Learn MapReduce and Design Patterns with a Shuffling Pattern Example

Table of Contents

1. Introduction
2. Shuffling Pattern Example
3. Implementation of Shuffling Design Pattern
4. Practical Demonstration
5. Understanding the Problem
6. Comment Shuffle MR Task
7. Comment Shuffle MR Task Implementation
8. XML Parsing
9. Creating Rows in the Output File
10. Shuffling Rows in Random Order
11. Comment Shuffle Reducer
12. Main Method
13. Creating the JAR File
14. Executing the Program
15. Viewing the Output

Introduction

In this article, we will discuss a shuffling pattern example and its implementation using the shuffling design pattern. We will explore the steps involved in shuffling data sets within an XML file and demonstrate how to write and execute Java code to obtain the desired outputs.

Shuffling Pattern Example

The shuffling pattern example involves the randomization of records within a comments.xml file using the shuffling design pattern. The comments.xml file contains multiple rows of comments, each with various fields such as ID, post ID, text, creation date, and user ID. Our objective is to shuffle these rows in a random order.

Implementation of Shuffling Design Pattern

To implement the shuffling design pattern, we will utilize a Java class called CommentShuffleMRTask. This class consists of an inner class, ShuffleCommandCommentsMapper, which extends the Mapper class and utilizes a Writable object for randomization. Additionally, we define a TextOutputValue object of Type Text.

Practical Demonstration

To demonstrate the practical implementation of the shuffling pattern example, we will work with a comments.xml file located under the "input/commands" folder. This file has a size of 37.98 MB and contains numerous user comments. We have selected specific rows within the tag for shuffling.

Understanding the Problem

Each row in the comments.xml file consists of fields such as ID, post ID, text, creation date, and user ID. Our goal is to shuffle these rows randomly. We will Create a STRING builder object to store the shuffled rows and write them to an output file.

CommentShuffleMRTask

CommentShuffleMRTask is the main Java class responsible for shuffling the comments. It contains the ShuffleCommandCommentsMapper inner class, which extends the Mapper class and utilizes an XML parse function to convert the XML file into a HashMap object.

CommentShuffleMRTask Implementation

Within the CommentShuffleMRTask class, we override the map() method and perform various operations Based on the keys and values obtained from the XML parts. We append the necessary data to the string builder object to construct each row.

XML Parsing

XML parsing is performed by the XML parse function within the CommentShuffleMRTask class. It takes an XML file as input and returns a HashMap object containing the parsed data. We iterate over the XML parts and retrieve the keys and values to construct the rows.

Creating Rows in the Output File

We create rows in the output file by appending the necessary data to the string builder object. This data includes the keys and values obtained from the XML parts, and we format them properly by adding blank spaces, equal signs, and double quotes.

Shuffling Rows in Random Order

After constructing the rows in the output file, we proceed to shuffle them in a random order. We use the random object to achieve randomness and ensure that each row is shuffled correctly.

Comment Shuffle Reducer

The CommentShuffleReducer class extends the Reducer class and is responsible for overriding the reduce() method. Within this method, we iterate over the values and write the key-value pairs using the Writeable object.

Main Method

The main method is the entry point of our program. It takes two arguments: the input folder path and the output folder path. These paths are used to specify the input and output directories for our MapReduce job.

Creating the JAR File

To execute the program, we need to create a JAR file. We Package all the necessary classes and dependencies into the JAR file and specify the main class that will be executed.

Executing the Program

Once the JAR file is created, we can execute the program using the "hadoop jar" command. We provide the class name, input folder path, and output folder path as arguments. The program will execute the shuffling of comments according to the implemented logic.

Viewing the Output

After the program finishes executing, we can view the output by using the "dfs -cat" command on the output path. This will display the Contents of the output file, showcasing the shuffled rows.

Highlights

• Shuffling pattern example implementation using the shuffling design pattern
• Handling XML parsing and data randomization
• Creating rows in the output file for shuffled comments
• Executing the program using MapReduce
• Obtaining the output and verifying the shuffling results

FAQs

Q: What is the purpose of the CommentShuffleMRTask class? A: The CommentShuffleMRTask class is responsible for shuffling the comments within the XML file using the shuffling design pattern.

Q: How does the XML parse function work? A: The XML parse function takes an XML file as input and converts it into a HashMap object containing the parsed data.

Q: How are the rows shuffled in random order? A: Randomization of rows is achieved using the random object, ensuring a random order for each shuffled row.

Q: Can I view the output directly after execution? A: Yes, you can view the output by using the "dfs -cat" command on the output path specified during program execution.