diff --git a/Chapter04/pom.xml b/Chapter04/pom.xml
index 254359c..68658d6 100644
--- a/Chapter04/pom.xml
+++ b/Chapter04/pom.xml
@@ -33,6 +33,11 @@
 			<artifactId>mysql-connector-java</artifactId>
 			<scope>runtime</scope>
 		</dependency>
+		<dependency>
+	        <groupId>com.h2database</groupId>
+	        <artifactId>h2</artifactId>
+	        <scope>runtime</scope>
+	    </dependency>
 		<dependency>
 			<groupId>org.springframework.boot</groupId>
 			<artifactId>spring-boot-starter-test</artifactId>
diff --git a/Chapter04/src/main/java/com/example/Chapter04/jobs/ChunkJob.java b/Chapter04/src/main/java/com/example/Chapter04/jobs/ChunkJob.java
index 397d3bc..e31cf8b 100644
--- a/Chapter04/src/main/java/com/example/Chapter04/jobs/ChunkJob.java
+++ b/Chapter04/src/main/java/com/example/Chapter04/jobs/ChunkJob.java
@@ -15,8 +15,32 @@
  */
 package com.example.Chapter04.jobs;
 
+import java.util.ArrayList;
+import java.util.List;
+import java.util.UUID;
+
+import org.springframework.batch.core.Job;
+import org.springframework.batch.core.Step;
 import org.springframework.batch.core.configuration.annotation.EnableBatchProcessing;
+import org.springframework.batch.core.configuration.annotation.JobBuilderFactory;
+import org.springframework.batch.core.configuration.annotation.StepBuilderFactory;
+import org.springframework.batch.core.configuration.annotation.StepScope;
+import org.springframework.batch.item.ItemWriter;
+import org.springframework.batch.item.support.ListItemReader;
+import org.springframework.batch.repeat.CompletionPolicy;
+import org.springframework.batch.repeat.policy.CompositeCompletionPolicy;
+import org.springframework.batch.repeat.policy.SimpleCompletionPolicy;
+import org.springframework.batch.repeat.policy.TimeoutTerminationPolicy;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.boot.SpringApplication;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.context.annotation.Bean;
+import org.springframework.core.task.TaskExecutor;
+import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;
+
+import com.example.Chapter04.batch.LoggingStepStartStopListener;
+import com.example.Chapter04.batch.RandomChunkSizePolicy;
 
 /**
  * @author Michael Minella
@@ -24,70 +48,80 @@
 @EnableBatchProcessing
 @SpringBootApplication
 public class ChunkJob {
-//
-//	@Autowired
-//	private JobBuilderFactory jobBuilderFactory;
-//
-//	@Autowired
-//	private StepBuilderFactory stepBuilderFactory;
-//
-//	@Bean
-//	public Job chunkBasedJob() {
-//		return this.jobBuilderFactory.get("chunkBasedJob")
-//				.start(chunkStep())
-//				.build();
-//	}
-//
-//	@Bean
-//	public Step chunkStep() {
-//		return this.stepBuilderFactory.get("chunkStep")
-////				.<String, String>chunk(1000)
-//				.<String, String>chunk(randomCompletionPolicy())
-//				.reader(itemReader())
-//				.writer(itemWriter())
-//				.listener(new LoggingStepStartStopListener())
-//				.build();
-//	}
-//
-//	@Bean
-//	public ListItemReader<String> itemReader() {
-//		List<String> items = new ArrayList<>(100000);
-//
-//		for (int i = 0; i < 100000; i++) {
-//			items.add(UUID.randomUUID().toString());
-//		}
-//
-//		return new ListItemReader<>(items);
-//	}
-//
-//	@Bean
-//	public ItemWriter<String> itemWriter() {
-//		return items -> {
-//			for (String item : items) {
-//				System.out.println(">> current item = " + item);
-//			}
-//		};
-//	}
-//
-//	@Bean
-//	public CompletionPolicy completionPolicy() {
-//		CompositeCompletionPolicy policy =
-//				new CompositeCompletionPolicy();
-//
-//		policy.setPolicies(
-//				new CompletionPolicy[] {
-//						new TimeoutTerminationPolicy(3),
-//						new SimpleCompletionPolicy(1000)});
-//
-//		return policy;
-//	}
-//
-//	@Bean
-//	public CompletionPolicy randomCompletionPolicy() {
-//		return new RandomChunkSizePolicy();
-//	}
-//
-//	public static void main(String[] args) {
-//		SpringApplication.run(ChunkJob.class, args);
-//	}
+
+	@Autowired
+	private JobBuilderFactory jobBuilderFactory;
+
+	@Autowired
+	private StepBuilderFactory stepBuilderFactory;
+
+	@Bean
+	public Job chunkBasedJob() {
+		return this.jobBuilderFactory.get("chunkBasedJob")
