when is bean instantiated from applicationContext.xml

[kamath_sv]

Below is the sample applicationContext.xml

<?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:aop="http://www.springframework.org/schema/aop"
	xmlns:tx="http://www.springframework.org/schema/tx" xmlns:context="http://www.springframework.org/schema/context"
	xmlns:util="http://www.springframework.org/schema/util" 
	xmlns:batch="http://www.springframework.org/schema/batch"
	xsi:schemaLocation="
    http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd
    http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.0.xsd
    http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.0.xsd
    http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-2.0.xsd
    http://www.springframework.org/schema/batch http://www.springframework.org/schema/batch/spring-batch-2.1.xsd
    http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd">

	<!-- 1) USE ANNOTATIONS TO CONFIGURE SPRING BEANS -->
	<context:component-scan base-package="com.batch" />
	<bean id="contextApplicationContextProvider" class="com.batch.fromdb.ApplicationContextProvider" />

	<!-- 2) DATASOURCE, TRANSACTION MANAGER AND JDBC TEMPLATE  -->
	<bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource">
			<property name="driverClassName" value="com.microsoft.sqlserver.jdbc.SQLServerDriver" />
			<property name="url" value="jdbc:sqlserver://NUSRV-DBDR\SQLINST1;DatabaseName=Nomura" />
			<property name="username" value="Shashank" />
			<property name="password" value="nuware@123" />
			<property name="initialSize" value="3" />
			<property name="maxActive" value="10" />
		</bean>


	<bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
		<property name="dataSource" ref="dataSource" />
	</bean>
	<tx:annotation-driven transaction-manager="transactionManager" />

	<bean id="jdbcTemplate" class="org.springframework.jdbc.core.JdbcTemplate">
		<property name="dataSource" ref="dataSource" />
	</bean>


	<!-- 3) JOB REPOSITORY - WE USE IN-MEMORY REPOSITORY FOR OUR EXAMPLE -->
	<bean id="jobRepository" class="org.springframework.batch.core.repository.support.MapJobRepositoryFactoryBean">
		<property name="transactionManager" ref="transactionManager" />
	</bean>

	<!-- 4) LAUNCH JOBS FROM A REPOSITORY 
	<bean id="jobLauncher"
		class="org.springframework.batch.core.launch.support.SimpleJobLauncher">
		<property name="jobRepository" ref="jobRepository" />
	</bean>
	-->

	<!--
		5) Define the job and its steps. In our case I use one step. Configure
		its readers and writers
	-->
	<batch:job id="simpleJob1">
			<batch:listeners>
				<batch:listener ref="appJobExecutionListener" />
			</batch:listeners>
		<batch:step id="step1" >
			<batch:tasklet>
				<batch:chunk reader="cursorReader" writer="flatFileWriter1"	commit-interval="2" />
				<batch:listeners>
					<batch:listener ref="headerCallback" />
					<batch:listener ref="footerCallback" />					
				</batch:listeners>
			</batch:tasklet>
			
		</batch:step>
	</batch:job>
	
	
	<batch:job id="simpleJob2">
			<batch:listeners>
				<batch:listener ref="appJobExecutionListener" />
			</batch:listeners>
		<batch:step id="step11">
			<batch:tasklet >
				<batch:chunk reader="cursorReader" writer="flatFileWriter2"	commit-interval="2" />
				<batch:listeners>
					<batch:listener ref="headerCallback" />
					<batch:listener ref="footerCallback" />	
				</batch:listeners>
			</batch:tasklet>
		</batch:step>
	</batch:job>

	<!-- ======================================================= -->
	<!--  6) READER -->
	<!-- ======================================================= -->
	<bean id="cursorReader"	class="com.batch.fromdb.CustomReader" scope="step"/>

	<!-- ======================================================= -->
	<!--  7) WRITER -->
	<!-- ======================================================= -->
	<bean id="flatFileWriter1" class="com.batch.fromdb.CustomWriter" scope="step">
		<property name="headerCallback" ref="headerCallback"/>
		<property name="footerCallback" ref="footerCallback" />
		<property name="resource" value="file:c:/tmp/simpleJob.txt"/>
		<property name="lineAggregator">
			<bean class="org.springframework.batch.item.file.transform.FormatterLineAggregator">
				<property name="format" value="%-3.5s|%-1.2s"/>	
				<property name="fieldExtractor">
					<bean class="org.springframework.batch.item.file.transform.BeanWrapperFieldExtractor">
						<property name="names" value="memberName,checkNumber" />
					</bean>
				</property>									
			</bean>			
		</property>
	</bean>
	
