Read csv file with java

How to read a CSV file in Java | with examples

A CSV file is a plain text file. Each line of the file represents a row of data. Fields in each row are separated by a delimiter, in this case , .

data.txt

First,Last,Age John,Doe,23 Sam,Smith,40 Jan,Miller,18

Notice how our sample file includes a header row. The header row describes what each column represents for a given row.

Read a CSV file in Java — Basic Example

import java.io.BufferedReader; import java.io.FileReader; public class CsvReader < public static void main(String[] args) < String file = "resources/data.txt"; String line; try (BufferedReader br = new BufferedReader(new FileReader(file))) < while((line = br.readLine()) != null)< System.out.println(line); >> catch (Exception e) < System.out.println(e); >> > 

output

First,Last,Age John,Doe,23 Sam,Smith,40 Jan,Miller,18 

Notice how we use the BufferedReader method readLine() to loop through each line of our file.

If you don’t know what a BufferedReader is, be sure to check out FileReader vs BufferedReader vs Scanner.

Also notice how we pass a BufferedReader instance br as an argument to our try. catch block. This is considered a try-with-resources block.

The try-with-resources block is new in Java SE 7+. This is the preferred way to handle I/O. Since the BufferedReader class implements java.lang.AutoCloseable , it will automatically close the resource regardless of how the try statement executes.

Using the try-with-resources block, we don’t need to worry about manually closing the resource.

Alternatively, we could manually close the BufferedReader with:

You would need to manually close the resource only if you’re using older versions of Java that don’t support try-with-resources .

Read CSV File into ArrayList

import java.io.BufferedReader; import java.io.FileReader; import java.util.ArrayList; import java.util.Arrays; import java.util.List; public class CsvReader < public static void main(String[] args) < String file = "resources/data.txt"; String delimiter = ","; String line; List> lines = new ArrayList(); try (BufferedReader br = new BufferedReader(new FileReader(file))) < while((line = br.readLine()) != null)< Listvalues = Arrays.asList(line.split(delimiter)); lines.add(values); > lines.forEach(l -> System.out.println(l)); > catch (Exception e) < System.out.println(e); >> >

output

[First, Last, Age] [John, Doe, 23] [Sam, Smith, 40] [Jan, Miller, 18] 

Notice how we use the same readLine() method to iterate over each row in the file.

We convert each row to an array by splitting the line based on a delimiter , .

This creates an array of arrays. Each row of data is added to the lines array.

Parse a CSV File using Scanner

As an alternative to BufferedReader , we can use Scanner to iterate over the CSV file.

import java.io.File; import java.util.ArrayList; import java.util.Arrays; import java.util.List; import java.util.Scanner; public class CsvReader < public static void main(String[] args) < String file = "resources/data.txt"; String delimiter = ","; String line; List> lines = new ArrayList(); try (Scanner s = new Scanner(new File(file))) < while(s.hasNext())< line = s.next(); Listvalues = Arrays.asList(line.split(delimiter)); lines.add(values); > lines.forEach(l -> System.out.println(l)); > catch (Exception e) < System.out.println(e); >> >

Scanner provides a similar method hasNext() for determining the end of the file. Using the s.next() method we are able to get the data for a given line.

Read a CSV File in Java with a Header

import java.io.BufferedReader; import java.io.FileReader; public class CsvReader < public static void main(String[] args) < String file = "resources/data.txt"; String headers; String line; try (BufferedReader br = new BufferedReader(new FileReader(file))) < headers = br.readLine(); while((line = br.readLine()) != null)< System.out.println(line); >> catch (Exception e) < System.out.println(e); >> >

Remember that the headers are simply the first row of the CSV file. We set the headers to a variable headers by reading the first line..

The better way. using Apache Commons CSV

These examples have all used native Java classes. While these are all viable solutions, libraries like Apache Commons CSV have made reading CSV files much easier.

Using Maven, you can add the Apache Commons CSV library as a dependency to your pom.xml file.

 org.apache.commons commons-csv 1.6 

Read a CSV File by Column Name

import org.apache.commons.csv.CSVFormat; import org.apache.commons.csv.CSVParser; import org.apache.commons.csv.CSVRecord; import java.io.BufferedReader; import java.io.FileReader; public class CsvReader < public static void main(String[] args) < try( BufferedReader br = new BufferedReader(new FileReader("resources/data.txt")); CSVParser parser = CSVFormat.DEFAULT.withDelimiter(',').withHeader().parse(br); ) < for(CSVRecord record : parser) < System.out.println(record.get("First")); >> catch (Exception e) < System.out.println(e); >> >

output

Notice how we can specify headers via the withHeader() method. This makes it easy to work with headers as we can now read the CSV file by column name.

Also notice how the first row of the file is correctly ignored by specifying withHeader() .

By using the Apache Commons CSV library we can more easily specify delimiters, formats, and headers. For these reasons, it’s generally preferred to use a library like Apache Commons for reading CSV files.

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Parse and Read a CSV File in Java

A CSV file is used to store tabular data in plain-text form. A comma delimiter is used to identify and separate different data tokens in the CSV file.

• CSV (Comma Separated Values) files are used by consumers, businesses, and scientific applications. Among its most common uses is moving tabular data between programs in runtime that natively operate on incompatible formats.
• CSV data is popular because so many programs and languages support some variation of CSV at least as an alternative import/export format.