+				.start(chunkStep())
+				.build();
+	}
+
+	@Bean
+	public Step chunkStep() {
+		return this.stepBuilderFactory.get("chunkStep")
+//				.<String, String>chunk(1000)
+				.<String, String>chunk(randomCompletionPolicy())
+				.reader(itemReader())
+				.writer(itemWriter())
+				.listener(new LoggingStepStartStopListener())
+				.taskExecutor(taskExecutor(0))
+				.build();
+	}
+
+	@Bean
+	@StepScope
+	public TaskExecutor taskExecutor(@Value("#{jobParameters['poolSize']}") int poolSize) {
+		ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
+		executor.setCorePoolSize(poolSize);
+		executor.setMaxPoolSize(poolSize);
+		return executor;
+	}
+
+	@Bean
+	public ListItemReader<String> itemReader() {
+		List<String> items = new ArrayList<>(100000);
+
+		for (int i = 0; i < 100000; i++) {
+			items.add(UUID.randomUUID().toString());
+		}
+
+		return new ListItemReader<>(items);
+	}
+
+	@Bean
+	public ItemWriter<String> itemWriter() {
+		return items -> {
+			for (String item : items) {
+				System.out.println(">> current item = " + item);
+			}
+		};
+	}
+
+	@Bean
+	public CompletionPolicy completionPolicy() {
+		CompositeCompletionPolicy policy =
+				new CompositeCompletionPolicy();
+
+		policy.setPolicies(
+				new CompletionPolicy[] {
+						new TimeoutTerminationPolicy(3),
+						new SimpleCompletionPolicy(1000)});
+
+		return policy;
+	}
+
+	@Bean
+	public CompletionPolicy randomCompletionPolicy() {
+		return new RandomChunkSizePolicy();
+	}
+
+	public static void main(String[] args) {
+		SpringApplication.run(ChunkJob.class, new String[] { "poolSize=null" });
+	}
 }
diff --git a/Chapter04/src/main/java/com/example/Chapter04/jobs/JobJob.java b/Chapter04/src/main/java/com/example/Chapter04/jobs/JobJob.java
index 1a02f6d..18d0d67 100644
--- a/Chapter04/src/main/java/com/example/Chapter04/jobs/JobJob.java
+++ b/Chapter04/src/main/java/com/example/Chapter04/jobs/JobJob.java
@@ -35,98 +35,98 @@
 @SpringBootApplication
 public class JobJob {
 
-	@Autowired
-	private JobBuilderFactory jobBuilderFactory;
-
-	@Autowired
-	private StepBuilderFactory stepBuilderFactory;
-
-	@Bean
-	public Tasklet loadStockFile() {
-		return (contribution, chunkContext) -> {
-			System.out.println("The stock file has been loaded");
-			return RepeatStatus.FINISHED;
-		};
-	}
-
-	@Bean
-	public Tasklet loadCustomerFile() {
-		return (contribution, chunkContext) -> {
-			System.out.println("The customer file has been loaded");
-			return RepeatStatus.FINISHED;
-		};
-	}
-
-	@Bean
-	public Tasklet updateStart() {
-		return (contribution, chunkContext) -> {
-			System.out.println("The start has been updated");
-			return RepeatStatus.FINISHED;
-		};
-	}
-
-	@Bean
-	public Tasklet runBatchTasklet() {
-		return (contribution, chunkContext) -> {
-			System.out.println("The batch has been run");
-			return RepeatStatus.FINISHED;
-		};
-	}
-
-	@Bean
-	public Job preProcessingJob() {
-		return this.jobBuilderFactory.get("preProcessingJob")
-				.start(loadFileStep())
-				.next(loadCustomerStep())
-				.next(updateStartStep())
-				.build();
-	}
-
-	@Bean
-	public Job conditionalStepLogicJob() {
-		return this.jobBuilderFactory.get("conditionalStepLogicJob")
-				.start(intializeBatch())
-				.next(runBatch())
-				.build();
-	}
-
-	@Bean
-	public Step intializeBatch() {
-		return this.stepBuilderFactory.get("initalizeBatch")
-				.job(preProcessingJob())
-				.parametersExtractor(new DefaultJobParametersExtractor())
-				.build();
-	}
-
-	@Bean
-	public Step loadFileStep() {
-		return this.stepBuilderFactory.get("loadFileStep")
-				.tasklet(loadStockFile())
-				.build();
-	}
-
-	@Bean
-	public Step loadCustomerStep() {
-		return this.stepBuilderFactory.get("loadCustomerStep")
-				.tasklet(loadCustomerFile())
-				.build();
-	}
-
-	@Bean
-	public Step updateStartStep() {
-		return this.stepBuilderFactory.get("updateStartStep")
-				.tasklet(updateStart())
-				.build();
-	}
-
-	@Bean
-	public Step runBatch() {
-		return this.stepBuilderFactory.get("runBatch")
-				.tasklet(runBatchTasklet())
-				.build();
-	}
-
-	public static void main(String[] args) {
