Interview Questions
Question: - Explain about bean life cycle in spring framework?
Answer: - Spring container is very much capable to hide most of the architecture complexity and about the complex communication that happens between the spring container and the spring beans. Below are the number of activities mentioned that take place between the time of bean instantiation and during the handover of the bean reference to the client application.
Spring Bean Life Cycle Steps:-
Instantiate: - spring container instantiates the bean.
Poluplate properties: - spring container injects the bean properties.
SetBeanName: - If the bean implements BeanNameAware interface, spring passes the bean’s ID to setBeanName() factory method.
SetBeanFactory: - If the bean implements the BeanFactoryAware interface, spring passes the BeanFactory instance to setBeanFactory() method.
postProcessBeforeInitialization:- If there are any BeanPostProcessors associated with the bean, spring calls their postProcessBeaforeInitialization() method.
Initialize Beans: - If the bean implements InitializingBean, its afterPropertiesSet() method will be called. If the bean has a custom init method declared, the specified Initialization method will be called.
postProcessAfterInitialization:- If there are any BeanPostProcessors associated with the bean, spring calls their portProcessAfterInitialization() method.
Bean is ready to use: - At this point the bean is ready to be used by the application and will remain.
Destroy bean: - If the bean implements DisposableBean, its destroy () method will be called, if the bean has a custom destroy-method decalred then the specified method will be called.
Question: - What is InitializingBean and DisposableBean interfaces in spring and how to use them?
Answer: - The InitializingBean and DisposableBean are two marker interfaces available in spring framework which calls the afterPropertiesSet () in the begining and destroy () method is invoked as part of the last action for destroying or destructing the bean.
Example to use Spring InitializingBean and DisposableBean interfaces are given below:-
System Requirements:-
- Eclipse Editor or any other.
- JDK 1.5 or higher(I am using jdk 1.7.0_03)
- Spring jars.
Required Jars are:-
- spring-core.jar
- spring-2.5.jar
- spring-beans.jar
- spring-context.jar
- commons-logging.jar
- dom4j-1.4.jar
- antlr.jar
- log4j.jar
Steps for creating Eclipse java project for implementing spring InitializingBean and DisposableBean interfaces:-
- Create a java project in eclipse.
- Create a package in the src folder with the name as com.gaurav.spring.core.initdestroy.impl.
- Create the below files in this package and place the corresponding code in those files.
- Create an XML file and name it as spring-core-initializablebean-disposablebean-impl.xml and place this file in the classpath outside the src folder.
- Execute the DatabaseServiceCaller.java by selecting the option Run as Java Application.
DatabaseServices.java
packagecom.gaurav.spring.core.initdestroy.impl;
importorg.springframework.beans.factory.DisposableBean;
importorg.springframework.beans.factory.InitializingBean;
public classDatabaseServices implements InitializingBean, DisposableBean {
privateString userName;
privateString password;
privateString url;
privateString driverClassName;
/**
* @return the userName
*/
publicString getUserName() {
returnuserName;
}
/**
* @param userName
* the userName to set
*/
publicvoid setUserName(String userName) {
this.userName = userName;
}
/**
* @return the password
*/
publicString getPassword() {
returnpassword;
}
/**
* @param password
* the password to set
*/
publicvoid setPassword(String password) {
this.password = password;
}
/**
* @return the url
*/
publicString getUrl() {
returnurl;
}
/**
* @param url
* the url to set
*/
publicvoid setUrl(String url) {
this.url = url;
}
/**
* @return the driverClassName
*/
publicString getDriverClassName() {
returndriverClassName;
}
/**
* @param driverClassName
* the driverClassName to set
*/
publicvoid setDriverClassName(String driverClassName) {
this.driverClassName = driverClassName;
}
@Override
publicvoid afterPropertiesSet() throws Exception {
System.out
.println("afterPropertiesSet() method is called and the required properties values for establishing database connection are : \nDriverClassName: "
+ driverClassName
+ " \nURL: "
+ url
+ " \nUserName: "
+ userName + "\nPassword: " + password);
}
@Override
publicvoid destroy() throws Exception {
System.out
.println("destroy() method is invoked and all database properties are destroyed");
}
}
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-2.5.xsd">
<bean id="databaseServiceID"
class="com.gaurav.spring.core.initdestroy.impl.DatabaseServices">
<property name="userName" value="system" />
<property name="password" value="system" />
<property name="url" value="jdbc:oracle:thin:@localhost:1521:XE"/>
<property name="driverClassName" value="oracle.jdbc.driver.OracleDriver"/>
</bean>
</beans>
DatabaseServiceCaller.java
packagecom.gaurav.spring.core.initdestroy.impl;
importorg.springframework.context.ConfigurableApplicationContext;
importorg.springframework.context.support.ClassPathXmlApplicationContext;
public classDatabaseServiceCaller {
publicstatic void main(String[] args) {
ConfigurableApplicationContext context = new ClassPathXmlApplicationContext(
newString[] { "spring-core-initializablebean-disposablebean-impl.xml" });
DatabaseServices databaseServicesBean = (DatabaseServices) context
.getBean("databaseServiceID");
System.out.println(databaseServicesBean);
context.close();
}
}
Result:-
log4j:WARN No appenders could be found for logger (org.springframework.context.support.ClassPathXmlApplicationContext).
log4j:WARN Please initialize the log4j system properly.
afterPropertiesSet() method is called and the required properties values for establishing database connection are :
DriverClassName: oracle.jdbc.driver.OracleDriver
URL: jdbc:oracle:thin:@localhost:1521:XE
UserName: system
Password: system
com.gaurav.spring.core.initdestroy.impl.DatabaseServices@1304ef4
destroy() method is invoked and all database properties are destroyed
Note: - The afterPropertiesSet() method is called, after all the DatabaseServices properties is set with the values, while the destroy() method is called after the context.close().