	<bean id="flatFileWriter2" class="com.batch.fromdb.CustomWriter" scope="step">
		<property name="headerCallback" ref="headerCallback"/>
		<property name="footerCallback" ref="footerCallback" />
		<property name="resource" value="file:c:/tmp/simpleJob111.txt"/>
		<property name="lineAggregator">
			<bean class="org.springframework.batch.item.file.transform.FormatterLineAggregator">
				<property name="format" value="***  %-3.5s|%-20.20s  ***"/>	
				<property name="fieldExtractor">
					<bean class="org.springframework.batch.item.file.transform.BeanWrapperFieldExtractor">
						<property name="names" value="memberName,checkNumber" />
					</bean>
				</property>									
			</bean>			
		</property>
	</bean>
	

	
	<!-- <bean id="flatFileWriter" class="org.springframework.batch.item.file.FlatFileItemWriter">
		<property name="resource" value="file:c:/tmp/ledgers.txt"/>
		<property name="lineAggregator">
			<bean class="org.springframework.batch.item.file.transform.FormatterLineAggregator">
				<property name="format" value="%-3.5s|%-1.5s"/>	
				<property name="fieldExtractor">
					<bean class="org.springframework.batch.item.file.transform.BeanWrapperFieldExtractor">
						<property name="names" value="memberName,checkNumber" />
					</bean>
				</property>									
			</bean>			
		</property>
		<property name="headerCallback" ref="headerCallback" />
		<property name="footerCallback" ref="footerCallback" />		
	</bean>
		-->
	<bean id="headerCallback" class="com.batch.Header" />
	<bean id="footerCallback" class="com.batch.Footer" />
	
	
	<bean id="jobDetail" class="org.springframework.scheduling.quartz.JobDetailBean">
		<property name="jobClass" value="com.batch.fromdb.FromDbLauncher" />
		<property name="group" value="quartz-batch" />
		<property name="jobDataAsMap">
			<map>
				<entry key="jobLocator" value-ref="jobRegistry" />
				<entry key="jobLauncher" value-ref="jobLauncher" />
			</map>
		</property>
	</bean>
	
	<bean class="org.springframework.batch.core.configuration.support.JobRegistryBeanPostProcessor">
		<property name="jobRegistry" ref="jobRegistry" />
	</bean>
	 
	<bean id="scheduleFactory" class="org.springframework.scheduling.quartz.SchedulerFactoryBean" />
	<bean id="jobRegistry" class="org.springframework.batch.core.configuration.support.MapJobRegistry" scope="singleton"/>

	<bean id="jobLauncher" class="org.springframework.batch.core.launch.support.SimpleJobLauncher" scope="singleton">
		<property name="jobRepository" ref="jobRepository" />
		<property name="taskExecutor" ref="taskExecutor"/>
	</bean>
	
	<bean id="taskExecutor" class="org.springframework.core.task.SimpleAsyncTaskExecutor" >
		<property name="concurrencyLimit" value="6"/>
	</bean>
	
<!--	<bean id="taskExecutor" class="org.springframework.scheduling.concurrent.ConcurrentTaskExecutor"/>-->
<!--<bean id="taskExecutor" class="org.springframework.core.task.SyncTaskExecutor"/>-->

</beans>

I have few question regarding the instantiation of the beans.
1. Is the bean instantiated only if we use it? or bean instances are created at the run-time when application Context is created ?
2. The same question with batch:job. (will instance be created only if we use them)


If we have unnecessary beans & jobs (XML definition in applicationContext.xml) will those be created even if not used... leading to performance issues?

[Marten Deinum]

I suggest a read of the reference guide (chapter 3) as that explains about the context.

1) Beans are instantiated by default (unless marked lazy, prototype or some custom scope which doesn't require eager instantiation for more info chapter 3 of the reference guide)

2) See 1