-		SpringApplication.run(HelloWorldJob.class, args);
-	}
+//	@Autowired
+//	private JobBuilderFactory jobBuilderFactory;
+//
+//	@Autowired
+//	private StepBuilderFactory stepBuilderFactory;
+//
+//	@Bean
+//	public Tasklet loadStockFile() {
+//		return (contribution, chunkContext) -> {
+//			System.out.println("The stock file has been loaded");
+//			return RepeatStatus.FINISHED;
+//		};
+//	}
+//
+//	@Bean
+//	public Tasklet loadCustomerFile() {
+//		return (contribution, chunkContext) -> {
+//			System.out.println("The customer file has been loaded");
+//			return RepeatStatus.FINISHED;
+//		};
+//	}
+//
+//	@Bean
+//	public Tasklet updateStart() {
+//		return (contribution, chunkContext) -> {
+//			System.out.println("The start has been updated");
+//			return RepeatStatus.FINISHED;
+//		};
+//	}
+//
+//	@Bean
+//	public Tasklet runBatchTasklet() {
+//		return (contribution, chunkContext) -> {
+//			System.out.println("The batch has been run");
+//			return RepeatStatus.FINISHED;
+//		};
+//	}
+//
+//	@Bean
+//	public Job preProcessingJob() {
+//		return this.jobBuilderFactory.get("preProcessingJob")
+//				.start(loadFileStep())
+//				.next(loadCustomerStep())
+//				.next(updateStartStep())
+//				.build();
+//	}
+//
+//	@Bean
+//	public Job conditionalStepLogicJob() {
+//		return this.jobBuilderFactory.get("conditionalStepLogicJob")
+//				.start(intializeBatch())
+//				.next(runBatch())
+//				.build();
+//	}
+//
+//	@Bean
+//	public Step intializeBatch() {
+//		return this.stepBuilderFactory.get("initalizeBatch")
+//				.job(preProcessingJob())
+//				.parametersExtractor(new DefaultJobParametersExtractor())
+//				.build();
+//	}
+//
+//	@Bean
+//	public Step loadFileStep() {
+//		return this.stepBuilderFactory.get("loadFileStep")
+//				.tasklet(loadStockFile())
+//				.build();
+//	}
+//
+//	@Bean
+//	public Step loadCustomerStep() {
+//		return this.stepBuilderFactory.get("loadCustomerStep")
+//				.tasklet(loadCustomerFile())
+//				.build();
+//	}
+//
+//	@Bean
+//	public Step updateStartStep() {
+//		return this.stepBuilderFactory.get("updateStartStep")
+//				.tasklet(updateStart())
+//				.build();
+//	}
+//
+//	@Bean
+//	public Step runBatch() {
+//		return this.stepBuilderFactory.get("runBatch")
+//				.tasklet(runBatchTasklet())
+//				.build();
+//	}
+//
+//	public static void main(String[] args) {
+//		SpringApplication.run(HelloWorldJob.class, args);
+//	}
 }
diff --git a/Chapter04/src/main/resources/application.properties b/Chapter04/src/main/resources/application.properties
index d382b4d..3546f83 100644
--- a/Chapter04/src/main/resources/application.properties
+++ b/Chapter04/src/main/resources/application.properties
@@ -1,8 +1,8 @@
-spring.datasource.driverClassName=com.mysql.cj.jdbc.Driver
-spring.datasource.url=jdbc:mysql://localhost:3306/spring_batch
-spring.datasource.username=root
-spring.datasource.password=p@ssw0rd
+#spring.datasource.driverClassName=com.mysql.cj.jdbc.Driver
+#spring.datasource.url=jdbc:mysql://localhost:3306/spring_batch
+#spring.datasource.username=root
+#spring.datasource.password=p@ssw0rd
 #spring.datasource.schema=schema-mysql.sql
 #spring.datasource.initialization-mode=always
-spring.batch.initialize-schema=always
-spring.batch.job.names=conditionalStepLogicJob
+#spring.batch.initialize-schema=always
+#spring.batch.job.names=conditionalStepLogicJob
diff --git a/Chapter04/src/main/resources/application.yml b/Chapter04/src/main/resources/application.yml
index fa0c7a2..8ef250b 100644
--- a/Chapter04/src/main/resources/application.yml
+++ b/Chapter04/src/main/resources/application.yml
@@ -1,9 +1,10 @@
-spring:
-  datasource:
-    driverClassName: com.mysql.cj.jdbc.Driver
-    url: jdbc:mysql://localhost:3306/spring_batch
-    username: root
-    password: p@ssw0rd
-  batch:
-    initialize-schema: always
-spring.batch.job.names=conditionalStepLogicJob
+#debug: true
+#spring:
+#  datasource:
+#    driverClassName: com.mysql.cj.jdbc.Driver
+#    url: jdbc:mysql://localhost:3306/spring_batch
+#    username: root
+#    password: p@ssw0rd
+#  batch:
+#    initialize-schema: always
+#spring.batch.job.names=conditionalStepLogicJob