Tomcat Session Manager

Giriş

Tomcat Session Manager sanırım hem server.xml hem de context.xml içinde tanımlanabilir

HazelcastSessionManager

Örnek

Şöyle yaparız

<Context>
  ...
  <Manager className="com.hazelcast.session.HazelcastSessionManager"/>
  ...
</Context>

Tomcat İle Gelen Session Manager Sınıfları

Açıklaması şöyle

A session manager is a component that creates and maintains HTTP sessions for a web application. Tomcat provides two standard implementations of session manager: StandardManager and PersistentManager

StandardManager 

Açıklaması şöyle

The StandardManager is the default session manager for Tomcat. It stores active sessions in memory and optionally persists them to a file across application restarts1. You can configure the StandardManager by using the <Manager> element inside the <Context> element of your web application2

Örnek

Şöyle yaparız

<Manager>
  <SessionManager>
    <className>org.apache.catalina.session.StandardSessionManager</className>
    <maxActive>100</maxActive>
    <maxIdle>30</maxIdle>
    <sessionTimeout>30</sessionTimeout>
  </SessionManager>
</Manager>

Örnek

Şöyle yaparız

<Context>
  <Manager className="org.apache.catalina.session.StandardManager"
           maxActiveSessions="100"
           pathname="myapp_sessions.ser"
           persistAuthentication="true"/>
</Context>

PersistentManager 

Açıklaması şöyle

The PersistentManager is an optional session manager that stores active sessions that have been swapped out to a storage location, such as a file or a database. You can configure the PersistentManager by using the <Manager> element with a nested <Store> element inside the <Context> element of your web application

Örnek - FileStore

Hem PersistentManager hem de StandardManager session bilgisini diske yazabiliyor. Aradaki fark şöyle

StandardManager ... it stores all sessions in a single file of an applications temporary directory. 

With PersistentManager using FileStore the situation is different: every session is saved in a separate file, according to its JSESSIONID.

Şöyle yaparız

<Context>
  <Manager className="org.apache.catalina.session.PersistentManager"
           maxActiveSessions="100"
           maxIdleSwap="10">
    <Store className="org.apache.catalina.session.FileStore"
           directory="/tmp/sessions"/>
  </Manager>
</Context>

Örnek - JDBCStore

Session bilgisini saklamak için JDBC kullanır. Açıklaması şöyle

It will then use the store to maintain the session on each http request. Note that the documentation assumes that only one http request will be made by the same client at a time.

This will allow you to use non sticky session load balancer in front of your java ee servers.

Şöyle yaparız

<Valve className="org.apache.catalina.valves.PersistentValve" />
<Manager className="org.apache.catalina.session.PersistentManager"
  distributable="true"  processExpiresFrequency="1" maxIdleBackup="1" maxIdleSwap="0"
   minIdleSwap="0" >
  <Store className="org.apache.catalina.session.JDBCStore"
    driverName="org.postgresql.Driver"
    connectionURL="jdbc:postgresql://localhost:5432/develop_4_5_0?currentSchema=datasuite"
    connectionName="*" connectionPassword="*"
    sessionAppCol="app_name" sessionDataCol="session_data" sessionIdCol="jsession_id"
    sessionLastAccessedCol="last_access" sessionMaxInactiveCol="max_inactive"
    sessionTable="tomcat_session" sessionValidCol="valid_session" />
</Manager>




List.subList metodu

Sabit Büyüklüğe Ayırmak

Partition by Size diyelim

Örnek

Şöyle yaparız

public static <T> List<List<T>> partitionList(List<T> list, int partitionSize) {
  List<List<T>> partitionedList = new ArrayList<>();
  int size = list.size();

  for (int i = 0; i < size; i += partitionSize) {
    int end = Math.min(size, i + partitionSize);
    partitionedList.add(list.subList(i, end));
  }
  return partitionedList;
}

Örnek - Guava

Lists.partition() kullanılabilir

Örnek - Apache Commons

ListUtils.partition() kullanılabilir

Sabit Sayıda Parçalara Ayırmak

Number of Partitions diyelim

Örnek

Şöyle yaparız. Listeyi 6 parçaya ayırırız

List<Integer> mylist = ...
int size = mylist.size();
int parts = 6;
int partSize = size / parts;
List<List<Integer>> result = 
    IntStream.range(0, parts)
             .mapToObj(i -> mylist.subList(i * partSize, (i + 1) * partSize)))
             .collect(Collectors.toList());

ArchUnit ClassFileImporter Sınıfı

Giriş

Şu satırı dahil ederiz

import com.tngtech.archunit.core.importer.ClassFileImporter;

importPackages metodu

Açıklaması şöyle

The returned object of type JavaClasses represents a collection of elements of type JavaClass, where JavaClass in turn represents a single imported class file. You can in fact access most properties of the imported class via the public API

Yani şöyle yapabiliriz

JavaClass clazz = classes.get(Object.class);
System.out.print(clazz.getSimpleName()); // returns 'Object'

Örnek

Şöyle yaparız

JavaClasses jc = new ClassFileImporter()
  .importPackages("com.baeldung.archunit.smurfs");

Monad

Giriş

Functional dillerde Monad, Function Composition için kullanılır

Örnek

Şöyle yaparız

bread = bake( mill(wheat) )

Java'da Monad yok. Ancak benzer bir sonucu iki farklı şekilde yapabiliriz.

