Add composite item reader implementation

Resolves #757

spring-batch-samples/src/main/java/org/springframework/batch/samples/compositereader/README.md

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+## Composite ItemReader Sample
+
+### About
+
+This sample shows how to use a composite item reader to read data with
+the same format from different data sources.
+
+In this sample, data items of type `Person` are read from two flat files
+and a relational database table.
+
+### Run the sample
+
+You can run the sample from the command line as following:
+
+```
+$>cd spring-batch-samples
+$>../mvnw -Dtest=CompositeItemReaderSampleFunctionalTests#testJobLaunch test
+```

spring-batch-samples/src/main/resources/org/springframework/batch/samples/compositereader/data/persons1.csv

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+1,foo1
+2,foo2

spring-batch-samples/src/main/resources/org/springframework/batch/samples/compositereader/data/persons2.csv

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+3,bar1
+4,bar2

spring-batch-samples/src/main/resources/org/springframework/batch/samples/compositereader/sql/data.sql

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+insert into person_source values (5, 'baz1');
+insert into person_source values (6, 'baz2');

spring-batch-samples/src/main/resources/org/springframework/batch/samples/compositereader/sql/schema.sql

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+create table person_source (id int primary key, name varchar(20));
+create table person_target (id int primary key, name varchar(20));

spring-batch-samples/src/test/java/org/springframework/batch/samples/compositereader/CompositeItemWriterSampleFunctionalTests.java

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+/*
+ * Copyright 2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.springframework.batch.samples.compositereader;
+
+import java.util.Arrays;
+
+import javax.sql.DataSource;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import org.springframework.batch.core.ExitStatus;
+import org.springframework.batch.core.Job;
+import org.springframework.batch.core.JobExecution;
+import org.springframework.batch.core.JobParameters;
+import org.springframework.batch.core.configuration.annotation.EnableBatchProcessing;
+import org.springframework.batch.core.job.builder.JobBuilder;
+import org.springframework.batch.core.launch.JobLauncher;
+import org.springframework.batch.core.repository.JobRepository;
+import org.springframework.batch.core.step.builder.StepBuilder;
+import org.springframework.batch.item.database.JdbcBatchItemWriter;
+import org.springframework.batch.item.database.JdbcCursorItemReader;
+import org.springframework.batch.item.database.builder.JdbcBatchItemWriterBuilder;
+import org.springframework.batch.item.database.builder.JdbcCursorItemReaderBuilder;
+import org.springframework.batch.item.file.FlatFileItemReader;
+import org.springframework.batch.item.file.builder.FlatFileItemReaderBuilder;
+import org.springframework.batch.item.support.CompositeItemReader;
+import org.springframework.context.ApplicationContext;
+import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.core.io.ClassPathResource;
+import org.springframework.jdbc.core.DataClassRowMapper;
+import org.springframework.jdbc.core.JdbcTemplate;
+import org.springframework.jdbc.datasource.embedded.EmbeddedDatabaseBuilder;
+import org.springframework.jdbc.datasource.embedded.EmbeddedDatabaseType;
+import org.springframework.jdbc.support.JdbcTransactionManager;
+import org.springframework.test.jdbc.JdbcTestUtils;
+
+public class CompositeItemWriterSampleFunctionalTests {
+
+	record Person(int id, String name) {
+	}
+
+	@Test
+	void testJobLaunch() throws Exception {
+		// given
+		ApplicationContext context = new AnnotationConfigApplicationContext(JobConfiguration.class);
+		JobLauncher jobLauncher = context.getBean(JobLauncher.class);
+		Job job = context.getBean(Job.class);
+
+		// when
+		JobExecution jobExecution = jobLauncher.run(job, new JobParameters());
+
+		// then
+		Assertions.assertEquals(ExitStatus.COMPLETED, jobExecution.getExitStatus());
+		JdbcTemplate jdbcTemplate = new JdbcTemplate(context.getBean(DataSource.class));
+		int personsCount = JdbcTestUtils.countRowsInTable(jdbcTemplate, "person_target");
+		Assertions.assertEquals(6, personsCount);
+	}
+
+	@Configuration
+	@EnableBatchProcessing
+	static class JobConfiguration {
+
+		@Bean
+		public FlatFileItemReader<Person> itemReader1() {
+			return new FlatFileItemReaderBuilder<Person>().name("personItemReader1")
+				.resource(new ClassPathResource("org/springframework/batch/samples/compositereader/data/persons1.csv"))
+				.delimited()
+				.names("id", "name")
+				.targetType(Person.class)
+				.build();
+		}
+
+		@Bean
+		public FlatFileItemReader<Person> itemReader2() {
+			return new FlatFileItemReaderBuilder<Person>().name("personItemReader2")
+				.resource(new ClassPathResource("org/springframework/batch/samples/compositereader/data/persons2.csv"))
+				.delimited()
+				.names("id", "name")
+				.targetType(Person.class)
+				.build();
+		}
+
+		@Bean
+		public JdbcCursorItemReader<Person> itemReader3() {
+			String sql = "select * from person_source";
+			return new JdbcCursorItemReaderBuilder<Person>().name("personItemReader3")
+				.dataSource(dataSource())
+				.sql(sql)
+				.rowMapper(new DataClassRowMapper<>(Person.class))
+				.build();
+		}
+
+		@Bean
+		public CompositeItemReader<Person> itemReader() {
+			return new CompositeItemReader<>(Arrays.asList(itemReader1(), itemReader2(), itemReader3()));
+		}
+
+		@Bean
+		public JdbcBatchItemWriter<Person> itemWriter() {
+			String sql = "insert into person_target (id, name) values (:id, :name)";
+			return new JdbcBatchItemWriterBuilder<Person>().dataSource(dataSource()).sql(sql).beanMapped().build();
+		}
+
+		@Bean
+		public Job job(JobRepository jobRepository, JdbcTransactionManager transactionManager) {
+			return new JobBuilder("job", jobRepository)
+				.start(new StepBuilder("step", jobRepository).<Person, Person>chunk(5, transactionManager)
+					.reader(itemReader())
+					.writer(itemWriter())
+					.build())
+				.build();
+		}
+
+		@Bean
+		public DataSource dataSource() {
+			return new EmbeddedDatabaseBuilder().setType(EmbeddedDatabaseType.HSQL)
+				.addScript("/org/springframework/batch/core/schema-drop-hsqldb.sql")
+				.addScript("/org/springframework/batch/core/schema-hsqldb.sql")
+				.addScript("/org/springframework/batch/samples/compositereader/sql/schema.sql")
+				.addScript("/org/springframework/batch/samples/compositereader/sql/data.sql")
+				.build();
+		}
+
+		@Bean
+		public JdbcTransactionManager transactionManager(DataSource dataSource) {
+			return new JdbcTransactionManager(dataSource);
+		}
+
+	}
+
+}