Java 8 Read File in Chunks of Lines

Hello readers, in this tutorial, we will see an instance of how to Read a File Line by Line in Java viii. We volition learn the Java 8 Stream's API for reading a file's content line by line and we will explore its different characteristics.

i. Introduction

These days in the programming universe reading the file content is i of the most habitual file manipulation tasks in Coffee. In the aboriginal Coffee world, the code to read the text file line past line was very dull. In Java8, JDK developers have added new methods to the java.nio.file.Files course which has opened new gateways for the developers and these new methods offer an efficient reading of the files using the Streams.

 Java8 has added the Files.lines() method to read the file data using the Stream. The attractiveness of this method is that it reads all lines from a file as a stream of strings. This method,

• Reads the file data only subsequently a Terminal operation (such as forEach(), count() etc.) is executed on the Stream
• Reads the file content line-by-line by using the Streams
• Works by reading the Byte from a file then decodes it into a Character using the UTF-8 character encoding

Do remember, Files.lines() is dissimilar from the Files.readAllLines() as the latter i reads all the lines of a file into a listing of String elements. This is not an efficient way as the complete file is stored as a List resulting in extra memory consumption.

Java8 also provides another method i.due east. Files.newBufferedReader() which returns a BufferedReader to read the content from the file. Since both Files.lines() and Files.newBufferedReader() methods return Stream, developers can use this output to carry out some extra processing.

At present, open upward the Eclipse Ide and nosotros will go over these methods to read a file line by line using the Java8 Lambda Stream.

2. Java 8 Read File Line by Line Instance

2.1 Tools Used

Nosotros are using Eclipse Oxygen, JDK 1.8, and Maven.

ii.2 Project Structure

Firstly, let’due south review the final project structure if you're confused nearly where you should create the corresponding files or folder later!

Fig. 1: Awarding Project Structure

2.3 Project Creation

This section will show how to create a Java-based Maven project with Eclipse. In Eclipse IDE, become to File -> New -> Maven Project.

Fig. 2: Create Maven Project

In the New Maven Project window, it will ask you to select the projection location. By default, 'Utilise default workspace location' will be selected. Select the 'Create a simple project (skip archetype choice)' checkbox and just click on the next push to go along.

Fig. 3: Project Details

It volition ask you to 'Enter the group and the antiquity id for the project'. We will input the details as shown in the below prototype. The version number will be by default: 0.0.i-SNAPSHOT.

Fig. 4: Archetype Parameters

Click on Finish and the creation of a maven project is completed. If you meet, information technology has downloaded the maven dependencies and a pom.xml file volition exist created. Information technology will have the following lawmaking:

pom.xml

Developers can beginning adding the dependencies that they desire. Let u.s.a. offset building the application!

3. Application Building

Below are the steps involved in explaining this tutorial.

3.1 Java Class Implementation

Let'south create the required Java files. Right-click on the src/main/java binder, New -> Package.

Fig. 5: Java Package Creation

A new pop window will open where we volition enter the package name as: com.jcg.coffee.

Fig. 6: Coffee Parcel Name (com.jcg.coffee)

Once the package is created in the awarding, we will demand to create the implementation class to show the Files.lines() and Files.newBufferedReader() methods usage. Right-click on the newly created package: New -> Class.

Fig. 7: Java Course Creation

A new pop window will open and enter the file name as: ReadFileLineByLineDemo. The implementation class volition be created within the package: com.jcg.java.

