The advanced function and expansion of the "CSV" framework in the Java class library
The advanced function and expansion of the "CSV" framework in the Java class library
CSV (COMMA-SEPARATED VALUES) is a commonly used data storage format that uses commas as a separatist symbol between fields.The Java class library provides many CSV frameworks, which can easily read, write and operate CSV files.In addition to the basic reading and writing functions, these frameworks also provide some advanced functions and some extensions, making it more convenient and flexible when processing CSV files.
1. The basic read and write function of the CSV framework
Using the CSV framework in the Java class library, we can read and write the CSV file through a few rows of simple code.The following is an example of reading CSV files:
import com.opencsv.CSVReader;
import java.io.FileReader;
import java.io.IOException;
public class CSVReaderExample {
public static void main(String[] args) {
try (CSVReader reader = new CSVReader(new FileReader("data.csv"))) {
String[] nextLine;
while ((nextLine = reader.readNext()) != null) {
for (String token : nextLine) {
System.out.print(token + " ");
}
System.out.println();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
The above code reads CSV data from a file named "Data.csv" by using the `csvreader` class and prints it to the console.Similarly, we can use the `csvwriter` class to write the data into the CSV file.
2. Advanced features
1. Treatment of fields containing quotation marks
In the CSV file, the field can contain the quotation marks, so that fields that include special characters such as comma or changes.Some CSV frameworks provide the function of processing the field containing quotes.For example, the `csvreader` class in the OpenCSV framework provides the` setquotechar () method, allows us to set the quotes character when reading the CSV file, and correctly analyze the fields containing quotes.
CSVReader reader = new CSVReader(new FileReader("data.csv"));
reader.setQuoteChar('"');
2. Write CSV data to multiple files
Sometimes we need to write a large amount of data into multiple CSV files.Some CSV frameworks support the function of writing data into multiple files.For example, the `CSVPrinter` class in the Apache Commons CSV framework provides the method of` printRecords (ITERABLE <CSVRecord>), allowing us to write multiple CSV records into different CSV files, respectively.
CSVPrinter printer = new CSVPrinter(new FileWriter("data1.csv"), CSVFormat.DEFAULT);
printer.printRecord("John", "Doe", "john.doe@example.com");
printer.printRecord("Jane", "Smith", "jane.smith@example.com");
printer.flush();
printer = new CSVPrinter(new FileWriter("data2.csv"), CSVFormat.DEFAULT);
printer.printRecord("Alice", "Brown", "alice.brown@example.com");
printer.printRecord("Bob", "Johnson", "bob.johnson@example.com");
printer.flush();
3. Custom field separation symbols and text limited symbols
The CSV file format is not strictly stipulated. Sometimes we may need to use custom field separators and text limits.Some CSV frameworks support setting custom separation and limited symbols.For example, the `csvpreference` class in the Super CSV framework allows us to set the configuration options of customized separators, limited characters, and other CSV files.
CsvPreference csvPreference = new CsvPreference.Builder(CsvPreference.EXCEL_PREFERENCE)
.delimiter(';')
.quoteChar('\'')
.build();
4. Use the injection map CSV field to Java object
When dealing with a large number of CSV fields, manual parsing and mapping each field may be very tedious and lengthy.Some CSV frameworks provide the function of using annotations to directly map the CSV field to the Java object.For example, the annotation of `@csvbindByname` in the OpenCSV framework allows us to automatically map the CSV field to the corresponding properties of the Java object through the field name.
public class Person {
@CsvBindByName(column = "Name")
private String name;
@CsvBindByName(column = "Age")
private int age;
// omit the getter and setter method
}
With the above annotations, we can use the following code to map the data in CSV to the Java object:
CSVReader reader = new CSVReader(new FileReader("data.csv"));
CsvToBean<Person> csvToBean = new CsvToBeanBuilder<Person>(reader)
.withType(Person.class)
.withIgnoreLeadingWhiteSpace(true)
.build();
List<Person> persons = csvToBean.parse();
5. Data conversion and formatting
Sometimes, we need to perform some data conversion or formatting operations when reading or writing CSV data.Some CSV frameworks provide data conversion and formatting functions.For example, the `csvparser` class in the Apache Commons CSV framework provides the` CSVFormat` object, we can set the data converter and the data formatr.
CSVParser parser = new CSVParser(new FileReader("data.csv"), CSVFormat.DEFAULT.withHeader());
for (CSVRecord record : parser) {
String name = record.get("Name");
int age = Integer.parseInt(record.get("Age"));
LocalDate birthday = LocalDate.parse(record.get("Birthday"), DateTimeFormatter.ofPattern("yyyy-MM-dd"));
// Convert data and formatting operations
}
3. Summary
The CSV framework in the Java class library provides the functions of flexible and convenient reading and writing and operating CSV files.In addition to the basic reading and writing functions, these frameworks also provide some advanced functions and extensions, such as processing fields containing quotes, writing CSV data to multiple files, custom field separators and text limited symbols, using annotation mapping CSV fieldsTo the Java object and data conversion and formatting.With these functions, we can handle data in the CSV file more efficiently and conveniently.
The above is an introduction article about the advanced function and extension of the "CSV" framework in the Java class library.I hope this article will help you understand and use the CSV framework.
Note: The CSV framework used in the above examples is OpenCSV, Apache Commons CSV, and Super CSV. Please select the appropriate CSV framework according to your own needs.
