest
static final ArchRule services_should_only_be_accessed_by_controllers_or_other_services =
  classes()
  .that()
  .resideInAPackage("..service..")
  .should()
  .onlyBeAccessed()
  .byAnyPackage("..controller..", "..service..");

Örnek

Şöyle yaparız

@ArchTest
static final ArchRule layer_dependencies_are_respected_with_exception =
  layeredArchitecture().consideringAllDependencies()
  .layer("Controllers").definedBy("com.tngtech.archunit.example.layers.controller..")
  .layer("Services").definedBy("com.tngtech.archunit.example.layers.service..")
  .layer("Persistence").definedBy("com.tngtech.archunit.example.layers.persistence..")
  
  .whereLayer("Controllers").mayNotBeAccessedByAnyLayer()
  .whereLayer("Services").mayOnlyBeAccessedByLayers("Controllers")
  .whereLayer("Persistence").mayOnlyBeAccessedByLayers("Services")
  .ignoreDependency(SomeMediator.class, ServiceViolatingLayerRules.class);

Örnek

Şöyle yaparız

@Test
public void testThatHexagonalLayerIsRespected() {
  JavaClasses classes = new ClassFileImporter()
    .importPackages("com.modern.app");

  layeredArchitecture()
    .consideringAllDependencies()
    .layer("application").definedBy("..application..")
    .layer("domain").definedBy("..domain..")
    .layer("infrastructure").definedBy("..infrastructure..")
    
    .whereLayer("domain").mayOnlyBeAccessedByLayers("application", "infrastructure")
    .whereLayer("application").mayOnlyBeAccessedByLayers("infrastructure")
    .whereLayer("infrastructure").mayNotBeAccessedByAnyLayer()
    .check(classes);
}

jcmd komutu Thread.print seçeneği - Thread Dump Alır

Giriş

Açıklaması şöyle. Uzunca bir çıktı verebilir.

This command is to get the thread dump i.e. it will print the stack trace of all threads currently running.

Örnek

Şöyle yaparız

# old schoool
jstack <pid>

# more modern
jcmd <pid> Thread.print
jcmd <class-name> Thread.print

# If no JDK, SIGQUIT dumps threads to System.out, extract from there
#   (this will just send a signal to the app, not trigger a shutdown)
kill -QUIT <pid>

# For a Kubernetes pod the java pid is typically 1
kubectl exec <pod-name> -- jstack 1

Örnek

Şöyle yaparız

jcmd pid Thread.print

AWS SDK Kullanımı

1. Java SDK

Şu satırı dahil ederiz

<dependency>
  <groupId>com.amazonaws</groupId>
  <artifactId>aws-java-sdk</artifactId>
  <version>1.12.525</version>
</dependency>

2. Java SDK Bundled Dependency

3. taraf bağımlıklarının başka paketlere taşındığı bir fat jar. Bu jar bayağı büyük. Şu satırı dahil ederiz

<dependency>
  <groupId>com.amazonaws</groupId>
  <artifactId>aws-java-sdk-bundle</artifactId>
  <version>${aws.sdk.version}</version>
</dependency>

Bir örnek burada

3. BOM Kullanımı

Örnek

Şu satırı dahil ederiz.  Burada Parent BOM'dan gelen bağımlılıkar versiyon olmadan <dependency> olarak tanımlanıyor.

<dependencyManagement>
  <dependencies>
    <dependency>
      <groupId>software.amazon.awssdk</groupId>
      <artifactId>bom</artifactId>
      <version>2.16.1</version>
      <type>pom</type>
      <scope>import</scope>
    </dependency>
  </dependencies>
</dependencyManagement>

<dependencies>
  <dependency>
    <groupId>software.amazon.awssdk</groupId>
    <artifactId>dynamodb</artifactId>
  </dependency>
</dependencies>

Retrofit

Giriş

Altta OKHttp kullanır

Örnek

Elimizde şöyle bir arayüz olsun

interface JsonPlaceholderApi {
    @GET("todos/{id}")
    Call<Todo> getTodo(@Path("id") int id);
}

class Todo {
    int userId;
    int id;
    String title;
    boolean completed;

    // getters and setters
}  

Şöyle yaparız

import retrofit2.Call;
import retrofit2.Callback;
import retrofit2.Response;
import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;


Retrofit retrofit = new Retrofit.Builder()
  .baseUrl("https://jsonplaceholder.typicode.com/")
  .addConverterFactory(GsonConverterFactory.create())
  .build();

JsonPlaceholderApi jsonPlaceholderApi = retrofit.create(JsonPlaceholderApi.class);

Call<Todo> call = jsonPlaceholderApi.getTodo(1);
call.enqueue(new Callback<Todo>() {
  @Override
  public void onResponse(Call<Todo> call, Response<Todo> response) {
    if (!response.isSuccessful()) {
      System.out.println("Unexpected code " + response);
      return;
    }
    Todo todo = response.body();
    System.out.println(todo);
  }
  @Override
  public void onFailure(Call<Todo> call, Throwable t) {
    t.printStackTrace();
  }
});

ASM Kullanımı - Insturmentation

Giriş

Açıklaması şöyle

ASM is a widely-used bytecode manipulation library. It provides a comprehensive API for analyzing and modifying bytecode. ASM operates at a low level, giving developers fine-grained control over bytecode manipulation.