Fig. 8: Coffee Class (ReadFileLineByLineDemo.java)

3.one.ane Example of Reading File in Java8

Here is the complete Java program to read an input file line by line using the Lambda Stream in Java8 programming. In this tutorial nosotros will talk about the three different approaches for reading a file:

• Approach 1: This approach (i.eastward. fileStreamUsingFiles(……) talks about reading a file into Java8 Stream and printing it line by line
• Arroyo 2: This approach (i.east. filterFileData(……)) talks about reading a file into Java8 Stream (like the one we'll be using in Arroyo 1) but also apply a filter to information technology (i.e. Read only those elements from the file that starting time with an alphabet (s) and print it onto the console). This approach gives an border to use criteria while reading the file
• Approach 3: This arroyo (i.e. fileStreamUsingBufferedReader(……) talks nigh a new Java8 method known as BufferedReader.lines(……) that lets the BufferedReader returns the content every bit Stream

Important points:

• In the above approaches, we accept omitted the try-with-resources concept for simplicity and mainly focused on the new ways of reading the file. Yet, just for developers curiosity endeavour-with-resource is a concept that ensures that each resource is closed at the cease of the argument execution
• With enhancements in Java and introduction to Stream in Java8, developers have stopped using the BufferedReader and Scanner classes to read a file line by line as it does not offering the facilities like the ones offered by Java8 Streams API

Let us move ahead and understand the 3 different approaches with a practical case.

ReadFileLineByLineDemo.coffee

01 02 03 04 05 06 07 08 09 10 eleven 12 13 xiv 15 16 17 xviii 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68

bundle com.jcg.java; import coffee.io.BufferedReader; import coffee.io.IOException; import java.nio.file.Files; import java.nio.file.Paths; import java.util.stream.Stream; public class ReadFileLineByLineDemo { public static void main(String[] args) { String fName = "config/days.txt" ; fileStreamUsingFiles(fName); Arrangement.out.println(); filterFileData(fName); System.out.println(); fileStreamUsingBufferedReader(fName); } private static void fileStreamUsingFiles(String fileName) { endeavour { Stream<String> lines = Files.lines(Paths.get(fileName)); System.out.println( "<!-----Read all lines every bit a Stream-----!>" ); lines.forEach(System.out :: println); lines.close(); } take hold of (IOException io) { io.printStackTrace(); } } private static void filterFileData(Cord fileName) { endeavour { Stream<Cord> lines = Files.lines(Paths.get(fileName)).filter(line -> line.startsWith( "s" )); Arrangement.out.println( "<!-----Filtering the file data using Java8 filtering-----!>" ); lines.forEach(Organization.out :: println); lines.shut(); } catch (IOException io) { io.printStackTrace(); } } private static void fileStreamUsingBufferedReader(String fileName) { effort { BufferedReader br = Files.newBufferedReader(Paths.become(fileName)); Stream <String> lines = br.lines().map(str -> str.toUpperCase()); Arrangement.out.println( "<!-----Read all lines by using BufferedReader-----!>" ); lines.forEach(Organisation.out::println); lines.close(); } grab (IOException io) { io.printStackTrace(); } } }

4. Run the Application

To run the awarding, developers need to right-click on the class, Run As -> Coffee Application. Developers can debug the example and meet what happens later on every step!

Fig. 9: Run Application

five. Project Demo

The above lawmaking shows the post-obit logs as output.

01 02 03 04 05 06 07 08 09 10 11 12 thirteen 14 xv 16 17 18 19 20 21 22 23

# Logs for 'ReadFileLineByLineDemo' # ===================================== <!-----Read all lines as a Stream-----!> lord's day monday tuesday wednesday thursday fri saturday <!-----Filtering the file information using Java8 filtering-----!> sunday saturday <!-----Read all lines past using BufferedReader-----!> SUNDAY MONDAY TUESDAY Midweek THURSDAY Fri SATURDAY

That is all for this mail. Happy Learning!

6. Java Read File Line past Line – Summary

In this tutorial, we had an in-depth await at:

• Java eight Files.lines() method in order to read a file line by line lazily and using the Stream API last operation (forEach(……)) to impress lines from the file
• Coffee eight Files.newBufferedReader() method in social club to read a file line by line. This method returns the contents as a Stream
• We likewise an introduction of Java viii Stream API methods to make ourselves familiar with this new concept

7. Download the Eclipse Project

This was an example of how to Read a File Line by Line in Java 8.

Last updated on April. 27th, 2020

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Source: https://examples.javacodegeeks.com/java-read-file-line-by-line-example/

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