1. Chaining Methods

2. Optional Kullanarak

1. Chaining Methods

Örnek

Şöyle yaparız

public Optional<Flour> mill(Wheat wheat) {
   // ...
}

public Optional<Bread> bake(Flour flour) {
   // ...
}

Optional<Bread> oopBread = harvest()
      .flatMap(wheat -> mill(wheat))
      .flatMap(flour -> bake(flour));

2. Optional Kullanarak

Diğer dillerde Maybe<>, Either<>, Optional<> gibi yapılar var Java'da sadece Optional var. Bu kullanım biraz daha Functional dillere benziyor. Ancak halen exception handling sıkıntısı var. Three Exception-Handling Alternatives Inspired by Functional Programming yazısına bakabilirsiniz

Örnek

Şöyle yaparız

public Optional<Flour> mill(Optional<Wheat> wheat) {
   // ...
}

public Optional<Bread> bake(Optional<Flour> flour) {
   // ...
}

Optional<Bread> fpBread = bake( mill( harvest() ) );

Reading Large Tables In Batches

1. SpringBoot Kullanıyorsak

PageRequest kullanılabilir

Örnek

Şöyle yaparız

PageRequest pageRequest = PageRequest.of(0,10);
Page<Account> page;
List<Account> list;
do {
    page = accountRepository.findAll(pageRequest);
    list = page.getContent();
    page = page.next();
} while (!page.isEmpty());

2. JPA Kullanıyorsak

TypedQuery kullanılabilir

Örnek

Şöyle yaparız

int startPosition = 0;
int batchSize = 10;

while(true) {

  TypedQuery<Account> query = em.createQuery("SELECT a FROM Account a", Account.class);
  query.setFirstResult(startPosition);
  query.setMaxResults(batchSize_size);
  
   List<Account> list = query.resultList();
    if (list.size() == 0) {
      break;
    }
    startPosition += batchSize; 
}

3. SQL ile Offset + Limit

TypedQuery kullanılabilir

Örnek

Şöyle yaparız

Session session = em.unwrap(Session.class);
session.doReturningWork(new ReturningWork<>() {
    @Override
    public Integer execute(Connection connection) throws SQLException {
      int offsetPos = 0;
      
      PreparedStatement preparedStatement = connection
                .prepareStatement("SELECT * FROM ACCOUNTS LIMIT ? OFFSET ?");
      while (true) {
        preparedStatement.setInt (1, 10);
        preparedStatement.setInt (2, offsetPos);
        ResultSet resultSet = preparedStatement.executeQuery();
        if(!resultSet.next()) break; // break when finish reading
        do {
          System.out.println(resultSet.getString("user_id"));
        } while (resultSet.next());
        offsetPos += 10;
      }
    }
}

4. Statement.setFetchSize kullanılabilir

JDBC Statement Arayüzü yazısına bakınız

Reading Large Files Line By Line

Giriş

Kullanılabilecek yöntemler şöyle

1. Files Sınıfı

2. BufferedReader Sınıfı

3. Scanner Sınıfı

Test İçin Büyük Dosya Yaratmak

Şöyle yaparız

public void prepFile() throws IOException {
  BufferedWriter bufferedWriter = Files.newBufferedWriter(Path.of(TARGET_FILE),
    StandardOpenOption.CREATE);
  IntStream.rangeClosed(1,100000000)
    .forEach(a-> write(bufferedWriter, a));
  bufferedWriter.flush();
}

public void write(BufferedWriter bufferedWriter, int a) {
  try {
    bufferedWriter.write(a + "\n");
  } catch (IOException e) {
    ...
    throw new RuntimeException(e);
  }
}

1. Files Sınıfı

Örnek

Şöyle yaparız

Path filePath = Paths.get("C:/temp/file.txt")
 
//try-with-resources
try (Stream<String> lines = Files.lines( filePath )) {
  lines.forEach(...); // Process the line
} catch (IOException e) {
  ...
}

2. BufferedReader Sınıfı

Bu sınıf 2 şekilde kullanılabilir.

1. lines metodu

2. readLine metodu

lines metodu

Aslında bunun yerine Files.lines() çok daha kolay

Örnek

Şöyle yaparız

public void usingBufferedReaderAndLambda() throws IOException {
  try (BufferedReader bufferedReader = Files.newBufferedReader(Path.of(TARGET_FILE))) {
    bufferedReader.lines()
    .forEach(...);  // Process the line
  }
}

readLine metodu

Örnek

Şöyle yaparız

public void usingBufferedReader() throws IOException {
  try(FileReader fileReader = new FileReader(new File(TARGET_FILE))){
    BufferedReader bufferedReader = new BufferedReader(fileReader);
    String readLine;
    while((readLine = bufferedReader.readLine())!=null){
      // Process the line
    }
  }
}

3. Scanner Sınıfı

Bir örnek burada

Eski ElasticSearchHighLevel IndicesClient Sınıfı

exists metodu

Örnek

Şöyle yaparız

GetIndexRequest request = new GetIndexRequest(props.getIndex().getName());
boolean exists = client.indices().exists(request, RequestOptions.DEFAULT);

if (!exists) {
  CreateIndexRequest indexRequest = new CreateIndexRequest(props.getIndex().getName());
  indexRequest.settings(Settings.builder()
       .put("index.number_of_shards", props.getIndex().getShard())
       .put("index.number_of_replicas", props.getIndex().getReplica())
  );

  CreateIndexResponse createIndexResponse = client.indices()
    .create(indexRequest, RequestOptions.DEFAULT);
  if (createIndexResponse.isAcknowledged()&& createIndexResponse.isShardsAcknowledged()) {
      log.info("{} index created successfully", props.getIndex().getName());
  } else {
    log.debug("Failed to create {} index", props.getIndex().getName());
  }
}