'Back-End'에 해당되는 글 135건

 Instanceof

- instanceof operator is used to test whether the object is an instance of the specified type

- It is also known as type comparison operator

- It returns either true or false

1. Example

public class Test{ public static void main(String[]args){ Test a = new Test(); System.out.println(a instanceof Test); } }

- true

2. instanceof in java with a variable that have null value

public class Test{ public static void main(String[]args){ Test a = null; System.out.println(a instanceof Test); } }  

- false

3. Downcasting with java instanceof operator

1) Downcasting

- When subclass type refers to the object of Parent class, it is known as downcasting

Dog d = new AnImal(); //Compilation error  

Dog d = (Dog) new Animal() // ClassCastException  

2) Possibility of downcasting with instanceof

package statics; class Animal{ } class Dog extends Animal{ static void method(Animal a){ if(a instanceof Dog){ Dog d = (Dog)a;//down } } } public class Test{ public static void main(String[]args){ Animal a = new Dog(); Dog.method(a); } }  

3) Downcasting without the use of instanceof

class Animal{ } class Dog extends Animal{ static void method(Animal a){ Dog d = (Dog)a;//down } } public class Test{ public static void main(String[]args){ Animal a = new Dog(); Dog.method(a); } }  

하이버네이트 + 스프링(2)

1. ServiceImpl

package sample.service; import java.util.List; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Service; import sample.dao.UserDao; import sample.domain.User; @Service public class UserServiceImpl implements UserService{ @Autowired private UserDao UserDao; public void saveUser(User user) { UserDao.saveUser(user); } public List<User> findUser(){ return UserDao.findUser(); } public void removeUser(User user){ UserDao.removeUser(user); } }

- 스프링 인티그레이션 기능으로 비즈니스 로직의 세션 관련 오브젝트가 삭제되었다

2. DaoImpl

package sample.dao; import java.util.List; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.orm.hibernate3.HibernateTemplate; import org.springframework.stereotype.Repository; import sample.domain.User; @Repository public class UserDaoImpl implements UserDao{ @Autowired private HibernateTemplate hibernateTemplate; public List<User> findUser(){ return hibernateTemplate.find("from User"); } public void saveUser(User user) { hibernateTemplate.saveOrUpdate(user); } public void removeUser(User user){ hibernateTemplate.delete(user); } }  

- 하이버네이트의 세션 오브젝트가 제공하는 CRUD는 HibernateTemplate 클래스를 통해 이용한다

3. 하이버네이트 3.0.1 이후 버전

- 3 이후 버전에서는 HibernateTemplate을 사용하지 않고 구현 가능

1) getCurrentSession

- SessionFactory의 getCurrentSession()를 실행하면 현재 사용중인 Session 오브젝트를 가져올수있다(트랜잭션 매니저로 관리되는 세션 오브젝트를 가져올 수 있다)

2) HibernateTemplate을 사용하지 않고 구현

@Repository public class UserDaoImpl implements UserDao{ @Autowired private SessionFactory sessionFactory; Session session = sessionFactory.getCurrentSession(); Query query = session.createQuery("from User"); return query.list(); }  

a. SessionFactory 직접 사용의 장점

- 하이버네이트에서 제공하는 모든 API를 사용가능

- 하이버네이트에 익숙한 개발자라면 API만 의식하면 되므로 효율적 개발가능

b. 단점

- 직접 세션 오브젝트를 사용하므로 위험할 수 있다

- HibernateTemplate은 안전하지만 버전 4에서 지원 안함

하이버네이트 + 스프링(1)

- 하이버네이트와 스프링을 같이 사용함으로 독립성 높인 간단한 코드가 된다

1. 폴더 구성

2. 정의 파일

<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context" xmlns:aop="http://www.springframework.org/schema/aop" xmlns:tx="http://www.springframework.org/schema/tx" xmlns:jee="http://www.springframework.org/schema/jee" xmlns:mvc="http://www.springframework.org/schema/mvc" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.1.xsd http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-3.1.xsd http://www.springframework.org/schema/jee http://www.springframework.org/schema/jee/spring-jee-3.0.xsd http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.0.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-3.0.xsd"> <mvc:annotation-driven/> <!-- 1 --> <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource"> <property name="driverClassName" value="oracle.jdbc.driver.OracleDriver"/> <property name="url" value="jdbc:oracle:thin:@localhost:1521:orcl1"/> <property name="username" value="HJEONG"/> <property name="password" value="1111"/> </bean> <!-- 2 --> <bean id="sessionFactory" class="org.springframework.orm.hibernate3.LocalSessionFactoryBean"> <property name="dataSource" ref="dataSource" /> <property name="mappingResources"> <list> <value>sample/dao/User.hbm.xml</value> </list> </property> <property name="hibernateProperties"> <props> <prop key="hibernate.dialect">org.hibernate.dialect.HSQLDialect</prop> <prop key="hibernate.show_sql">true</prop> </props> </property> </bean> <!-- 3 --> <bean class="org.springframework.orm.hibernate3.HibernateTemplate"> <property name="sessionFactory" ref="sessionFactory"/> </bean> <!-- 4 --> <bean id="transactionManager" class="org.springframework.orm.hibernate3.HibernateTransactionManager"> <property name="sessionFactory" ref="sessionFactory"/> </bean> <!-- 5 --> <aop:config> <aop:advisor advice-ref="txAdvice" pointcut="execution(* *..*Service*.*(..))" /> </aop:config> <tx:advice id="txAdvice" transaction-manager="transactionManager"> <tx:attributes> <tx:method name="find*" read-only="true" /> <tx:method name="add*" propagation="REQUIRED"/> <tx:method name="remove*" propagation="REQUIRED"/> </tx:attributes> </tx:advice> <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver"> <property name="prefix" value="/WEB-INF/views/"/> <property name="suffix" value=".jsp"/> </bean> <context:component-scan base-package="sample"/> </beans>

1) 데이터 베이스를 정의한다

2) 하이버네이트의 세션 오브젝트를 작성하고 SessionFactory 클래스를 정의한다

3) 스프링이 제공하는 HibernateTemplate 클래스를 정의한다

- 하이버네이트를 더 단순하게 사용할 수 있고 범용 데이터 엑세스 예외로 변환 해준다

- HibernateTemplate 내부는 SessionFactory를 사용, 그러므로 2에서 정의한 프로퍼티를 받는다

4,5) 하이버네이트 트랜잭션 설정

- 하이버네이트 트랜잭션 매니저로 HibernateTransactionManager를 사용한다

- 위 예제는 선언적 트랜잭션으로 Service로 이름이 끝나거나 find, add, remove 모두 대상이됨

Static Binding and Dynamic Binding

1. Binding

- Connecting a method call to the method body is known ad binding

1) static binding(early binding)

2) dynamic binding(late binding)

2. Static binding

- When type of the object is determined at compiled time, is is known as static binding

- If there is any private, final or static method in class, there is static binding

class Dog{ private void eat(){System.out.println("dog"); public static void main(String[] args){ Dog d1 = new Dog(); d1.eat(); } }

3. Dynamic binding

- When type of the object is determined at run-time, it is known as dynamic binding

class Animal{ void eat(){System.out.println("animal"); } class Dog{ void eat(){System.out.println("dog");} public static void main(String[] args){ Animal d1 = new Dog(); d1.eat(); } }  

- Object type can't be determinded by the compiler, because the instance of Dog is also an instance of Animal, so Compiler doesn't know its type