简而言之
读取一个20 MB的CSV文件，并为每一行实例化一个对象，总共花费不到1秒的时间。
详情
你没有定义“慢”这个术语。所以我进行了一个实验，一个随意的基准测试。
首先我们创建一个20 MB的文件，包含40,000个Person记录。每个Person都有一个法语的名字和姓氏、一个UUID，以及一些任意文本作为描述。数据被写成四列，以CSV文件的形式在UTF-8中编写。我使用Apache Commons CSV库进行写入和读取。
其次，读取这个已经写好的文件。每一行数据都被读入内存，然后用于实例化和收集一个Person对象。
阅读该文件，并为每一行实例化一个
Person对象，总共花费的时间少于1秒。每一行大约需要20K
纳秒。实际上，这包括对文件进行两次扫描，因为我们需要扫描以计算数据行数，以设置收集实例的初始容量。此外，我们还将16进制字符串输入解析为
UUID的128位值，因此我们需要花费一些时间进行数据处理（而不仅仅是读取）。
对于Java 16+，将
Person类定义为
记录。我们重写
toString以避免打印长的
description内容。
record Person ( String givenName , String surname , UUID id , String description )
{
static public String LOREM_IPSUM = "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.";
@Override
public String toString ()
{
return "Person{ " +
"givenName='" + givenName + '\'' +
" | surname='" + surname + '\'' +
" | id='" + id + '\'' +
" }";
}
}
对于早期的Java版本，请编写传统的Person类。
package work.basil.example;
import java.util.UUID;
public class Person
{
static public String LOREM_IPSUM = "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.";
public String givenName, surname, description;
public UUID id;
public Person ( String givenName , String surname , UUID id , String description )
{
this.givenName = givenName;
this.surname = surname;
this.id = id;
this.description = description ;
}
@Override
public String toString ()
{
return "Person{ " +
"givenName='" + givenName + '\'' +
" | surname='" + surname + '\'' +
" | id='" + id + '\'' +
" }";
}
}
这是一个完整的应用程序，它可以编写并读取20 MB的文件。请仔细研究和评价，因为我匆忙之间完成了这个应用程序。我没有检查过我的工作。
您会发现一个“write”方法和一个“read”方法。 “main”方法调用两者，并跟踪时间。
package work.basil.example;
import org.apache.commons.csv.CSVFormat;
import org.apache.commons.csv.CSVPrinter;
import org.apache.commons.csv.CSVRecord;
import java.io.BufferedReader;
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.time.Duration;
import java.time.Instant;
import java.time.temporal.ChronoUnit;
import java.util.ArrayList;
import java.util.List;
import java.util.UUID;
import java.util.concurrent.ThreadLocalRandom;
public class CsvSpeed
{
public List < Person > read ( Path path )
{
// TODO: Add a check for valid file existing.
List < Person > list = List.of(); // Default to empty list.
try
{
// Prepare list.
int initialCapacity = ( int ) Files.lines( path ).count();
list = new ArrayList <>( initialCapacity );
// Read CSV file. For each row, instantiate and collect `DailyProduct`.
BufferedReader reader = Files.newBufferedReader( path );
Iterable < CSVRecord > records = CSVFormat.RFC4180.withFirstRecordAsHeader().parse( reader );
for ( CSVRecord record : records )
{
String givenName = record.get( "givenName" );
String surname = record.get( "surname" );
UUID id = UUID.fromString( record.get( "id" ) );
String description = record.get( "description" );
// Instantiate `Person` object, and collect it.
Person person = new Person( givenName , surname , id , description );
list.add( person );
}
} catch ( IOException e )
{
e.printStackTrace();
}
return list;
}
public void write ( final Path path )
{
ThreadLocalRandom random = ThreadLocalRandom.current();
try ( final CSVPrinter printer = CSVFormat.RFC4180.withHeader( "givenName" , "surname" , "id" , "description" ).print( path , StandardCharsets.UTF_8 ) ; )
{
int limit = 40_000; // 40_000 yields about 20 MB of data.