In Java, there are different ways of reading and parsing CSV files. Let us discuss some of the best approaches:

OpenCSV is a brilliant library for operating on CSV files. It has the following features:

• Reading arbitrary numbers of values per line
• Ignoring commas in quoted elements
• Handling entries that span multiple lines
• Configurable separator and quote characters
• Read all the entries at once, or use an Iterator-style model

Import the latest version of OpenCSV into project dependencies.

Example 1: Reading the CSV File line by line into String[]

In the given example, we are using CSVReader class from OpenCSV library which wraps a FileReader for reading the actual CSV file. The file uses the delimiter comma.

• Using the reader.readNext() , we read the CSV file line by line.
• It throws IOException if an error occurs in reading the file.
• It throws CsvValidationException if the read line is not a valid CSV string.
• When all the lines are read, readNext() method returns null and the program terminates.

try(CSVReader reader = new CSVReader(new FileReader("SampleCSVFile.csv"))) < String [] nextLine; //Read one line at a time while ((nextLine = reader.readNext()) != null) < //Use the tokens as required System.out.println(Arrays.toString(nextLine)); >> catch (IOException | CsvValidationException e)

2. Using Super CSV Library

Super CSV is to be the foremost, fastest, and most programmer-friendly, free CSV package for Java. It supports a very long list of useful features out of the box, such as:

• Ability to read and write data as POJO classes
• Automatic encoding and decoding of special characters
• Custom delimiter, quote character and line separator
• Support for cell processors to process each token in a specific manner
• Ability to apply one or more constraints, such as number ranges, string lengths or uniqueness
• Ability to process CSV data from files, strings, streams and even zip files

Add the latest version of the latest version of Super CSV in the project.

 net.sf.supercsv super-csv 2.4.0 

Example 2: Reading the CSV File into POJO

We will read the following CSV file.

CustomerId,CustomerName,Country,PinCode,Email 10001,Lokesh,India,110001,abc@gmail.com 10002,John,USA,220002,def@gmail.com 10003,Blue,France,330003,ghi@gmail.com

The corresponding POJO class is:

Remember that the column names should match up exactly with the bean’s field names, and the bean has the appropriate setters defined for each field.

import java.io.FileReader; import java.io.IOException; import org.supercsv.cellprocessor.Optional; import org.supercsv.cellprocessor.ParseInt; import org.supercsv.cellprocessor.ParseLong; import org.supercsv.cellprocessor.constraint.NotNull; import org.supercsv.cellprocessor.constraint.StrRegEx; import org.supercsv.cellprocessor.ift.CellProcessor; import org.supercsv.io.CsvBeanReader; import org.supercsv.io.ICsvBeanReader; import org.supercsv.prefs.CsvPreference; public class ReadCSVFileExample < static final String CSV_FILENAME = "data.csv"; public static void main(String[] args) throws IOException < try(ICsvBeanReader beanReader = new CsvBeanReader(new FileReader(CSV_FILENAME), CsvPreference.STANDARD_PREFERENCE)) < // the header elements are used to map the values to the bean final String[] headers = beanReader.getHeader(true); //final String[] headers = new String[]; final CellProcessor[] processors = getProcessors(); Customer customer; while ((customer = beanReader.read(Customer.class, headers, processors)) != null) < System.out.println(customer); >> > /** * Sets up the processors used for the examples. */ private static CellProcessor[] getProcessors() < final String emailRegex = "[a-z0-9\\._]+@[a-z0-9\\.]+"; StrRegEx.registerMessage(emailRegex, "must be a valid email address"); final CellProcessor[] processors = new CellProcessor[] < new NotNull(new ParseInt()), // CustomerId new NotNull(), // CustomerName new NotNull(), // Country new Optional(new ParseLong()), // PinCode new StrRegEx(emailRegex) // Email >; return processors; > >

The Scanner class breaks its input into tokens using a specified delimiter pattern. The default delimiter is whitespace.

• We can use a separate Scanner to read lines, and another scanner to parse each line into tokens. This approach may not be useful for large files because it is creating one scanner instance per line.
• We can use the delimiter comma to parse the CSV file.
• The CSV tokens may then be converted into values of different datatypes using the various next() methods.

Example 3: Parsing a CSV file using Scanner

try(Scanner scanner = new Scanner(new File("SampleCSVFile.csv"))) < //Read line while (scanner.hasNextLine()) < String line = scanner.nextLine(); //Scan the line for tokens try (Scanner rowScanner = new Scanner(line)) < rowScanner.useDelimiter(","); while (rowScanner.hasNext()) < System.out.print(scanner.next()); >> > > catch (FileNotFoundException e)

4. Using BufferedReader and String.split()

In this approach, we use BufferedReader to read the file line by line. Then the String.split() function is used to get tokens from the current line based on provided delimiter as the method parameter.

It is useful for small strings or small files.

Example 4: Splitting the CSV String or CSV File

In the given example, we are reading a file line by line. Then each line is split into tokens with a delimiter comma.

try(BufferedReader fileReader = new BufferedReader(new FileReader(«SampleCSVFile.csv»))) < String line = ""; //Read the file line by line while ((line = fileReader.readLine()) != null) < //Get all tokens available in line String[] tokens = line.split(","); //Verify tokens System.out.println(Arrays.toString(tokens)); >> catch (IOException e)

Reading a CSV file is possible with many approaches in Java. As Java does not directly have dedicated APIs for CSV handling, we can rely on open-source libraries such as SuperCSV that are very easy to use and highly configurable.

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Read csv file with java

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