OpenCSV framework source code analysis and its implementation principle in the Java class library
OpenCSV framework source code analysis and its implementation principle in the Java class library
Overview:
OpenCSV is a Java class library for processing the CSV (comma separation value) file.It provides a simple and flexible way to read and write CSV files, which are widely used in data processing tasks such as data import and export, data conversion, and ETL (Extract Transform load).This article will analyze the source code of the OpenCSV framework and explore its implementation principles in the Java library.
1. The structure and component of the OpenCSV framework
The OpenCSV framework consists of the following core components:
1.1 CSVReader: It is used to read data from the CSV file, provides a series of methods to read the CSV file one by one, and analyze each line of data into a string array or Java object.
1.2 CSVWRiter: Used to write data into CSV files, providing a series of methods to write the string array or Java object in the CSV format.
1.3 CSVPARSER: Urchatted CSV files and parsing each line of data into string arrays.
1.4 MAPPINGSTRATEGY: It is used to map the data in the CSV file as the Java object. By implementing the MAPPINGSTRATEGY interface, the mapping rules between the CSV file and the Java object can be customized.
1.5 CSVPrinter: For formatting output CSV data, assist CSVWriter to write the data into the file in CSV format.
2. Analysis of the OpenCSV framework
2.1 CSVReader source code analysis
The core logic of CSVReader In the Readnext method, this method analyzes it into a string array by reading each line of the file.
public String[] readNext() throws IOException {
return hasNext ? nextLine() : null;
}
private String[] nextLine() throws IOException {
...
return parseLine(line);
}
private String[] parseLine(String nextLine) throws IOException {
...
return tokenizer.parseLineMulti(nextLine);
}
2.2 CSVWriter source code analysis
The Writnext method of CSVWriter is the core method of writing a line of data into the CSV file.This method formats the data in the CSV format and write it into the file.
public void writeNext(String[] nextLine) throws IOException, CsvException {
writer.write(parser.parseToLine(nextLine));
writer.write(CSVParser.RFC4180_LINE_END);
}
2.3 CSVPARSER source code analysis
The main function of CSVParser is to resolve the text line in the CSV format into a string array.Among them, the PARSELINE method is the core method of analyzing a line of CSV text.
public String[] parseLine(String nextLine) throws IOException, CsvException {
...
return tokenizer.parseLine(nextLine);
}
2.4 MAPPINGSTRATEGY source code analysis
Mappingstrategy interface is used to map data in the CSV file as a Java object.Developers can customize the mapping rules between CSV data and Java objects by implementing the interface.
public interface MappingStrategy<T> {
T createBean();
void setType(T type);
void buildMapping(Reader reader) throws IOException, CsvException;
String[] transmuteBean(String[] values) throws CsvException;
String[] transmuteCsv(T bean) throws CsvException;
}
2.5 CSVPrinter source code analysis
CSVPrinter is used to format the output CSV data, which assists CSVWriter to write the data in the CSV format.
public class CSVPrinter {
...
public Writer print(String value) throws IOException {
...
}
public Writer print(int value) throws IOException {
...
}
public Writer print(long value) throws IOException {
...
}
public Writer print(double value) throws IOException {
...
}
public Writer print(char value) throws IOException {
...
}
public Writer print(boolean value) throws IOException {
...
}
...
}
3. The implementation principle of the OpenCSV framework
The implementation principle of the OpenCSV framework mainly involves the following key steps:
3.1 File read: Read the CSV file through Java file reading mechanism.
3.2 CSV Analysis: Each line in the CSV file through CSVPARSER analyzes it into a string array.
3.3 Data formatting: CSVReader formatted the string array or Java object that the obtained by parsing into CSV data.
3.4 file writing: Through the Java file writing mechanism, write the formatted CSV data into the file.
4. Examples of the OpenCSV framework
4.1 Read the CSV file
CSVReader reader = new CSVReader(new FileReader("file.csv"));
String[] nextLine;
while ((nextLine = reader.readNext()) != null) {
// Processing CSV data
}
reader.close();
4.2 Write into CSV file
CSVWriter writer = new CSVWriter(new FileWriter("file.csv"));
String[] nextLine = {"John", "Doe", "john.doe@example.com"};
writer.writeNext(nextLine);
writer.close();
Summarize:
The OpenCSV framework is a convenient and easy -to -use Java class library for reading and writing to CSV files.By analyzing its source code, we can understand the implementation of its core components.In actual use, you can choose the appropriate method to process CSV data according to the needs, and realize the function of data introduction, data conversion, and ETL.