List < String > givenNames = List.of( "Adrien" , "Aimon" , "Alerion" , "Alexis" , "Alezan" , "Ancil" , "Andre" , "Antoine" , "Archard" , "Aurélien" , "Averill" , "Baptiste" , "Barnard" , "Bartelemy" , "Bastien" , "Baylee" , "Beale" , "Beau" , "Beaumont" , "Beauregard" , "Bellamy" , "Berger" , "Blaize" , "Blondel" , "Boyce" , "Bruce" , "Brunelle" , "Brys" , "Burcet" , "Burnell" , "Burrell" , "Byron" , "Canaan" , "Carden" , "Carolas" , "Cavell" , "Chace" , "Chanler" , "Chante" , "Chappel" , "Charles" , "Chasen" , "Chason" , "Chemin" , "Chene" , "Cher" , "Chevalier" , "Cheyne" , "Clément" , "Clemence" , "Corbin" , "Coty" , "Cygne" , "Damien" , "Dandre" , "Dariel" , "Darl" , "Dauphine" , "Davet" , "Dax" , "Dean" , "Delice" , "Delmon" , "Destin" , "Dominique" , "Donatien" , "Duke" , "Eliott" , "Elroy" , "Enzo" , "Erwan" , "Etalon" , "Ethan" , "Fabron" , "Ferrand" , "Filberte" , "Florent" , "Florian" , "Fontaine" , "Forest" , "Fortune" , "Franchot" , "Francois" , "Fraser" , "Frayne" , "Gaëtan" , "Gabin" , "Gage" , "Gaige" , "Garland" , "Garner" , "Gaston" , "Gauge" , "Gaylord" , "Germain" , "Germaine" , "German" , "Gervaise" , "Giles" , "Gilles" , "Gitan" , "Grosvener" , "Guifford" , "Guion" , "Guy" , "Guzman" , "Henri" , "Holland" , "Hugo" , "Hugues" , "Hyacinthe" , "Jérémy" , "Jacquan" , "Jacques" , "Jacquez" , "Janvier" , "Jardan" , "Jay" , "Jaye" , "Jehan" , "Jemond" , "Jocquez" , "Jonathan" , "Jules" , "Julien" , "Justus" , "Karoly" , "Lado" , "Lafayette" , "Lamond" , "Lancelin" , "Landis" , "Landry" , "Laron" , "Larrimore" , "Laurent" , "LaValle" , "Leandre" , "Leggett" , "Leonce" , "Leron" , "Leverett" , "Lilian" , "Loïc" , "Lorenzo" , "Louis" , "Lowell" , "Luc" , "Lucien" , "Lukas" , "Macaire" , "Mace" , "Mahieu" , "Maison" , "Malleville" , "Manneville" , "Mantel" , "Marc" , "Marcel" , "Marion" , "Marius" , "Markez" , "Markis" , "Marmion" , "Marquis" , "Marquise" , "Marshall" , "Martial" , "Maslin" , "Mason" , "Matheo" , "Mathias" , "Mathys" , "Matthieu" , "Maxence" , "Mayson" , "Mehdi" , "Merle" , "Merville" , "Montague" , "Montaigu" , "Monte" , "Montgomery" , "Montreal" , "Montrel" , "Moore" , "Morel" , "Mortimer" , "Nerville" , "Neuveville" , "Nicolas" , "Noë" , "Noah" , "Noe" , "Norman" , "Norville" , "Nouel" , "Olivier" , "Onfroi" , "Paien" , "Parfait" , "Parnell" , "Pascal" , "Patrice" , "Paul" , "Peppin" , "Percival" , "Percy" , "Pernell" , "Peverell" , "Philipe" , "Pierpont" , "Pierre" , "Pomeroy" , "Prewitt" , "Purvis" , "Quennell" , "Quentin" , "Quincey" , "Quincy" , "Quintin" , "Rémi" , "Rafaelle" , "Ranger" , "Raoul" , "Raphaël" , "Rapier" , "Rawlins" , "Ray" , "Raynard" , "Remi" , "René" , "Renard" , "Rene" , "Reule" , "Reynard" , "Robin" , "Romain" , "Rondel" , "Roy" , "Royal" , "Ruff" , "Rush" , "Russel" , "Rustin" , "Sabastien" , "Sacha" , "Salomon" , "Samuel" , "Satordi" , "Saville" , "Scoville" , "Sebastien" , "Sennett" , "Severin" , "Shant" , "Shantae" , "Sidney" , "Siffre" , "Simeon" , "Simon" , "Sinclair" , "Sofiane" , "Somer" , "Stephane" , "Sully" , "Sydney" , "Sylvain" , "Talbot" , "Talon" , "Telford" , "Tempest" , "Teppo" , "Théo" , "Thayer" , "Thibault" , "Thibaut" , "Thiery" , "Tiennan" , "Tiennot" , "Titouan" , "Toussaint" , "Travaris" , "Tyson" , "Urson" , "Vachel" , "Valentin" , "Valere" , "Vallis" , "Verdun" , "Victoir" , "Victor" , "Waltier" , "William" , "Wyatt" , "Yanis" , "Yann" , "Yves" , "Yvon" , "Zosime" , "Abrial" , "Abrielle" , "Abril" , "Adele" , "Alair" , "Alerion" , "Amee" , "Angelique" , "Annette" , "Antonella" , "Arian" , "Ariane" , "Armandina" , "Aubree" , "Aubrielle" , "Audra" , "Avril" , "Bella" , "Berneta" , "Bette" , "Blaise" , "Blanche" , "Blasa" , "Bonte" , "Brie" , "Brienne" , "Brigit" , "Cachay" , "Calice" , "Camille" , "Camylle" , "Caprice" , "Caressa" , "Caroline" , "Catin" , "Celesta" , "Celeste" , "Cera" , "Cerise" , "Chablis" , "Chalice" , "Chambray" , "Champagne" , "Chandell" , "Chaney" , "Chantal" , "Chante" , "Chanterelle" , "Chantile" , "Chantilly" , "Chantrice" , "Charla" , "Charlotte" , "Charmane" , "Chaton" , "Chemin" , "Chenetta" , "Cher" , "Chere" , "Cheri" , "Cheryl" , "Christine" , "Cidney" , "Cinderella" , "Claire" , "Claudette" , "Colette" , "Cordelle" , "Cydnee" , "Daeja" , "Daija" , "Daja" , "Damzel" , "Darelle" , "Darlene" , "Darselle" , "Dejanelle" , "Deleena" , "Delice" , "Demeri" , "Deni" , "Denise" , "Desgracias" , "Desire" , "Desiree" , "Destanee" , "Destiny" , "Dior" , "Domanique" , "Dominique" , "Elaina" , "Elaine" , "Elayna" , "Elise" , "Eloisa" , "Elyse" , "Emeline" , "Emmaline" , "Emmeline" , "Estella" , "Estrella" , "Etiennette" , "Evette" , "Fabienne" , "Fabrienne" , "Fanchon" , "Fancy" , "Fawna" , "Fayana" , "Fayette" , "Fifi" , "Fleur" , "Fleurette" , "Fontanna" , "Fosette" , "Francine" , "Frederique" , "Gabriel" , "Gabriele" , "Gabrielle" , "Gaby" , "Garcelle" , "Gena" , "Genie" , "Georgette" , "Germaine" , "Gervaise" , "Gitana" , "Harriet" , "Heloisa" , "Holland" , "Honnetta" , "Isabelle" , "Ivette" , "Ivonne" , "Jacqueena" , "Jacquetta" , "Jacquiline" , "Jacyline" , "Jaime" , "Jakqueline" , "Janeen" , "Janelly" , "Janina" , "Janiqua" , "Janique" , "Jannnelle" , "Jaquita" , "Jardena" , "Jeanetta" , "Jermaine" , "Jessamine" , "Jewel" , "Jewell" , "Joli" , "Jolie" , "Josephine" , "Jozephine" , "Julieta" , "Karessa" , "Karmaine" , "Klara" , "Laine" , "Lanelle" , "Laramie" , "Layne" , "Layney" , "Leala" , "Leonette" , "Lissette" , "Lizette" , "Lourdes" , "Lucienne" , "Ly" , "Lyla" , "Lysette" , "Madelaine" , "Malerie" , "Manette" , "Marais" , "Marcelle" , "Marché" , "Mardi" , "Margo" , "Marguerite" , "Marie" , "Marie Claude" , "Marie Frances" , "Marie Joelle" , "Marie Pascale" , "Marie Sophie" , "Marjolaine" , "Marquise" , "Marvella" , "Mathieu" , "Matisse" , "Maurelle" , "Maurissa" , "Mavis" , "Melisande" , "Michelle" , "Miette" , "Mignon" , "Mimi" , "Mirya" , "Monet" , "Moniqua" , "Monteen" , "Musetta" , "Myrlie" , "Nadeen" , "Nadia" , "Nadiyah" , "Naeva" , "Nanon" , "Natalle" , "Naudia" , "Nettie" , "Nicholas" , "Nicki" , "Nicky" , "Nicole" , "Nicolette" , "Nicolina" , "Nicolle" , "Nikolette" , "Ninette" , "Ninon" , "Noelle" , "Nycole" , "Odelette" , "Opaline" , "Orane" , "Orva" , "Page" , "Parisa" , "Parnel" , "Parris" , "Patrice" , "Peridot" , "Pippi" , "Prairie" , "Rachele" , "Rachelle" , "Racquel" , "Raphaelle" , "Raquelle" , "Remi" , "Renée" , "Renea" , "Renelle" , "Renita" , "Risette" , "Rochelle" , "Romy" , "Rosabel" , "Rosiclara" , "Ruba" , "Russhell" , "Saleena" , "Salina" , "Satin" , "Sedona" , "Serene" , "Shandelle" , "Shanta" , "Shante" , "Shariah" , "Sharita" , "Sharleen" , "Sheree" , "Shereen" , "Sherell" , "Sherice" , "Sherry" , "Sidnee" , "Sidney" , "Sidnie" , "Sidonie" , "Sinclaire" , "Solange" , "Solen" , "Sorrel" , "Suzette" , "Sydnee" , "Sydney" , "Tallis" , "Tempest" , "Toinette" , "Turquoise" , "Veronique" , "Vignette" , "Villette" , "Violeta" , "Virginie" , "Voleta" , "Vonny" );
List < String > surnames = List.of( "Arceneau" , "Aucoin" , "Babin" , "Babineaux" , "Benoit" , "Bergeron" , "Bernard" , "Bertrand" , "Bessette" , "Blanc" , "Blanchard" , "Bonnet" , "Boucher" , "Bourg" , "Bourque" , "Boutin" , "Bouvier" , "Braud" , "Broussard" , "Brun" , "Chevalier" , "David" , "Depaul" , "Desmarais" , "Disney" , "Dubois" , "Dupont" , "Dupuis" , "Durand" , "Fortescue" , "Fournier" , "Garnier" , "Gaudet" , "Gillet" , "Gillette" , "Girard" , "Gravois" , "Grosvenor" , "Lambert" , "Landry" , "Laroche" , "Laurent" , "Lefevre" , "Leroy" , "Leveque" , "Lisle" , "Martin" , "Michel" , "Molyneux" , "Moreau" , "Morel" , "Neville" , "Pelletier" , "Petit" , "Prideux" , "Renard" , "Richard" , "Robert" , "Rousseau" , "Roux" , "Rufus" , "Simon" , "Thomas" );
for ( int i = 1 ; i <= limit ; i++ )
{
String givenName = givenNames.get( random.nextInt( 0 , givenNames.size() ) );
String surname = surnames.get( random.nextInt( 0 , surnames.size() ) );
UUID id = UUID.randomUUID();
String description = Person.LOREM_IPSUM;
printer.printRecord( givenName , surname , id , description );
}
} catch ( IOException e )
{
e.printStackTrace();
}
}
public static void main ( final String[] args )
{
// Launch the app.
CsvSpeed app = new CsvSpeed();
// Write.
String when = Instant.now().truncatedTo( ChronoUnit.SECONDS ).toString().replace( ":" , "•" );
Path pathOutput = Paths.get( "/Users/basilbourque/persons.csv" );
app.write( pathOutput );
System.out.println( "Writing file: " + pathOutput );
// Read.
long start = System.nanoTime();
Path pathInput = Paths.get( "/Users/basilbourque/persons.csv" );
List < Person > list = app.read( pathInput );
long stop = System.nanoTime();
// Time.
long elapsed = ( stop - start );
Duration d = Duration.ofNanos( elapsed );
System.out.println( "Reading elapsed: " + d );
System.out.println( "Reading took nanos per row: " + ( elapsed / list.size() ) );
System.out.println( "nanos elapsed: " + elapsed + " | list.size: " + list.size() );
}
}
运行时:
写入文件：/Users/basilbourque/persons.csv
读取时间：PT0.857816234秒
每行读取时间：21445纳秒
总时间：857816234纳秒 | 列表大小：40000
技术栈:
- Java 11.0.2 — Zulu by Azul Systems (基于OpenJDK构建)
- 在IntelliJ 2019.1中运行
- macOS Mojave
- MacBook Pro (Retina, 15-inch, Late 2013)
- 处理器: 2.3 GHz Intel Core i7 (4核, 8线程)
- 16 GB 1600 MHz DDR3
- 存储：由Apple内置的固态硬盘
