Detailed explanation of the technical principles of 'table/IO CSV support' framework in the Java class library
Detailed explanation of the technical principles of the "Table/IO CSV Support" framework in the Java class library
introduction:
CSV (comma division value) is a commonly used text file format that is used to transmit and store table data between different systems.In Java development, we often encounter the need to read or write the CSV file.To simplify this process, the Java class library provides some powerful frameworks to support the read and write operation of CSV files.This article will introduce the technical principles of the "Table/IO CSV Support" framework in Java in detail.
1. CSV file format
The CSV file consists of a series of records. Each record consists of multiple fields, and the comma is separated by a comma.Each record usually occupies a line, and the fields can contain various data types, such as text, numbers, and dates.CSV files are usually expanded by `.csv`.
2. "Table/IO CSV Support" Framework Overview
The Java class library provides some popular frameworks to handle CSV files, including Apache Commons CSV, OpenCSV and Univocity.These frameworks provide a convenient API for reading and writing CSV files, and processing and conversion of data of CSV files.
3. Apache Commons CSV principle
Apache Commons CSV (https://commons.apache.org/proper/commons- CSV/) is an open source Java library that provides a complete CSV file read and write function.The core principle of the framework is to analyze the CSV file using the status machine mode.
Below is a sample code that demonstrates the basic usage of reading and writing CSV files using Apache Commons CSV:
import org.apache.commons.csv.CSVFormat;
import org.apache.commons.csv.CSVParser;
import org.apache.commons.csv.CSVPrinter;
import org.apache.commons.csv.CSVRecord;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.Reader;
import java.io.Writer;
public class CSVExample {
public static void main(String[] args) {
try {
// Read the CSV file
Reader reader = new FileReader("input.csv");
CSVParser csvParser = new CSVParser(reader, CSVFormat.DEFAULT);
for (CSVRecord csvRecord : csvParser) {
String name = csvRecord.get(0);
int age = Integer.parseInt(csvRecord.get(1));
System.out.println("Name: " + name + ", Age: " + age);
}
csvParser.close();
// Write into CSV files
Writer writer = new FileWriter("output.csv");
CSVPrinter csvPrinter = new CSVPrinter(writer, CSVFormat.DEFAULT);
csvPrinter.printRecord("John Doe", 30);
csvPrinter.printRecord("Jane Smith", 25);
csvPrinter.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
In the above code, we use the `FileRereader` and` CSVPARSER` to read the CSV file.Then, we traverse each record and obtain the value of each field through the `Get ()` method.
Similarly, we use the `Filewriter` and` csvprinter` to write the CSV file.Use the `PrintRecord () method to print a record and save it into the CSV file.
4. OpenCSV principle
OpenCSV (https://opencsv.sourceForge.io/) is another popular Java CSV framework, which provides similar CSV file reading and writing functions.The principle of OpenCSV is to separate and transfer through comma and quotes.
The following is an example code that reads and writes to the CSV file with OpenCSV:
import com.opencsv.CSVReader;
import com.opencsv.CSVWriter;
import java.io.FileReader;
import java.io.FileWriter;
public class CSVExample {
public static void main(String[] args) {
try {
// Read the CSV file
CSVReader csvReader = new CSVReader(new FileReader("input.csv"));
String[] nextRecord;
while ((nextRecord = csvReader.readNext()) != null) {
String name = nextRecord[0];
int age = Integer.parseInt(nextRecord[1]);
System.out.println("Name: " + name + ", Age: " + age);
}
csvReader.close();
// Write into CSV files
CSVWriter csvWriter = new CSVWriter(new FileWriter("output.csv"));
csvWriter.writeNext(new String[]{"John Doe", "30"});
csvWriter.writeNext(new String[]{"Jane Smith", "25"});
csvWriter.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
In the above code, we use the `csvreader` and` csvwriter` classes to read and write CSV files.You can read the CSV file by calling the method by calling the `Readnext ()` method and return a string array, which contains the value of each field.Similarly, we use the `writenext ()` method to write a string array into the CSV file.
5. UNIVOCITY principle
Univocity (https://www.univocity.com/pages/univocity_parsers_documentation) is another powerful Java CSV framework that provides high -performance CSV file read and write functions.The principle is to analyze and write CSV files using graphic data structure and highly optimized algorithm.
The following is an example code that reads and writes with the CSV file with Univocity:
import com.univocity.parsers.csv.CsvParser;
import com.univocity.parsers.csv.CsvParserSettings;
import com.univocity.parsers.csv.CsvWriter;
import com.univocity.parsers.csv.CsvWriterSettings;
import java.io.FileReader;
import java.io.FileWriter;
public class CSVExample {
public static void main(String[] args) {
try {
// Read the CSV file
CsvParserSettings parserSettings = new CsvParserSettings();
CsvParser parser = new CsvParser(parserSettings);
String[] nextRecord;
parser.beginParsing(new FileReader("input.csv"));
while ((nextRecord = parser.parseNext()) != null) {
String name = nextRecord[0];
int age = Integer.parseInt(nextRecord[1]);
System.out.println("Name: " + name + ", Age: " + age);
}
parser.stopParsing();
// Write into CSV files
CsvWriterSettings writerSettings = new CsvWriterSettings();
CsvWriter writer = new CsvWriter(new FileWriter("output.csv"), writerSettings);
writer.writeRow("John Doe", "30");
writer.writeRow("Jane Smith", "25");
writer.close();
} catch (Exception e) {
e.printStackTrace();
}
}
}
In the above code, we use the `csvparser` and` csvwriter` classes to read and write the CSV file.By using the appropriate parser and writinger settings, we can analyze the CSV file according to the line and use the `PARSENEXT ()` method to gradually obtain each record.Similarly, we use the `writerow ()` method to write a line of data into the CSV file.
Summarize:
The "Table/IO CSV Support" framework in the Java class library provides a powerful CSV file reading and writing function, enabling developers to easily handle CSV files.In this article, we introduced in detail the three mainstream CSV frameworks of Apache Commons CSV, OpenCSV, and Univocity, and provided example code for reading and writing with these frameworks for CSV files.It is hoped that readers can understand the working principle of these frameworks through this article and be able to use it flexibly in actual development.
