如何在 java 中有效地解析巨大的 csv 文件

Question

My application is currently using CSV Parser to parse csv files and persist to database. It loads the entire csv into memory and taking a lot of time to persist, sometimes even times out. I have seen on the site
seeing mixed recommendations to use Univocity parser. Please advice the best approach to process large amounts of data which takes less time.
Thank you.

Code:

 int numRecords = csvParser.parse( fileBytes );

  public int parse(InputStream ins) throws ParserException {
    long parseTime=  System.currentTimeMillis();
    fireParsingBegin();
    ParserEngine engine = null;
    try {
        engine = (ParserEngine) getEngineClass().newInstance();
    } catch (Exception e) {
        throw new ParserException(e.getMessage());
    }
    engine.setInputStream(ins);
    engine.start();
    int count = parse(engine);
    fireParsingDone();
    long seconds = (System.currentTimeMillis() - parseTime) / 1000;
    System.out.println("Time taken is "+seconds);
    return count;
}


protected int parse(ParserEngine engine) throws ParserException {
    int count = 0;
    while (engine.next()) //valuesString Arr in Engine populated with cell data
    {
        if (stopParsing) {
            break;
        }

        Object o = parseObject(engine); //create individual Tos
        if (o != null) {
            count++; //count is increased after every To is formed
            fireObjectParsed(o, engine); //put in into Bo/COl and so valn preparations
        }
        else {
            return count;
        }
    }
    return count;

Answer 1

使用Apache的Commons CSV库。

Answer 2

univocity-parsers is your best bet on loading the CSV file, you probably won't be able to hand code anything faster. The problems you are having come from possibly 2 things:

1 - loading everything in memory. That's generally a bad design decision, but if you do that make sure to have enough memory allocated for your application. Give it more memory using flags -Xms8G and Xmx8G for example.

2 - you are probably not batching your insert statements.

My suggestion is to try this (using univocity-parsers):

    //configure input format using
    CsvParserSettings settings = new CsvParserSettings();

    //get an interator
    CsvParser parser = new CsvParser(settings);
    Iterator<String[]> it = parser.iterate(new File("/path/to/your.csv"), "UTF-8").iterator();

    //connect to the database and create an insert statement
    Connection connection = getYourDatabaseConnectionSomehow();
    final int COLUMN_COUNT = 2;
    PreparedStatement statement = connection.prepareStatement("INSERT INTO some_table(column1, column2) VALUES (?,?)"); 

    //run batch inserts of 1000 rows per batch
    int batchSize = 0;
    while (it.hasNext()) {
        //get next row from parser and set values in your statement
        String[] row = it.next(); 
        for(int i = 0; i < COLUMN_COUNT; i++){ 
            if(i < row.length){
                statement.setObject(i + 1, row[i]);
            } else { //row in input is shorter than COLUMN_COUNT
                statement.setObject(i + 1, null);   
            }
        }

        //add the values to the batch
        statement.addBatch();
        batchSize++;

        //once 1000 rows made into the batch, execute it
        if (batchSize == 1000) {
            statement.executeBatch();
            batchSize = 0;
        }
    }
    // the last batch probably won't have 1000 rows.
    if (batchSize > 0) {
        statement.executeBatch();
    }

This should execute pretty quickly and you won't need not even 100mb of memory to run.

For the sake of clarity, I didn't use any try/catch/finally block to close any resources here. Your actual code must handle that.

Hope it helps.

Answer 3

Streaming with Apache Commons IO

try (LineIterator it = FileUtils.lineIterator(theFile, "UTF-8")) {
    while (it.hasNext()) {
        String line = it.nextLine();
        // do something with line
    }
}