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java - Bean property is not readable or has an invalid getter method: Does the return type of the getter match the parameter type of the setter? Spring Batch

I am developing Spring Batch CompositeItemReader & Writer Example. I developed XML file and able to compile code successfully, but when running mu sample code gives me following error. Not sure what is going wrong?

org.springframework.beans.NotReadablePropertyException: Invalid property 'customerNumber' of bean class [java.lang.String]: Bean property 'customerNumber' is not readable or has an invalid getter method: Does the return type of the getter match the parameter type of the setter?
    at org.springframework.beans.AbstractNestablePropertyAccessor.getPropertyValue(AbstractNestablePropertyAccessor.java:619)
    at org.springframework.beans.AbstractNestablePropertyAccessor.getPropertyValue(AbstractNestablePropertyAccessor.java:610)
    at org.springframework.batch.item.file.transform.BeanWrapperFieldExtractor.extract(BeanWrapperFieldExtractor.java:57)
    at org.springframework.batch.item.file.transform.ExtractorLineAggregator.aggregate(ExtractorLineAggregator.java:54)
    at org.springframework.batch.item.file.FlatFileItemWriter.write(FlatFileItemWriter.java:267)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:317)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:190)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157)
    at org.springframework.aop.support.DelegatingIntroductionInterceptor.doProceed(DelegatingIntroductionInterceptor.java:133)
    at org.springframework.aop.support.DelegatingIntroductionInterceptor.invoke(DelegatingIntroductionInterceptor.java:121)
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179)
    at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:207)
    at com.sun.proxy.$Proxy4.write(Unknown Source)
    at org.springframework.batch.core.step.item.SimpleChunkProcessor.writeItems(SimpleChunkProcessor.java:175)
    at org.springframework.batch.core.step.item.SimpleChunkProcessor.doWrite(SimpleChunkProcessor.java:151)
    at org.springframework.batch.core.step.item.SimpleChunkProcessor.write(SimpleChunkProcessor.java:274)
    at org.springframework.batch.core.step.item.SimpleChunkProcessor.process(SimpleChunkProcessor.java:199)
    at org.springframework.batch.core.step.item.ChunkOrientedTasklet.execute(ChunkOrientedTasklet.java:75)
    at org.springframework.batch.core.step.tasklet.TaskletStep$ChunkTransactionCallback.doInTransaction(TaskletStep.java:406)
    at org.springframework.batch.core.step.tasklet.TaskletStep$ChunkTransactionCallback.doInTransaction(TaskletStep.java:330)
    at org.springframework.transaction.support.TransactionTemplate.execute(TransactionTemplate.java:133)
    at org.springframework.batch.core.step.tasklet.TaskletStep$2.doInChunkContext(TaskletStep.java:271)
    at org.springframework.batch.core.scope.context.StepContextRepeatCallback.doInIteration(StepContextRepeatCallback.java:77)
    at org.springframework.batch.repeat.support.RepeatTemplate.getNextResult(RepeatTemplate.java:368)
    at org.springframework.batch.repeat.support.RepeatTemplate.executeInternal(RepeatTemplate.java:215)
    at org.springframework.batch.repeat.support.RepeatTemplate.iterate(RepeatTemplate.java:144)
    at org.springframework.batch.core.step.tasklet.TaskletStep.doExecute(TaskletStep.java:257)
    at org.springframework.batch.core.step.AbstractStep.execute(AbstractStep.java:198)
    at org.springframework.batch.core.job.SimpleStepHandler.handleStep(SimpleStepHandler.java:148)
    at org.springframework.batch.core.job.flow.JobFlowExecutor.executeStep(JobFlowExecutor.java:64)
    at org.springframework.batch.core.job.flow.support.state.StepState.handle(StepState.java:67)
    at org.springframework.batch.core.job.flow.support.SimpleFlow.resume(SimpleFlow.java:162)
    at org.springframework.batch.core.job.flow.support.SimpleFlow.start(SimpleFlow.java:141)
    at org.springframework.batch.core.job.flow.FlowJob.doExecute(FlowJob.java:134)
    at org.springframework.batch.core.job.AbstractJob.execute(AbstractJob.java:304)
    at org.springframework.batch.core.launch.support.SimpleJobLauncher$1.run(SimpleJobLauncher.java:135)
    at org.springframework.core.task.SyncTaskExecutor.execute(SyncTaskExecutor.java:50)
    at org.springframework.batch.core.launch.support.SimpleJobLauncher.run(SimpleJobLauncher.java:128)
    at com.common.batch.main.CompositeMain.main(CompositeMain.java:24)

