In this post, We will learn very basic program How to read a file in Java. Very useful scenario which is prominently used in our real time projects.
How to read csv file in java. This is a common use case.
java.io package has utility classes for reading and writing files.
We can do reading a file in java 4 ways.
1) Using BufferedReader
2) Using JDK 7 try-with-resources
3) Using Files.readAllBytes
4) Using Files.readAllLines
How to read csv file in java. This is a common use case.
java.io package has utility classes for reading and writing files.
We can do reading a file in java 4 ways.
1) Using BufferedReader
2) Using JDK 7 try-with-resources
3) Using Files.readAllBytes
4) Using Files.readAllLines
First, Create a csv file with the following data in your computer(File name : employee.csv).
100,Jhon,20
101,Cena,24
102,Mike,19
1) Using BufferedReader:
This is very classic method to read a file using BufferedReader, FileReader. We will read the csv file using BufferedReader api and prints values of Id, Name, Age from csv file.
package com.adeepdrive.arraylist;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
public class ReadingFile {
public static void main(String[] args) {
// file name
String FILE_NAME = "D:\\adeepdrive\\employee.csv";
BufferedReader br = null;
FileReader fr = null;
try {
fr = new FileReader(FILE_NAME);
br = new BufferedReader(fr);
String currentLine;
while ((currentLine = br.readLine()) != null) {
String[] values = currentLine.split(",");
System.out.println("Id: " + values[0] + ", Name: " + values[1] + ", Age: " + values[2]);
}
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (br != null)
br.close();
if (fr != null)
fr.close();
} catch (IOException ex) {
ex.printStackTrace();
}}
}
Output:
Id: 100, Name: Jhon, Age: 20
Id: 101, Name: Cena, Age: 24
Id: 102, Name: Mike, Age: 19
FILE_NAME holds file name and location of csv file. This can be flat file or csv file.
BufferedReader class has a method to read the file content line by line using readLine() method.
File reading operation throws IOException. So, we have put the code in try and catch block.
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2) Using JDK 7 try-with-resources:
The same above program is rewritten in java 7 using try with resources concept which closes the br and fr automatically implicitly.
String FILE_NAME = "D:\\adeepdrive\\employee.csv";
try (BufferedReader br = new BufferedReader(new FileReader(FILE_NAME))) {
String currentLine;
while ((currentLine = br.readLine()) != null) {
String[] values = currentLine.split(",");
System.out.println("Id: " + values[0] + ", Name: " + values[1] + ", Age: " + values[2]);
}
} catch (IOException e) {
e.printStackTrace();
}Output:
Id: 100, Name: Jhon, Age: 20
Id: 101, Name: Cena, Age: 24
Id: 102, Name: Mike, Age: 19
3) Using Files.readAllBytes:
Files is a class that consists exclusively of static methods that operate on files, directories, or other types of files.Files has a static method readAllBytes(Path path). This method reads entire file content at once and stores in String.
Static in Java.
package com.adeepdrive.arraylist;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
public class ReadingFiles {
public static void main(String[] args) throws IOException {
// file name
String FILE_NAME = "D:\\adeepdrive\\employee.csv";
String content = new String(Files.readAllBytes(Paths.get(FILE_NAME)));
System.out.println("CSV File Content : ");
System.out.println(content);
}
}Output:
CSV File Content :
100,Jhon,20
101,Cena,24
102,Mike,19
4) Using Files.readAllLines:
Method readAllLines(Path path) returns list which stores all lines. Reading file in Java.
String FILE_NAME = "D:\\adeepdrive\\employee.csv";
List<String> content = Files.readAllLines(Paths.get(FILE_NAME));
System.out.println("CSV File Content : ");
for (String line : content) {
String[] values = line.split(",");
System.out.println("Id: " + values[0] + ", Name: " + values[1] + ", Age: " + values[2]);
}
Output:
CSV File Content :
Id: 100, Name: Jhon, Age: 20
Id: 101, Name: Cena, Age: 24
Id: 102, Name: Mike, Age: 19
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