實現功能： 編寫一個自定義的監聽器，將逗號分隔符檔案（csv）中的資料載入到一種資料結構--“由Map組成的List”中。

antlr4檔案：

grammar CSV;
file : hdr row+ ;
hdr : row ;
row : field (',' field)* '\r'? '\n' ;
field
: TEXT # text
| STRING # string
| # empty
;
TEXT : ~[,\n\r"]+ ;
STRING : '"' ('""'|~'"')* '"' ;

LoadCSV.java 檔案：

import org.antlr.v4.runtime.CharStream;
import org.antlr.v4.runtime.CharStreams;
import org.antlr.v4.runtime.CommonTokenStream;

import org.antlr.v4.runtime.tree.ParseTreeWalker;

import java.io.*;
import java.util.ArrayList;
import java.util.LinkedHashMap;
import java.util.List;
 
import java.util.Map;

class Loader extends CSVBaseListener {
    public static final String EMPTY = "";
    /**
     * Load a list of row maps that map field name to value
     */
    List<Map<String, String>> rows = new ArrayList<Map<String, String>>();
    /**
     * List of column names
     
 
*/
    List<String> header;
    /**
     * Build up a list of fields in current row
     */
    List<String> currentRowFieldValues;

    public void exitString(CSVParser.StringContext ctx) {
        currentRowFieldValues.add(ctx.STRING().getText());
    }
    public void exitText(CSVParser.TextContext ctx) {
        currentRowFieldValues.add(ctx.TEXT().getText());
    }
    public void exitEmpty(CSVParser.EmptyContext ctx) {
        currentRowFieldValues.add(EMPTY);
    }
    public void exitHdr(CSVParser.HdrContext ctx) {
        header = new ArrayList<String>();
        header.addAll(currentRowFieldValues);
    }
    public void enterRow(CSVParser.RowContext ctx) {
        currentRowFieldValues = new ArrayList<String>();
    }
    public void exitRow(CSVParser.RowContext ctx) {
        // If this is the header row, do nothing
        // if ( ctx.parent instanceof CSVParser.HdrContext ) return; OR:
        if ( ctx.getParent().getRuleIndex() == CSVParser.RULE_hdr ) return;
        // It's a data row
        Map<String, String> m = new LinkedHashMap<String, String>();
        int i = 0;
        for (String v : currentRowFieldValues) {
            m.put(header.get(i), v);
            i++;
        }
        rows.add(m);
    }

}

public class LoadCSV {
    public static void main(String[] args) throws IOException {
        /*
        新的版本已經拋棄
        File csvFile = new File("F:\\IDEA_JAVA\\CSV\\test\\test.csv");
        InputStream fi = new FileInputStream(csvFile);
        ANTLRInputStream inputStream = new ANTLRInputStream(fi);
        CSVLexer lexer = new CSVLexer(inputStream);
        CommonTokenStream tokenStream = new CommonTokenStream(lexer);
        CSVParser parser = new CSVParser(tokenStream);
        ParseTreeWalker walker = new ParseTreeWalker();
        Loader loader = new Loader();
        walker.walk(loader, parser.file());
        System.out.println(loader.rows);
        */
        String path = "F:\\IDEA_JAVA\\CSV\\test\\test.csv";
        CharStream inputStream = CharStreams.fromFileName(path);
        CSVLexer lexer = new CSVLexer(inputStream);
        CommonTokenStream tokenStream = new CommonTokenStream(lexer);
        CSVParser parser = new CSVParser(tokenStream);
        ParseTreeWalker walker = new ParseTreeWalker();
        Loader loader = new Loader();
        walker.walk(loader, parser.file());
        System.out.println(loader.rows);
    }
}

完整工程

提取碼：i4xh