jdbc-composite-item-reader-job.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:batch="http://www.springframework.org/schema/batch" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="
    http://www.springframework.org/schema/batch http://www.springframework.org/schema/batch/spring-batch.xsd
        http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">

    <import resource="classpath:context-datasource.xml" />

    <!-- JobRepository and JobLauncher are configuration/setup classes -->
    <bean id="jobRepository" class="org.springframework.batch.core.repository.support.MapJobRepositoryFactoryBean" />

    <bean id="jobLauncher"  class="org.springframework.batch.core.launch.support.SimpleJobLauncher">
        <property name="jobRepository" ref="jobRepository" />
    </bean>


    <!-- Step will need a transaction manager -->
    <bean id="transactionManager"
        class="org.springframework.batch.support.transaction.ResourcelessTransactionManager" />


    <!-- =========================================================== -->    
    <job id="compositeJdbcReaderJob" xmlns="http://www.springframework.org/schema/batch">
        <step id="compositeJdbcReaderStep" next="compositeJdbcReaderStep2">
            <tasklet>
                <chunk reader="compositeItemReader" writer="itemWriter" commit-interval="5" />
            </tasklet>
        </step>

        <step id="compositeJdbcReaderStep2">
            <tasklet>
                <chunk reader="compositeItemReader2" writer="itemWriter2" commit-interval="5" />
            </tasklet>
        </step>
    </job>


    <!-- ============= Composite Item Reader ================ -->
    <bean id="compositeItemReader" class="com.common.batch.reader.CompositeCursorItemReader">
        <property name="unifyingMapper">
            <bean class="com.common.batch.mapper.DefaultUnifyingStringItemsMapper" />
        </property>
        <property name="cursorItemReaders">
            <list>
                <ref bean="itemReader1" />
            </list>
        </property>
    </bean>

    <bean id="compositeItemReader2" class="com.common.batch.reader.CompositeCursorItemReader">
        <property name="unifyingMapper">
            <bean class="com.common.batch.mapper.DefaultUnifyingStringItemsMapper" />
        </property>
        <property name="cursorItemReaders">
            <list>
                <ref bean="itemReader2" />                 
            </list>
        </property>
    </bean>


    <!-- ========== ItemReader =============== -->
    <bean id="itemReader1" class="org.springframework.batch.item.database.JdbcCursorItemReader">
        <property name="dataSource" ref="dataSource" />

        <property name="saveState" value="true" />

        <property name="sql">
            <value>
                <![CDATA[ ${select.sql.customers} ]]>
            </value>
        </property>
        <property name="rowMapper">
            <bean class="com.common.batch.mapper.CustomerMapper" />
        </property>
    </bean>


    <bean id="itemReader2" class="org.springframework.batch.item.database.JdbcCursorItemReader">
        <property name="dataSource" ref="dataSource" />

        <property name="saveState" value="true" />

        <property name="sql">
            <value>
                <![CDATA[ ${select.sql.employees} ]]>
            </value>
        </property>
        <property name="rowMapper">
            <bean class="com.common.batch.mapper.EmployeeMapper" />
        </property>
    </bean>


    <!-- ============= Flat File Writters ============= -->
    <bean id="itemWriter" class="org.springframework.batch.item.file.FlatFileItemWriter" scope="step">
        <property name="resource" value="${output.file.location}" />
        <!-- <property name="appendAllowed" value="true" /> -->
        <property name="lineAggregator">

            <!-- An Aggregator which converts an object into delimited list of strings -->
            <bean class="org.springframework.batch.item.file.transform.DelimitedLineAggregator">

                <property name="delimiter" value="|" />
                <property name="fieldExtractor">
                    <!-- Extractor which returns the value of beans property through reflection -->
                    <bean class="org.springframework.batch.item.file.transform.BeanWrapperFieldExtractor">
                        <property name="names" value="customerNumber,customerName,contactLastName,contactFirstName,phone,addressLine1,
addressLine2,city,state,postalCode,country,salesRepEmployeeNumber,creditLimit" />
                    </bean>
                </property>
            </bean>

        </property>
    </bean>


    <bean id="itemWriter2" class="org.springframework.batch.item.file.FlatFileItemWriter" scope="step">
        <property name="resource" value="${output.file.location}" />
        <property name="appendAllowed" value="true" />
        <property name="lineAggregator">
            <!-- An Aggregator which converts an object into delimited list of strings -->
            <bean class="org.springframework.batch.item.file.transform.DelimitedLineAggregator">

                <property name="delimiter" value="|" />
                <property name="fieldExtractor">
                    <!-- Extractor which returns the value of beans property through reflection -->
                    <bean class="org.springframework.batch.item.file.transform.BeanWrapperFieldExtractor">
                        <property name="names" value="employeeNumber,lastName,firstName,extension,email,officeCode,reportsTo,jobTitle" />
                    </bean>
                </property>
            </bean>
        </property>
    </bean>
</beans>

Employee.java

public class Employee implements Serializable{
    private static final long serialVersionUID = 1L;

    private Integer employeeNumber;
    private String lastName;
    private String firstName;
    private String extension;
    private String email;
    private String officeCode;
    private Integer reportsTo;
    private String jobTitle;
  

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Spring is trying to get the property cutomerNumber from the String class :

 Invalid property 'customerNumber' of bean class [java.lang.String]

which is wrong because the String is not supposed to be configured as the item of your job 's step, the Item in this context is supposed to be the Customer.

your beans are configured correctly except for one bean :compositeItemReader

The read method of this bean is returning a String instead of a Customer which is because of this :

public class CompositeCursorItemReader<T> implements ItemStreamReader<T> {

/** Registered ItemStreamReaders. */
private List<AbstractCursorItemReader<?>> cursorItemReaders;
/** Mandatory Unifying Mapper Implementation. */
private UnifyingItemsMapper<T> unifyingMapper;

@Override
public T read() throws Exception, UnexpectedInputException, ParseException, NonTransientResourceException {
    // read from all registered readers
    List items = new ArrayList();
    for (AbstractCursorItemReader<?> cursorItemReader : cursorItemReaders) {
        items.add(cursorItemReader.read());
    }
    // delegate to mapper
    return unifyingMapper.mapItems(items);
}
}

Its property UnifyingMapper is configured as follow:

  <property name="unifyingMapper">
                <bean class="com.common.batch.mapper.DefaultUnifyingStringItemsMapper" />
      </property>

here is the implementation of the UnifyingItemsMapper you are using:

 public class DefaultUnifyingStringItemsMapper implements UnifyingItemsMapper<String> {

    /** {@inheritDoc} */
    @Override
    public String mapItems(List<?> items) throws Exception {
        if (items != null && items.size() > 0) {
            StringBuilder sb = new StringBuilder();
            for (Object item : items) {
                if (item != null) {
                    sb.append(item);
                }
            }
            if (sb.length() > 0) {
                return sb.toString();
            } else {
                return null;
            }
        } else {
            return null;
        }
    }
}

the solution to this is to create a new Class that implements UnifyingItemsMapper<Customer> and configure it for your CompositeCursorItemReader#unifyingMapper

Or just use your itemReader directly if you don't need a UnifyingItemsMapper:

 <job id="compositeJdbcReaderJob" xmlns="http://www.springframework.org/schema/batch">
        <step id="compositeJdbcReaderStep" next="compositeJdbcReaderStep2">
            <tasklet>
                <chunk reader="itemReader1" writer="itemWriter" commit-interval="5" />
            </tasklet>
        </step>

        <step id="compositeJdbcReaderStep2">
            <tasklet>
                <chunk reader="itemReader2" writer="itemWriter2" commit-interval="5" />
            </tasklet>
        </step>
    </job>

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