Örnek

Şöyle yaparız

import org.objectweb.asm.*;

public class ASMExample {
  public static void main(String[] args) throws Exception {
    ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_FRAMES);
    cw.visit(Opcodes.V11, Opcodes.ACC_PUBLIC, "com/example/Calculator", null,
  "java/lang/Object", null);
        
    MethodVisitor mv = cw.visitMethod(Opcodes.ACC_PUBLIC, "add", "(II)I", null, null);
    mv.visitCode();
    mv.visitVarInsn(Opcodes.ILOAD, 1);
    mv.visitVarInsn(Opcodes.ILOAD, 2);
    mv.visitInsn(Opcodes.IADD);
    mv.visitInsn(Opcodes.IRETURN);
    mv.visitMaxs(2, 3);
    mv.visitEnd();
        
    cw.visitEnd();
        
    byte[] bytecode = cw.toByteArray();
        
    // Use the generated bytecode...
  }
}

ClassFileTransformer Arayüzü - Instrumentation API

Giriş

Şu satırı dahil ederiz

import java.lang.instrumen.Instrumentation;

Açıklaması şöyle

The ClassFileTransformer interface is a critical component of the Instrumentation API. It provides a transform() method that is called when a class is being loaded by the JVM. The transform() method receives the original class bytecode and returns the modified bytecode.

Örnek

Şöyle yaparız

import java.lang.instrument.Instrumentation;

public class LoggingAgent {
  public static void premain(String agentArgs, Instrumentation inst) {
    inst.addTransformer(new LoggingTransformer());
  }
}

import java.lang.instrument.ClassFileTransformer;
import java.lang.instrument.IllegalClassFormatException;
import java.security.ProtectionDomain;

public class LoggingTransformer implements ClassFileTransformer {
  @Override
  public byte[] transform(
    ClassLoader loader, 
    String className, 
    Class<?> classBeingRedefined, 
    ProtectionDomain protectionDomain, 
    byte[] classfileBuffer) throws IllegalClassFormatException {
        
    // Check if the class should be instrumented for logging
    if (className.startsWith("com.example")) {
      System.out.println("Instrumenting class: " + className);
            
      // Inject logging code into the class bytecode
      // ...
    }
    return classfileBuffer;
  }
}

Örnek

Şöyle yaparız

import java.lang.instrument.ClassFileTransformer;
import java.lang.instrument.IllegalClassFormatException;
import java.security.ProtectionDomain;

public class MethodTransformer implements ClassFileTransformer {
  @Override
  public byte[] transform(
    ClassLoader loader, 
    String className, 
    Class<?> classBeingRedefined, 
    ProtectionDomain protectionDomain, 
    byte[] classfileBuffer) throws IllegalClassFormatException {
        
    if (className.equals("com.example.Calculator")) {
      System.out.println("Instrumenting class: " + className);
            
      // Modify the bytecode of the add() method
      return modifyAddMethod(classfileBuffer);
    }
        
    return classfileBuffer;
  }
    
  private byte[] modifyAddMethod(byte[] originalBytecode) {
    // ... Bytecode manipulation to modify the add() method ...
  }
}

SequencedSet Arayüzü - Java 21 İle Geliyor

Giriş

SequencedCollection ile aynıdır. İlave olarak reversed() metodu sağlar. Kod şöyle

interface SequencedSet<E> extends SequencedCollection<E>, Set<E> {
  SequencedSet<E> reversed();
}

SequencedMap Arayüzü - Java 21 İle Geliyor

Giriş

Arayüz şöyle. LinkedHashMap, SortedMap  artık SequencedMap arayüzünden kalıtıyor

interface SequencedMap<K,V> extends Map<K,V> {

    // new methods
    SequencedMap<K,V> reversed();
    SequencedSet<K> sequencedKeySet();
    SequencedCollection<V> sequencedValues();
    SequencedSet<Entry<K,V>> sequencedEntrySet();
    V putFirst(K, V);
    V putLast(K, V);
    // methods promoted from NavigableMap
    Entry<K, V> firstEntry();
    Entry<K, V> lastEntry();
    Entry<K, V> pollFirstEntry();
    Entry<K, V> pollLastEntry();
}

SequencedCollection Arayüzü - Java 21 İle Geliyor

Giriş

Arayüz şöyle. List , Deque arayüzleri artık SequencedCollection arayüzünden kalıtıyor

interface SequencedCollection<E> extends Collection<E> {
  // new method
  SequencedCollection<E> reversed();
  // methods promoted from Deque
  void addFirst(E);
  void addLast(E);
  E getFirst();
  E getLast();
  E removeFirst();
  E removeLast();
}

getFirst metodu

Eskiden şöyle yapmak gerekiyordu

// First Element 
list.get(0)

Artık şöyle yaparız

list.getFirst()

getLast metodu

Eskiden şöyle yapmak gerekiyordu

// Last Element 
list.get(list.size()-1)

Artık şöyle yaparız

list.getLast()

reversed metodu

Açıklaması şöyle. Yani SequencedMap, SequencedSet gibi arayüzler SequencedCollection değil kendi tiplerini dönüyorlar

Covariant Return Types is an important Java feature that I feel has gotten less coverage than the others listed above. The addition of Sequenced Collections in Java 21 brings some recent attention to this important feature that was added in Java 5. The SequencedCollection interface has a method named reversed that has covariant overrides with more specific return types in SequencedSet, Deque, List, etc.