See this page for more details about Pail:
http://deals.manningpublications.com/pail.pdf

|+ mtitek-pail-object-samples
   |+ src
      |+ main
         |+ java
            |+ mtitek.pail.object.samples
               |+ Payload.java
               |+ PailStructurePayload.java
               |+ PailPayload.java
   |+ pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>mtitek.pail.object.samples</groupId>
    <artifactId>mtitek-pail-object-samples</artifactId>
    <version>1.0.0-SNAPSHOT</version>

    <dependencies>
        <dependency>
            <groupId>org.apache.hadoop</groupId>
            <artifactId>hadoop-common</artifactId>
            <version>2.7.3</version>
        </dependency>

        <dependency>
            <groupId>com.backtype</groupId>
            <artifactId>dfs-datastores</artifactId>
            <version>1.3.6</version>
        </dependency>
    </dependencies>
</project>

A simple POJO java class that will be used as an example to show how to write/read Objects to/from pail.

► src/main/java/mtitek/pail/object/samples/Payload.java

package mtitek.pail.object.samples;

public class Payload implements java.io.Serializable {
    private static final long serialVersionUID = -4058347141743162269L;

    private Integer field1;

    public Integer getField1() {
        return field1;
    }

    public void setField1(Integer field1) {
        this.field1 = field1;
    }

    @Override
    public String toString() {
        return "Payload [field1=" + field1 + "]";
    }
}

This java class is an implementation of the PailStructure interface that the Pail API will use to serialize/deserialize the payload objects.

► src/main/java/mtitek/pail/object/samples/PailStructurePayload.java

package mtitek.pail.object.samples;

import java.util.Collections;
import java.util.List;

import org.apache.commons.lang.SerializationUtils;

import com.backtype.hadoop.pail.PailStructure;

public class PailStructurePayload implements PailStructure<Payload> {
    private static final long serialVersionUID = 4759079091041385329L;

    public byte[] serialize(Payload object) {
        return SerializationUtils.serialize(object);
    }

    public Payload deserialize(byte[] serialized) {
        return (Payload) SerializationUtils.deserialize(serialized);
    }

    public Class<Payload> getType() {
        return Payload.class;
    }

    public boolean isValidTarget(String... dirs) {
        return true;
    }

    public List<String> getTarget(Payload object) {
        return Collections.emptyList();
    }
}

This java class shows how to use the Pail API to write/read Objects to/from pail.

► src/main/java/mtitek/pail/object/samples/PailPayload.java

package mtitek.pail.object.samples;

import java.io.IOException;
import java.util.Random;

import org.apache.hadoop.fs.Path;

import com.backtype.hadoop.pail.Pail;

public class PailPayload {
    private static final String PAIL_PATH = "/tmp/pail-test/pail-payload";

    public static void main(String[] args) throws IOException {
        @SuppressWarnings("unchecked")
        final Pail<Payload> pail = Pail.create(PailString.PAIL_PATH, new PailStructurePayload(), false);

        writePayloads(pail);

        readPayload(pail);
    }

    private static void writePayloads(final Pail<Payload> pail) throws IOException {
        final Pail<Payload>.TypedRecordOutputStream typedRecordOutputStream = pail.openWrite();

        final Payload payload = new Payload();

        payload.setField1(new Random().nextInt());

        typedRecordOutputStream.writeObject(payload);

        typedRecordOutputStream.close();
    }

    private static void readPayload(final Pail<Payload> pail) throws IOException {
        for (final Payload payload : pail) {
            System.out.println(payload);
        }
    }
}